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.

Updraft and Downdraft Core Size and Intensity as Revealed by Radar Wind Profilers: MCS Observations and Idealized Model Comparisons

“…In Figure 4, we introduce the MAO and SGP data sets by plotting the cumulative mean, 5th (downdraft) and 95th (updraft) percentile profiles for the vertical air motion (| W |> 1.5 m/s) in convective regions. These composites are similar to the ones found in Wang et al (2019) and other observational summaries. In Figure 4b, we demonstrate that when segregating according to updraft‐only ( W > 1.5 m/s) and downdraft‐only ( W < ‐1.5 m/s) conditions, SGP events are associated with more intense air motions.…”

“…Those statements were based on differences between normalized histograms of the vertical velocity retrievals under various regime breakdowns that sampled a wide variety of isolated to organized convective events. For these particular Amazon MCS events, Wang et al (2019) suggested that Amazon dry or transitional seasons favored more intense maximum updraft profile signatures (distribution tails), with the dry season favoring deeper and more intense downdrafts. However, Wang et al (2019) were careful to indicate those results as noisy and/or limited by event sampling.…”

“…For example, the soundings feature relatively higher 0–5 km RH (90%) and reduced CIN (‐22.4 J/kg) conditions than is typical for either the SGP or MAO conditions (Table S3). Note that a higher 0–5 km RH may promote weaker downdraft intensity or structures less typical of the SGP events (e.g., see discussions in Wang et al, 2019). Similarly, higher RH conditions are also associated with wider and intense updrafts in simulations (Morrison, 2017).…”

“…This study is motivated by the need to better document DCC updraft/downdraft properties as can be retrieved using an extended radar wind profiler (RWP) data set. To narrow our observational scope, the analyzed data set is drawn from a mesoscale convective system (MCS) archive recently summarized by Wang et al (2019). As among the largest and most intense type of convective storms, MCSs are recognized for their important role at local (e.g., severe weather warning) to global (e.g., general circulation and water cycle) scales (e.g., Del Genio & Kovari, 2002; Feng et al, 2016, 2018; Fritsch et al, 1986; Hartmann et al, 1984; Houze, 2004, 2018; Nesbitt et al, 2006; Roca et al, 2014).…”

Planetary boundary layer evolution over the Amazon rainforest in episodes of deep moist convection at the Amazon Tall Tower Observatory

“…Previous studies of tropical DMC-PBL interaction have demonstrated the importance of characterizing morphological aspects of the convective activity that disturbs the PBL with the aid of radar imagery (e.g., SR98; Schiro and Neelin, 2018;Wang et al, 2019). In this study, all four of the storm events investigated consisted of either a single cell or a small cluster of multicell storms (Moller et al, 1994).…”