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D. Rind
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D. Rind

Abstract

A new general circulation model, developed to run on a coarse grid (8 × 10° resolution) at the Goddard Institute for Space Studies is employed to investigate the potential use of ground moisture anomalies for seasonal climate prediction. For three different summertime simulations, the ground moisture on 1 June over the United States is reduced to ¼ of its value in the control run. The results show that the subsequent surface air temperature is significantly higher throughout most of the summer, while the precipitation decreases, especially in June and July. Knowledge of late spring ground moisture anomalies should thus be an aid in predicting summertime climate.

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D. Rind

Abstract

The atmospheric dynamics of five different climate simulations with the GISS GCM are compared to investigate the changes that occur as climate warms or cools. There are two ice age simulations, the current and doubled CO2 climates, and a simulation of the warm Cretaceous. These climates have a range of global average surface air temperature of 13°C. The results are compared with those of other models, as well as to paleoclimate and recent observations.

The study shows that many zonally averaged processes do not change systematically as climate changes. In particular, the January Hadley cell, jet stream, mean precipitation patterns and total atmospheric transport show surprisingly little variation among the different climate simulations. While eddy energy increases as climate cools, the effective eddy forcing of the mean zonal wind and temperature fields is not significantly greater. All these features result from balances between competing factors, and while individual processes differ in the cold and warm climates, there is much compensation.

Additional results show that the relative humidity remains fairly constant as climate changes. The ratio of stationary to transient eddy kinetic energy also remains relatively constant. Eddy energy transports increase in colder climates, primarily due to changes in the stationary eddy transports. Cloud cover decreases as climate warms due to decreases in low-level clouds. The lapse rate in all the simulations follows the moist adiabatic ,value at low latitudes, and is close to the critical baroclinic adjustment value at upper midlatitudes. The latitudinal temperature gradients at midlatitudes of both the sea surface temperature and the vertically integrated air temperature are very similar in the diverse climates. It is speculated that this is due to the properties of the water molecule, and is the cause for much of the observed compensation.

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D. Rind

Along with the continuing uncertainty associated with global climate sensitivity [2°–4.5°+, for doubled CO2 in the latest Intergovernmental Panel on Climate Change (IPCC) report], we have not made much progress in improving our understanding of the past/future sensitivity of low- and high-latitude climates. Disagreements in paleoclimate interpretations, and diverse results from the IPCC Fourth Assessment Report future climate model simulations suggest that this uncertainty is still a factor of 2 in both latitude regimes. Cloud cover is the primary reason for model discrepancies at low latitudes, while snow/sea ice differences along with cloud cover affect the high-latitude response. While these uncertainties obviously affect our ability to predict future climate-change impacts in the tropics and polar regions directly, the uncertainty in latitudinal temperature gradient changes affects projections of future atrriospheric dynamics, including changes in the tropical Hadley cell, midlatitude storms, and annual oscillation modes, with ramifications for regional climates. In addition, the uncertainty extends to the patterns of sea surface temperature changes, with, for example, no consensus concerning longitudinal gradient changes within each of the tropical oceans. We now know a good deal more about how latitudinal and longitudinal gradients affect regional climates; we just do not know how these gradients will change. New satellite observations and field programs are underway, which should help improve our modeling capability, although there is no guarantee that these issues will be resolved before a substantial global warming impact is upon us. A review of this topic is presented here.

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D. Rind and X. Liao

Abstract

Individual profile measurements from the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument aboard the Earth Radiation Budget Satellite have been used to create latitude-longitude maps of monthly mean aerosols, ozone, water vapor, relative humidity and NO2 on up to 14 standard pressure levels. Color maps and gridded data from 1985 through 1993 are available on a CD-ROM that can be obtained from the Distributed Active Archive Center (DAAC) at NASA Langley Research Center. Examples are shown of the ozone hole and related phenomenon, and aerosol loading associated with the Mount Pinatubo volcano. By presenting the data in this visible and easy-to-use format, we hope that it will reach a larger community and result in better understanding of atmospheric aerosols and trace gases. Similar presentations will be generated for SAGE III data, expected to begin in 1998 as part of the Earth Observing System (EOS).

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W. L. Donn and D. Rind

Abstract

Microbaroms are regular pressure variations of a few microbars (dyn cm−2) produced by the passage of infrasound (∼5 see period) radiated from ocean waves. Their amplitudes show prominent diurnal, semidiurnal and seasonal variations that are shown to depend on the presence or absence of one or two atmospheric sound ducts between the surface and an elevation of ∼120 km. These ducts depend on the vertical temperature and wind structure of the atmosphere. For our station (Palisades, N.Y.), ducting of sound from the most common source of microbaroms (Atlantic Ocean storms) requires the presence of strong easterly winds at some upper reflection level. Variations (such as tidal) in these winds, as derived from available reports, are shown to account for the observed patterns of microbaroms. In particular, these patterns are shown to be controlled by effects of tidal and seasonal wind variations and stratospheric warmings. Having established the dependence of microbaroms on upper temperature and winds, we use the relationship to interpret these upper atmospheric conditions. Finally, we suggest that use of an expanded “synoptic” network of infrasound recorders would provide a simple procedure to monitor conditions in the upper atmosphere.

