What we do (don’t) know about Antarctic clouds David H. Bromwich 1, Julien P. Nicolas 1 and Jennifer E. Kay 2 International Workshop on Antarctic Clouds Columbus, July Polar Meteorology Group, Byrd Polar Research Center, The Ohio State University, Columbus, OH 2 National Center for Atmospheric Research, Boulder, CO

Outline Introduction Observation methods Cloud spatial distribution (horizontal/vertical) Temporal (seasonal) variability Physical properties (phase) Trends/observed changes Conclusions

Introduction Why knowledge of Antarctic is important  Antarctic radiative budget 1. Clouds reflect solar energy 2. Clouds absorb long-wave radiation emitted from the surface  Over high-albedo surfaces, the short-wave flux absorbed at the surface is already small: effect 2 > effect 1  Impact on Antarctic surface mass balance  Role of stratospheric clouds in ozone depletion – Polar stratospheric clouds support chemical reactions conducive to the destruction of stratospheric ozone

Observing Antarctic clouds

Ground-based measurements Dedicated effort to study and measure Antarctic clouds – South Pole Atmospheric Radiation and Cloud LIDAR Experiment (SPARCLE) Instruments: – Polar Atmospheric Emitted Radiance Interferometer (PAERI) – Tethered Balloon System – Micropulse Lidar – South Pole Transmissometer Results: – Climatology of clouds (e.g., M. Town) – Cloud microphysics (e.g., V. P. Valden)

Ground-based measurements Visual observations – Provide the longest observational record of Antarctic clouds – Problem 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) visual PAERI pyrgeometer

Passive remote sensing VIS/IR channels But cloud tops have albedo and temperature comparable to ice sheet’s surface  Weak contrast on satellite imagery over ice-covered surface  Problematic for detection of Antarctic thin clouds [Image: AMRC/SSEC/UW Madison]

Active remote sensing: Lidar Lidar measurements onboard an LC-130 flown between McM and South-Pole, Jan Multilayering of clouds Ice crystals trails from high-elevated cirrus observed to “seed” the mid-level clouds Morley et al., 1989 McM SP

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

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

Mean cloud distribution

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

Cloud cover over West Antarctica Tongue of higher cloud fraction/frequency over central West Antarctica seen in Oct. 03 and in the annual mean Denotes the frequent intrusions of marine air inland associated with the cyclonic activity over the Ross/Amundsen Seas. GLAS Lidar AMPS AMPS cloud fraction Cloud frequency over Antarctica in Oct [Spinhirne et al. 2005; Nicolas and Bromwich, 2010]

Cloud cover climatology Coastal areas: McMurdo Mean 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 Sea Maximum cloud cover in DJF/MAM, minimum in JJA Cloudiest region found over the quasi-permanent polynya (N-E of McM) [Monaghan et al., 2005] JJA 02SON 02 DJF 02-03MAM 03

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

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

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

PSCs: linkages to troposphere Formation of PSC associated with deep tropospheric cloud systems: – Cooling of the lower stratosphere through adiabatic and radiative processes – Air transport from the lower troposphere up to the upper tropo. / lower stratosphere Figure: 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 interior Some deep synoptic weather system do penetrate over the Antarctic interior Figure: Mosaic of AVHRR images of East Antarctica on Dec showing a blocking-high related cloud band [Massom et al., 2004]

Cloud microphysics

Measurements 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 microphysics Measurements from tethered balloon at South Pole on 2 Feb [Valden et al., 2005]  super-cooled water clouds ~450m above sfc Pressure (hPa)Temperature -30°C RH wrt. water

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

Long-term changes in Antarctic cloud cover?

Trends in Antarctic cloud cover Decadal 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 cover Mean monthly anomalies in cloud fraction based on AVHRR observations [Comiso and Stock, 2001] Negative trends in cloud fraction: ± 0.06% (ice sheet >2000m) ± 0.04% (ice sheet <2000m) ± 0.03% (sea ice area) ± 0.01% (open ocean)

PSCs and tropospheric warming Significant mid-tropospheric warming has been observed in winter over Antarctica The warming may be related to larger amounts of PSCs induced by increased tropospheric CO 2 concentration and the associated stratospheric cooling [modeling studies from Lachlan-Cope et al., 2009] [Turner et al., 2006] At 500-hPa from ERA-40 ( ) Trends in mid-tropospheric temp. At Ant. Stations ( )  600hPa

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

References Comiso, J. C and L. V. Stock, 2001: Studies of Antarctic cloud cover variability from 1982 through Proc. of the Int. Geosci. and Remote Sensing Symposium, vol. 4, 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, 9–14 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 12 th Conference on Atmospheric Radiation, AMS, Madison, Hatzianastassiou, N., et al., 2001: Polar cloud climatology from ISCCP C2 and D2 datasets. J. Climate, 14, Hines, K. M., et al., 2004: Antarctic clouds and radiation within the NCAR climate models. J. Climate, 17, Hu, Y., et al., 2009: CALIPSO/CALIOPcloud phase discrimination algorithm. J. Atmo. Ocean. Tech, 26, Lachlan-Cope, T. A., et al., 2009: Antarctic wintertropospheric warming – the potential role of polar stratospheric clouds, a sensitivity study.Atmos. Sci. Let., 10, Morley, B. M., et al., 1989: Airborne lidar observations of clouds in the Antarctic troposphere. Geophys. Res. Lett., 16(6), Lubin, D., et al., 1998: The impact of Antarctic cloud radiative properties on a GCM climate simulation. J. Climate, 11,

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), 1914–1928. 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, 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, L Wylie, D., et al., 2007: A comparison of cloud cover statistics from the GLAS lidar with HIRS. J. Climate, 20, Yamanouci, T. and Y. Shudou, 2007: Trends in cloud amount and radiative fluxes at Syowa Station, Antarctica. Polar Science, 1,

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