HR: 1330h
AN: A42B-0760    [PDF]
TI: Model Investigations Into Bimodal Arctic Surface-Atmosphere Interaction
AU: * Stramler, K
EM: kstramler@giss.nasa.gov
AF: Columbia University, Armstrong Hall 2880 Broadway, New York, NY 10025 United States
AU: Del Genio, A D
EM: adelgenio@giss.nasa.gov
AF: NASA/GISS, Armstrong Hall 2880 Broadway, New York, NY 10025 United States
AU: Rossow, W B
EM: wrossow@giss.nasa.gov
AF: NASA/GISS, Armstrong Hall 2880 Broadway, New York, NY 10025 United States
AB: Observations at the SHEBA (Surface Heat Budget of the Arctic Ocean) site revealed that the Arctic ocean-surface-atmosphere system displays two stable states of behavior. The state dominant during winter is an atmospherically quiescent one, characterized by the presence of clear skies (or optically thin clouds), by -40 W/m**2 surface net longwave radiation, and by surface temperatures that the ocean's constant upward heat flux anchors near 235K. The secondary mode, one of surface-atmosphere equilibrium, occurs in association with the advection of moisture and temperature from lower latitudes, and is characterized by the presence of optically thick clouds in the lowest few kilometers of the atmosphere, and by surface temperatures near 250K. ARM NSA/AAO (Atmospheric Radiation Measurement Program, North Slope of Alaska/Adjacent Arctic Ocean) observations exhibit modal behavior similar to that at SHEBA, although with differing magnitude and persistence. In addition, NSA exhibits interannual variability, during which the surface net longwave modes shift by 10 W/m**2, and in some winters NSA has but a single mode in the surface net longwave distribution. The goal of the research presented is to develop a deeper understanding of the physical mechanisms that maintain the Arctic ocean-surface-atmosphere in the two observed states. Preliminary results show that the Goddard Institute for Space Studies (GISS) Global Climate Model (GCM) exhibits the same discrete surface net longwave modes over the SHEBA ice-covered ocean site as do the observations, while the GCM only exhibits one of the net longwave modes observed at the NSA coastal continental site. The GISS Single Column Model (SCM), derived from the GISS GCM, is used here to determine the conditions required to attain and to maintain these stable modes over sea ice, and to investigate why the GCM was unable to reproduce the behavior observed over land. The SCM is also used to ascertain the conditions required for each equilibrium state to exist, and hence whether the ice-covered Arctic Ocean can be expected to exhibit the same two stable states every winter.
DE: 1863 Snow and ice (1827)
DE: 3307 Boundary layer processes
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3349 Polar meteorology
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting