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David Rind

Abstract

Even though five different general circulation models are all currently producing about a 4° ± 1°C warming for doubled CO2, there is still substantial model disagreement about the degree of high latitude amplification of the surface temperature change. The consequences of this disagreement are investigated by comparing doubled CO2 climates with different latitudinal gradients of sea surface temperature. The GISS 4° × 5° general circulation model (GCM) was run with doubled CO2 and two sets of sea surface temperatures: one set derived from the equilibrium doubled CO2 run of the 8° × 10° GISS GCM, with minimal high latitude amplification, and the other set more closely resembling the GFDL results, with greater amplification. While the experiments differ in their latitudinal distribution of warming, they have the same global mean surface air temperature change. The differences in energy balance, atmospheric dynamics and regional climate simulations are discussed.

The results show that the two experiments often produce substantially different climate characteristics. With reduced high latitude amplification, and thus more equatorial warming, there is a greater increase in specific humidity and the greenhouse capacity (the concentration of infrared-absorbing gases) of the atmosphere, resulting in a warmer atmosphere in general. Features such as the low latitude precipitation, Hadley cell intensity, jet stream magnitude and atmospheric energy transports all increase compared to the control run. In contrast, these features all decrease in the experiment with greater high latitude amplification. There are also significant differences in the cloud cover and stationary eddy energy responses between the two experiments, as well as most regional climate changes; for example, there is greater drying of the midlatitude summer continents and greater polar ice melting when the high latitude amplification is greater. Predictions of the coming doubled CO2 climate and its societal consequences must be tempered by the current uncertainty in the degree of high latitude amplification.

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David Rind and William B. Rossow

Abstract

The Hadley cell is involved in the energy, momentum and moisture budgets in the atmosphere; it may be expected to change as sources and sinks of these quantities are altered due to climate perturbations. The nature of the Hadley cell change is complicated since alterations in one budget generally result in alterations in the others. Thus, Hadley cell sensitivity needs to be explored in an interactive system. In the GISS GCM (model I), a number of experiments are performed in which physical processes in each of the three budgets are omitted, the system adjusts, and the resultant circulation is compared to that of the control run. This procedure highlights which effects are most important and reveals the nature of the various interactions.

The results emphasize the wide variety of processes that appear capable of influencing the mean circulation. The intensity of the circulation is related to the coherence of the thermal forcing, and to the thermal opacity of the atmosphere. When all frictional forcing is removed, the circulation is restricted to the equatorial region. The latitudinal extent appears to be controlled primarily by eddy processes (Ferrel cell intensity). The implications for climate modeling and climate projections (e.g., rainfall changes) are discussed.

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David Rind and William L. Donn

Abstract

This is a further study of the use of natural infrasound in the atmosphere to monitor tidal circulation in the lower thermosphere. The height of this circulation is determined with the use of a reference atmospheric model, which is then used to calibrate infrasound/microseism ratios in terms of height. Also, we show from continuous observation over six years at 41°N, 74°W that the winter semidiurnal tide is present at least 62% of the time and the diurnal, at least 42% of the time.

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David H. Rind and William L. Donn

Abstract

Observations of natural infrasound produce a continual record of the sound velocity, a function of wind and temperature, at the reflection level in the upper atmosphere. Under normal conditions in winter the reflection level, for sound generated by ocean waves to the east of Palisades, N. Y., is in the lower thermosphere. During the circulation changes associated with stratospheric warmings, winds near the stratopause may become east or north, allowing infrasound to be reflected from this level. We are then provided with a continuous record of sound velocity near the stratopause. The methods which are used to distinguish between stratosphere and thermospheric sound reflection are discussed, and circulation changes for each year are cataloged.

During the warming event sound velocities in the stratosphere are shown to vary radically, with fluctuations of up to 60 m s−1 in a few hours time period. These short time period variations, observable only because of the continuous nature of infrasound recording, are greater than expected and indeed constitute a significant fraction of the total wind and temperature variation associated with the event at our latitude. As such they imply significant energy variations on shorter time scales than those usually considered important in stratospheric dynamics. Some possible explanations for these observations are given.

