Socorro Medina

Research Scientist
Department of Atmospheric Sciences
University of Washington
Seattle, WA, US
  Curriculum Vitae 

RESEARCH INTERESTS

PUBLICATIONS

CLASS RELATED MATERIAL

LINKS OF INTEREST

RESEARCH INTERESTS

My recent research has been in the area of orographic precipitation. In particular, I'm interested in how precipitation from mid-latitude cyclones is enhanced over the windward side of a mountain range. To understand this problem, it is necessary to analyze both the terrain-modified airflow and the microphysical processes that convert water vapor into precipitation. Recent multi-platform, multi-institution field projects conducted over the European Alps   (MAP) and the Oregon Cascade Mountains  (IMPROVE-2) collected detailed meteorological data during the passage of mid-latitude cyclones over orography. In particular, Doppler radars provided continuous information on the orographic airflow and precipitation. Additionally, polarimetric radars provided information on hydrometeor type, which gives some indication on the microphysical growth mechanisms.

We have identified and documented two distinct terrain-modified cross-barrier flow patterns (termed Type A and B) based on the analysis of data collected during these two field experiments. For each flow pattern, new conceptual models of windward enhancement of mid-latitude precipitation were derived. In Type A storms the low static stability low-level air rises easily as it encounters the first peaks of the terrain (Fig. 1; Medina and Houze 2003). Lifting of the moist low-level air produces high liquid water content over these peaks, which favor growth of the pre-existing precipitation particles by coalescence below the 0 degree level and by riming above. If the upstream flow is potentially unstable, convective cells will be triggered in the upslope ascent. These cells produce pockets of especially high liquid water content where the coalescence and riming processes are accentuated.

Type B storms exhibit a shear layer on the windward slopes (Fig. 2; Houze and Medina 2005). The combination of high shear and static stability produces conditions that support dynamical instability manifested in the form of Kevin-Helmholtz billows and turbulent overturning cells (bottom panel in Fig. 3). Aggregation of ice particles falling from the baroclinic system into the layer of cells is aided by the turbulent motions. The strong updrafts produce pockets of high liquid water content, which favor riming and coalescence.

Therefore, during the passage of mid-latitude cyclones over a mountain range, windward precipitation is enhanced by small-scale cellularity regardless of the static stability of the upstream flow. In Type A storms static instability is responsible for the updraft generation, whereas dynamic instability produces updraft motions in Type B storms. In both scenarios, the updrafts are strong enough to activate the accretion growth processes (coalescence, aggregation and riming), which are capable of producing large particles that fallout rapidly on the windward side of the terrain.

Currently, I'm analyzing numerical simulations of Type A and B storms to evaluate whether mesoscale models are capable of reproducing the observed terrain-modified flows. The predominant observed and simulated hydrometeors during orographic storms are being analyzed and intercompared. Finally, the microphysical processes responsible of orographic precipitation production in numerical simulations and its consistency with observations will be evaluated.
 

PUBLICATIONS