A study of the seasonal migration of ITCZ and the quasi-periodic oscillations in a simple monsoon system using an energy balance model

Summary A zonally averaged global energy balance model with feedback mechanisms was constructed to simulate (i) the poleward limits of ITCZ over the continent and over the ocean and (ii) a simple monsoon system as a result of differential heating between the continent and the ocean. Three numerical experiments were performed with lower boundary as (1) global continent, (2) global ocean and (3) continent-ocean, with freezing latitudes near the poles. Over the continent, midlatitude deserts were found and the ITCZ migrates 25° north and south with seasons. Over a global swamp ocean results do not show migration of ITCZ with time but once the ocean currents are introduced the ITCZ migrates 5° north and south with seasons. It was found that the seasonal migration of ITCZ strongly depends on the meridional distribution of the surface temperature. It was also found that continent influences the location of the oceanic ITCZ. In the tropics northward progression of quasi-periodic oscillations called events are found during the pre- and post-monsoon periods with a period of 8 to 15 days. This result is consistent with the observed quasi-periodic oscillations in the tropical region. Northward propagation of the surface temperature perturbation appears to cause changes in the sensible heat flux which in turn causes perturbations in vertical velocity and latent heat flux fields.List of Symbols vertical average - ₀ zonal average - vertical mean of the zonal average - _0s zonal average at the surface - _0a zonal average at 500 mb level - latitudeWe now define the various symbols used in the model rate of atmospheric heating due to convective cloud formation (K/sec) - dp/dt (N/m²/sec) - density - potential temperature (K) - rate of rotation of the earth (rad/sec) - empirical constant - humidity mixing ratio - ^* saturated humidity mixing ratio - opacity of the atmosphere - ₁,₂ factors for downward and upward effective black body long wave radiation from the atmosphere - Stefan-Boltzmann constant - emissivity of the surface - _D subsurface temperature (K) - a specific volume - _0xs,_0ys eastward and northward components of surface frictional stress - ^* vertical velocity at the top of the boundary layer (N/m²/sec) - P Thickness of the boundary layer (mb) - nondimensional function of pressure - P pressure - P_a pressure of the model atmosphere (N/m²) - P_s pressure at the surface (N/m²) - t time (sec) - U eastward wind speed (m/sec) - V northward wind speed (m/sec) - surface water availability - T absolute temperature (K) - heat addition due to water phase changes - g acceleration due to gravity (m²/sec) - a radius of the earth (m) - R gas constant for dry air (J/Kg/K) - C_p specific heat of air at constant pressure (J/Kg/K) - k R/C_p - L latent heat of condensation (J/Kg) - f coriolis parameter (rad/sec) - H_s H_0s⁽¹⁾+H_0s⁽²⁾+H_0s⁽³⁾+H_0s⁽⁴⁾+H_0s⁽⁵⁾(J/m²/Sec)=sum of the rates of vertical heat fluxes per unit surface area, directed toward the surface - H_a H_0a⁽¹⁾+H_0a⁽²⁾+H_0a⁽³⁾+H_0a⁽⁴⁾(J/m²/Sec)=sum of the rates of heat additions to the atmospheric column per unit horizontal area by all processes - H_0s⁽¹⁾,H_0a⁽¹⁾ heat flux due to short wave radiation - H_0s⁽²⁾,H_0a⁽²⁾ heat flux due to long wave radiation - H_0s⁽³⁾,H_0a⁽³⁾ heat flux due to small scale convection - H_0s⁽⁴⁾ heat flux due to evaporation - H_0a⁽⁴⁾ heat flux due to condensation - H_0s⁽⁵⁾ heat flux due to subsurface conduction and convection - e^* saturation vapor pressure - R solar constant (W/m²) - r_a albedo of the atmosphere - r_s albedo of the surface - b₂ empirical constant (J/m²/sec) - c₂ empirical constant (J/m²/sec) - e₂ nondimensional empirical constant - f₂ empirical constant (J/m₂/sec) - factor proportional to the conductive capacity of the surface medium - a_s constant used in Sellers model - b_s positive constant of proportionality used in the Sellers model (kg m²/J/sec²) - K_HT coefficient for eddy diffusivity of heat (m²/sec) - K_HE exchange coefficient for water vapor (m²/sec) - h depth of the water column (m) - z height (m) - V_0ws meridional component of surface current (m/sec) - n cloud amount - G_0,n long wave radiation form the atmosphere for cloud amount n (W/m²) - B₀ long wave radiation from the surface (W/m²) - S_0,n short wave radiation from the atmosphere for cloud amount n (W/m²) - A_n albedo factor for a cloud amount n - R_f1 large scale rainfall (mm/day) - R_f2 small scale rainfall (mm/day)With 22 Figures