Plan Tropical Meteorology Training course realized in 2005 by Florent Beucher, ENM/EGM...
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Transcript of Plan Tropical Meteorology Training course realized in 2005 by Florent Beucher, ENM/EGM...
PlanPlanTropical MeteorologyTropical Meteorology
Training course realized in 2005 byTraining course realized in 2005 byFlorent Beucher, ENM/EGMFlorent Beucher, ENM/EGM
[email protected]@meteo.fr office : C153 office : C153 : 94-30 : 94-30
Objectives :
Descriptive knowledge of the medium state and the variability of the tropical atmosphere for a 15 to 20 hours training course
This course is available on this web site :
general contents
http://webrp.enm.meteo.fr/cms/view/12/content/meteo_trop/cours_meteotrop_anglais
Tropical MeteorologyTropical MeteorologyBibliography of this course :
• S.Hastenrath : Climate and circulations of the tropics, 1985
• G.C Asnani : Tropical Meterology (Vol.1 et vol.2), 1982
• Adrian E. Gill : Atmosphere-Ocean Dynamics (chap.11 on tropics)
• Ding Yihui : China Monsoon,1994
• Herbert Riehl : Climate and Weather in the tropics, 1979
• Robert A. Houze : Clouds dynamics
• In French : OMM n° 305 : guide su systeme mondial du traitement des données, chap.5 , written in 1993
• And various paper from JAS, MWR etc…
More details about tropical meteorology
on UFR Web-site :http://intra-ufr.enm.meteo.fr/pages/UFR/ufr_index.htm
general contents
Tropical MeteorologyTropical Meteorology
Definition :
• Tropics are located between the both belt of subtropical high pressure = about 50% of the sphere (30°N/30°S)
• These belts as the tropic regions move with the season.
Equator
A
A
Ridge = 30°N
Ridge = 30°S
Location of tropical atmosphere in annual mean or at equinox :
general contents
Tropical MeteorologyTropical MeteorologyTropical MeteorologyTropical Meteorology
Definition :
• Tropics are located between the both belt of subtropical high pressure = about 50% of the sphere (30°N/30°S)
• These belts as the tropic regions move with the season.
Equator
A
A
Ridge = 35°N
Ridge = 25°S
Location of tropical atmosphere in august :
Northwardshift of tropicalatmospherefrom februaryto august
general contents
Tropical MeteorologyTropical Meteorology
Definition :
• Tropics are located between the both belt of subtropical high pressure = about 50% of the sphere (30°N/30°S)
• These belts as the tropic regions move with the season.
Equator
A
A
Ridge = 25°N
Ridge = 35°S
Southwardshift of tropicalatmosphere fromfrom august to february
Location of the tropical atmosphere in february :
general contents
equator
A
A
Ridge = 25°N
Ridge = 35°S
Météorologie Tropicale Météorologie Tropicale
= vertical sounding
- Realize a radiosondage in the summer hemisphere of the tropical atmosphere :
general contents
Location of the tropical atmosphere in february :
Southwardshift of tropicalatmosphere fromfrom august to february
Acentre de ladorsale = 25°N
• As the tropical atmosphere is nearly barotropic, the vertical shear is light :- trades winds in low tropo. (5 à 10kt)- easterlies in mid-tropo. (10kt)- easterlies in upper tropo. (20 kt)
• This representative vertical souding is observed : - in february within a latitud band 10°N-15°S, - in august within a latitud band 30°N-10°S
general contents
equator
A
A
Ridge = 25°N
Ridge = 35°S
Météorologie Tropicale Météorologie Tropicale
= vertical sounding
- Realize a radiosondage in the winter hemisphere of the tropical atmosphere :
general contents
Location of the tropical atmosphere in february :
Southwardshift of tropicalatmosphere fromfrom august to february
Acentre de ladorsale = 25°N
• Comme l’atmosphère tropicale est quasi-barotrope, le cisaillement vertical de vent est faible :- alizés en basses couches (5 à 10kt)- vent d’est en moyenne tropo (10kt)- vent d’est en haute tropo (20 kt)
• Ce radiosondage typique s’observe : - en février entre 10°N-15°S, - en août entre 30°N-10°S
• On the poleward flanks ofthe tropical atmosphere, the baroclinicity and the vertical wind shear increase :- trades winds in low tropo. (5 à 10kt)- light westerlies in mid-tropo. (10kt)- strong westerlies in upper tropo. (60 kt)= JOST
• For instance, during the winter season in the french tropical islands, the mean state of the tropical atmosphere nearly behaves like in mid-latitudes. The theory ofAnasyg-Presyg could be work ?
