THE SENSITIVITY OF PRECIPITATION TO CIRCULATION DETAILS - PART-I - ANANALYSIS OF REGIONAL ANALOGS

Citation
Pj. Roebber et Lf. Bosart, THE SENSITIVITY OF PRECIPITATION TO CIRCULATION DETAILS - PART-I - ANANALYSIS OF REGIONAL ANALOGS, Monthly weather review, 126(2), 1998, pp. 437-455
Citations number
36
Categorie Soggetti
Metereology & Atmospheric Sciences
Journal title
ISSN journal
00270644
Volume
126
Issue
2
Year of publication
1998
Pages
437 - 455
Database
ISI
SICI code
0027-0644(1998)126:2<437:TSOPTC>2.0.ZU;2-V
Abstract
In this paper, the sensitivity of precipitation associated with ordina ry baroclinic continental winter storms to small variations in the syn optic-scale circulation is explored using ensembles of observed region al analogs. When seeking time-coherent analogs for periods of 1-2 days in length on the basis of anomaly correlation scores at both the surf ace and 500 hPa, the observed precipitation structures are strongly de pendent on circulation details, reflecting subtle differences at both the synoptic scale and mesoscale. It has also been found that when see king time-coherent regional analogs on the basis of the observed preci pitation distributions, such analogs cannot be identified. However, co herent precipitation structures that are identified for shorter period s (order 1 day) are found to occur in association with highly dissimil ar circulations. Thus, the sensible weather that results from a partic ular circulation is crucially dependent on the details of the how. The authors believe that these findings provide some explanation for the relatively slow advance of precipitation forecast skill in the face of continuously improving forecasts of the large-scale circulation. The study of the evolution of the base case and its closest circulation an alog is split into two successive 24-h periods. During the first 24 h, the substantial differences in the observed precipitation are linked to the complex interplay between precipitation events prior to the per iod of interest (which led to the generation of upwind sources of mois ture) and synoptic-scale dynamics (primarily differences in the struct ure and intensity of the subtropical jet, which led to slight deviatio ns in the low level flow between the two cases and subsequent differen ces in moisture advection from the Gulf of Mexico and moisture converg ence). During the second 24 h, differences in the observed precipitati on are tied to differences in the convective response despite similarl y potentially unstable environments, reflecting differences in synopti c and mesoscale triggering mechanisms. To more fully resolve the relat ive importance of these mechanisms, experiments with a mesoscale numer ical model will be reported in a subsequent paper.