What we do (dont) know about Antarctic cloudsDavid H. Bromwich1, Julien P. Nicolas1 and Jennifer E. Kay2International Workshop on Antarctic CloudsColumbus, 14-15 July 20101Polar Meteorology Group, Byrd Polar Research Center, The Ohio State University, Columbus, OH2 National Center for Atmospheric Research, Boulder, CO

OutlineIntroductionObservation methodsCloud spatial distribution (horizontal/vertical)Temporal (seasonal) variabilityPhysical properties (phase)Trends/observed changesConclusions

IntroductionWhy knowledge of Antarctic is importantAntarctic radiative budget1. Clouds reflect solar energy2. Clouds absorb long-wave radiation emitted from the surfaceOver high-albedo surfaces, the short-wave flux absorbed at the surface is already small: effect 2 > effect 1Impact on Antarctic surface mass balanceRole of stratospheric clouds in ozone depletionPolar stratospheric clouds support chemical reactions conducive to the destruction of stratospheric ozone

Observing Antarctic clouds

Ground-based measurementsDedicated effort to study and measure Antarctic cloudsSouth Pole Atmospheric Radiation and Cloud LIDAR Experiment (SPARCLE) 1999-2001Instruments:Polar Atmospheric Emitted Radiance Interferometer (PAERI)Tethered Balloon System Micropulse LidarSouth Pole TransmissometerResults:Climatology of clouds (e.g., M. Town)Cloud microphysics (e.g., V. P. Valden)

Ground-based measurementsVisual observationsProvide the longest observational record of Antarctic cloudsProblem in winter (underestimation of cloud cover)

More about ground-based cloud observations with Erika Key and Irina Gorodetskaya[Town et al.,2007]CLOUD COVER AT SOUTH POLE (MONTHLY MEANS)visualPAERIpyrgeometer

Passive remote sensingVIS/IR channelsBut cloud tops have albedo and temperature comparable to ice sheets surfaceWeak contrast on satellite imagery over ice-covered surfaceProblematic for detection of Antarctic thin clouds[Image: AMRC/SSEC/UW Madison]

Active remote sensing: LidarLidar measurements onboard an LC-130 flown between McM and South-Pole, Jan. 1986Multilayering of cloudsIce crystals trails from high-elevated cirrus observed to seed the mid-level cloudsMorley et al., 1989McMSP

Active remote sensing: LidarEx.: Geoscience Laser Altimeter System (GLAS) on ICESatBackscatter cross-section from GLAS over Antarctica at 15:00 UTC, 1 Oct. 2003[Spinhirne et al., 2005]

Active vs passive cloud remote sensing Cloud frequency over Antarctica in Oct. 2003from GLAS, MODIS and ISCCP [Hart et al., 2006]Cloud frequencyfrom GLAS and HIRS (NOAA-14) fromOct. 1-Nov. 16 2003[Wylie et al. 2007] More about cloud satellite remote sensing with Dan Lubin

Mean cloud distribution

200720082007-08 mean seasonal cloud fraction (from Cloudsat radar/Calipso lidar)

Cloud cover over West AntarcticaTongue of higher cloud fraction/frequency over central West Antarctica seen in Oct. 03 and in the 06-07 annual meanDenotes the frequent intrusions of marine air inland associated with the cyclonic activity over the Ross/Amundsen Seas.GLAS LidarAMPSAMPS cloud fraction2006-2007Cloud frequency over Antarctica in Oct. 2003[Spinhirne et al. 2005; Nicolas and Bromwich, 2010]

Cloud cover climatologyCoastal areas: McMurdoMean seasonal cloud cover over McMurdo area in Jun 02-May 03 from AMPS forecasts[Monaghan et al., 2005]Cloud cover primarily influenced by the presence of open water in the Ross SeaMaximum cloud cover in DJF/MAM , minimum in JJACloudiest region found over the quasi-permanent polynya (N-E of McM)[Monaghan et al., 2005]JJA 02SON 02DJF 02-03MAM 03

20072008Cloud vertical profile: West Antarctica(from Cloudsat/Calipso)

Cloud vertical profile: East Antarctica(from Cloudsat/Calipso)20072008

Polar Stratospheric Clouds (PSCs)TropopauseGLAS backscatter ratio for Sept. 29 (top) and 30 (bot.), 2003(western Dronning Maud Land sector)

PSCs: linkages to troposphereFormation of PSC associated with deep tropospheric cloud systems:Cooling of the lower stratosphere through adiabatic and radiative processesAir transport from the lower troposphere up to the upper tropo. / lower stratosphereFigure: Measurements from CloudSat/CALIPSO. Example of a deep cloud system associated with a PSC system in the Weddell Sea[Wang et al., 2008]Height (km)Weddell SeaWest Antarc.Ross Sea

Offshore synoptic system penetrating over the Antarctic interiorSome deep synoptic weather system do penetrate over the Antarctic interior

Figure: Mosaic of AVHRR images of East Antarctica on Dec. 29 2001 showing a blocking-high related cloud band [Massom et al., 2004]

