STEADY LINEAR-RESPONSE TO TROPICAL HEATING IN BAROTROPIC AND BAROCLINIC MODELS

The atmospheric response to tropical heating is examined using both th e linear, multilevel baroclinic model with;io imposed tropical heat so urce, and the one-level barotropic model with a tropical divergence fo rcing. The divergent component of the response in the baroclinic model is characterized by a tropical divergence confined to the heated regi on, plus convergence and divergence centers away from the tropical hea ted region at the outflow level. The rotational component of the respo nse is depicted by a local baroclinic response in the Tropics and a re mote equivalent barotropic wave train in the extratropics. The barotro pic model responses to a fixed tropical divergence are highly sensitiv e to the strength of the zonal mean zonal Row at different vertical le vels in the upper troposphere. The sensitivity is induced by the depen dence of the propagation speed of the stationary Rossby wave rays on t he strength of the zonal mean zonal Row. The barotropic response to a tropical divergence when linearized about the zonal mean state at the outflow level differs significantly from the equivalent barotropic wav e train in the baroclinic model. However. when the barotropic model is Linearized about the zonal mean flow at the equivalent barotropic lev el, around 350 mb in winter and 500 mb in summer, its response to trop ical divergence forcing is very similar to the baroclinic model result . The similarity confirms that the nature of the remote atmospheric re sponse is indeed equivalent barotropic, but it is important to apply t he barotropic model at the appropriate upper-tropospheric level. The b arotropic Rossby wave energy dispersion can be applied to the baroclin ic atmosphere when the equivalent barotropic level is chosen.