Understanding Land-Atmosphere Coupling and its Predictability at the ARM Southern Great Plains Site

Abstract:

Ten years ago, the Global Energy and Water EXchanges Global Land Atmosphere Coupling Experiment (GLACE) spotlighted the Southern Great Plains (SGP) for being one of three hotspots globally for land-derived precipitation predictability. Since then, the GLACE results have served as the underlying motivation for numerous subsequent land-atmosphere (L-A) coupling studies over the SGP domain. The range of these studies includes: local point scale studies leveraging surface meteorological and flux measurements at the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement SGP (ARM-SGP) Central Facility, regional pentad to monthly scale atmospheric moisture budget analyses based on atmospheric reanalysis, and regional limited duration (2-7 day) coupled model sensitivity experiments. This study has the following three objectives: (1) to provide the common historical context necessary for bridging past and future interdisciplinary characterizations of L-A coupling, (2) to isolate the mechanism(s) for the region’s L-A coupling signal, and (3) to evaluate the short range (12-18hr) predictability of soil moisture-precipitation feedbacks. We produce a convective triggering potential—low-level humidity index (CTP-HI)—based climatology of L-A coupling at ARM-SGP for the period 1979-2014 using North American Regional Reanalysis and North American Land Data Assimilation System Phase 2 data. We link the underlying coupling regime classification timeseries to corresponding synoptic-mesoscale weather patterns and bulk atmospheric moisture budget analyses. On the whole, the region’s precipitation variability is largely dependent on large-scale moisture transport and the role of the land is nominal. However, we show that surface sensible heat flux can play an important role in modulating diurnal precipitation cycle phase and amplitude—either directly (enhancing CTP) in water-limited conditions or indirectly (increasing HI) in energy-limited conditions. In fact, both 0700 LT soil moisture and 1300 LT sensible heat flux are significantly correlated with afternoon peak (AP) precipitation occurrence and amplitude. To finish, we evaluate retrospectively the predictability of AP precipitation events during summer 2015 considering only early morning meteorological parameters.