Martinson, D. G. and M. Steele, 2001: Future of the Arctic sea ice cover: Implications of an Antarctic analog. Geophysical Research Letters, 28(2): 307-310.
Recent observations reveal a significant change in the upper ocean characteristics of the eastern Arctic in 1995. The change is manifested through the loss of a near-surface layer known as the cold halocline layer (CHL). Without the CHL, the Arctic water column looks and behaves like the Antarctic water column. The expected local impact is the appearance of significant winter ocean heat fluxes (15 - 20 W/m(2)) and reduction of winter ice growth by 70 - 80% relative to years in which the CHL was present. Preliminary results suggest a partial recovery of the CHL in the late 1990's, tracking the weakening of the Arctic Oscillation.
Muench, R. D., J. H. Morison, L. Padman, D. Martinson, P. Schlosser, B. A. Huber and R. Hohmann, 2001: Maud Rise revisited. Journal of Geophysical Research-Oceans, 106(C2): 2423-2440.
An oceanographic field program called the Antarctic Zone Flux experiment was carried out in the eastern Weddell Sea during austral winter (July-September) 1994. Data from a drift buoy array were used in concert with shipboard observations to provide exceptionally high horizontal resolution of upper ocean hydrographic parameters near Maud Rise. Chemical and tracer data were obtained from the ship. We identify a "warm pool" southwest of the rise as a dynamically necessary region of positive (cyclonic) vorticity that is associated with a Taylor column over the rise. Both a warm "halo" surrounding the Taylor column and the warm pool are associated with thermocline shoaling that is a necessary condition for high upward heat fluxes to occur. These features extend the influence of Maud Rise bottom topography on upper ocean heat flux over a region that is larger, by a factor of at least 2, than the area directly overlying the rise. Areal mean upward heat fluxes of about 25 W m(-2) are derived using both upper ocean T ("instantaneous") values and tracer data ("integrated") values. Fluxes derived over the warm halo and pool regions using only upper ocean T exceeded 100 W m(-2) at specific sites. Elsewhere in the region, the T-derived heat fluxes varied widely from <10 to >50 W m(-2), whereas the tracer-derived heat fluxes showed a considerably more uniform distribution. Our mean values are similar to those that have been previously reported. Historical ice cover data have shown that the geographical region encompassed by Maud Rise and the warm pool area to the southwest is a preferred site for polynya formation, consistent with these findings. Time series analyses of the historical upper ocean data set suggest that conditions conducive to polynya formation are correlated with climate processes remote from the Southern Ocean.
Parkinson, C. L., D. Rind, R. J. Healy and D. G. Martinson, 2001: The impact of sea ice concentration accuracies on climate model simulations with the GISS GCM. Journal of Climate, 14(12): 2606-2623.
The Goddard Institute for Space Studies global climate model (GISS GCM) is used to examine the sensitivity of the simulated climate to sea ice concentration specifications in the type of simulation done in the Atmospheric Model Intercomparison Project (AMIP), with specified oceanic boundary conditions. Results show that sea ice concentration uncertainties of +/-7% can affect simulated regional temperatures by more than 6 degreesC, and biases in sea ice concentrations of +7% and -7% alter simulated annually averaged global surface air temperatures by -0.10 degrees and +0.17 degreesC, respectively, over those in the control simulation. The resulting 0.27 degreesC difference in simulated annual global surface air temperatures is reduced by a third, to 0.18 degreesC, when considering instead biases of +4% and -4%. More broadly, least squares fits through the temperature results of 17 simulations with ice concentration input changes ranging from increases of 50% versus the control simulation to decreases of 50% yield a yearly average global impact of 0.0107 degreesC warming for every 1% ice concentration decrease, that is, 1.07 degreesC warming for the full +50% to -50% range. Regionally and on a monthly average basis, the differences can be far greater, especially in the polar regions, where wintertime contrasts between the +50% and -50% cases can exceed 30 degreesC. However, few statistically significant effects are found outside the polar latitudes, and temperature effects over the nonpolar oceans tend to be under 1 degreesC, due in part to the specification of an unvarying annual cycle of sea surface temperatures. The +/-7% and +/-4% results provide bounds on the impact (on GISS GCM simulations making use of satellite data) of satellite-derived ice concentration inaccuracies, +/-7% being the current estimated average accuracy of satellite retrievals and +/-4% being the anticipated improved average accuracy for upcoming satellite instruments. Results show that the impact on simulated temperatures of imposed ice concentration changes is least in summer, encouragingly the same season in which the satellite accuracies are thought to be worst. Hence, the impact of satellite inaccuracies is probably less than the use of an annually averaged satellite inaccuracy would suggest.
