Tropical cyclogenesis is attributed to an equatorial wave when the filtered rainfall anomaly exceeds a threshold value at the genesis location. It is argued that 0 mm day (simply requiring a positive anomaly) is too small a threshold because unrelated noise can produce a positive anomaly. A threshold of 6 mm day is too large because two-thirds of storms would have no precursor disturbance. Betw...

Regions of the occurrence of different phenomena related to the development of baroclinic disturbances are reviewed for the Northern Hemisphere extratropics, using National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data. The occurrence of height lows appears to be related to the orography near the earth's surface and with surface- and upper-air cyc...

the mediterranean is one of the most important cyclogenesis regions in the northern hemisphere. the depressions occurring in specific areas of the mediterranean region and cyclonic tracks have been the subject of extensive climatological research. the climate of the mediterranean region is conditioned by its position in the transition area between the sub-tropical high pressure belt and the mid...

Central to tropical cyclogenesis is the changing behavior of moist convection as the cyclone evolves. Based on a cumulus ensemble model run in weak temperature gradient mode, we suggest that the mid-level vortex created by early-stage convection stabilizes the environment in way that favors further development. In particular, modeled convection occurring in the more stable environment produces ...

The total quasigeostrophic (QG) vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to, and along, the geostrophic vertical shear, respectively. The physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones. The analysi...

The Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin waves on the formation of two tropical cyclones. Typhoons Rammasun and Chataan developed in the weste...