ATOC 4720 class 40: Thermally-driven circulation in tropics Maintenance of thermal wind equilibrium; The monsoon circulation; 3. Circulation over the troical oceans: ITCZ;

Previous class: Symmetric Hadley Cells (f=0) High P Pressure High P High P Low P

OBSERVATIONS: WINTER EQ

EFFECT OF ROATION! Assume an air parcel at EQ, u=0 Westerly winds! Geostrophic winds: parallel to isobars!

Maintenance of thermal wind equilibrium CF: generate Motion “along isobars”

OBSERVATIONS: monsoon&ITCZ SUMMER

OBSERVED MONTHLY WIND AND PRECIPITATION JAN ITCZ APR ITCZ JULY MONSOON OCT ITCZ

NCEP winds and satellite TRMM SST JAN APR JULY OCT

Heavy precipitation in the tropics are characterized by: [1] SST slightly higher than surroundings; [2]A slight depression (low level low pressure, high level high pressure (upward bulge) of p surfaces); [3]Cyclonic flow in the lower and anticyclonic flow in the upper troposphere; [4] Lower tropospheric convergence and upper level divergence; [5]An upward mass-flux with mamximum values in the middle Troposphere (rising motion);

Dynamical and thermodynamial explanations using the equations we have learnt: Demonstrate on blackboard;

Idealized monsoon circulation: no rotation

Realistic surface feature of the monsoon

ITCZ: refer to previous figures Low pressure beult; Wind convergence; part of Hadley Cell; Higher SST; Heavy precipitation;