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gfdl's home page > gfdl's bibliography > abraham h. oort > Journal of Geophysical Research, 79 (9), 1253-1260.
Year-to-year variations in the energy balance of the Arctic atmosphere
| Oort, A. H., 1974: Year-to-year variations in the energy balance of the Arctic atmosphere. Journal of Geophysical Research, 79 (9), 1253-1260. |
| Abstract: In order to understand better the processes responsible for maintaining the arctic climate, a study has been made of the energy budget at high latitudes. For simplicity this study is restricted to budget calculations for a polar cap that contains almost the entire atmospheric mass north of latitude 60 degrees N. The computations are based on 5 years of daily upper air observations of wind, temperature, geopotential height, and specific humidity for the period May 1958-April 1963, contained in the so-called MIT general circulation library. From the hemispheric network of radiosonde stations available in the library, more than 200 stations are located north of 50 degrees N. All these stations were used in the analyses to define the meteorological parameters in the Arctic. Averaged over the year, about 75% of the energy needed to balance radiative cooling in the polar cap is found to be transported by atmospheric processes across the southern boundary. The remaining 25% is probably supplied through a direct exchange of sensible and latent heat at the earth's surface in the polar cap. Throughout the year the influx of sensible heat plus potential energy dominates over that of latent heat. A further breakdown according to the mechanism of transfer shows that at 60 degrees N transient and stationary disturbances are far more effective than the mean meridional circulation in transporting energy poleward. By using Budyko's values for the surface energy flux, indirect estimates could be made of the radiative heat loss in the polar cap that are in good agreement with earlier direct estimates. The computed cooling curve has an interesting asymmetry; it shows a rapid decrease of cooling from about -1.4 degrees C/day in winter to about -0.6 degrees C/day in May, followed by a slow increase throughout the summer and fall. The year-to-year variability in inflow of energy from middle latitudes seems to be large, especially during the winter half year. Since observed temperature deviations in the polar cap appear to be, on the average, a factor of 5 smaller than the variations in inflow, these deviations must be largely compensated by variations in radiative cooling or in heat supply from the earth's surface. The present evidence tends to underline the complexity of the mechanism responsible for climatic anomalies in the Arctic. |