• This representative vertical sounding is observed : : -in february northward of 15°N and southward of 25°S, -in august northward of 35°N and southward of 15°S
general contents
Radiosondage Analyse ARP1.5 Source : Météo-France
5 main characteristics of the tropics :
The first three ones because of radiative considerations:
① Between 30°S/30°N, radiative energy >0 at the top of atmosphere
Outward tropics, radiative energy <0 at the top of atmosphere :
⇨ we observe a strong meridional meridional radiative desequilibrium between the equator and the poles
⇨ initiates a planetary-scale meridian circulation in atmopshere called ‘Hadley Cell’‘Hadley Cell’
⇨ initiates a planetary-scale ocean circulation directed northward (Gulf Stream, Kuroshio etc..)
② Close to the equator, the radiative energy is much higher at surface than at the top of atmosphere :
⇨ we observe a strong verticalvertical radiative desequilibrium between surface and top of atmosphere
⇨ initiates strong vertical velocities = ascent branch of
both Walker cells and Hadley cells
③ Diurnal variability is higher than annual variability ⇨ the diurnal cycle is very important under tropics
Tropical MeteorologyTropical Meteorology
general contents
Tropical MeteorologyTropical Meteorology
5 main characteristics of the tropics (the continuation) :
The last two ones because of light Coriolis parameter f (10-5 s-1 at 10° of latitude) :
④ Horizontal gradient of geopotential slack compared with mid-latitude ⇨ the tropics are nearly ‘barotropic’
⑤ The flow is essentially divergent in tropics, i.e. the rotational part of the flow is insignificant except two cases :
- at planetary scale as equatorial waves (geostrophic balance)- cyclones (cyclostrophic balance)
general contents
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
Chap.1 Different scales of the atmosphere
Meso-scale
or convective scale
= ‘little scale’
Synoptic or
Planetary scale
= ‘large scale’
R ~ NH/(f+ ζr)Atmospheric deformation radius
(depends on f, stability of the atmosphere
and the relative vorticity)
Quasi-horizontal
balanced flow :
Geostophic and hydrostatic
equilibrium
Moi
st c
onve
ctiv
e in
stab
lilit
y 3D
Méso
-scale
MCS
R
(km)
11
100
10
10 000
1000
10010 10 0001000L (km) =
Horizontal
scale
Source : Ooyama 1982
L = L
= H
H thickness of
the atmosphere
10 km
Mid-
Latitudes
Tropics
Tropical
Cyclone
general contents
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
200 hPa
Interactions between the convection (little scale) and larger scales :
Chap 2.Energy sources for the initiation and growth of the equatorial waves and tropical disturbances
⇨ The convection produces synoptic disturbances over a horizontal-scale λR (about 1000 km under tropics) after 1/f time-scale (about 1 day under tropics)
⇨ Interactions between convection and larger scale are realized through inertial-gravity waves (IG)
⇨ But this interaction is efficient only if release of latent heat is important (big population of cumulonimbus)
850 hPa
200 hPa
850 hPa
time
general contents
Source : Météo-FranceLafore
Illustration of this process at the end of May after the Indian Monsoon onset :
Chap 2.Energy sources for the initiation and growth of the equatorial waves and tropical disturbances
• All over tropics [30°N-30°S], by thermal forcing we observe high geopotential but with a slack gradient since tropics arenearly barotropic• By release of latent heat over Indian and Asian monsoon occur an increase of geopotential
H H
H
general contents
Géopotentiel at 200 hPa; 22/07/05; Analyse CEP 1.5. Source : Météo-France
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
PlanPlan
1. Different scales of the atmosphere
2. Energy sources for the initiation and the growth of the equatorial waves and tropical disturbances
