Alexander P. Makshtas

Trends and variations in Arctic Climate System

Prominent changes of the Arctic atmosphere-ice-ocean system observed in recent years have sparked intense discussions as to whether these changes represent episodic events or long-term shifts in the Arctic environment. In the past, the lack of long-term observations in the Arctic made it difficult to explore this issue. Although the length of available instrumental records is often too short to give a quantitative, statistical description of processes at multi-decadal time scales, these Arctic records, which are similar in length to the global records, provide insight into long-term variations of the Arctic climate system and suggest that high-latitude climate feedbacks merit further study.

Dynamic–Thermodynamic Sea Ice Model: Ridging and Its Application to Climate Study and Navigation

Abstract A dynamic–thermodynamic sea ice model with the ocean mixed layer forced by atmospheric data is used to investigate spatial and long-term variability of the sea ice cover in the Arctic basin. The model satisfactorily reproduces the averaged main characteristics of the sea ice and its extent in the Arctic Basin, as well as its decrease in the early 1990s. Employment of the average ridge shape for describing the ridging allows the authors to suggest that it occurs in winter and varies from year to year by a factor of 2, depending on an atmospheric circulation pattern. Production and horizontal movement of ridges are the focus in this paper, as they show the importance of interannual variability of the Arctic ice cover. The observed thinning in the 1990s is a result of reduction in ridge formation on the Pacific side during the cyclonic phase of the Arctic Oscillation. The model yields a partial recovery of sea ice cover in the last few years of the twentieth century. In addition to the sea ice cover...

Distribution of solar radiation in the Barents Sea marginal ice zone during summer

Field measurements during the Barex-95 expedition in the marginal ice zone of the Barents Sea provided new data of solar radiation under different conditions of cloudiness and sea ice cover during the thawing. We found a strong dependence of angular and spectral redistribution of radiation on cloud optical thickness and surface albedo. We developed a Monte Carlo model for radiative transfer through a homogeneous cloud layer above sea ice with given concentration and homogeneous snow on top. This simple Monte Carlo model reproduced the observed angular distribution of solar intensity and cloud albedo as a function of solar zenith angle, optical thickness of the clouds, and surface albedo. The model allowed us to estimate the influence of surface tilt on irradiance and to give a qualitative explanation of how the sea ice relief transforms during summer. Data of short wave radiation below clouds enabled the estimation of the effect of clouds on the distribution of radiative heating of the upper ocean for spectral ranges 350-1000 and 400-700 nm (photosynthetically active radiation range). Spectral sensitivity of absorption of solar radiation in clouds relatively decreases radiative heating in the upper centimeters of the water up to 25 and 5% for 350-1000 and 400-700 nm, respectively.

Ice Ridging Over Various Space Scales

A model of a single ice ridge is constructed based on the laws of mass, impulse and energy balance and on the representation of a ridge as a discontinuity line. Self-oscillations of the ice cover induced by the buildup of two ridges are investigated. The approach to the modeling of an ice cover with numerous ridges in the onedimensional case is formulated.