Astronomi

Hvad er forskellen mellem vind, stråle og udstrømning?

Hvad er forskellen mellem vind, stråle og udstrømning?


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For jetfly fandt jeg en pdf-fil her

Jet: kollimeret stråle af stof med høj hastighed

kilder: unge stjerner, aktive galaktiske kerner, $ mu $ -kvasarer, gammastrålesprængninger, planetariske tåger, pulsarer

jetkilder er vært for tiltrædelsesdiske

Hvad med vind og udstrømning? Kan nogen gøre nogle præciseringer for tre begreber , deres korrelation og forskel?


Jeg er ikke sikker på, at der er meget klare officielle definitioner, men her er min opfattelse af accepteret brug i stjerneformationssamfundet:

Udstrømning - generel betegnelse, der beskriver både vind og jetfly.

Stråler - kollimerede udstrømninger langs magnetiske poler.

Vind - udstrømning fra stjernefladen i alle retninger, ikke kun langs polerne.

Stjernevind er det, der kommer fra individuelle lyse stjerner. Stråler kan være protostjernede stråler fra unge stjerner eller i større skala fra galaktiske kerner.


Simulering og forståelse af kløftudstrømningen og den oceaniske reaktion over Tehuantepec-bugten under GOTEX

Numeriske simuleringer fanger det observerede fanlignende mønster med stærk kløftudstrømning med en signifikant døgnvariation under GOTEX.

Undersøgelsen afslører afkølingsmønsteret for SST under kløften vinden afspejler temperaturadvarsel fra de nærliggende havvirvler for at have en halvmåne.

Effekten af ​​overfladevindsspænding er at fremkalde mere afkøling i det blandede lag under hulvinden gennem opsving forbundet med Ekman-divergens på overfladen.

Virkningen af ​​overfladevarmestrøm på havet er mere begrænset til de øverste 30 m inden i det blandede lag og er symmetrisk med hulstrømsområdet ved at afkøle havet under hulstrømsområdet og reducere opvarmningen på begge sider.

Det blandede lags varmebudget bekræfter, at overfladevarmestrømmen har større indflydelse på det bredere område, og vindspændingen har større indflydelse i et dybere område.


CYKLONER EKSTRA TROPISKE

Feedback af cykloner i stor skala

Alle de cykloner, der udvikler sig, ledsages i deres mest aktive fase af store poleward og opadgående varmestrømme. Dette gentager grundlæggende kun, at cykloner er den form, der antages af den globale varmeveksling på mellembreddegrader. Et eksempel på kvantificering af disse strømninger i en reel situation, der er typisk nok til at understøtte sammenligning med idealiserede livscyklusser, er vist i figur 22.

Figur 22. Breddegradssnit sektioner af den zonemæssigt gennemsnitlige nordlige varmestrøm ved 700 hpa i K ms −1 (A) og nordlig momentum flux ved 300 hpa i m 2 s −2 (B) for zonebølgetal 5 til 7. Negative strømninger er rettet mod poleward , som angivet med den store pil, da dette er en casestudie på den sydlige halvkugle. Dagen for maksimal aktivitet, dag 9 på panelerne, er den 13. december 1979. (Tilpasset fra Randel WJ, Stanford JL (1985) Journal of the Atmospheric Sciences 42: 1364–1373.)

Denne figur viser yderligere, at cykloner også fører til store poleward-strømninger af zonemoment. Med andre ord synes jetstrømmen, som den meridionale cirkulation bygger på subtropiske breddegrader, at være forskudt bagud, og det skyldes hovedsageligt cykloner. Desuden er distributionen af ​​cykloner, som allerede nævnt, ikke homogen, selv på den sydlige halvkugle. Denne poleward forskydning af strålen finder derfor sted i stormspor. Zonets symmetri af jetstrømmen er brudt, og flere grene stammer fra de forskellige stormspor. Nogle gennemsnitlige tværgående tværsnit viser to vestlige jetstrømmesystemer: den ene ved høje breddegrader, undertiden kaldet polarstrålen, og den anden ved lavere breddegrader, den subtropiske stråle. Polarstrålen er faktisk resultatet af den subtropiske stråles brud og poleward-forskydning, idet de laveste og højeste nåede breddegrader er ret stabile. Imellem er variationen meget stor og vises derfor ikke på gennemsnittet.

En mere subtil effekt af befolkningen i cykloner er, at de forskellige strømme, de genererer (både af varme og af momentum), bidrager til opretholdelsen af ​​langsomt udviklende eller endda stabile meget store mønstre kaldet vejrregimer. Det nordatlantiske stormspor er kendt for at være forbundet med fire stationære regimer, såsom zonestyret (strålen krydser hele havet) eller det blokerende regime (stormsporet deler sig midt i havet, en blok sidder over det østlige bassin ). Stillehavets stormspor har også regimer, men dens størrelse er sådan, at de formerer sig som Rossby-bølger. Mens cykloner kollektivt bidrager til opretholdelsen af ​​regimer, menes det, at regimeovergang, som er hurtig, er baseret på enkeltbegivenheder, der stærkt påvirker deres større miljø.

Sidstnævnte punkt kan forstås ved at vende tilbage til et enkelt cyklonsynspunkt og til undersøgelser af deres langsigtede udvikling. Det er nyttigt at overveje, at de tidlige stadier af en livscyklus er domineret af den envejs indflydelse af den barokliniske zone på cyklonen. I de sene stadier af livscyklussen, når cyklonen er i en meget ikke-lineær fase, kan den dog ændre sit miljø stærkt.

Ser man på et antal idealiserede primitive ligningssimuleringer af cyklons livscyklusser og et antal reelle tilfælde, ser ændringen af ​​den store strømning af individuelle cykloner ud til at tage to paradigmatiske former. Disse kaldes livscyklus type 1 (LC1) og livscyklus type 2 (LC2) (figur 23). LC1-livscyklussen er kendetegnet ved, at cyklonens øverste niveau har form af et stadig mere langstrakt langstrakt trug, der til sidst afskærer fra den polære hvirvel. Det detaljerede eksempel præsenteret tidligt i denne artikel hører naturligvis til denne kategori (figur 1 og 6). Afskæringen eller endda spidsen af ​​truget kan generere en yderligere cyklon i mindre skala i bakken til den oprindelige. Livscyklusser af denne art bidrager til vedligeholdelse af blokke, hvis man er til stede ved enden af ​​stormsporet.

Figur 23. En enkelt konturoversigt over de foretrukne længerevarende udviklinger af idealiserede ekstratropiske cykloner. Konturlinjen er fra et konserveret felt på det øvre niveau, enten potentiel vorticitet eller potentiel temperatur, på en materialeflade, såsom en overflade med konstant værdi af det alternative felt. Den stiplede linje antyder den relative placering af det øverste niveau jet. Top: LC1-type livscyklus. Nederst: LC2-type livscyklus. (Tilpasset fra Thorncroft CD, Hoskins BJ, McIntyre ME (1993) Kvartalsjournal for Royal Meteorological Society 119: 17–55.)

LC2-livscyklussen svarer på den anden side til en opskalere vækst af hele cyklonen med sin øvre niveau komponentopbygning i en stor pulje med høj potentiel vorticitet, kold luft vest for cyklonen. Denne pulje kan være afskåret fra den polære hvirvel i de meget sene stadier, men dette er ikke systematisk.


