Linear Response of the Global Atmosphere to Thermal Forcing during Northern Summer

Abstract

Linear responses of the stationary planetary scale disturbances to subtropical and tropical heat sources are investigated for summer northern hemisphere. The model with high vertical resolution is used. Its top is 80km. Zonal mean flows are assumed using FGGEIIIB data by ECMWF. If there are heat sources at 30*N and 10*N, the solutions agree well with observations. The wave of zonal wave number 1 propagates to 60*N. It has two maxima around 30*N and 60*N and minimum at 40*N. The wave of wave number 5 can propagate to 45*N and has only one maximum there.The results suggest that Indian Monsoon activities and heat sources over the Tibetan Plateau can affect on the stationary patterns in middle and high latitudes through poleward propagation of stationary Rossby waves even in summer. On the other hand, the meridional profiles of zonal flows significantly affect on whether the waves forced by heating at ITCZ can propagate northward or not.

Low-Frequency Interactions between the Summer Monsoon and the Northern Hemisphere Westerlies

“…In other words , the "window of interaction" between the monsoon and the mid-latitude westerlies seems to open only in or near the break phase (i.e., when the monsoon trough shifts to the Himalayan side) . Recent numerical model studies (e.g., Lin,1983;Huang , 1985;Kuma, 1985) also pertinently showed that only the forcing located in the mid-latitude westerlies can contribute the latitudinal propagation and interaction of waves among latitudes .…”

On the Processes of Transitions between Circulation Regimes during Winter over the Pacific and North America

“…This idea is similar to one discussed by Lau and Philips (1986). Another mechanism is the fluctuations in the sensitivity of an extra-tropical circulation response to tropical convection over the Pacific (as shown in Kuma, 1985). The overreflection theory (Lindzen and Tung, 1978) may also be considered as a candidate for the explanation of this mechanism.…”

Relationships between the Quasi-Stationary Rossby Waves in the Subtropical Jet and the Mass and Heat Transport in the Northern Periphery of the Tibetan High

“…Especially, the intraseasonal variations in the Asian summer monsoon have been expected to affect the extratropical circulation. Kuma (1985) and Yasunari (1986) emphasized the possibility of the influence of the thermal forcing by the variations of the monsoon convections on the extratropics, through excitation of Rossby waves. However, they could not show strong signals in observational data, which shows distinct Rossby wave responses to the variations of convective activity, especially in the upper troposphere.…”