3. Regional climates in tropics
4. Equatorial trapped waves and planetary waves oscillations (MJO,QBO)
5. Conceptual models of synoptic tropical disturbances in summer
6. Interactions between the mid-latitudes and the tropics
7. ENSO
Meridional desequilibrium energy : Hadley cell in annual mean
Between 30°S/30°N, the radiative energy is positive at the top of atmosphere (# 60 W/m2 at equator):
Planetary-scale meridian circulation called ‘Hadley Cell’
+ 60 W/m2
Circulation linked to the Hadley cell ofSouthern hemisphere
km
Circulation linked to the Hadley cell ofNorthern hemisphere
-100 W/m-100 W/m22-100 W/m-100 W/m22
°N°S
general contents
Modèle 2D méridien ; Source : Météo-France
Seasonal variability :Hadley cell in march (spring equinox)
ITCZ located at equator
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 1°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 2°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 3°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 4°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 5°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 6°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 7°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 8°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 9°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 10°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 11°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
ITCZ located at 12°N
Seasonal variability of the Hadley cell from march to july
general contents
Modèle 2D méridien ; Source : Météo-France
Circulation linked to the Hadley cell of summer hemisphere
Circulation linked to theHadley cell of the winterhemisphere, 10 times more developped than in summer
⇨ Consequently, the upper troposheric jet at 30° of latitude, called ‘subtropical Jet or STJ’ is much more developped in the winter hemisphere than in the summer hemisphere
+ 100 W/m+ 100 W/m22- 180 W/m- 180 W/m22 - 80 W/m- 80 W/m22
°N°S
Seasonal variability : Hadley cell in july
ITCZ
12°N
Retour début animation
STJ STJ
general contents
Modèle 2D méridien ; Source : Météo-France
Vertical desequilibrium energy : Walker and Haldey cells
Close to the equator, the radiative energy is much higher at surface (+140 W/m2) than at the top of atmosphere (+60 W/m2) :
⇨ we observe a strong verticalvertical radiative desequilibrium between surface and top of atmosphere
⇨ initiates strong vertical velocities = ascent branch of both Walker cells and Hadley cells
general contents
Source : Météo-France. Florent Beucher
Walker cell :Shematic description
• When vertical- zonalvertical- zonal circulations are averaged over one year and over a latitude band 15°N-15°S, the averaged circulation is nearly vertical-equatorial vertical-equatorial (see the figure above) and called ‘Walker cell’
• The 3 ascending branches explains the 3 deep convection pole : Africa, Indonesia in january then India in july, Central America
• The 3 descending branches explains subsidence over Eastern Pacific, Eastern Atlantic and Western Ocean Indian
Annual mean [15°S-15°N] vertical cross-section of circulationSource : Newell, 1979
z
equator
general contents
References
- De Moor G. et P. Veyre, 1991 : ‘Les bases de la météorologie dynamique’ Cours et Manuel n°6 - p.193 - Lafore : Support de cours ‘Convection’, Partie 2 écrite par J. P. Lafore CNRM/GMME.
- Morel P. éditeur (1973) : ‘Dynamic Meteorology’ –D. Reidel Publishing Company – 622 p.
- Newell, R. E., 1979 : ‘Climate and the Ocean’ . Amer. Sci., 67, pp. 405-416
- Ooyama, 1982 : ‘Conceptual evolution of the theory and modeling of the tropical cyclone. J. Meteor. Soc. Japan,, 60, pp. 369-380