HORIZONTAL STRUCTURE AND SEASONALITY OF LARGE-SCALE CIRCULATIONS ASSOCIATED WITH SUBMONTHLY TROPICAL CONVECTION

The relationship between deep tropical convection and large-scale atmo spheric circulation in the 6-30-day period range is examined. Regressi on relationships between filtered outgoing longwave radiation at vario us locations in the Tropics and 200- and 850-mb circulation are mapped for the standard seasons, and the spatial structure and seasonal depe ndence of the results are interpreted in view of the basic-state circu lation. In regions where the convection is embedded in upper-level eas terlies, anomalous equatorial easterly flow is typically present at 20 0 mb within and to the west of the convective signal, along with patte rns of meridional outflow into subtropical anticyclonic perturbations. Lagged relationships suggest that the convection is forcing the circu lation in many of these cases. The outflow and subtropical circulation s are strongest into the winter hemisphere during the solstitial seaso ns, with more symmetric signals about the equator seen in the equinoct ial seasons. The longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due pol eward or just to the east of the convection. There tends to be a first baroclinic mode vertical structure to these circulations, such that e quatorial westerlies are present at 850 mb within the convection, with closed circulations on either side of the equator resembling equatori al Rossby modes especially common over the Atlantic and Pacific sector s. As a contrast, in regions located within upper-level westerlies or along the margin of influence of upper westerly disturbances, convecti on appears to be forced by upper-level wave energy propagating into th e deep Tropics, with the heating located in the upward motion region a head of upper-level troughs. This occurs over the Atlantic and eastern Pacific sectors during northern winter and spring, and over Australia , the South Pacific, and South America during southern summer, when up per westerlies are at relatively low latitudes where they can interact with deep tropical convection. The results confirm theoretical and mo deling ideas that suggest that Rossby wave energy is able to propagate into the deep Tropics in regions where upper-level westerlies exist i n the Tropics.