Tropical Cyclogenesis Associated with Premonsoon Climatological Dryline over the Bay of Bengal

Abstract

Tropical cyclones of the Bay of Bengal (BoB) that formed near the synoptic-scale dryline usually intensified over a short distance (~600-800 km) within 3 days and caused severe destruction after landfall. High-resolution simulations of very severe cyclonic storms in association with dryline indicate that the meridional shear aids in the development of a group of linear convective cells that mature as an east-west oriented quasi-linear convective system (QLCS) within the boundary between the dry-moist air masses. The leading edge deep convections are supported by low-level moist southwesterly inflow; however, the typical mid-level mesoscale convective vortex (MCV) associated with these QLCS is unremarkable due to a very narrow trailing stratiform region within the QLCS. Supercells are likely to be organized within the QLCS due to extremely unstable atmospheric conditions resulting from a strong vertical shear of 27-39 m s−1 between 0-6 km and large convective available potential energy of >3000 J kg−1. The vertical shear veering with height causes several numbers of low-level mesovortices having diameters less than 10 km at the leading edge in the different convective stages of the QLCS. The dryline aloft in the BoB produces horizontal positive shear vorticity of the order 10–5 s−1 with higher values in the levels 850-600 hPa. The advection of intense cloud-scale cyclonic vortices (~10–3 s−1) assists and enhances a cyclonic vortex to the rear side of the QLCS that performs as an MCV for cyclogenesis over the BoB.

Hot Extremes and Climatological Drought Indicators in the Transitional Semiarid-Subtropical Region of Sinaloa, Northwest Mexico

“…The stations with the highest annual intensities were Guasave (15 HE year -1 for 2002), El Playón (AAD = 30 HE -1 year -1 for 1982), Ixpalino and Potrerillos (ADD = 112 day year -1 for 2004 and 2013, respectively), and San Joaquín (I = 43.66ºC year -1 for 1982). The results are consistent with those of [2], who argue that for the study period 1952-2013, the highest cyclonic rainfall in northern Mexico was recorded in the years 1982, 1983 and 1984, and according to [45,46], these events typically occurred in the summer (June-September, for Sinaloa), because they are an important mechanism for atmospheric circulation of warm temperatures on the earth's surface. The accumulated daily effect of HEs in Sinaloa, specifically near the Ixpalino and Portrerillos stations in 2004 and 2013, has led to consequences such as, for example, 90% to 100% of the crop area in Sinaloa being sown with improved maize [47], and as a result, more area is now planted with irrigated maize than with rainfed maize, also mainly due to the increasing irregularity of rainfall [48].…”