Hvad er forskellen mellem vind, stråle og udstrømning? - Astronomi

Kan du venligst fortælle mig, hvilke faktorer der medfører, at flytider varierer mellem rejser mod øst og vest.

Det er interessant, at du spørger dette - jeg oplever det lige nu, når jeg sidder i et fly fra Storbritannien. Det tog 5 timer at gå vest-øst på denne rejse, men det tager cirka 7 øst-vest. Årsagen til forskellen er et atmosfærisk fænomen kendt som jetstrømmen. Jetstrømmen er en vind i meget høj højde, der altid blæser fra vest mod øst over Atlanterhavet. Flyene, der bevæger sig med en konstant lufthastighed, går således hurtigere i vest-øst retning, når de bevæger sig med vinden end i den modsatte retning.

Hver planet / måne har global vind, der for det meste bestemmes af den måde, hvorpå planeten / månen roterer, og hvor jævnt solen oplyser den. På Jorden får ækvator meget mere sol end polerne. hvilket resulterer i varmere luft ved ækvator end polerne og skaber cirkulationsceller (eller "Hadley-celler"), som består af varm luft, der stiger over ækvator og derefter bevæger sig nord og syd fra den og tilbage rundt.

Jorden roterer også. Når ethvert fast legeme roterer, bevæger bit af det, der er nærmere dets akse, langsommere end dem, der er længere væk. Når du bevæger dig nord (eller syd) fra ækvator, bevæger du dig tættere på jordens akse, og luften, der startede ved ækvator og bevægede sig nord (eller syd), bevæger sig hurtigere end jorden den er over (den har jordens rotationshastighed ved ækvator, ikke den jord, som nu er forbi). Dette resulterer i vind, der altid bevæger sig fra vest til øst i de midterste breddegrader.

Alle de globale vindmønstre er illustreret i nedenstående diagram taget fra Harvard Equable Climate Dynamics-webstedet.

Denne side blev sidst opdateret den 27. juni 2015.

Om forfatteren

Karen Masters

Karen var kandidatstuderende ved Cornell fra 2000-2005. Hun fortsatte med at arbejde som forsker i galakse-redshift-undersøgelser ved Harvard University og er nu på fakultetet ved University of Portsmouth tilbage i sit hjemland i Storbritannien. Hendes forskning har for nylig fokuseret på at bruge galaksernes morfologi til at give spor til deres dannelse og udvikling. Hun er projektforsker for Galaxy Zoo-projektet.


Magnetfelter driver astrofysiske stråleformer

Dette billede taget med Hubble-rumteleskopet viser, hvordan en lys, klumpet stråle, der skubbes ud fra en ung stjerne, har ændret sig over tid. Kredit: NASA

Udstrømning af stof er generelle træk, der stammer fra systemer, der drives af kompakte genstande som sorte huller, aktive galaktiske kerner, pulsarvindtåger, tilvækstende genstande som Young Stellar Objects (YSO) og modne stjerner som vores sol.

Men formen på disse udstrømninger eller astrofysiske stråler varierer afhængigt af magnetfeltet omkring dem.

I nye eksperimenter fandt en videnskabsmand fra Lawrence Livermore National Laboratory (LLNL) og internationale samarbejdspartnere, at forskydning af udstrømning / magnetfelt er en sandsynlig nøgleproces, der regulerer stråledannelse. Forskningen vises i Naturkommunikation.

Ved hjælp af en højtydende laser ved École Polytechnique skabte holdet hurtige materialestrømme i et stærkt anvendt magnetfelt som et sted at erstatte potentielle astrofysiske forhold. Holdet kiggede specifikt på indvirkningen på stråledannelse af en forkert justering mellem hvor strålen først dannes og derefter magnetfeltet.

Ved små forskydninger dannes en magnetisk dyse og omdirigerer udstrømningen i en parallel stråle. Ved større fejljusteringer bliver denne dyse mere og mere asymmetrisk og forstyrrer stråledannelsen.

"Vi fandt ud af, at udstrømning / magnetfeltjustering er en sandsynlig nøgleproces, der regulerer strålekollimering i en række forskellige objekter fra vores solstrømme til ekstragalatiske jetfly," sagde LLNL-plasmafysiker Drew Higginson, en medforfatter af papiret. "De kunne også give en mulig fortolkning af den observerede strukturering af astrofysiske jetfly."

Astrofysiske jetfly har varierede morfologier fra meget højt formatforhold, kollimerede jetfly til korte, der enten er tydeligt fragmenterede eller bare observeres og ikke er i stand til at opretholde en høj tæthed over et langt interval.

Elektrondensitetskort over 3D-plasmaudstrømningssimuleringer med et lidt (10 grader) og meget (45 grader) forkert justeret magnetfelt. Dette arbejde viste, at stråledannelse er mulig med et let forkert felt, men ikke med en stor forskydning. Kredit: Lawrence Livermore National Laboratory

Men mekanismerne bag disse forskellige morfologier har været uklare. I lyset af observationer foretaget på en række astrofysiske objekter udtænkte holdet et muligt scenario, hvor den relative orientering mellem udstrømningen og det store omgivende magnetiske felt omkring objektet kan spille en vigtig rolle, der orienterer dynamikken i udstrømningen fra et kollimeret en til en stunt, fragmenteret.


Varm tilvækst flyder rundt om sorte huller

Tilstrømninger med sort hul tilvækst kan opdeles i to brede klasser: koldt og varmt. Mens kolde tilvækststrømme består af kølig optisk tyk gas og findes ved relativt høje massetilvæksthastigheder, er varme tiltrædelsesstrømme emnet for denne gennemgang viralt varme og optisk tynde og forekommer ved lavere massetilvæksthastigheder. De beskrives ved tilvækstningsløsninger såsom den adveksionsdominerede tilvækststrøm og lysstrømmen med varm tilvækst. På grund af energitilførsel er strålingseffektiviteten af ​​disse strømme generelt lavere end for en standard tynd tilvækstningsskive. Desuden falder effektiviteten med faldende massetilvækst. Observationer viser, at varme tilvækststrømme er forbundet med jetfly. Derudover antyder teoretiske argumenter, at varme strømme skal producere stærk vind. Det antages, at varme tilvækststrømme er til stede i aktive, galaktiske kerner med lav lysstyrke og i røntgenstråler med sort hul i hårde og hvilende tilstande. Prototypen er Sgr A *, det supermassive sorte hul med ultralav lysstyrke i vores galaktiske centrum. Strålen, vinden og strålingen fra et supermassivt sort hul med en varm tiltrædelsesstrøm kan interagere med det eksterne interstellare medium og ændre udviklingen i værtsgalaksen.


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Instrument Starttidspunkt Nettoeksponering (ksec)
CXO / ACIS + HETGS 2003-05-01T21: 41: 03 48.8
RXTE / PCA 1a 2003-05-01T17: 00: 32 25.2
RXTE / PCA 1b 2003-05-02T00: 02: 24 0.8
RXTE / PCA 1c 2003-05-02T00: 54: 08 3.3
CXO / ACIS + HETGS 2003-05-28T04: 09: 21 45.5
RXTE / PCA 2a 2003-05-28T05: 28: 48 1.5
RXTE / PCA 2b 2003-05-28T06: 44: 16 16.1
RXTE / PCA 2c 2003-05-28T14: 28: 32 5.6
CXO / ACIS + HETGS 2003-06-23T15: 56: 10 50.0
RXTE / PCA 3 2003-06-23T17: 05: 20 13.3
CXO / ACIS + HETGS 2003-07-30T15: 57: 58 50.2
RXTE / PCA 4a 2003-07-30T19: 48: 48 0.6
RXTE / PCA 4b 2003-07-30T21: 22: 40 0.6
RXTE / PCA 4c 2003-07: 31T00: 32: 48 0.6

Bemærk. - Chandra og RXTE observationer diskuteret i dette arbejde er tabelleret ovenfor. Starttiden er angivet i “TT” -enheder. Nettoeksponeringen er eksponeringen efter anvendelse af standard Chandra- og RXTE-filtrering.

