Point Comparison in the Arctic (Barrow N, 156.6W ) Part I - Assessing Satellite (and surface) Capabilities for Determining Cloud Fraction, Cloud Optical Depth Part II Cloud effects on Determining Surface Temperatures Taneil Uttal, Shelby Frisch, Sunny Sun-Mack, Jeff Key, Axel Schweiger Patrick Minnis, Xuanji Wang, Andy Heidinger

March 2007 – March 2009 has been designated The International Polar Year The first IPY was in

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For the Arctic region there is not yet a consensus about whether or not seasonal cloud fraction is increasing or decreasing OR if cloud fraction is a significant measure of cloud radiative effects OR if clouds are creating a net warming or a net cooling effect on the Arctic surface OR the relative effect compared to other Arctic system factors Xuanji Wang and Jeffrey R. Key, 2005, Arctic Surface, Cloud, and Radiation Properties Based on the AVHRR Polar Pathfinder Data Set. Part I: Spatial and Temporal Characteristics, J. Climate, Vol.18, No.14, , Xuanji Wang and Jeffrey R. Key, 2004, Arctic Surface, Cloud, and Radiation Properties Based on the AVHRR Polar Pathfinder Data Set. Part II: Recent Trends, J. Climate, Vol.18, No.14, , Jennifer A. Francis, Elias Hunter, Jeffrey R. Key, and Xuanji Wang, 2005, Clues to Variability in Arctic Minimum Sea Ice Extent, Geophys. Res. Lett., Vol.32, L21501, doi: /2005GL024376, Schweiger, Axel. J. Changes in seasonal cloud cover over the Arctic seas from satellite and surface observations, Geophysical Research Letters, Vol 31, L12207, doi: /2004GL020067, Intrieri, J.M., C.W. Fairall, M.D. Shupe, P.O.G. Persson, E.L. Andreas, P. Guest, and R.M. Moritz, 2002: An annual cycle of Arctic surface cloud forcing at SHEBA. J. Geophys. Res., 107(C10), doi: /2000JC Zuidema, P., B. Baker, Y. Han, J. Intrieri, J. Key, P. Lawson, S. Matrosov, M. Shupe, R. Stone, and T. Uttal, 2005: An Arctic sprintime mixed-phase cloudy boundary layer observed during SHEBA. J. Atmos. Sci., 62, Shupe, M.D., and J.M. Intrieri, 2004: Cloud radiative forcing of the Arctic surface: The influence of cloud properties, surface albedo, and solar zenith angle. J. Climate, 17,

8 years of data from the North Slope of Alaska DOE/ARM site

Barrow Alert Eureka Summit Ny-Alesund Abisko Tiksi Sammultunturi

New radar-lidar-radiometer facility in Eureka, Canada since Aug 2005

Eureka – 80N 86W July Ground-based Radar CLDSAT

APPROACH Focus cloud fraction and cloud optical depth studies on Barrow where there are independent surface-based measurements (will add Eureka, Canada as a second comparison site) Compare monthly averages without regard to the different temporal and spatial sampling issues Assume the satellite and surface data sets are now long enough to produce meaningful statistical comparisons of annual and interannual variability Part I Assessing Satellite Capabilities for Determining Cloud Fraction, Cloud Optical Depth

Radar Data Disclaimer

Monthly Average Cloud Fraction (* indicate months will less than 15 days of radar data) AVHRR (APPX) RADAR MODIS (CERES-TEAM) TOVS (Polar Pathfinder) PAMOSX

Monthly Averages of Annual Cycle of Cloud Fraction Note: APPX data calculated from CERES TEAM data calculated from Radar data calculated from TOVS data calculated from PATMOSX data calculated from 1998 to 2004 AVHRR (APPX) RADAR MODIS (CERES-TEAM) TOVS (Polar Pathfinder) PAMOSX

Many satellite to surface comparisons have focused on cloud fraction. In the Arctic, cloud optical depth appears to be a much more important parameter in defining the radiative impact of clouds on the surface (Also noted by Dr. Hayasaka)

Zuidema et al.2005

Figure from Shupe, 2004 using data over the Arctic Ocean (SHEBA) Radar detects no cloud Clouds with Liquid Cloud with no Liquid

Monthly Averages of Cloud Optical Depth (* indicate months will less than 15 days radar of data) AVHRR (APPX) RADAR MODIS (CERES-TEAM)

Monthly Averages of Annual Cycle of Cloud Optical Depth AVHRR (APPX) RADAR MODIS (CERES-TEAM) Note: APPX data calculated from CERES TEAM data calculated from Radar data calculated from

APPROACH Focus surface temperature comparisons on weather station sites that are or will be the location of future Atmospheric observatories Examine monthly averages of surface temperature partitioned by cloud fraction Don’t assume that the surface temperature measurements at the surface are correct Part II Assessing Satellite Capabilities for Determining Surface Temperature Surface Meteorological Data Disclaimer

Monthly means of [surface temperature (in-situ daily mean) – APPX surface temperature (0400 and 1400 LST average)] for

Alert – March 0400 LST Alert – March 1400 LST Alert – July at 0400 LST Alert – July 1400 LST Solid Line – Surface Grey Line – APPX Dashed Line – “Corrected” APPX

Preliminary Conclusions and Work in Progress Monthly mean values of cloud fraction are in good agreement between the AVHRR (APPX), TOVS (Polar Pathfinder), MODIS (CERES-TEAM), and surface measurements. WE CAN TRUST OUR SEASONAL CYCLE MEASUREMENTS OF CLOUD FRACTION IN THE ARCTIC Monthly mean values of cloud optical depth is more problematic. The AVHRR (APPX) appears to have problems with detecting annual trends in optical depth. The MODIS (CERES-TEAM) does better with annual trends but the summer values of optical depth in summer time are considerably lower than the retrievals from the surface. IMPROVED RETRIEVAL OF OPTICAL DEPTH SHOULD BE A PRIORITY Data from Barrow, SHEBA and Eureka show significant supercooled liquid water in Arctic clouds in all seasons DON’T ASSUME ARCTIC CLOUDS ARE ALL ICE

The surface data has calibration errors, operational problems, data gaps, and more DON’T ASSUME THE SURFACE DATA IS “TRUTH” The APPX surface temperature measurements appear to have biases compared to the surface that change as a function of cloud fraction, season, and location. In general APPX surface temperatures are too cold in the summer and too warm in the winter. NEED TO INVESTIGATE SEASONAL AND REGIONAL CORRECTIONS SINCE THE ARCTIC IS SO CLOUDY AND WE NEED THE SATELLITES FOR SURFACE TEMPERATURE Preliminary results indicate that the Arctic has important sub- regions, with significant differences in cloud properties. OVER AVERAGING OF CLOUD CLIMATOLOGIES MAY BE PARTICULARLY PROBLEMATIC FOR THE ARCTIC – FORGET THE LATITUDINAL AVERAGING