Changes In Shortwave Radiation Research Articles

On nature and structure of atmospheric circulation anomalies in opposite seasons

In this paper, we consider circulation anomalies obtained in the model of atmospheric general circulation when incoming short wave radiation changes and the initial state anomalies are given. We also consider circulation differences during the years of high and low moisture content in the atmosphere, using the reanalysis data.

Modeling orbital forcing of lake level change: Lake Gosiute (Eocene), North America

The sedimentary record of Lake Gosiute, a lake that existed in southwestern Wyoming during the Eocene, contains evidence for lake level fluctuations thought to be caused by the earth's precession cycle. However, it is not clear how the effects of these orbital variations were transferred through the climate system and into the sedimentary record. We carry out a series of experiments using a general circulation model (GCM), a lake energy balance model and a lake water balance model to better understand the processes by which these orbital variations could have altered lake evaporation, on-lake precipitation and runoff from the lake's catchment. GCM simulations indicate significant differences in surface incident shortwave radiation between the two end-members of the precession cycle. These differences cause lake evaporation to be ∼25% higher when perihelion occurs at the summer solstice. GCM simulations also indicate significant seasonal changes in the amount of precipitation between the two end-members, but no change in the annual mean precipitation. Preliminary experiments with a lake water balance model show that local effects such as changes in vegetation, in snowmelt runoff, or in the area of mudflats surrounding the lake could have a large impact on lake level. However, more data need to be collected to determine the importance of these effects. Our results challenge previous interpretations of paleoclimate that were based on geologic data and simple assumptions regarding the effects of orbital variations on the water balance of the lake. In particular, we find that (1) changes in shortwave radiation may have been more important than changes in temperature or moisture in causing lake level fluctuations and (2) changes in catchment and lake characteristics should be further examined. In order to make an accurate reconstruction of past climatic change from a lake level record, climate system processes and local non-climatic variables must be considered explicitly.

Effects of reductions in stratospheric ozone on tropospheric chemistry through changes in photolysis rates

The observed reductions in stratospheric ozone since the late 1970s are likely to have affected the penetration of UV radiation into the troposphere. We have examined the sensitivity and the response of the tropospheric chemistry to such changes in UV radiation. Based on observations of ozone column densities and model calculations of changes in the ozone column densities after 1970, photodissociation rates for selected years (1970, 1980, 1990, 2000 and 2050) are calculated. These calculations give significant changes in the dissociation rates of some gases, particularly in the dissociation rate for O 3 yielding O( 1 D). This increase in photodissociation rates initiates increases in tropospheric OH. However, the model studies show that the OH changes are somewhat damped compared to the changes in short wave radiation due to strong interactions between key species in the troposphere. Ozone is reduced in most areas when the UV radiation increases, but the percentage reductions in ozone are significantly smaller than the percentage UV increases. However, during spring, O 3 increases in regions where NO x is enhanced. The calculations give increased levels of H 2 O 2 , although the magnitude of the response varies considerably with time of year and with region, and they are largest at high latitudes during spring. The relative changes in methane are found to be less than the relative changes in global average of OH since the largest relative OH changes take place outside the region of most importance for the methane oxidation (low latitudes and low altitudes). In addition, the effect is delayed in accordance with the chemical lifetime of methane (∼ 10 years). The results indicate that increased fluxes of UV due to reduced ozone columns may have contributed to the reduction in the growth rate of methane, and the magnitude of this effect is estimated to ∼ 1 3 of the reduction. It is therefore unlikely that changes in UV fluxes is the main cause of the reduction in the growth rate of methane which has been observed during the 1980s. The mechanism constitutes a negative indirect chemical effect on climate change from the ozone depleting substances, mainly the CFCs. DOI: 10.1034/j.1600-0889.1992.t01-3-00001.x-i1