Bemærk. - Resultaterne af spektral tilpasning til RXTE PCU-2 og HEXTE-A spektre i 3-100 keV båndet er præsenteret ovenfor. Observationsnumrene svarer til dem i tabel 1. Da observationer, der falder sammen med det fjerde Chandra-spektrum, er diskdominerede og viser ringe variation, var de tilpasset i fællesskab. Individuelle tilpasninger afslørede, at NH bestod af 2,3 × 10 22 cm - 2 for hver observation, og blev derfor fastgjort i de tilpasninger, der er rapporteret her. Normaliseringen af ​​power-law-komponenten er p h o t o n s c m - 2 s - 1 k e V - 1 ved 1 keV. Ovenstående flux er "ikke-absorberede" flux. Afstanden til H 1743 - 322 er ukendt, og det antages, at afstanden til Galactic Center på d = 8,5 kpc beregner hver lysstyrkeværdi. Alle fejl er 90% tillidsfejl. Den øvre grænse på 95% konfidens for den ækvivalente bredde af smalle og brede Fe K α-emissionslinjer er angivet nederst i tabellen.

Tabel 2: Kontinuerlige røntgenparametre for spektral tilpasning

RXTE-spektret af H 1743 - 322 fra observation 2b er vist ovenfor udstyret med en flerfarvet disk sortlegeme plus power-law kontinuummodel (se tabel 2). Spektret er bemærkelsesværdigt uformelt og uden bevis for diskrefleksionsfunktioner. I betragtning af de højfrekvente (240 Hz) QPO'er blev detekteret i disse data - hvilket indikerer, at disken sandsynligvis er meget tæt på det formodede sorte hul - kunne vi have forventet at se stærkt skæve diskrefleksionsfunktioner.

Lyskurver fra RXTE-observation 1b er vist ovenfor. Dataene er blevet bundet i 32 s skraldespande. Variationen set på f w × 100 s tidsskalaer er meget lig den, der ses i Chandra-lyskurverne (se figur 5).

2–60 keV effekttæthedsspektret for RXTE-observation 1a er vist ovenfor. Poisson-niveauet er trukket fra. Det brede træk ved ca. 4 × 10 - 3 Hz svarer til variabiliteten set i lyskurven vist i figur 2, denne funktion kan passe sammen med en Lorentzian.

Bemærk. - Tilpas parametre for He-lignende Fe XXV (1s 2 –1s2p) og H-lignende Fe XXVI (1s-2p) resonansabsorberingslinjer, der er detekteret i de kombinerede første ordens Chandra / HEG-spektre af H 1743 - 322. Fejlene på alle linjetilpasningsparametre er 1 σ tillidsfejl. Fejl i parentes er symmetriske fejl i det sidste ciffer. Positive hastighedsskift svarer til røde skift og negative hastighedsskift svarer til blå skift. Signifikante linjer blev ikke detekteret i observation 2 95% konfidens øvre grænser rapporteres under antagelse af den samme linje centroid og FWHM værdier som målt i observation 1. Kun Fe XXVI linjerne i observationer 1 og 4 er løst. Ækvivalente neutrale hydrogensøjletætheder blev beregnet under antagelse af en Fe-overflod på 3,3 x 10 - 5 i forhold til hydrogen. Linjebølgelængder og oscillatorstyrker er taget fra Verner et al. (1996b).

Tabel 3: røntgenabsorptionslinjer i spektrene af H 1743 - 322

Obs. Ion Teorien. Måling Flytte FWHM Strøm W N Z N H
(EN) (EN) (km / s) (10 - 3 Å) (km / s) (10 - 3 ph / cm 2 / s) (mÅ) (10 17 c m - 2) (10 22 c m - 2)
1 (& gt middelværdi) Fe XXV 1.850 & lt 10 & lt. 1600 & lt 0,6 & lt 1.8 & lt 0,8 & lt 0,2
1 (& betyder det) Fe XXV 1.850 1.848(1) − 320 ± 160 & lt 10 & lt. 1600 0.6 ( 1 ) 1.9 ( 3 ) 0.8 ( 1 ) 0.24 ( 4 )
1 (& gt middelværdi) Fe XXVI 1.780 1.776(1) − 670 ± 170 11.8 ± 4.7 2000 ± 700 1.3 ( 2 ) 4.3 ( 7 ) 3.7 ( 6 ) 1.1 ( 2 )
1 (& betyder det) Fe XXVI 1.780 1.776(1) − 670 ± 170 10 + 1 − 2 1700 + 200 − 400 1.4 ( 2 ) 5 ( 1 ) 4 ( 1 ) 1.3 ( 3 )
1 (gennemsnit + 5 c / s) Fe XXV 1.850 & lt 10 & lt. 1600 & lt 0,8 & lt 0,24 & lt 1 & lt 0,3
1 (middel - 5 c / s) Fe XXV 1.850 1.849(1) − 160 ± 160 & lt 10 & lt. 1600 0.9 ( 1 ) 2.8 ( 3 ) 1.2 ( 1 ) 0.36 ( 4 )
1 (gennemsnit + 5 c / s) Fe XXVI 1.780 1.775(1) − 840 ± 170 11.8 ± 4.7 2000 ± 700 1.4 ( 2 ) 4.6 ( 7 ) 3.9 ( 6 ) 1.2 ( 2 )
1 (middel - 5 c / s) Fe XXVI 1.780 1.777(1) − 510 ± 170 14 ± 5 2400 ± 900 1.5 ( 2 ) 5 ( 1 ) 4 ( 1 ) 1.3 ( 3 )
3 (norm.) Fe XXV 1.850 & lt 10 & lt. 1600 & lt 0,3 & lt 1.5 & lt 0,6 & lt 0,2
3 (dip) Fe XXV 1.850 1.850(1) 0 ± 160 & lt 10 & lt. 1600 0.7 ( 1 ) 4.3 ( 6 ) 1.5 ( 2 ) 0.45 ( 7 )
3 (norm.) Fe XXVI 1.780 1.777(1) − 510 ± 170 & lt 10 & lt 1600 0.5 ( 1 ) 3.1 ( 6 ) 2.1 ( 5 ) 0.6 ( 2 )
3 (dip) Fe XXVI 1.780 1.778(1) − 340 ± 170 & lt 10 & lt. 1600 0.6 ( 1 ) 4.4 ( 7 ) 3.8 ( 6 ) 1.2 ( 2 )

Bemærk. - Tilpas parametre for He-lignende Fe XXV (1s 2 –1s2p) og H-lignende Fe XXVI (1s-2p) resonansabsorberingslinjer detekteret i de kombinerede første ordens optællingshastighed valgte Chandra / HEG-spektre af H 1743 - 322 Fejlene på alle parametre for linjetilpasning er 1 σ tillidsfejl. Fejl i parentes er symmetriske fejl i det sidste ciffer. Hvor linjer ikke detekteres, gives 95% konfidens øvre grænser. Hvor målinger ikke er rapporteret, er de fastgjort til dem, der måles i de tidsgennemsnitlige spektre (se tabel 3). Positive hastighedsskift svarer til røde skift og negative hastighedsskift svarer til blå skift. Ækvivalente neutrale hydrogensøjletætheder blev beregnet under antagelse af en Fe-overflod på 3,3 x 10 - 5 i forhold til hydrogen. Linjebølgelængder og oscillatorstyrker er taget fra Verner et al. (1996b).

