Comparison of TOA and BOA LW Radiation Fluxes Inferred From Ground‐Based Sensors, A‐Train Satellite Observations and ERA Reanalyzes at the High Arctic Station Eureka Over the 2002–2020 Period. Issue 11 (1st June 2021)

• Record Type: Journal Article
• Authors: Blanchard, Yann; Pelon, Jacques; Cox, Christopher J.; Delanoë, Julien; Eloranta, Edwin W.; Uttal, Taniel
• Is Part Of: Journal of geophysical research. Volume 126:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-01
• Subjects: clouds -- high Arctic -- intercomparison -- radiation -- re‐analyses -- satellite data; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033615
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: This study focuses on the accuracy of longwave radiation flux retrievals at the top and bottom of the atmosphere at Eureka station, Canada, in the high Arctic. We report comparisons between seven products derived from (a) calculations based on a combination of ground‐based and space‐based lidar and radar observations, (b) standard radiometric observations from the CERES sensor, (c) direct observations at the surface from a broadband radiation station, and (d) the ERA‐Interim and ERA5 reanalyzes. Statistical, independent analyses are first performed to look at recurring bias and trends in fluxes at Top and Bottom of the Atmosphere (TOA, BOA). The analysis is further refined by comparing fluxes derived from coincident observations decomposed by scene types. Results show that radiative transfer calculations using ground‐based lidar‐radar profiles derived at Eureka agree well with TOA LW fluxes observed by CERES and with BOA LW fluxes reference. CloudSat‐CALIPSO also shows good agreement with calculations from ground‐based sensor observations, with a relatively small bias. This bias is shown to be largely due to low and thick cloud occurrences that the satellites are insensitive to owing to attenuation from clouds above and surface clutter. These conditions of opaque low clouds, cause an even more pronounced bias for CERES BOA flux calculation in winter, due to the deficit of low clouds identified by MODIS. ERA‐I and ERA5 fluxes behave differently, the large positive bias observed with ERA‐I is much reduced in ERA5. ERA5 is closer to reference observations due to better behavior of low and mid‐level clouds and surface temperature. Plain Language Summary: Satellite and reanalysis data sets are widely used for climate and process studies in the Arctic in order to complement sparse ground‐based measurements. This study compares ground‐based observations of Arctic clouds and longwave fluxes at a Canadian High Arctic station with satellite and reanalysis products. Both statistical and coincident analyses show a good top of the atmosphere agreement, but reveal biases in surface fluxes that are due to the underestimation of the occurrence of low and thick clouds, frequent in the Arctic. The results allow for an evaluation of flux product uncertainties and an assessment of their limitations. The outcomes of this study can be applied over the entire Arctic region and can inform the instrumentation choices at various polar ground‐based sites. Key Points: Top‐of‐atmosphere flux observations, model calculations, and reanalyzes agree within the measurement uncertainty at a High Arctic Station Large bottom‐of‐Atmosphere biases are observed among data sets (reduced for ERA5) and are mainly due to incorrect vertical representation of low opaque clouds Ground‐based active sensors are essential to complement space‐based cloud observations in order to better understand Arctic climate change