Soil moisture signature in global weather balloon soundings

Abstract

The land surface influences the atmospheric boundary layer (ABL) through its impacts on the partitioning of available energy into evaporation and warming. Previous research on understanding this complex link focused mainly on site-scale flux observations, gridded satellite observations, climate modeling, and machine-learning experiments. Observational evidence of land surface conditions, among which soil moisture, impacting ABL properties at intermediate landscape scales is lacking. Here, we use a combination of global weather balloon soundings, satellite-observed soil moisture, and a coupled land-atmosphere model to infer the soil moisture impact on the ABL. The inferred relationship between soil moisture and surface flux partitioning reflects distinctive energy- and water-limited regimes, even at the landscape scale. We find significantly different behavior between those two regimes, associating dry conditions with on average warmer (≈3 K), higher (≈400 m) and drier (≈1 kPa) afternoon ABLs than wet conditions. This evidence of land–atmosphere coupling from globally distributed atmospheric measurements highlights the need for an accurate representation of land–atmosphere coupling into climate models and their climate change projections.

Widespread shift from ecosystem energy to water limitation with climate change

“…In water-limited regions, typically ELI > 0, cor(SM′,ET′) > 0 and cor(R n ′,ET′) is either close to zero or negative. In these regions, the soil moisture is typically between the wilting point and the critical soil moisture content (SM crit ), which is defined as the soil moisture content above which plants can sustain their maximum evaporative fraction [9][10][11] . So when SM wilt < SM < SM crit , positive soil moisture anomalies tend to increase the terrestrial evaporation, while negative soil moisture anomalies achieve the contrary (cor(SM′,ET′) > 0).…”

“…The water and carbon cycles are coupled via vegetation, which assimilates CO 2 during photosynthesis, while simultaneously transpiring through the stomata. From an energy balance perspective, transpiration (T) cools the surface air at the expense of energy which would otherwise contribute to surface heating [9][10][11] . Through this water-vegetation-climate feedback, changes in soil moisture influence evaporative cooling and consequently surface warming 10 .…”

Soil drought can mitigate deadly heat stress thanks to a reduction of air humidity

“…To quantify causal relationships and decipher the complex role of soil desiccation on human heat stress via air temperature and humidity, we use a recently developed atmospheric modeling framework, CLASS4GL ( 29 ) (Materials and Methods). Using worldwide morning balloon soundings to initialize the model, the diurnal cycle of the ABL is simulated, constrained by satellite and reanalysis data describing atmosphere and land conditions, and especially soil moisture ( 29 , 35 ). The framework allows us to infer the diurnal sensitivity of the ABL to the fluxes of heat and moisture from above (free troposphere) and below (land surface), as well as to horizontal advection of heat and moisture.…”

Understanding the diurnal cycle of land–atmosphere interactions from flux site observations

“…Tawfik et al (2015b) demonstrated linkages between land surface fluxes and convective initiation from radiosonde data. Denissen et al (2021) found soil moisture signals globally in boundary layer profiles. Zhang et al (2020) have applied sounding data from commercial aircraft to quantify land surface drivers of boundary layer development.…”