The Atmosphere: Part 6: The Hadley Circulation Composition / Structure Radiative transfer Vertical and latitudinal heat transport Atmospheric circulation Climate modeling Suggested further reading: James, Introduction to Circulating Atmospheres (Cambridge, 1994) Lindzen, Dynamics in Atmospheric Physics (Cambridge, 1990) Calculated rad-con equilibrium T vs. observed T pole-to-equator temperature contrast too big in equilibrium state (especially in winter) Zonally averaged net radiation Diurnally-averaged radiation Implied energy transport: requires fluid motions to effect the implied heat transport Observed radiative budget Roles of atmosphere and ocean Trenberth & Caron (2001) net ocean atmosphere Rotating vs. nonrotating fluids u sin f = 0 f > 0 f < 0 Hypothetical 2D atmosphere relaxed toward RCE 2D: no zonal variations Annual mean forcing symmetric about equator A 2D atmosphere forced toward radiative-convective equilibrium T e (,p) (J = diabatic heating rate per unit volume) Hypothetical 2D atmosphere relaxed toward RCE a r Above the frictional boundary layer, Absolute angular momentum per unit mass Angular momentum constraint Above the frictional boundary layer, In steady state, Angular momentum constraint Above the frictional boundary layer, In steady state, Either 1) v=w=0 Or 2) but m constant along streamlines T = T e (,z) U(ms -1 ) (if u=0 at equator) Angular momentum constraint Above the frictional boundary layer, In steady state, Either 1) v=w=0 Or 2) but m constant along streamlines T = T e (,z) U(ms -1 ) (if u=0 at equator) solution (2) no good at high latitudes Near equator, u finite (and positive) in upper levels at equator; angular momentum maximum there; not allowed solution (1) no good at equator Hadley Cell T = T e solution (2) no good at high latitudes Near equator, u finite (and positive) in upper levels at equator; angular momentum maximum there; not allowed solution (1) no good at equator Hadley Cell T = T e Observed Hadley cell v,w Structure within the Hadley cell Hadley Cell T = T e In upper troposphere, Structure within the Hadley cell Hadley Cell T = T e In upper troposphere, J Observed Hadley cell u v,w Subtropical jets Structure within the Hadley cell Hadley Cell T = T e Near equator, In upper troposphere, But in lower troposphere, (because of friction ). T~ 4 Te~2Te~2 Structure within the Hadley cell Hadley Cell T = T e Near equator, In upper troposphere, But in lower troposphere, (because of friction ). T~ 4 Te~2Te~2 Vertically averaged T very flat within cell Observed Hadley cell T v,w Structure within the Hadley cell Hadley Cell T = T e Near equator, In upper troposphere, But in lower troposphere, (because of friction ). T~ 4 Te~2Te~2 TT e : diabatic cooling downwelling edge of cell The symmetric Hadley circulation JJA circulation over oceans (ITCZ = Intertropical Convergence Zone) Monsoon circulations (in presence of land) summerwinter Satellite-measured (TRMM) rainfall, Jan/Jul 2003 Satellite-measure (TRMM) rainfall, Jan/Jul 2003 ITCZ South Asian monsoon deserts Heat (energy) transport by the Hadley cell Poleward mass flux (kg/s) = M ut Equatorward mass flux (kg/s) = M lt Mass balance: M ut = M lt = M Moist static energy (per unit mass) E = c p T + gz + Lq Net poleward energy flux F = M ut E ut M lt E lt = M(E ut E lt ) But (i)Convection guarantees E ut = E lt at equator (ii) Hadley cell makes T flat across the cell weak poleward energy transport Roles of atmosphere and ocean Trenberth & Caron (2001) net ocean atmosphere