Tabel 4: røntgenabsorptionslinjer i count-rate-valgt spektre af H 1743 - 322

Observation n r m a x (c m - 3) r m i n (c m) r m a x (c m) N (c m - 2) ˙ M 300 (g s - 1)
1 1.1 × 10 12 1.2 × 10 9 4.0 × 10 10 4.4 × 10 22 1.3 × 10 18
2 & lt 1,2 × 10 10 4.0 × 10 11 & lt 5,3 × 10 21
3 2.2 × 10 11 1.5 × 10 9 1.0 × 10 11 2.2 × 10 22 1.7 × 10 18
4 1.8 × 10 11 3.2 × 10 7 1.3 × 10 9 3.7 × 10 22 2.1 × 10 14

Bemærk. - Parametre for den absorberende plasmamodel, der er beskrevet i teksten, er angivet her. Et enkelt-zoneabsorberende medium i fotoioniseringsligevægt antages af modellen. Parameteren ˙ M 300 refererer til masseudstrømningshastigheden under antagelse af en hastighed på 300 km / s. Parameteren n r m a x er densiteten ved r m a x.

Tabel 5: Absorberende plasmaparametre

Variable He-lignende Fe XXV (λ = 1.850 Å) og H-lignende Fe XXVI (λ = 1.780 Å) absorptionslinjer i de kombinerede tidsgennemsnitlige første ordens Chandra / HEG-spektre af H 1743 - 322 er vist ovenfor. Spektrene er nummereret i rækkefølge efter observation. Dataene er tegnet i sort, 1 σ-fejlbjælker er tegnet i blåt, og modellen for hvert spektrum er tegnet i rødt. Kontinuummodellerne består af phenomonelogiske power-law-komponenter med galaktisk absorption for at levere de passende neutrale Fe K-kanter fra ISM. Absorptionslinierne blev modelleret ved hjælp af enkle Gaussiske komponenter. Der er ingen signifikant absorption i spektrene fra observation 2.

0.5-10.0 keV-lyskurverne fra Chandra-observationer 1–4 er vist ovenfor. Dataene blev genbundet til at have skraldelængder på 100 sekunder. Den gennemsnitlige 1 σ-fejl i hver bin ovenfor er mindre end 1,5 tællinger / sek. Den observerede ekstreme variation er faktisk reel. Den gennemsnitlige optællingshastighed i hver observation (eksklusive dip i observation 3, markeret med lodrette blå linjer) er vist med en vandret rød linje. ∼ 14 ksec-dip set i observation 3 indikerer, at H 1743 - 322 sandsynligvis ses ved en høj hældning, svagere dyp kan ses i slutningen af ​​observation 1 og starten på observation 2.

Count-rate-valgt Chandra / HETGS-spektre fra observationer 1–4 er vist ovenfor. I observationer 1, 2 og 4 svarer de sorte data til perioder over den gennemsnitlige optællingshastighed, og de røde data svarer til perioder under den gennemsnitlige optællingshastighed. Den bedst egnede model for de sorte data vises i grønt, og den bedst egnede model for de røde data vises i blåt. I observation 1 er der tegn på, at Fe XXV (λ = 1.850 Å) og Fe XXVI (λ = 1.780 Å) absorptionslinjer er stærkere ved lave optællingshastigheder. De sorte data fra observation 3 svarer til spektret før ∼ 14 ksec dip set i fig. 5, og de røde data svarer til spektret inden i dip. Fe XXV absorptionslinjen er tydeligvis stærkere inden for dip.

Count-rate valgte spektre fra Chandra observation 1 er vist ovenfor. Spektret i sort blev taget fra tidsintervaller med tællingshastigheder større end gennemsnittet plus 5,0 tællinger / sek, mens spektret i rødt blev taget fra tidsintervaller med tællingshastigheder mindre end middelværdien minus 5,0 tællinger / sek. Disse spektre viser en mere tydelig ændring i dybden af ​​Fe XXV-linjen end dem, der er vist i panel 1 i fig. 6.

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5. Vindstrålernes konstruktioner

Selvom NSCAT-dataene giver hidtil uset rumlig og tidsmæssig dækning af strukturen af ​​overfladevind, er målinger af andre dynamisk vigtige variabler (f.eks. Atmosfærisk tryk og den lodrette struktur af det turbulente grænselag) ikke tilgængelige på de rumlige skalaer, der kan løses af NSCAT-vinde til tillader detaljerede analyser af kraftbalancerne i dyserne. NSCAT-dataene er ikke desto mindre nyttige til fortolkning af tidligere offentliggjorte observationer og modeller af jetflyene. Disse tidligere undersøgelser har næsten udelukkende fokuseret på Tehuantepec-strålen, sandsynligvis fordi den er langt den mest energiske af de tre jetfly (se fig. 11b i CFE) og på grund af den næsten fuldstændige mangel på direkte observationer af Papagayo- og Panama-jetflyene. En historisk oversigt over tidligere observationer af Tehuantepec-jetens struktur er præsenteret i afsnit 5a. Strukturerne for hver af de tre jetfly udledt fra NSCAT-observationer er derefter opsummeret i afsnit 5b – d.

En. Historiske observationer af Tehuantepec-strålen

Det har længe været kendt, at Tehuantepec-vindene strækker sig langt ind i Stillehavet. På grund af de sparsomme vindobservationer, der er tilgængelige offshore, bliver strålens detaljerede struktur imidlertid efter at den forlader kysten og blæser over Tehuantepec-bugten først nu klar. Hurd (1929) bemærkede, at Tehuantepec-vindene spredte sig hundreder af kilometer ind i Stillehavet, og at vindretningerne var betydeligt variable i den nedre del af Tehuantepec-bugten. Men der er ingen tegn på, at han var opmærksom på, at vinden drejer anticyklonisk mod vest over bugten. Parmenters (1970) analyse af en enkelt Tehuantepec-vindhændelse fra satellitsky-billeder viste en skurrende linje, der blev fortolket som den forreste kant af kold luft i huludstrømningen. Squall-linjen startede som en ret symmetrisk bue over den nordlige kløft. Efterhånden som tiden skred, forsvandt bueskyen på den østlige side og bevægede sig hurtigt mod vest. Det er uklart, om Parmenter anerkendte dette som bevis for anticyklonisk drejning af aksen for maksimale vinde.

Det første omfattende forsøg på at syntetisere et billede af overfladevindfeltet over Tehuantepec-bugten var en analyse af handelsskibsobservationer foretaget af Roden (1961). Selvom han konkluderede, at kvaliteten af ​​disse historiske data kun var moderat, var han i stand til at vise, at vinden faldt hurtigt øst og vest for jetaksen. Søen mod kysten faldt vindhastigheden dog langsomt, og strålen strakte sig flere hundrede kilometer mod syd. Roden fortolkede linjen med nul vindspænding krøller som aksen for Tehuantepec jet. Nul konturen i hans kort over februar vindstress krølle udviste en meget svag anticyklon krumning, men ikke nok til at antyde nogen væsentlig drejning af Tehuantepec vindstrålen.

