Abstract
The Asian summer monsoon was studied viewed from the energy budget by analyzing the radiative flux budget at the top of the atmosphere and the atmospheric heat budget. (1) The contrast of heat sources in northern summer between land and sea and between the upper and lower atmosphere over land, and (2) atmospheric heat advection moderating these contrasts are summarized as follows;
(1) The net radiative flux at the top of the atmosphere (NET) over land dominates that over the ocean in mid and high latitudes during northern summer. The NET land-ocean contrast is created by stratus clouds over the ocean in high latitudes after snow cover mostly disappears over land. Seen from the vertically integrated atmospheric energy budget, seasonal change similar to that of NET is found in sensible heating over land in high latitudes. In mid-latitudes, sensible heating is dominant from spring to early summer, and evaporation is active in late summer. Energy estimated exceeding NET is transported from the atmosphere to the ocean in high latitudes besides NET in July-August.
Before the onset of the summer monsoon circulation (in April), sensible heating near the surface contributes to increase the low-level temperature over land, especially under the downward motion of Hadley circulation and extratropical stationary waves (Iran Plateau and northern China).
(2) After the onset of summer monsoon circulation (in June), the heat source due to precipitation in Southeast Asia dominates sensible heating over the Eurasian Continent. Upward motion balances this condensational heat source.
Strengthened downward motion warms upper-level air over central Asia and sensible heating near the surface is canceled by northerly cold advection. Strengthened warm southerly advection contributes to troposphere warming over the Tibetan Plateau and the northwestern Pacific in the mid-latitudes. Condensational heating in both of the above regions appears to contribute to the strengthening of the lower-level southerly flow.
