A Linear Dynamic Model Of The East African Jet In A Stratified Atmosphere (somalia, Summer Monsoon, India)

The motion forced by prescribed heat sources in the Indian summer monsoon region was investigated using a global linear primitive equations model in a stratified atmosphere. The response, without topography, to steady large-scale latent heating at the latitude of northern India showed broad, weak cross-equatorial flow, with the largest subsidence occurring to the west of the heating. The response to a 14-day oscillation in the heat source, representing the active/break cycle of the monsoon, exhibited a somewhat larger cross-equatorial flow, associated with westward propagating geopotential anomalies in both hemispheres.The north-south topographic barrier formed by the East African Highlands was modeled as a western wall, and the response to the steady and the oscillatory monsoon heat source was investigated using a fine resolution model in a limited longitudinal domain. For the steady monsoon heat source, a western boundary jet was produced, and this separated abruptly from the boundary to flow eastward into the region of the heat source. The oscillating monsoon heat source produced oscillations in the boundary jet in the near equatorial region comprised of jets of alternating sign which propagated westward into the boundary and increased in amplitude as they did so. At the equator this boundary wave was nearly out of phase with the monsoon heating.Steady prescribed low-level sensible heating along the coastline of Somalia and Saudi Arabia was found to result in a low-level western boundary jet comparable in strength near the surface to that forced by the steady monsoon heat source. This local-heat-source jet was situated along the western wall at the equator, but separated from the wall to run along the coast at higher tropical latitudes. Superposition of this local heating response onto the response to the steady monsoon heating would result in a departure of the jet from the western wall at a lower latitude and would also provide a more gradual curvature to the jet as it turns eastward to flow into the monsoon heat source region. Such modifications would improve the comparison of the model simulation with the observations