Rind, D., M. Chandler, J. Lerner, D. G. Martinson and X. Yuan, 2001: Climate response to basin-specific changes in latitudinal temperature gradients and implications for sea ice variability. Journal of Geophysical Research-Atmospheres, 106(D17): 20161-20173.
We use experiments with the GISS general circulation model to investigate how changes in latitudinal temperature gradients affect atmospheric circulation in different ocean basins, with particular attention paid to the implications for high-latitude sea ice. The results are relevant to both estimated past climate changes, current climate gradient changes (e.g., El Nino-Southern Oscillation events), and proposed future climate responses to greenhouse gases. Sea surface temperature gradients are increased/decreased in all ocean basins, and in the Pacific and Atlantic separately, without changing sea ice or global average temperature. Additional experiments prescribe sea ice growth/reduction with global cooling/warming. As expected, increased gradients strengthen the subtropical jet stream and deepen the subpolar lows in each hemisphere, but results in the Northern and Southern Hemispheres differ in fundamental ways. In the Northern Hemisphere, increased storm intensities occur in the ocean basin with the increased gradient; in the Southern Hemisphere the deeper storms occur in the ocean basin with the decreased gradient. Alterations of the gradient in one ocean basin change longitudinal temperature gradients; an increased gradient in one basin from tropical heating results in subsidence in the tropics in the other basin, mimicking the effect of a decreased gradient in that basin. The subtropical jet is therefore strengthened over the basin with the increased gradient and decreased over the other ocean basin. Hence in many respects, regional effects, such as the strength of subpolar lows in an individual basin, are amplified when the gradient changes are of opposite sign in the two ocean basins. The Southern Hemisphere response occurs because gradient increases in one ocean basin, by strengthening the subtropical jet, shift storm tracks equatorward and away from the potential energy source associated with cold air advection from Antarctica. At the same time, with a weaker subtropical jet in the other basin, storms move poleward and strengthen. This latter effect may explain observed sea ice variations that are out of phase in the Atlantic and Pacific Ocean basins in the Southern Hemisphere (referred to as the Antarctic dipole) as well as upper ocean variability in the Weddell gyre. Gradient changes produce little effect on sea level pressure in the Arctic, unless sea ice is changed. With Arctic sea ice reductions, the sea ice response acts as a positive feedback, inducing cyclonic circulation changes that would enhance its removal, as may be occurring due to the current high phase of the North Atlantic Oscillation.
Ukita, J. and D. G. Martinson, 2001: An efficient adjustable-layering thermodynamic sea-ice model formulation for high-frequency forcing. Annals of Glaciology, 33: 253-260.
Recent observations suggest that high-frequency forcing events have profound influence oil the air-sea-ice interactions in the polar region. Studying these events with sea-ice models requires close examination of the model sensitivity that may arise from the high-frequency variability of the forcing. We show that the maximum layer thickness is dictated by the time-scale of the forcing variability and that the computation of the surface temperature develops enhanced sensitivity at high-frequency forcing. We resolve these constrains by developing all "adjustable-layering" thermodynamic formulation for ice and snow that re-computes the number of layers required each time-step to satisfy this maximum thickness, which preserves the total enthalpy and general internal thermal gradients. The conservation equations form a tri-diagonal system ideal for a Fast and efficient implicit solution. Furthermore, we resolve the issue of the high sensitivity of the surface flux balance by solving the linearized version of the flux boundary condition simultaneously with the overall conservation system. In this paper we develop the analyses specifying the model requirements, describe the model system and test its algorithmic implementation.
Yuan, X. J. and D. G. Martinson, 2001: The Antarctic Dipole and its predictability. Geophysical Research Letters, 28(18): 3609-3612.
This study investigates the nature of interannual variability of Antarctic sea ice and its relationship with the tropical climate. We find that the dominant interannual variance structure in the sea ice edge and surface air temperature fields is organized as a quasi-stationary wave which we call the "Antarctic Dipole" (ADP). It is characterized by an out-of-phase relationship between the ice and temperature anomalies in the central/eastern Pacific and Atlantic sectors of the Antarctic. The dipole consists of a strong standing mode and a weaker propagating motion within each basin's ice field. It has the same wavelength as the Antarctic Circumpolar Wave (ACW) and dominates the ACW variance. The dipole is clearly associated with tropical ENSO events; it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead. The prediction performs better in extreme warm/cold years, and best in La Niña years.
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