Gridding cloud and irradiance to quantify variability at the ARM Southern Great Plains site: An update to the Surface Cloud Grid VAP

 

Authors

Laura Dian Riihimaki — CIRES | NOAA ESRL GML
Chuck N. Long (deceased) — NOAA- Earth System Research Laboratory
Krista Gaustad — Pacific Northwest National Laboratory

Category

Radiation

Description

Example 15-minute gridded cloud fraction from the Surface Cloud Grid VAP (bottom) compared to Satellite cloud fraction from VISST data product (top). Cloud fraction from individual extended facility measurements are also shown in colored circles (bottom). Data shown from SGP at 20:00 UTC Jun-12-2016.
Ground-based radiometers provide the most accurate measurements of surface irradiance. However, geometry differences between surface point measurements and large area climate model grid boxes or satellite-based footprints can cause systematic differences in surface irradiance comparisons. We recently updated the Surface Cloud Grid VAP for the new higher density configuration of extended facility sites at the ARM SGP site. The data product uses a Gaussian weighted interpolation scheme to interpolate broadband irradiance measurements, and derived quantities onto a 0.25-degree latitude and longitude grid. The purpose is to provide spatial averages for better statistical comparison with larger areas such as that used in climate models, plane parallel radiative transfer calculations, and other statistical and climatological research. In addition to the measured irradiance, we use the Radiative Flux Analysis algorithm to estimate SW and LW clear sky irradiance and cloud fraction giving a more complete picture of the radiative impact of clouds. The gridded cloud fraction compares well with the spatial distribution of clouds from satellite-derived cloud fraction, and substantially improves agreement over point measurements.