Evaluation of a land-atmosphere coupling metric computed from a ground-based infrared interferometer

Science

Land-atmosphere coupling metrics are a useful tool for quantifying the relative role of the land surface in driving planetary boundary layer (PBL) processes as well as development (or suppression) of convective precipitation. Our work leverages the higher temporal resolution offered by the atmospheric emitted radiance interferometer (AERI) to evaluate uncertainties associated with applications of a frequently used land-atmosphere coupling metric using remotely sensed thermodynamic profiles.

Impact

Process-level land-atmosphere coupling metrics often benefit from atmospheric thermodynamic profiles, such that availability of radiosonde observations often limits observational application of these metrics. Our results suggest that future studies can confidently employ thermodynamic profiles from the AERI to evaluate various land-atmosphere coupling metrics with high temporal resolution and limited uncertainty.

Summary

Land–atmosphere feedbacks are a critical component of the hydrologic cycle. Vertical profiles of boundary-layer temperature and moisture, together with information about the land surface, are used to compute land–atmosphere coupling metrics. The convective triggering potential and low-level humidity index (collectively referred to as CTP-HI_low framework) is a popular coupling metric that uses morning vertical profiles of moisture and temperature to diagnose the likelihood of convective precipitation over wet or dry soils. Combinations of CTP (a measure of instability) and HI_low(a measure of moisture) are used to categorize the atmospheric preconditioning for convection given initial soil moisture conditions. Radiosonde- versus AERI-based computations of CTP and HI_lowproduced the same diagnosis of atmospheric preconditioning a majority of the time. The AERI’s ability to represent this coupling metric well enabled novel exploration of temporal variability within the overnight period in CTP and HI_low.

Accumulated net radiation during morning radiosonde observations can vary zonally such that a morning radiosonde in Denver may occur before sunrise, while the same morning radiosonde would occur after sunrise in Long Island. This motivated an evaluation of uncertainty in the metric depending upon accumulated net radiation at a given site to represent this zonal variability. Observations of CTP-HI_low computed within a few hours of 1200 UTC were essentially equivalent; however, with greater differences in time there arose greater differences in CTP and HI_low.