Clarke (1988) ser ud til at have været den første til at antyde, at Tehuantepec-vindstrålen drejer anticyklonisk mod vest efter at have forladt kysten. Hans beviser var imidlertid indirekte baseret på satellitmålinger af SST, der viste en kold tunge af vand, der dannedes næsten umiddelbart efter starten af ​​en Tehuantepec-vindhændelse i januar 1986. MinimumsSTT i denne kolde tunge strakte sig sydpå fra kysten og derefter drejet mod vest langs 12,5 ° N. Clarke hævdede, at det pludselige udseende af koldt vand må have været induceret af vindblanding langs vindstrålens sti. Det buede mønster af minimum SST blev derfor fortolket som sammenfaldende med vindstrålens sti.

Schultz et al. (1997) fremlagde for nylig yderligere indirekte beviser til støtte for Clarkes (1988) hypotese om, at Tehuantepec-vindstrålen følger en inerti-sti efter at have forladt kysten. Satellitobservationer viste den forreste kant af kløftudstrømningen under en større Tehuantepec-vindbegivenhed i marts 1993, der blev markeret med en bueformet linje med cumuluskonvektion, der lignede en rebsky, formodentlig orienteret vinkelret på vindretningen. På en måde, der kvalitativt er i overensstemmelse med en vindstråle, der følger en inerti-bane, vendte isokroner af rebskyen anticyklonisk mod vest. Fra de begrænsede direkte vindobservationer, der var tilgængelige på tidspunktet for skyobservationerne, var det ikke muligt at afgøre, om en inerti-balance var kvantitativt gyldig. Imidlertid Schultz et al. (1997) viste, at de 1 ° × 1 ° gitterede analyser af 10 m vinde fra European Center for Medium-Range Weather Forecasts (ECMWF) for den interesserede periode vendte anticyklonisk mod vest langs en sti, der i det mindste var kvalitativt i overensstemmelse med en inerti-sti.

Det eneste forsøg, som vi er opmærksomme på, at konstruere et billede af den detaljerede struktur af overfladevindfeltet i strålen fra direkte observationer over et bredt område af Tehuantepec-bugten, er rapporteret i et par papirer af Barton et al. (1993) og Trasviña et al. (1995). De præsenterede et 3-ugers sammensat gennemsnitskort over overfladevindobservationer fra et par skibe, der undersøgte de oceanografiske og meteorologiske forhold under en moderat Tehuantepec-vindhændelse i slutningen af ​​januar 1989. På trods af begrænsningerne med et 3-ugers sammensat gennemsnit i en periode, hvor the wind strength changed considerably, the anticyclonic turning of the wind jet is clearly evident along the southernmost ship track in their survey. Their wind observations also reveal a symmetric off-axis fanning of the wind jet away from the head of the gulf. They suggested that this fanning contradicted Clarke’s (1988) model of the gap outflow as a narrow inertial jet. The fan-shaped pattern on the edges of the jet evidently indicates a cross-flow component of force away from the axis of the jet.

Because of the difficulty in acquiring high-resolution surface wind measurements with broad areal coverage over the Gulf of Tehuantepec, the most detailed description of a Tehuantepec wind jet that is available to date was developed from a model simulation. The March 1993 Tehuantepec event discussed by Schultz et al. (1997) has recently been simulated by Steenburgh et al. (1998) using the high-resolution Pennsylvania State University–National Center for Atmospheric Research mesoscale model MM5. The model simulation produced an off-axis fanning of the gap outflow similar to the January 1989 event described by Barton et al. (1993) and Trasviña et al. (1995). The winds were strongly anticyclonic to the west of the jet axis and less anticyclonic to the east.

From a careful analysis of the cross-flow momentum balance along Lagrangian trajectories in their simulation, Steenburgh et al. (1998) concluded that the axis of the jet was in almost perfect inertial balance over the distance considered in their analysis. The radii of curvature for trajectories close to the jet axis closely matched those of an inertial path for the gap outflow of 22 m s −1 . The most southerly point considered was at a latitude of about 14.2°, which is about 200 km from the coast. The Steenburgh et al. analysis thus indicates that the jet axis in the model maintained an inertial trajectory over at least this distance.

Away from the jet axis, the Lagrangian trajectories in the model did not follow inertial paths. Trajectories on the west side of the jet had stronger anticyclonic curvature (smaller radii of curvature) than inertial trajectories. The opposite was true on the east side of the jet where trajectories were very nearly straight southward. The momentum balances on the sides of the jet axis indicated that the off-axis fanning of the jet was caused by a strong cross-flow pressure gradient away from the jet axis. The opposing pressure gradients on opposite sides of the model jet axis were established by a mesoscale pressure ridge that developed along the jet axis from the southward advection of cold air of higher-latitude origin. On the west side of the jet, the model pressure gradient augmented the Coriolis acceleration, resulting in a trajectory with stronger anticyclonic curvature than the inertial path along the axis. On the east side of the jet, the pressure gradient opposed the Coriolis acceleration, resulting in less curvature than along the jet axis.

A noteworthy inconsistency between the Tehuantepec winds simulated by Steenburgh et al. (1998) and the observations by Barton et al. (1993) and Trasviña et al. (1995) is a distinct difference in the wind directions on the east side of the jet axis. The observed winds had a much stronger westerly component than the model winds. In fact, the model winds had virtually no westerly component at all. The significance of this discrepancy in the off-axis fanning east of the jet axis is difficult to judge because the observations and model simulation are for two different wind events separated by four years. In addition, composite averaging over 3 weeks was necessary to construct the map of the January 1989 wind field from the ship observations it is conceivable that the greater observed westerly component in this event could be an artifact of the nonsynopticity of the observations. One of the objectives of this study is to investigate the detailed structure of the Tehuantepec wind jet from the NSCAT observations and thus assess the validity and significance of the more extensive off-axis fanning of the jet suggested by the ship observations on the east side of the jet axis.

B. NSCAT observations of the Tehuantepec jet

The structure of the surface wind field over the Gulf of Tehuantepec is clearly depicted in the 2-day composite maps constructed from NSCAT data for the case studies described by CFE. Except during the influence of tropical storm Marco in the late stages of the November case study, the cores of the Tehuantepec jets in all three case studies turned anticyclonically to the west and winds fanned outward from the core of the jet. As noted previously by CFE from the 9-month vector-average wind field and the alignment of the major axes of the velocity variance ellipses, the anticyclonic turning and fanning are persistent features of the Tehuantepec jet. In this section, we quantitatively test the notion that the observed paths of the Tehuantepec jets are consistent with those of inertial jets over the wide range of jet intensities observed during the 9-month NSCAT data record. We also investigate the structure of the off-axis fanning of the jet and relate the observations to the modeling results of Steenburgh et al. (1998).

A purely inertial jet implies circular motion from the centrifugal force that balances the Coriolis force on an air parcel exiting the gap. The addition of frictional forces would retard the wind velocity, resulting in a spiral trajectory with a radius of curvature that decreases with increasing distance from the gap (e.g., Clarke 1988). This theoretical inward spiral is in stark contrast to the NSCAT observations the radius of curvature of the core of the jet consistently increased with increasing distance from the gap, ultimately becoming approximately zonal along 10°N (effectively equivalent to an infinite radius).

