Abstract
Convective transition statistics serve as diagnostics for the parameterization of convection in climate and weather forecast models by characterizing the dependence of convection on the humidity-temperature environment. The observed strong pickup of precipitation as a function of layer-averaged water vapor and temperature is captured in models with varying accuracy. For independent observational verification, a low-Earth orbiting satellite constellation of Global Navigation Satellite System (GNSS) polarimetric radio occultation (PRO) measurements would be spaced such that adjacent RO would capture different profiles within and immediately adjacent to convection. Here, the number of profile observations needed to distinguish between convective transition relations by different tropospheric temperature ranges is determined, over different tropical oceanic basins. To obtain these, orbit simulations were performed by flying different satellite constellations over global precipitation from the Global Precipitation Measurement (GPM) mission, varying the numbers of satellites, orbit altitude, and inclination. A 45-degree orbit inclination was found to be a good tradeoff between maximizing the number of observations collected per day, and the desired 50–150-km spacing between individual RO ray paths. Assuming a set of reasonable assumptions for net data yield, three tropospheric temperatures can be distinguished by 1 K with a six-month on-orbit duration from a constellation of at least three satellites.
Highlights
Despite the ongoing improvement in the resolution of weather and climate models [1], convective parameterization remains a major contributor to the uncertainty of future projections of global precipitation
Since these convective transition statistics capture the fast time scale associated with convective development, these diagnostics provide a set of constraints on the convective parameterizations used in climate models [6,29]
Assuming that occultations from two Global Navigation Satellite System (GNSS) telemetries are tracked, a 50% data processing yield with added 50% margin, the convective transition relationships can be distinguished by three tropospheric temperatures separated by 1 K, with a six-month on-orbit duration from a constellation of at least three satellites
Summary
Despite the ongoing improvement in the resolution of weather and climate models [1], convective parameterization remains a major contributor to the uncertainty of future projections of global precipitation. Coupled with its innate fine vertical resolution, an RO measurement is an inherently fine-scale measurement in two of the three spatial dimensions (Figure 1) In this graphical depiction, an on-Earth projection of the lowest 200-km segment of the RO ray paths (corresponding to the low levels where the majority of the water vapor is present) is shown intersecting precipitation, centered upon the corresponding on-Earth tangent point. While the wide-swath (2200 km) ATMS radiometers are exploited for RO assessment [22,23], their observations can provide additional precipitation context [24] to the constellation PRO observations
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