NSF Award
2414425
This award supports the continuing efforts of the Principal Investigators (PIs) to develop a theory of tropical convective precipitation that relates the characteristics of convection to the large-scale atmospheric conditions in which it develops. The work is a follow-on to the OTREC field campaign (Organization of Tropical East Pacific Convection, see AGS-1627109), which collected aircraft measurements of temperature, humidity, winds, and other meteorological variables over the convectively active regions of the eastern equatorial Pacific and southwestern Caribbean. The PIs produced a gridded dataset using the campaign data and have used it to relate the structure of convection to ambient conditions, looking in particular at whether the convection is "bottom heavy", with most of the vertical motion and mass flux of the convection happening in the lower troposphere, or "top heavy", with mass flux occurring at higher levels. They further related the top- and bottom-heavy mass flux profiles to rainfall intensity and to bulk measures of atmospheric stability and humidity.<br/><br/>Work performed here extends the analysis of convective rainfall using data from reanalysis products, satellites (particularly GPM, the Global Precipitation Mission), and several earlier field campaigns including PREDICT (Pre-Depression Investigation of Cloud Systems in the Tropics), and EUREC4A (Elucidating the Role of Clouds-Circulation Coupling in Climate). The primary focus of the project is the connection between the PIs' thermodynamic characterization of convective rainfall and the classification of rainfall into "rains" and "showers" proposed in the 1970s for monsoon rainfall over continents. The PIs hypothesize that the traditional classification should be understood as a bifurcation in the dynamics of mesoscale convective systems which can be explained in terms of saturation fraction (a kind of column-integrated relative humidity) and atmospheric instability. Observational analysis is complemented by simulations using an idealized model, the spectral weak temperature gradient (SWTG) model, which can reproduce the showers/rains dichotomy given observed thermodynamic variables. The model can also be used in idealized setting to explore the range of behaviors for rains and showers, including multiple equilibrium behavior.<br/><br/>The work is of societal as well as scientific interest given its relevance to improving the representation of convection and rainfall in models used for weather prediction and climate projection. The work also develops international scientific collaborations with researchers in Latin America, particularly Colombia and Chile. The PIs conduct outreach activities with local schools including classes offered to high school teachers and the development of 3D-printed weather stations for school use. The project supports a graduate student, thereby providing for the future workforce in this research area.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
