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Alan Robock
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Alan Robock

Abstract

A Russian group, under the initial leadership of M. I. Budyko, has produced the first comprehensive analysis of monthly average surface temperature (January 1891 through May 1980) for the Northern Hemisphere on a 5°×10° latitude-longitude grid. This data set and the magnetic tape of the data are described. Other collections of surface temperature data are also described and compared on the bases of temporal and spatial coverage, and analysis methods.

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Alan Robock
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Alan Robock

While tropical sea surface temperatures certainly influence the atmosphere; winter circulation, temperature, and precipitation over Northen Hemisphere continents are also influenced by circulation patterns related to the stratosphere. In particular, large tropical volcanic eruptions produce winter warming patterns over Northern Hemisphere continents because of a dynamical effect forced by gradients of radiative heating from sulfate aerosols in the lower stratosphere. These effects must be included for accurate dynamical seasonal predictions of Northern Hemisphere winter temperature over both North America and Eurasia.

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Alan Robock

Abstract

A new parameterization of snow and ice area and albedo as functions of surface temperature is presented based on recent satellite observations of snow and ice extent. This parameterization is incorporated into a seasonal energy-balance climate model. Experiments are conducted with the model to determine the effects of this parameterization change on the latitudinal and seasonal distribution of model sensitivity to external forcings of climate change, such as solar constant variations and changes in the atmospheric carbon dioxide amount.

The sea ice-thermal inertia feedback is found to be the determining factor in this sensitivity pattern, producing enhanced sensitivity in the polar regions in the winter and decreased sensitivity in the polar regions in the summer. The albedo feedbacks (snow-area and snow/ice-meltwater) are weak and produce a small amount of additional sensitivity, but do not change the pattern. The response pattern is the same as that found by Manabe and Stouffer (1980) with a general circulation model. The enhanced sensitivity in the summer found by Ramanathan et al. (1979) is shown to be due to a surface albedo feedback parameterization which does not allow the thermal inertia to change. The sensitivity of an annual average version of the model is approximately the same as that of the seasonal model.

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Alan Robock

Abstract

Satellite data are used to construct monthly mean snow cover maps for the Northern Hemisphere. The zonally averaged snow cover from these maps is calculated and used, along with zonally averaged sea ice cover and detailed data on land surface types, to calculate the seasonal cycle of zonally averaged surface albedo. A parameterization is presented of the solar zenith angle effect on ocean albedo. The effects of meltwater on the surface, solar zenith angle and cloudiness are all parameterized and included in the calculations of snow and ice albedo. It is found that meltwater effects are very important, but that zenith angle and cloudiness effects are negligible.

The albedo results for January, April, July, and October and the annual average results are compared to calculations by several other workers. The discrepancies are explained in terms of the above-mentioned effects and the averaging methods used. It is found that several other workers failed to weight the albedos by solar radiation when calculating annual averages. The global average surface albedo is calculated to be 0.150.

The data presented here allow a calculation of surface albedo for any land or ocean 10° latitude band as a function of surface temperature and ice and snow cover. The relationship between the seasonal cycles of snow and ice cover and surface temperature are also analyzed for possible use in a complete surface albedo parameterization for an energy balance climate model. The correct determination of the ice boundary is found to be more important than the snow boundary for accurately simulating the ice (a.-id snow)-albedo feedback. Annual average calculations are also presented. Northern and Southern Hemisphere sea-ice-temperature regressions give differing results for the seasonal cycle but similar ones for annual average values.

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Alan Robock

An update of the Kellogg and Schneider climate feedback diagram that incorporates thermal inertia, meltwater, and vegetation feedbacks, and more clearly distinguishes external forcing and heat fluxes, is presented. This diagram will be of use in helping to understand the complex interactions in the climate system that can feed back on surface air temperature.

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Alan Robock

Abstract

A numerical climate model is used to simulate climate change forced only by random fluctuations of the atmospheric heat transport. This short-term natural variability of the atmosphere is shown to be a possible “cause” not only of the variability of the annual world average temperature about its mean, but also long-term excursions from the mean.

Various external causes of climate change are also tested with the model and the results compared with observations for the past 100 years. Volcanic dust is shown to have been an important cause of climate change, while the effects of sunspot-related solar constant variation and anthropogenic forcing are not evident.

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John Scialdone and Alan Robock

Abstract

No abstract available.

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Alan Robock and Dale Kaiser

Abstract

The effects of snow and cloud cover on bidirectional reflectance were examined using visible radiation (0.5–0.7 μm) data measured by NOAA polar orbiting satellites between June 1974 and February 1978. Reflectances resulting from different cloud/snow cover conditions were compared using Northern Hemisphere snow cover maps, surface weather charts, satellite photos and data on land surface types. This was done for the prevalent surface types found in regions which, at certain times during the Northern Hemisphere winter, showed marked interannual variations in snow cover,

None of the cases studied showed that concurrent cloud and snow cover produced significantly different reflectances than cloud cover alone. Cloud cover alone was found to yield higher reflectances (∼0.62) than snow cover alone, with the difference being greatest over forested areas. Clear-sky reflectances over farming and grazing lands [snow (0.45), no snow (0.15)] were found to be significantly higher than those over forested regions [snow (0.33), no snow (0.11)]. Variations in satellite zenith angle wore not found to produce significant effects in most cases studied. Local viewing times at high latitudes for the polar orbiting satellites wore found to vary from 0800 to as late as 1200 LST.

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