Chapter 3 Flashcards
Trade winds are ………….. in winter and are …………….. in summer over ………..
easterlies
westerlies
monsoon areas
variation with heigh depends on
meridional temperature gradient
Easterlies in winter become ….jet
westerly
what winds will exist on upper level:
- winds are westerlies through the year
- atlantic and
- much of the pacific (E and C)
- high level easterlies
- west pacific
- indian ocean
- africa
- Summer monsoon
- NHS summer
- In other areas, the easterlies at higher levels diverge and become westerlies
- the upper level westerlies strengthen and reach jet stream speed to subtropical jet close to 30 N and S
In general summer monsoon circulation have
westerlies at low levels
easterlies at high level (middle and upper troposphere)
During NH summer
strong easterly winds (E Jet stream) stretch from SE asia to africa
TEJ
Tropical easterly Jetstream
(100-200)
TEJ are formed
- during NH summer (june to sept/oct)
- over southeast asia to north africa
- between 5 and 20 N
- in the layer between 100-200 hPa
TEJ strength:
Its Maximum speed 40-50 m/s
westerly jet stream
direct circulation in the west (entrance) and indirect circulation in east (exit) of jet
AEJ
african easterly jet
(west african mid trop. Jet)
(600-700)
charactaristics of AEJ
- AEJ is formed over N tropical africa and adjoining east atlantic
- found during NHS summer. It is fully developed April - November
- Found between 700 and 600 hPa between 13 and 17 N
- Strongest During west african monsoon (Jan - Sep)
- wind speed 10-25 m/s
cause of formation of AEJ
- strong reversal in meridional temperature gradient (increase of temperature from equator towards the pole)
- due to saharn air layer (elevated warm air)/ SAL
- created by saharan desert to the north
- when AEJ is furthest north (15-20 N) it is maintained by the mechanical effect of the topography, which perturbs (small changes) low level easterlies and results in acceleration of the winds (provides energy for the maintenance) particularly in the lee of the mountains. (provides energy for AEJ)
- due to saharn air layer (elevated warm air)/ SAL
(THERMAL)
Maintenace of AEJ
Mechanical
effect of AEJ
- Strong vertical wind shear generated by
- the AEJ and surface monsoon westerlies to help to organize deep convection north and south of the AEJ
Tropical easterly Jet is caused by:
- high temperature (cause reversal in meridional temperature gradient)
- upper level anticyclone
over the Tibetan plateau (unique feature)
circulations around TEJ:
- east of the Jet/ entrance (direct)
- south east asia
- west of the jet/ exit (indirect)
- North africa
effect of TEJ
- Entrance region
- enhance convection over south india and the adjoining ocean
- Exit region
- surpresses vertical motion over near equatorial africa and the atlantic
East african low level Jet
somali jet
charactaristics of east african low level jet
- maximum wind speeds are found near 850 hPa
- it is a south westerly jet stream (cross equatorial jet)
- it is intense from june to august, with average monthly max speed of 18 m/s (on daily basis the maximum may be 50 m/s)
- maximum wind speed are found north of madagascar and off somali coast
- a split in the axis of the jet over the arabian sea
cause of the somali jet:
the southeasterly trades on the northern side of the subtropical high near the mascarene turn to the righ (due to corriolis effect) and blow from the SW to the North of the equator
importance of somali jet
feeds moisture to the indian summer monsoon
