The Relationship of Cloud Number and Size With Their Large‐Scale Environment in Deep Tropical Convection

Abstract

Accurately representing the properties and impact of tropical convection in climate models requires an understanding of the relationships between the state of a convective cloud ensemble and the environment it is embedded in. We investigate this relationship using 13 years of radar observations in the tropics. Specifically, we focus on convective cell number and size and quantify their relationship to atmospheric stability, midtropospheric vertical motion and humidity. We find several key convective states embedded in their own unique environments. The most area‐averaged rainfall occurs with a moderate number of moderate size convective cell in an environment of high humidity, strong vertical ascent, and moderate convective available potential energy (CAPE) and convective inhibition (CIN). The strongest rainfall intensities are found with few large cells. Those exist in a dry and subsiding environment with both high CAPE and CIN. Large numbers of convective cells are associated with small CAPE and CIN, weak ascent, and a moist midtroposphere.

Assessing Convective Organization in Tropical Radar Observations

“…Precipitation generally peaks during the late afternoon, but CPI, which is the average rain rate over convective pixels only, peaks about 1–2 hr later than mean convective precipitation (MCP), which is the average convective rain rate across the whole radar scan area. Because MCP is an extensive quantity and is largely a function of convective rain area (Davies et al, ; Louf et al, ; Peters et al, ), the offset between the peaks suggest the presence of wide spread, but relatively low intensity convective rain before 3 p.m. local time. After 3 p.m., the total convective area begins to decrease, while CPI stays about constant until 6 p.m.…”

“…To validate ROME's behavior in more realistic scenarios, we apply ROME to the comprehensive multiyear radar data set developed for a C‐band radar, named C‐POL, nearby Darwin in northern Australia (Jackson et al, ; Keenan et al, ; Louf et al, ). The radar is located circa 12° south of the equator.…”

Mesoscale marine tropical precipitation varies independently from the spatial arrangement of its convective cells

“…The variations of P as a function of and N as displayed by Figure look also very similar to the precipitation variations obtained by Louf et al . () based on 13‐year of radar observations over Darwin.…”

Convective Precipitation Efficiency Observed in the Tropics

“…That the instantaneous precipitation rate of convective events is not modulated strongly by synoptic regimes is initially surprising, given that greater precipitation totals are associated with active monsoon compared to breaks (e.g., Nguyen et al, ; Protat et al, ). However, for northern Australia the area‐averaged precipitation totals relate much more strongly to the convective area fraction than the convective intensity (Davies et al, ; Louf, Jakob, et al, ). In the present study we only consider instantaneous precipitation rates for convective events, which may be similar in intensity between regimes but differ in other ways, which we do not consider here such as frequency and duration of rain.…”