Development and Analysis of a Global, Terrestrial Sensible Heat Flux Dataset

Abstract:

Energy exchange between the atmosphere and the Earth’s surface is manifested through sensible and latent heat turbulent fluxes, with their mean states and variability central features of regional climate. Estimating these fluxes using global data sets and understanding their variability is still unresolved but is a central focus of WCRP’s Global Energy and Water Exchange (GEWEX) Data Assessment Panel (GDAP) through the LandFlux activities. In recent years, LandFlux has made progress developing terrestrial latent heat data sets, but the progress developing a consistent, multi-decadal sensible heat product has been limited by challenges such as the poorly measured surface temperature gradient and the parameterization of the aerodynamic resistance. While wind and surface roughness control the turbulent transfer of heat, stable boundary layer conditions offer additional challenges.

GDAP strives for satellite and input consistency across the data sets. For the sensible heat data product, this manifests itself primarily in the land surface temperature (LST) (being consistent with the High Resolution Infrared Radiation Sounder (HIRS) observations). Due to its sparse coverage (swath and cloud-contamination), a HIRS-consistent, hourly, global, 0.5 degree resolution LST dataset for clear and cloudy conditions (1979 to 2009) is developed through merging of the NCEP Climate Forecast System Reanalysis (CFSR) estimates with HIRS retrievals, which are validated against the Baseline Surface Radiation Network (BSRN)-based LST. The surface air temperature is estimated by adding the temperature gradient from CFSR to the HIRS-consistent LST data product, and validated against ~10,000 surface stations. The aerodynamic resistance is based on optimized values at 70 global FluxNet towers and extended globally through an objective analysis with land cover and climate covariates.

These products are used to form a global terrestrial, hourly, 0.5 degree spatial resolution sensible heat dataset. The spatial, seasonal, and inter-annual variability of the dataset is presented. The sensible heat flux is combined with the LandFlux latent heat estimates and the surface radiation budget ver. 3 (SRB-3) to assess the space-time variability in the combined surface fluxes (e.g. Bowen ratio) as well as budget closure.