Cloud microphysics

Cloud microphysicsMeasurements with the PAERI allow for the retrieval of cloud microphys. properties Figure: relative occurrence of different cloud types in Feb. 01 at South Pole[Ellison et al., 2006]Cloud types at South Pole

Cloud microphysicsMeasurements from tethered balloon at South Pole on 2 Feb. 2001 [Valden et al., 2005] super-cooled water clouds~450m above sfcPressure (hPa)Temperature-30CRH wrt. water

Cloud microphysicsDiscrimination cloud phase on a global scale possible through Space-borne lidar measurements[Hu et al., 2009]Ice cloud observations from CALIPSO/CALIOP lidar, Jan. 2007

Cloud microphysics: climatic impactLubin et al. (1998) evaluated the impact of changes in cloud properties over Antarctica10-m ice clouds vs (control) 10-m water clouds:[Lubin et al., 1998]

Long-term changes in Antarctic cloud cover?

Trends in Antarctic cloud coverDecadal changes in cloud cover based on long-term records of visual observations at some Antarctic stations allow . But large significant uncertainty, esp. in winter.[Yamanouchi et al., 2007]Syowa South Pole[Town et al., 2007]

Trends in Antarctic cloud coverMean monthly anomalies in cloud fraction 1982-1999 based on AVHRR observations[Comiso and Stock, 2001]Negative trends in cloud fraction:-0.50 0.06% (ice sheet >2000m)-0.21 0.04% (ice sheet

PSCs and tropospheric warmingSignificant mid-tropospheric warming has been observed in winter over AntarcticaThe warming may be related to larger amounts of PSCs induced by increased tropospheric CO2 concentration and the associated stratospheric cooling [modeling studies from Lachlan-Cope et al., 2009][Turner et al., 2006]At 500-hPa from ERA-40 (1979-2001)Trends in mid-tropospheric temp.At Ant. Stations(1971-2003) 600hPa

ConclusionsAntarctic cloud studies are in a new era with the spaceborne observations (CloudSat, CALIPSO)Validation is needed in the full range of Antarctic environmentsThe record is short and temporal resolution is limited

ReferencesComiso, J. C and L. V. Stock, 2001: Studies of Antarctic cloud cover variability from 1982 through 1999. Proc. of the Int. Geosci. and Remote Sensing Symposium, vol. 4, 1782-1785.Ellison, M. E., et al., 2006: Properties of water-only, mixed-phase, and ice-only clouds over the South Pole. Proceedings of the 12th conference on cloud physics and 12th conference on atmospheric radiation, 914 July 2006, Madison, WI, Amer. Meteor. Soc. (ed), Boston, MA Hart, W. D., et al., 2006: Global and polar cloud cover from the Geoscience Laser Altimeter System, observations and implications. Extended abstract of the 12th Conference on Atmospheric Radiation, AMS, Madison, 2006.Hatzianastassiou, N., et al., 2001: Polar cloud climatology from ISCCP C2 and D2 datasets. J. Climate, 14, 3851-3862.Hines, K. M., et al., 2004: Antarctic clouds and radiation within the NCAR climate models. J. Climate, 17, 1198-1212.Hu, Y., et al., 2009: CALIPSO/CALIOPcloud phase discrimination algorithm. J. Atmo. Ocean. Tech, 26, 2293-2309.Lachlan-Cope, T. A., et al., 2009: Antarctic wintertropospheric warming the potential role of polar stratospheric clouds, a sensitivity study.Atmos. Sci. Let., 10, 262-266.Morley, B. M., et al., 1989: Airborne lidar observations of clouds in the Antarctic troposphere. Geophys. Res. Lett., 16(6), 491-494.Lubin, D., et al., 1998: The impact of Antarctic cloud radiative properties on a GCM climate simulation. J. Climate, 11, 447-462.

References (cont.)Massom, R.A., et al., 2004: Precipitation over the interior East Antarctic Ice Sheet related to mid-latitude blocking-high activity. J. Climate, 17(10), 19141928.Nicolas, J. P. and D. H. Bromwich, 2010: Marine signature in West Antarctica. J. Climate, in press.Palm, S. P., et al., 2005: Observations of Antarctic polar stratospheric clouds by the Geoscience Laser Altimeter System. Geophys. Res. Lett., 32, L22S04.Spinhirne, J. D., et al., 2005: Antarctica cloud cover for October 2003 from GLAS satellite lidar profiling. 32, L22S05.Town, M. S., et al., 2007: Cloud cover over the South Pole from visual observations, satellite retrievals, and surface-based infrared radiation measurements. J. Climate, 20, 544-559.Walden, V. P., et al., 2005: Properties of super-cooled water clouds over South Pole. Preprints, Eighth Conf. on Polar Meteorology and Oceanography, San Diego, CA, Amer. Meteor. Soc.Wang, Z., et al., 2008: Association of Antarctic polar stratospheric cloud formation on tropospheric cloud systems. Geophys. Res. Lett., 35, L13806.Wylie, D., et al., 2007: A comparison of cloud cover statistics from the GLAS lidar with HIRS. J. Climate, 20, 4968-4981.Yamanouci, T. and Y. Shudou, 2007: Trends in cloud amount and radiative fluxes at Syowa Station, Antarctica. Polar Science, 1, 17-23.

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