Simple dynamical considerations indicate that geostrophic adjustment of the wind jet should occur over a distance of the order of the Rossby radius of deformation (about 600 km over the Gulf of Tehuantepec, as noted in section 5a). For a gap outflow of 15 m s −1 , the radius of an inertial circle at 15°N is r = 400 km. An arc length of 600 km along this inertial circle corresponds to an anticyclonic turning of 86°. The Tehuantepec jet would therefore come into geostrophic equilibrium after about a quarter revolution of an inertial circle. A cross-stream pressure gradient force must develop along the trajectory toward the left of the direction of motion (in opposition to the Coriolis force) so that a near-geostrophic balance is established by the time the gap outflow becomes an easterly jet. Near the coast, the gap outflow cannot be purely inertially balanced off the axis of the jet since lateral turbulent mixing introduces additional accelerations. Nonetheless, it is not unreasonable to hypothesize that the axis of the jet is inertially balanced sufficiently close to the gap.

A rigorous test of the validity of the inertial balance along the axis of the wind jet has not been possible from previous observations since measurements have not been available with sufficient spatial and temporal coverage over the Gulf of Tehuantepec. The approach used here to investigate the possibility of an inertial balance was to determine an inertial path based on each 2-day composite average NSCAT measurement of the speed of the gap outflow. The predicted wind direction was then compared with the observed wind direction at several points along the inertial path.

Because the NSCAT data coverage decreases near the coast owing to land contamination in the radar footprints, a reference location for the speed of the gap outflow was defined to be 15.25°N, 95°W, which is far away from any possibility of land contamination of the radar return. The NSCAT measurements of wind direction at this location were very consistent, averaging about 10° clockwise from north (Fig. 9). Since this reference location is about 75 km south of the coast, some anticyclonic turning is to be expected if the jet is in inertial balance at the gap. Because the reduction of wind speed from frictional effects is small over this short distance, it is reasonable to calculate the radius of an inertial circle based on the wind speed at the reference location. The inertial path for this wind speed was then defined by assuming a wind direction of 0° (northerly) at the gap location of 15.75°N, allowing a geometrical determination of the predicted wind direction at any latitude along the inertial path.

The NSCAT observations of wind directions are shown in Fig. 10 at three latitudes along inertial paths defined as described above, based on the observed wind speeds at the reference location. The solid lines represent the predicted wind direction for an inertial jet as a function of wind speed for wind speeds in excess of 5 m s −1 , which usually constitute a well-defined jet. At wind speeds below about 13 m s −1 there is considerable scatter of the observed wind directions. The scatter decreases at higher wind speeds. At all wind speeds, there are very few cases for which the observed wind direction was larger (more clockwise from north) than the predicted wind direction the predicted wind direction thus constitutes a well-defined upper bound on the distribution of observed wind directions at all three latitudes. The observed anticyclonic turning of the Tehuantepec jets after they leave the coast is thus almost always less than or equal to the predicted turning of a purely inertial jet.

The smaller discrepancies between the predicted and observed wind directions at the highest latitude considered here (top panel of Fig. 10) has implications for the validity of the inertial balance. For gap outflows higher than about 13 m s −1 , the observed wind directions are indistinguishable from the wind direction of a purely inertial jet. At the two more southerly latitudes farther from the coast (middle and bottom panels of Fig. 10), the discrepancies between predicted and observed wind directions increase. This would occur if some lateral force develops in opposition to the Coriolis force, thus causing the winds to veer less anticyclonically than a purely inertial jet. Dynamically, the geostrophic adjustment of large-scale flows results in a cross-stream pressure gradient force that develops in opposition to the Coriolis force soon after the jet leaves the coast. A near-geostrophic balance is established over a distance comparable to the ∼600 km Rossby radius of deformation.

These comparisons between observations and theory must take into account the fact noted by CFE that the spatially averaged NSCAT wind measurements can underestimate the wind speed in regions of strong horizontal gradients such as those near the cores of the Tehuantepec wind jets. The effects of this spatial smoothing are difficult to quantify since the bias, if it exists, is not known. The discrepancy between the observed and predicted wind directions can be almost entirely accounted for if the NSCAT spatially averaged wind speeds are biased low by 20%, which is probably an upper bound on the actual value. However, frictional forces will decrease the wind speed with increasing distance along the axis of the jet [see Fig. 16 of Steenburgh et al. (1998)]. It can be seen from Figs. 11 and 12 below that the wind speed decreases by more than 20% between the coast and the 12.75°N latitude shown in the bottom panel of Fig. 10. This decrease in the wind speed would completely offset any bias from NSCAT underestimates of the speed of the gap outflow.

We therefore conclude that the anticyclonic turning of the Tehuantepec wind jet at the two most southerly latitudes considered in Fig. 10 is generally less than the predicted turning of an inertial jet. This is consistent with the dynamical notion that the forces on an air parcel in the core of the wind jet are in inertial balance at the gap outflow and adjust toward a geostrophic balance with increasing distance from the gap.

Investigation of the off-axis fanning of the Tehuantepec wind jet after it leaves the coast yields additional insight into the dynamical balances within the jet. As noted previously in section 5a, a composite average of three weeks of ship observations by Barton et al. (1993) and Trasviña et al. (1995) suggested a divergent fanning of the jet that is considerably stronger than the fanning in the model simulation of a different event by Steenburgh et al. (1998). From the case studies presented by CFE, the stronger fanning deduced from the ship observations is much more representative of the wind field observed by NSCAT.

An enlargement of the Gulf of Tehuantepec region for the 2-day period 19–20 December 1996 during the December case study described by CFE is shown in the upper-left panel of Fig. 11. The association of this wind event with high SLP in the Gulf of Mexico is shown in Fig. 4 of CFE. The divergence and relative vorticity of this 2-day composite average wind field are shown on the left in the middle and bottom panels, respectively. The jet was strongly divergent in the upper reaches of the gulf with small areas of convergent flow near the coast on the east and west sides of the jet. The concentration of the flow in the core of the jet is evident by the consistently positive relative vorticity east of the jet axis and the consistently negative relative vorticity west of the jet axis.

For comparison, the 2-day composite average of 1° × 1° × 6-h gridded ECMWF analyses 3 of 10-m winds is shown in the upper-right panel of Fig. 11. To avoid interpretational difficulties owing to possible NSCAT sampling errors, this wind field was constructed by trilinear interpolation of the 1° × 1° × 6-h gridded ECMWF winds to the same times and locations as the NSCAT observations. Overall, the ECMWF analyses of this event are qualitatively quite good. The underestimation of the wind speed and the offshore displacement of the maximum intensity of the jet are characteristic features of the ECMWF analyses over the 9-month duration of the NSCAT data record.

The most striking difference between the NSCAT and ECMWF wind fields is the much stronger westerly component in the NSCAT winds on the east side of the jet. In fact, there is no westerly component on the east side of the jet axis in the ECMWF wind field. As a consequence of the discrepancy between the off-axis fanning of the jet in the NSCAT observations and ECMWF analyses, the wind jet is much less divergent in the ECMWF wind field (middle panels of Fig. 11). The NSCAT and ECMWF relative vorticity fields also differ significantly on the east side of the jet (see bottom panels of Fig. 11). In comparison, the relative vorticity fields are more similar on the west side of the jet.

