TITLE

Upper-Level Frontogenesis Associated with the Birth of Mobile Troughs in Northwesterly Flow

AUTHOR(S)
Schultz, David M.; Sanders, Frederick
PUB. DATE
November 2002
SOURCE
Monthly Weather Review;Nov2002, Vol. 130 Issue 11, p2593
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Previous studies have shown that 500-hPa mobile trough births (or genesis) occur preferentially in north-westerly flow during upper-level frontogenesis, and that cold advection assists in, and is a product of, mobile trough intensification. This study focuses on the synoptic environments and thermal-advection patterns of upper-level fronts associated with mobile trough births in northwesterly flow. A climatology of 186 such events, derived from an earlier study by Sanders, shows that most births tend to occur within uniform or diffluent flow and that most tend to be associated with relatively weaker 500-hPa thermal advection. Most mobile trough births in diffluence, however, tend to be associated with increasing 500-hPa cold advection, typically indicated by a cyclonic rotation of isentropes, whereas, most mobile trough births in confluence tend to be associated with weaker 500-hPa thermal advection. Two cases of upper-level frontogenesis associated with mobile trough genesis -- one in diffluence and one in confluence -- are compared to determine the processes acting to produce the differing thermal-advection patterns at 500 hPa. A thermal-advection tendency equation is developed and shows that the magnitude of the temperature advection can be changed by accelerating the advecting wind speed or by changing the temperature gradient (i.e., vector frontogenesis). The latter can be accomplished either by changing the magnitude of the temperature gradient (the frontogenetical component F[SUBn], also known as scalar frontogenesis) or by rotating the direction of the temperature gradient relative to the flow (the rotational component F[SUBs]. The dominant processes acting on F[SUBn] for the diffluence and confluence cases are tilting and deformation frontogenesis, respectively. The dominant process acting on F[SUBs] for the diffluence case is rotation of the isentropes due to the vorticity term, whereas rotation of the isentropes due to the vorticity and tilting...
ACCESSION #
7444560

 

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