Diurnal Cycle of Monsoon Convection

Abstract

The diurnal variability of monsoon precipitation and associated circulation features, e.g. land/sea breezes, mountain/valley breezes, and low-level jets, in the monsoon regions of the world are reviewed, with a particular focus on the Asian monsoon. The dominant pattern of diurnal variability is a maximum in rainfall over land during the afternoon/evening in response to solar heating of the surface and a morning maximum over the oceans; however, there are important exceptions to this pattern over both land and ocean. Nocturnal maxima in rainfall are found over land in proximity to major mountain barriers, e.g., at the foot of the Himalayas; downstream of the Tibetan Plateau, the Rocky Mountains, and the Andes; and within interior basins such as the Sichuan Basin. Daytime maxima in rainfall are observed over partially enclosed seas such as the Bay of Bengal, the South China Sea, and the Gulf of Guinea. These latter regions are characterized by seaward propagation of convection from adjacent coastlines.The mechanisms for the diurnal cycle of convection over land, particularly the afternoon maximum in precipitation, are generally well understood, but the timing of precipitation is often not well handled in models. Several theories for the diurnal cycle over the ocean have been proposed, involving surface and free-tropospheric radiative heating or their horizontal gradients; however, the precise mechanisms remain unclear and are not well represented in global models. Mechanisms for propagation of convective systems over both land and ocean are not completely understood and require further research.

A Study of Two Propagating Heavy-Rainfall Episodes near Taiwan during SoWMEX/TiMREX IOP-8 in June 2008. Part II: Sensitivity Tests on the Roles of Synoptic Conditions and Topographic Effects

“…During the past decade, the behavior of rainfall episodes to the lee of the Tibetan Plateau (TP) in East Asia are also studied using both satellite (Wang et al 2004(Wang et al , 2005aJohnson 2011;Bao et al 2011;Xu and Zipser 2011;Wang et al 2011b) and rain gauge data (e.g., Yu et al 2007;Zhou et al 2008;Chen et al 2010). Similar to the events in the United States, the roles of the MPS between eastern TP and its lee and the diurnal variation of the LLJ over southern-central China have been the foci of much investigation (e.g., Huang et al 2010;Chen et al 2009Chen et al , 2013.…”

Upscale Effects of Deep Convection during the North American Monsoon

“…Since NAM convection has a distinct diurnal cycle (e.g., Stensrud et al 1995;Johnson 2011) and the active convective region can shift in location and extent within the monsoon area from day to day, Rossby waves of nonzero frequency may be produced. Yang and Hoskins (1996) show that the general propagation characteristics of zero-and nonzero-frequency Rossby waves are similar, such that the results from ray tracing still apply.…”

The Role of Diurnal Solenoidal Circulation on Propagating Rainfall Episodes near the Eastern Tibetan Plateau

“…This intimate tie of episodes in their phase to the diurnal cycle of certain mountains at a fixed location, together with the longevity of some events, suggests a potential to improve warm-season rainfall forecasts (Carbone et al 2002), for which the present skill is relatively low (e.g., Olson et al 1995;Fritsch and Carbone 2004). Although Wang et al (2004Wang et al ( , 2005 employed only satellite infrared (IR) brightness temperature T B data, the eastward shift in summer rainfall peaking time along the Yangtze River valley (YRV) near 308N-from midnight at the upper reaches (the SB area) to the morning at the middle reaches and then to the afternoon at the lower reaches-is confirmed using rain gauge data (Yu et al 2007) and Tropical Rainfall Measuring Mission (TRMM) 3B42 merged satellite observations (e.g., Johnson 2010). Although Wang et al (2004Wang et al ( , 2005 employed only satellite infrared (IR) brightness temperature T B data, the eastward shift in summer rainfall peaking time along the Yangtze River valley (YRV) near 308N-from midnight at the upper reaches (the SB area) to the morning at the middle reaches and then to the afternoon at the lower reaches-is confirmed using rain gauge data (Yu et al 2007) and Tropical Rainfall Measuring Mission (TRMM) 3B42 merged satellite observations (e.g., Johnson 2010).…”