Year-to-year variations in the energy balance of the arctic atmosphere

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°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°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°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°C/day in winter to about −0.6°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.

Synoptically Driven Arctic Winter States

“…There is greater variability in the NetLW values comprising the two modes over the Arctic basin, which is to be expected since temperature, humidity, etc., vary geographically over the Arctic. Regardless, the bimodal character of the Arcticwide NetLW histogram indicates that the radiatively clear and opaquely cloudy states observed at SHEBA may indeed have analogs that span the Arctic basin and suggests caution in interpreting winter mean polar cap energy budget components (e.g., Oort 1974;Nakamura and Oort 1988), which combine the effects of both states as if they occurred simultaneously.…”

Atmospheric heat budgets of the polar regions

“…In the present study we use techniques resembling the ones shown by Oort [1974] for a polar cap north of 60øN. However, we consider here two polar caps, one covering the Arctic from 70øN to the north pole and the other covering the Ant- arctic from 70øS to the south pole.…”

“…It is not an easy task to estimate FsF C in view of the limited number of observational data available. Oort [1974] used a map provided by Budyko [1963] to estimate FsF C. However, the description over the polar regions of this map lacked welldefined features. In this study we will therefore compute FsF c as a residual from the other three factors in the balance equation (1).…”

Moisture transport into the Arctic: Source‐receptor relationships and the roles of atmospheric circulation and evaporation

“…From a general point of view, variations in moisture transport can be due to (a) changes in general circulation patterns, (b) increases or reductions in moisture supply from particular sources caused by changes in evaporation, or (c) a combination of these two effects [ Gimeno et al ., , ]. Several previous studies have shown the influence of circulation patterns and evaporation [e.g., Aagaard and Greisman , ; Oort , ; Hanssen‐Bauer and Førland , ; Rogers et al ., ; White et al ., ; Gimeno et al ., ] on the Arctic atmospheric hydrological system. Most studies related to the transport of moisture into the Arctic region make use of three different methodologies: analytical and box models, physical water vapor tracers (isotopes), and numerical water vapor tracers (WVT).…”