Tropical Stationary Wave Response to ENSO: Diabatic Heating Influence on the Indian Summer Monsoon

Abstract

he atmospheric response to boreal summer tropical diabatic heating is studied in the atmospheric model component of the Community Atmosphere Model [CAM, version 3 (CAM3)] of the National Center for Atmospheric Research. An idealized heating function (with broad vertical but localized horizontal structure) is added to CAM3 near the equator; the circulation response is studied as a function of the sign of the heating and its longitude (Indian Ocean to eastern Pacific Ocean). The atmospheric circulation forced by the added heating interacts with all the physical and dynamical processes in CAM3; the total heating is the sum of the added heating and that produced by CAM3. In experiments using climatological sea surface temperature, added cooling (heating) over the Maritime Continent induces asymmetric anticyclonic (cyclonic) circulation extending toward India, opposing (reinforcing) the climatological monsoon flow and weakening (strengthening) the Indian monsoon. The anchoring of the anticyclonic (cyclonic) circulation over India as the added cooling (heating) is moved eastward over warm SST regions is greatly reduced when a slab ocean model is used. A negative (positive) air?sea feedback over the Indian Ocean is identified when heating (cooling) is added in the Indonesian region. Experiments in which the total heating is similar to estimates of the observed heating for the summer of 1987 are examined.