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Abstract. The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a largescale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerly flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer over the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for modCorrespondence to: K. M. Lau (william.k.lau@nasa.gov) erate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

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The South China Sea Monsoon Experiment (SCSMEX) is an international field experiment with the objective to better understand the key physical processes for the onset and evolution of the summer monsoon over Southeast Asia and southern China aiming at improving monsoon predictions. In this article, a description of the major meteorological observation platforms during the intensive observing periods of SCSMEX is presented. In addition, highlights of early results and discussions of the role of SCSMEX in providing valuable in situ data for calibration of satellite rainfall estimates from the Tropical Rainfall Measuring Mission are provided. Preliminary results indicate that there are distinctive stages in the onset of the South China Sea monsoon including possibly strong influences from extratropical systems as well as from convection over the Indian Ocean and the Bay of Bengal. There is some tantalizing evidence of complex interactions between the supercloud cluster development over the Indian Ocean, advancing southwest monsoon flow over the South China Sea, midlatitude disturbances, and the western Pacific subtropical high, possibly contributing to the disastrous flood of the Yangtze River Basin in China during June 1998.

Key Points NB's claim in refuting the EHP hypothesis was unjustified They use correlation to infer causality, which is wrong They argued narrowly their interpretation of EHP, ignoring current literature

A case of torrential precipitation associated with the mei-yu front, an Asian summer monsoon system east of the Tibetan Plateau, is studied using the coupled fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) and the NASA Goddard Space Flight Center Parameterization for Land-Atmosphere-Cloud Exchange model. The impact of both remote and local sources of water vapor on the location and intensity of mei-yu precipitation are studied by numerical experiments. The results demonstrate that the main source of water vapor for this heavy precipitation event over the Yangtze River Valley is the Bay of Bengal. Moisture is transported by a southwesterly low-level jet (LLJ) southeast of the Tibetan Plateau. Although the LLJ is largely manipulated by large-scale forcing, the mesoscale circulation that results from mei-yu condensational heating acts to increase the maximum wind speed of the jet. The condensation-induced local circulation strengthens the moisture transport in the LLJ, providing a positive feedback that sustains the mei-yu precipitation system. Precipitation recycling increases the total precipitation in the Yangtze River Valley only slightly, but it tends to shift the maximum rainfall center toward the warmer side of the mei-yu rain belt. This shift is due to the pronounced increase in atmospheric moisture and decrease in surface temperature over the warm side of the rain belt.