Enlargements of the Gulf of Tehuantepec region during the November 1996 and March 1997 case studies described in sections 3b and 3c of CFE are shown in Fig. 12. The wind divergence and relative vorticity fields (not shown) were similar to the December example in Fig. 11. As in the December example, the NSCAT winds in the November and March examples had large westerly components on the east side of the jet. Also similar to the December example, the ECMWF winds on the east side of the jet had only a weak westerly component during the 2-day period 8–9 November and no westerly component at all during the 2-day period 7–8 March.

The discrepancies between the NSCAT and ECMWF wind directions on the east side of the Tehuantepec jet in the three examples considered above are a general feature over the 9-month NSCAT data record. This is summarized in Fig. 13, which shows the NSCAT and ECMWF wind directions at a location 1° east of the jet axis at 15°N, which is about 100 km south of the gap outflow. The ECMWF wind directions cluster tightly around 0° (northerly). While there is more directional variability at low to moderate wind speeds, the NSCAT wind directions on the east side of the jet axis are almost always more westerly than the ECMWF wind directions, clustering about 27° counterclockwise from north.

Although less consistent than on the east side of the jet, there are systematic differences between the NSCAT and ECMWF wind directions on the west side of the jet as well. As shown in Fig. 14, the NSCAT wind directions west of the jet axis are more variable than the ECMWF wind directions. With increasing wind speed, the wind generally becomes more easterly in the NSCAT data but more northerly in the ECMWF analyses. At wind speeds higher than about 14 m s −1 , the NSCAT wind directions cluster around 45° while the ECMWF wind directions cluster about 30°. The ECMWF wind directions at high wind speeds are thus consistently more northerly than the NSCAT observations on the west side of the jet axis. The fanning of strong wind jets is therefore also generally weaker on the west side of the jet axis in the ECMWF wind fields.

The weak fanning of the jet in the ECMWF analyses is almost identical to the weak fanning in the mesoscale model simulation of a March 1993 Tehuantepec wind event by Steenburgh et al. (1998). The detailed analysis of the momentum balance by Steenburgh et al. may therefore provide insight into the reason for the weak fanning on the east side of the jets in the ECMWF analyses. They determined the force balance along three Lagrangian trajectories in a jet with gap outflow of 22 m s −1 . Along a trajectory that corresponded to the axis of the jet, they found a zero cross-flow pressure gradient and near-perfect inertial balance in the upper reaches of the gulf within 200 km of the coast considered in their analysis. This is consistent with the results in the top panel of Fig. 10.

Because of the high degree of scatter in the relationships between the NSCAT and ECMWF wind directions on the west side of the jet axis, it is difficult to relate the NSCAT observations to the analysis of the momentum balance by Steenburgh et al. However, on the east side of the jet axis where the wind directions in the NSCAT observations and ECMWF analyses are systematically different, the Lagrangian trajectory of an air parcel in the Steenburgh et al. model was almost due southward, as in the winds east of the jet axis in the ECMWF analyses in Figs. 11 and 12. The force balances responsible for the weak fanning in the Steenburgh et al. model may therefore be similar to the force balances on the east side of the jet in the ECMWF analyses. Along the trajectory analyzed by Steenburgh et al., the cross-flow pressure gradient force exceeded the Coriolis force in the model simulation. The precise nature of the westward residual force required to balance the forces on the parcel was not explicitly identified by Steenburgh et al., except to state that it was a combination of diffusion, the parameterized boundary-layer processes in the model, and numerical truncation error.

The consistently greater degree of fanning of the winds on the east side of the jet in the NSCAT observations implies that there is too much westward acceleration in the mesoscale model and the ECMWF “first-guess” fields in this data-sparse region. This could arise either from an insufficient eastward pressure gradient or an excessive westward residual force. The latter might be an indication of systematic errors in model parameterizations of boundary layer processes. In any case, it is highly unlikely that the stronger fanning on the east side of the jet in the NSCAT observations could be attributed to systematic errors in the NSCAT winds. It is much more likely indicative of errors in the Steenburgh et al. simulation and the ECMWF analyses.

C. NSCAT observations of the Panama jet

An examination of the Panama wind events during the 9-month NSCAT data record reveals that the wind field over the upper reaches of the Gulf of Panama (within a few hundred kilometers of the coast) often shows characteristics similar to the Tehuantepec wind jet. In particular, the core of the jet tends to turn anticyclonically toward the west, suggesting that the jet may be in inertial balance at the gap. The winds also fan away from the axis of the jet as in the Tehuantepec examples considered in section 5b. Because the wind speeds are low in the Panama jet (seldom exceeding 8 m s −1 , see CFE), the anticyclonic turning is easily disrupted by other meteorological phenomena unrelated to the gap outflow. This is especially true in the southern reaches of the gulf where the anticyclonic turning of the Panama wind jet can be altered by the southwesterly cross-equatorial flow often found in the eastern tropical Pacific.

An enlargement of the Gulf of Panama region during a particularly clear example of the Panama wind jet at a time when there was no cross-equatorial flow is shown in Fig. 15. The map of the surface vector wind field in the upper-left panel and the corresponding maps of the divergence and relative vorticity fields in the middle and bottom panels were constructed from NSCAT observations over the 2-day period 9–10 March 1997 during the March case study described by CFE. For this event, the characteristics of the Panama jet are very similar to those of the Tehuantepec examples shown in Figs. 11 and 12. The Panama jet turned anticyclonically to the west with a radius of curvature larger than the inertial path and there was a strongly divergent fanning of the jet in the upper reaches of the Gulf of Panama.

The ECMWF analyses of this event are shown in the right panels of Fig. 15. As in the Tehuantepec examples in section 5b, the divergent fanning of the Panama jet during this event was much weaker in the ECMWF wind fields. The relative vorticity (bottom panels of Fig. 15) is similar on the east side of the jet axis in the NSCAT and ECMWF wind fields. On the west side, however, the anticyclonic turning of the jet is much stronger in the NSCAT observations.

D. NSCAT observations of the Papagayo jet

The characteristics of the Papagayo jet were fundamentally different from the Tehuantepec and Panama wind jets. The core of the Papagayo jet never turned anticyclonically to the north during the 9-month NSCAT data record. The inertial balance evidently plays no significant role in the dynamics of the Papagayo gap outflow. This may be an indication that the gap through the Nicaraguan lake district is sufficiently wide that a near-geostrophic balance is maintained over Central America as the Caribbean trade winds blow across the isthmus and over the eastern Pacific Ocean. The 2.5° × 2.5° resolution of the NCEP SLP fields analyzed in section 4 is too coarse to quantitatively test the validity of the geostrophic balance in the Papagayo gap. However, the speculation about the geostrophic nature of the Papagayo jet is consistent with the zonal alignment of the cross-isthmus contours of the correlation between Papagayo winds and SLP in the middle panel of Fig. 8 and the high correlation of 0.82 between Papagayo winds and the meridional pressure gradient in the Caribbean noted in section 4.

An inspection of the topographic map in Fig. 1 of CFE questions the validity of the above speculation. The width of the Nicaraguan lake district is comparable to that of the Panama gap, yet the tendency for anticyclonic turning of the Panama jet suggests that the inertial balance has relevance to the winds over the Gulf of Panama. The answer to this paradox may lie in the fact that the Panama gap is oriented from southwest to northeast but the winds are predominantly northerly in the upper reaches of the Gulf of Panama. The effective gap width perpendicular to northerly winds blowing across the Isthmus of Panama is therefore much narrower than the actual gap width.

