The Characteristics of Tropical and Midlatitude Mesoscale Convective Systems as Revealed by Radar Wind Profilers

Abstract

This study contrasts characteristics of mature squall-line mesoscale convective systems (MCSs) observed by extended ground-based radar wind profiler (RWP) deployments from the U.S. Department of Energy Atmospheric Radiation Measurement program. This analysis compares the dynamical structure, precipitation, and cold pool properties associated with MCS events over RWP sites in Oklahoma, USA, (midlatitude) to those observed during a 2-year RWP deployment to Manaus, Brazil, during GoAmazon2014/5 campaign (tropical). The MCSs indicate similar convective line rainfall rates and total rainfall accumulations. However, midlatitude events suggest a larger fractional stratiform contribution to total precipitation. For both regions, convective line cold pools are associated with sharp decreases (approximately 10 K) in the surface equivalent potential temperature (θe) near the time of line passage. Surface θe properties for both regions suggest a modest relationship between rainfall rate and the probability of observing measurable surface rainfall. The probability of observing convective updrafts in both tropical and midlatitude MCS events is found to be similar as a function of low-level radar reflectivity. However, midlatitude MCSs are associated with more intense convective updrafts, with upward air motions (mean, maximum) peaking at higher altitude. The most pronounced contrast is the propensity for deeper and more intense downdrafts in midlatitude MCSs. An analysis based on observed downdraft properties is performed using simple mixing assumptions. For these events, the vertical gradient of θe in the lower troposphere is relatively consistent between the Amazon and Oklahoma, suggesting similar mixing rates for downdrafts originating below 3 km (0.1 km−1). However, if downdrafts originate nearer to the level of minimum θe at SGP, mixing may be occurring at rates comparable to 0.3 km−1.