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Drew T. Shindell, David Rind, and Nambath Balachandran

Abstract

Simulations were performed with the Goddard Institute for Space Studies GCM including a prescribed quasi-biennial oscillation (QBO), applied at a constant maximum value, and a physically realistic parameterization of the heterogeneous chemistry responsible for severe polar ozone loss. While the QBO is primarily a stratospheric phenomenon, in this model the QBO modulates the amount and propagation of planetary wave energy in the troposphere as well as in the stratosphere. Dynamical activity is greater in the easterly than in the unforced case, while westerly years are dynamically more quiescent. By altering zonal winds and potential vorticity, the QBO forcing changes the refraction of planetary waves beginning in midwinter, causing the lower-stratospheric zonal average temperatures at Southern Hemisphere high latitudes to be ∼3–5 K warmer in the easterly phase than in the westerly during the late winter and early spring. Ozone loss varies nonlinearly with temperature, due to the sharp threshold for formation of heterogeneous chemistry surfaces, so that the mean daily total mass of ozone depleted in this region during September was 8.7 × 1010 kg in the QBO easterly maximum, as compared with 12.0 × 1010 kg in the westerly maximum and 10.3 × 1010 kg in the unforced case. Through this mechanism, the midwinter divergence of the Eliassen–Palm flux is well correlated with the subsequent springtime total ozone loss (R 2 = 0.6). The chemical ozone loss differences are much larger than QBO-induced transport differences in our model.

Inclusion of the QBO forcing also increased the maximum variability in total ozone loss from the ∼20% value found in the unforced runs to ∼50%. These large variations in ozone depletion are very similar in size to the largest observed variations in the severity of the ozone hole. The results suggest that both random variability and periodic QBO forcing are important components, perhaps explaining some of the difficulties encountered in previous attempts to correlate the severity of the ozone hole with the QBO phase.

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David Rind, William L. Donn, and Ellen Dede

Abstract

In a continuing study of the feasibility of using microbarom (natural infrasound) observations to define characteristics of upper air winds, we determined the seasonal mean trace velocity of microbaroms. We show that this is equal to the acoustic velocity at an upper reflection level. This velocity is the sum of the sound speed based on temperature alone and the wind speed. We determine the former from the vertical temperature profile and can thus calculate the wind speed at particular reflection levels in the stratosphere and ionosphere. Our results compare well with direct observations.

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Drew T. Shindell, Sun Wong, and David Rind

Abstract

To study the interannual variability of the Antarctic ozone hole, a physically realistic parameterization of the chemistry responsible for severe polar ozone loss has been included in the GISS GCM. The ensuing ozone hole agrees well with observations, as do modeled surface UV increases of up to 42%. The presence of the ozone hole causes a reduction in lower stratospheric solar heating and an increase in upper stratospheric descent and dynamical heating in the model, as expected. Both the degree of ozone depletion and the dynamical response exhibit large interannual variability, however. These variations are driven by differences in the midwinter buildup of tropospheric wave energy in the model, which affect the dynamics globally for several months according to the mechanism detailed herein. Starting by July, strong tropospheric wave activity leads to greater energy reaching the lower stratosphere, and therefore warmer temperatures, than in years with weak wave activity. The warmer temperatures persist throughout the austral spring, resulting in ozone losses that are only ∼80% of those seen in the years with weaker wave activity. Significant differences also occur in the zonal wind field, setting up conditions that ultimately affect the propagation of wave energy in the spring. Differences in the propagation of wave energy lead to an October increase in upper stratospheric dynamical heating that is more than three times larger in the years with weak wave activity than in years with strong wave activity. Modeled interannual variations in both upper stratospheric temperatures and ozone loss are of similar magnitude to observations, though the largest observed variations exceed those seen here, indicating that unforced variability likely plays a significant role in addition to periodic forcings such as the QBO. The results are in accord with observational studies showing a strong anticorrelation between the interannual variability of tropospheric wave forcing and of the Antarctic ozone hole, suggesting that midwinter tropospheric wave energy may be the best predictor of the severity of the ozone hole the following spring.

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