Environmental Controls on MCS Lifetime Rainfall Over Tropical Oceans

Abstract

Mesoscale convective systems (MCSs) contribute a majority of rainfall over tropical oceans. However, our understanding of the environmental controls on tropical oceanic MCS precipitation remains incomplete. Using 20‐year of satellite observations, reanalysis data, and MCS tracking, we found that MCSs initiating in a mesoscale environment with enhanced lower‐free‐tropospheric moisture, warmer middle troposphere, stronger low‐level ascent, and stronger deep‐layer (surface‐400 hPa) wind shear tend to produce more precipitation during their lifetimes. While most of these environmental factors are correlated with one another, the deep‐layer shear is not. A rapid pickup in MCS lifetime rainfall is found when the lower‐free‐tropospheric specific humidity exceeds 10 g kg−1. This nonlinearity is mostly dominated by the nonlinear increase in MCS area. On the other hand, both MCS area and rain rate increase quasi‐linearly with the deep‐layer shear. The increase in rain rate is related to the enhancement of heavy precipitating convective activity with deep‐layer shear.

Contribution of Mesoscale Convective Systems to Floods in the East Asian Summer Monsoon Region

“…In addition, previous studies show that lower-free-tropospheric moisture and deep-layer shear play important roles in affecting the area and duration of MCS (Chen et al, 2023). More effort should be devoted to the understanding of the physical processes that determine the differences in lower-free-tropospheric moisture and deep-layer shear among the four types of MCS identified in this study.…”

Near-storm Environmental Relationships with Tropical Oceanic Convective Structure Observed during NASA CPEX and CPEX-AW

“…Furthermore, quasi-linear MCSs in the west Pacific have also been linked to strong deep layer vertical speed shear owing to more expansive stratiform precipitation and anvil advection (Saxen & Rutledge, 2000). The analysis of these shear-convection relationships has been extended to the greater tropics using convection-permitting model (CPM), spaceborne remote sensing, European Centre for Medium-Range Weather Forecasts Reanalysis-Interim (ERA-Interim) reanalysis, and ERA5 reanalysis datasets, finding similar deep layer speed shear relationships with tropical squall lines specifically (Tompkins, 2001) and tropical MCSs more generally (Igel & van den Heever, 2015;Chen et al, 2023). However, Tompkins (2001) acknowledges CPM limitations (e.g., limited vertical dimension and unrealistic cyclic boundary conditions), while Igel and van den Heever (2015) acknowledges biases stemming from inconsistent storm-relative CloudSat measurements that are a natural consequence of random chance convective sampling of low Earth orbit satellites.…”

“…Similar to wind shear, field campaign data in the western Pacific and Indian Ocean basins, along with broader tropical oceanic CPM, ERA-Interim, and ERA5 reanalysis data, have been used to investigate near-storm environmental moisture relationships with TOC structure. Analysis of these datasets have shown mid-tropospheric relative humidity (RH) to positively correlate with TOC precipitation area and intensity due to decreased dry air entrainment (Brown & Zhang, 1997;LeMone et al, 1998;Tompkins, 2001;Cetrone & Houze, 2006;Savarin et al, 2014;Chen et al, 2016;Schiro et al, 2020;Chen et al, 2023). However, the relationships between lower-tropospheric RH and TOC precipitation area and intensity vary, in both strength and sign, across tropical oceanic studies, even within similar regions (Tompkins, 2001;Cetrone & Houze, 2006;Schiro et al, 2020).…”

Near‐Storm Environmental Relationships With Tropical Oceanic Convective Structure Observed During NASA CPEX and CPEX‐AW

“…Furthermore, quasi-linear MCSs in the west Pacific have also been linked to strong deep layer vertical speed shear owing to more expansive stratiform precipitation and anvil advection (Saxen & Rutledge, 2000). The analysis of these shear-convection relationships has been extended to the greater tropics using convection-permitting model (CPM), spaceborne remote sensing, European Centre for Medium-Range Weather Forecasts Reanalysis-Interim (ERA-Interim) reanalysis, and ERA5 reanalysis data sets, finding similar deep layer speed shear relationships with tropical squall lines specifically (Tompkins, 2001) and tropical MCSs more generally (Chen et al, 2023;Igel & van den Heever, 2015). However, Tompkins (2001) acknowledges CPM limitations (e.g., limited vertical dimension and unrealistic cyclic boundary conditions), while Igel and van den Heever (2015) acknowledges biases stemming from inconsistent storm-relative CloudSat measurements that are a natural consequence of random chance convective sampling of low Earth orbit satellites.…”

“…Similar to wind shear, field campaign data in the western Pacific and Indian Ocean basins, along with broader tropical oceanic CPM, ERA-Interim, and ERA5 reanalysis data, have been used to investigate near-storm environmental moisture relationships with TOC structure. Analysis of these data sets have shown midtropospheric relative humidity (RH) to positively correlate with TOC precipitation area and intensity due to decreased dry air entrainment (Brown & Zhang, 1997;Cetrone & Houze, 2006;Chen et al, 2016Chen et al, , 2023LeMone et al, 1998;Savarin et al, 2014;Schiro et al, 2020;Tompkins, 2001). However, the relationships between lower-tropospheric RH and TOC precipitation area and intensity vary, in both strength and sign, across tropical oceanic studies, even within similar regions (Cetrone & Houze, 2006;Schiro et al, 2020;Tompkins, 2001).…”