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D. Rind, N. K. Balachandran, and R. Suozzo

Abstract

The effects of volcanic aerosols on the middle atmosphere are investigated with the Goddard Institute for Space Studies (GISS) Global Climate/Middle Atmosphere model. Volcanic aerosols with a visible optical depth of 0.15 are put into the lower stratosphere, and their influence is explored for different time scales: instantaneous effect (sea surface temperatures not allowed to adjust); influence for the first few years, with small tropospheric cooling; and long-term effect (50 years) with significant tropospheric cooling.

The aerosols induce a direct stratospheric response, with warming in the tropical lower stratosphere, and cooling at higher latitudes. On the shorter time scales, this radiative effect increases tropospheric static stability at low- to midlatitudes, which reduces the intensity of the Hadley cell and Ferrel cell. There is an associated increase in tropospheric standing wave energy and a decrease in midlatitude west winds, which result in additional wave energy propagation into the stratosphere at lower midlatitudes in both hemispheres. Convergence of this flux in the middle atmosphere increases the residual circulation, producing low-latitude cooling and high-latitude warming near the stratopause. The dynamical changes are on the order of 10%, and are generally similar to occurrences following major volcanic eruptions in the last 30 years.

On the longer time scale, a strong hemispheric asymmetry arises. In the Northern Hemisphere eddy energy decreases, as does the middle-atmosphere residual circulation, and widespread stratospheric cooling results. In the Southern Hemisphere, the late increase in sea ice increases the tropospheric latitudinal temperature gradient, leading to increased eddy energy, an increased middle-atmosphere residual circulation, and some high-latitude stratospheric warming.

The different experiments emphasize that the middle-atmosphere response to climate change depends on both the direct and indirect (i.e., tropospheric) effects. Similarly, the tropospheric changes are not simply the products of the direct climate perturbation; they depend as well on what happens to the stratosphere. Such examples of the coupled systems underline the need to include both the troposphere and middle atmosphere in studying the effects of climate change.

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D. Rind, R. Suozzo, and N. K. Balachandran

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The variability which arises in the GISS Global Climate-Middle Atmosphere Model on two time scales is reviewed: interannual standard deviations, derived from the five-year control run, and intraseasonal variability as exemplifited by stratospheric warmings. The model's extratropical variability for both mean fields and eddy statistics appears reasonable when compared with observations, while the tropical wind variability near the stratopause may be excessive, possibly due to inertial oscillations. Both wave 1 and wave 2 warmings develop, with connections to tropospheric forcing. Variability on both time scales results from a complex set of interactions among planetary waves, the mean circulation, and gravity wave drag. Specific examples of these interactions are presented, which imply that variability in gravity wave forcing and drag may be an important component of the variability of the middle atmosphere.

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D. Rind, R. Healy, C. Parkinson, and D. Martinson

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As a first step in investigating the effects of sea ice changes on the climate sensitivity to doubled atmospheric CO2, the authors use a standard simple sea ice model while varying the sea ice distributions and thicknesses in the control run. Thinner ice amplifies the atmospheric temperature sensitivity in these experiments by about 15% (to a warming of 4.8°C), because it is easier for the thinner ice to be removed as the climate warms. Thus, its impact on sensitivity is similar to that of greater sea ice extent in the control run, which provides more opportunity for sea ice reduction. An experiment with sea ice not allowed to change between the control and doubled CO2 simulations illustrates that the total effect of sea ice on surface air temperature changes, including cloud cover and water vapor feedbacks that arise in response to sea ice variations, amounts to 37% of the temperature sensitivity to the CO2 doubling, accounting for 1.56°C of the 4.17°C global warming. This is about four times larger than the sea ice impact when no feedbacks are allowed. The different experiments produce a range of results for southern high latitudes with the hydrologic budget over Antarctica implying sea level increases of varying magnitude or no change. These results highlight the importance of properly constraining the sea ice response to climate perturbations, necessitating the use of more realistic sea ice and ocean models.

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D. Rind, D. Shindell, P. Lonergan, and N. K. Balachandran

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The response of the troposphere–stratosphere system to doubled atmospheric CO2 is investigated in a series of experiments in which sea surface temperatures are allowed to adjust to radiation imbalances. The Goddard Institute for Space Studies (GISS) Global Climate Middle Atmosphere Model (GCMAM) warms by 5.1°C at the surface while the stratosphere cools by up to 10°C. When ozone is allowed to respond photochemically, the stratospheric cooling is reduced by 20%, with little effect in the troposphere. Planetary wave energy increases in the stratosphere, producing dynamical warming at high latitudes, in agreement with previous GCMAM doubled CO2 simulations; the effect is due to increased tropospheric generation and altered refraction, both strongly influenced by the magnitude of warming in the model’s tropical upper troposphere. This warming also results in stronger zonal winds in the lower stratosphere, which appears to reduce stratospheric planetary wave 2 energy and stratospheric warming events. The dynamical changes in the lower stratosphere are weakened when O3 chemistry on polar stratospheric cloud effects are included at current stratospheric chlorine levels. Comparison with the nine-level version of the GISS GCM with a top at 10 mb shows that both the stratospheric and tropospheric dynamical responses are different. The tropospheric effect is mostly a function of the vertical resolution in the troposphere; finer vertical resolution leads to increased latent heat release in the warmer climate, greater zonal available potential energy increase, and greater planetary longwave energy and energy transports. The increase in planetary longwave energy and residual circulation in the stratosphere is reproduced when the model top is lifted from 30 to 50 km, which also affects upper-tropospheric stability, convection and cloud cover, and climate sensitivity.

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