The Structure of the Arabian Heat Low. Part II: Bulk Tropospheric Heat Budget and Implications

Abstract

An investigation of the Arabian heat low is carried out based on observations from various satellites, an experimental aircraft and a surface energy budget monitoring station. The observations suggest that during the spring period the Arabian heat low is nearly radiatively neutral and lacks the properties of an energy sink characteristic of conventional desert heat lows. Satellite derived top-of-atmosphere radiation budget analyses illustrate the high contrast properties of the radiative exchange fields over the southern Arabian Peninsula with respect to its surroundings. However, an examination of a four-month time series of daily averaged net radiative exchange over the Arabian Empty Quarter, derived from Nimbus-7 Earth Radiation Budget (ERB) measurements, indicates that the heat low region is in slight relative excess. Combining these results with estimates of the surface energy budget inside the Arabian Empty Quarter (described in Part I), and previously estimated tropospheric radiative heating rate profiles, provide a closed set of flux terms used to evaluate the energy exchange process within the heat low region. A synthesis of these results indicates that the heat low is a total energy source region. A conceptual structure of the heat low is offered based on a three-layer stratification of the heating mechanisms. The possible role of the Arabian heat low in controlling thermodynamic conditions and forcing baroclinicity in the western Arabian Sea is discussed. It is concluded that the surplus energy properties of the heat low may serve as an important mechanism in controlling moisture transport into the southwest monsoon rainfall regions.