Although there is no anticyclonic turning of the core of the Papagayo wind jet, the fanning of the wind field away from the jet axis is qualitatively similar to the fanning observed in the Tehuantepec and Panama wind jets. This is evident from the case study examples presented by CFE. An enlargement of the Papagayo region during the period 4–5 March 1997 in the March case study summarized in section 3c of CFE is shown in Fig. 16. The divergence of the fanning away from the axis of the jet near the coast is considerably weaker and more spatially variable than in the Tehuantepec and Panama examples presented in the previous sections. These characteristics of the divergence field are typical of the Papagayo wind jet over the NSCAT data record. The nearly zonal line of zero relative vorticity emanating from the Papagayo gap indicates that there was very little turning of the axis of the jet after leaving the coast in this particular event.

From the ECMWF maps of this March 1997 Papagayo wind event (right panels of Fig. 16), the fanning of the wind jet was well reproduced in the ECMWF analyses. However, the winds were much more concentrated near the axis of the jet in the NSCAT observations, as evidenced by the band of stronger negative relative vorticity on the north side of the jet axis.


Astronomy: Revealing the complex outflow structure of binary UY Aurigae

An international team of astronomers, led by Dr. Tae-Soo Pyo (Subaru Telescope, NAOJ), has revealed a complicated outflow structure in the binary UY Aur (Aurigae). The team observed the binary using the Gemini North"s NIFS (Near-Infrared Integral Field Spectrometer) with the Altair adaptive optics system. The team found that the primary star has a wide, open outflow, while the secondary star has a well-collimated jet.

Because many stars form together as companions in binary or multiple systems, investigating these systems is essential for understanding star and planet formation. Although jets (i.e., narrow bright streams of gas) and outflows (i.e., less collimated flows of gas) from single young stars are ubiquitous, only a few observations have shown jets or outflows from multiple, low-mass young stars. Therefore, the current team chose to examine the outflow structure of binary UY Aur, which is a close binary system composed of young stars separated by less than an arcsecond (0." 89).

UY Aur has a very complicated structure. Both the primary star (UY Aur A, more masive and brighter) and the secondary star (UY Aur B, fainter and cooler) have small circumstellar disks (disks of gas and material orbiting around them). In addition, a circumbinary disk of the type that has been resolved and imaged . Receding ("redshifted") jets have been observed, and approaching ("blueshifted") ones have been reported for this system. However, their driving sources are not clear, because the spatial resolution of the images was too low (> one arcsecond).

To better understand this system, the team began by trying to identify the driving source of the receding jets. To separate the binary stars and distinguish their driving sources, they used Gemini North's NIFS with its adaptive optics system to observe this close binary system in the 1-micrometer infrared wavelength region. Since ionized iron gas ([Fe II]) traces shocked gas in jets and outflows very well, the team used iron gas emissions to examine the emission gas distribution. They found that [Fe II] is associated with both the primary and the secondary stars.

In addition, they found that the shape of the gas distribution conformed to simulations of gas streaming between the primary and secondary stars. However, the high velocity of the gas (100 km/s or > 20,000 mile/h) indicated that it emanated from the close vicinity of stars rather than arose in the disk gas around the two stars.

Further investigation of the emission structure involved separation of the receding and approaching emissions. The team found that the distribution of gas was different for each of the stars. While the approaching gas was widely spread in an outflow from the primary star and slightly connected with the secondary star, the receding gas was spread widely toward the secondary star and flowing beyond it.

What explains this difference? The team analyzed the system in terms of bipolar outflow, i.e., each star has a disk and ejects both blueshifted (approaching) and redshifted (receding) outflows or jets. The primary ejects wide, open bipolar outflows. Its redshifted (receding) outflow overlaps with the secondary. In contrast, the approaching gas from the secondary is distributed in a well-collimated bipolar jet, with its blueshifted flow tilted toward the wide, open wind from the primary. It is known from mid-infrared (wavelength of

10 micrometer) observations that the circumstellar disk of the secondary is not aligned with the plane of the circumbinary disk. This misalignment is consistent with jet from the secondary tilted toward the wide, open outflow from the primary star.

Two jets from a binary system can be explained if the jets emanate from each of the star-disk system. Some binaries show only one jet or outflow. A larger sample of [Fe II] gas distribution toward binary and multiple young-star systems can clarify how typical the outflow structure of the UY Aur system is.


What is the difference between wind, jet and outflow? - Astronomi

Can you please tell me what factors cause airplane times to differ between travels to east and to west.

It's interesting that you ask this - I am directly experiencing it right now as I sit on an airplane from the UK. It took 5 hours to go West-East on this journey, but is taking about 7 East-West. The reason for the difference is an atmospheric phenomena known as the jet stream. The jet stream is a very high altitude wind which always blows from the West to the East across the Atlantic. The planes moving at a constant air speed thus go faster in the West-East direction when they are moving with the wind than in the opposite direction.

Every planet/moon has global wind that are mostly determined by the way the planet/moon rotates and how evenly the Sun illuminates it. On the Earth the equator gets much more Sun than the poles. resulting in warmer air at the equator than the poles and creating circulation cells (or "Hadley Cells") which consist of warm air rising over the equator and then moving North and South from it and back round.

The Earth is also rotating. When any solid body rotates, bits of it that are nearer its axis move slower than those which are further away. As you move north (or south) from the equator, you are moving closer to the axis of the Earth and so the air which started at the equator and moved north (or south) will be moving faster than the ground it is over (it has the rotation speed of the ground at the equator, not the ground which is is now over). This results in winds which always move from the west to the east in the mid latitudes.

All of the global wind patterns are illustrated in the below diagram taken from the Harvard Equable Climate Dynamics Website.

Denne side blev sidst opdateret den 27. juni 2015.

Om forfatteren

Karen Masters

Karen var kandidatstuderende ved Cornell fra 2000-2005. Hun fortsatte med at arbejde som forsker i galakse-redshift-undersøgelser ved Harvard University og er nu på fakultetet ved University of Portsmouth tilbage i sit hjemland i Storbritannien. Hendes forskning har for nylig fokuseret på at bruge galaksernes morfologi til at give spor til deres dannelse og udvikling. Hun er projektforsker for Galaxy Zoo-projektet.


Bifurcated outflow jet in a solar wind reconnection exhaust

We present new observations of the reconnection outflow jet obtained from the crossing of a solar wind reconnection exhaust by the Wind spacecraft on 5 March 2001. The outflow jet is characterized by a bifurcated configuration, which is different from typical reconnection exhausts. The two outflow jets are mainly distributed in the region close to the exhaust boundaries. Between the two jets, the bulging of the magnetic field and the slight depression of the plasma density are observed. The possible mechanism for the bifurcation of the outflow jet has also been investigated by using a magnetohydrodynamics (MHD) simulation of Petschek-type reconnection. The dynamic patterns of the reconnection exhaust are analyzed in detail. We find that the bifurcated jet is one of the transient configurations produced in the magnetic reconnection. Other observed features of the exhaust show similar agreement with the predictions from the simulation. The study of the reconnection exhaust, over multiple spatial scales, provides an insight into the dynamic evolution of solar wind reconnection exhausts.

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