Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........56l&link_type=abstract
Thesis (PH.D.)--STATE UNIVERSITY OF NEW YORK AT ALBANY, 1995.Source: Dissertation Abstracts International, Volume: 56-05, Secti
Computer Science
Scientific paper
The origin of upper-tropospheric cyclogenetic precursor disturbances is not well understood, in part due to a lack of observational documentation. The goals of this dissertation are to: (i) document the life cycles of upper-tropospheric precursor disturbances with emphasis on their origin, and (ii) seek a relationship between upper precursor life cycles and planetary-scale flow features. The planetary-scale cyclogenetic environment is examined through construction of a composite based on 43 cyclone cases. We then examine the individual life cycles of 18 upper-tropospheric precursors, seeking common signatures among the cases and a relationship between these signatures and the planetary -scale flow. A life cycle dubbed the compactor is found to be particularly common, and is frequently associated with intense lower-tropospheric cyclonic development. Important features of the cyclogenetic environment revealed by the composite include: (i) an enhanced Pacific jet stream, (ii) a large-amplitude ridge over western North America, (iii) a predecessor upper trough crossing the East Coast prior to the cyclogenetic trough, (iv) the appearance of an upper-tropospheric jet streak in northwesterly flow 24 h prior to surface cyclogenesis, (v) an amplifying, mobile upper trough that forms near the exit region of the jet streak, and (vi) a developing upper-tropospheric ridge over the western North Atlantic. Features (i) and (ii) persist throughout the composite evolution. Diagnosis of compactor events reveals that: (i) an essential element of the compactor is a midtropospheric jet-front that forms in northwesterly flow downstream of a ridge centered over western North America; (ii) ageostrophic circulations associated with the jet-front materially deform the dynamic tropopause, resulting in a steepening and lowering of the tropopause prior to lower-tropospheric cyclogenesis; and (iii) strengthening of eddy kinetic energy in the jet streak is due largely to the Reynolds stress. The configuration of jet streaks in northwesterly flow in conjunction with the pattern of mean deformation over central North America is conducive to the growth of eddy kinetic energy (jet streaks) due to the Reynolds stress.
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