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David Rind

Abstract

Climate model results are now being used to asses the potential societal impact of climate change, and to compare with paleoclimate indicators. The models used for these purposes currently employ relatively coarse resolution, and a key question is how the results might change as resolution is improved. To examine this issue, doubled-CO2 and ice age simulations with boundary conditions identical for two different resolutions are run with the GISS model. The resolution dependency of climate change sensitivity, atmospheric dynamics, and regional climate depiction are discussed.

The results show that model resolution affects two key processes in the control runs, moist convection and the nonlinear transfer of kinetic energy into the zonal mean flow. The finer resolution model has more penetrative convection but less convection overall, aspects which alter its temperature and wind structure relative to those of the coarser grid model. With finer resolution there are also stronger winds, more evaporation and a more active hydrological cycle. While some of these changes are not particularly, their characteristics are mirrored in the warm and cold climate simulations.

In comparison with the coarser resolution model, the finer grid doubled CO2 run has a greater decrease in high-level cloud cover, eddy energy, and eddy energy transports, and a greater increase in atmospheric temperature surface winds, precipitation, and penetrative convection. The ice age finer grid run shows the opposite effect when compared with the medium grid: greater eddy energy and eddy transport increases, greater reduction in hydrologic cycle and atmospheric temperature. Regional climate changes also differ with resolution, due to both the local expression of the different dynamical responses and the differing spatial possibilities. The development of higher resolution models, and the practical use of climate change results, should incorporate an awareness of the potential impact of resolution on model process and climate change depiction.

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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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Colin Price and David Rind

Abstract

A general circulation model (GCM) is used to model global lightning distributions and frequencies. Both total and cloud-to-ground lightning frequencies are modeled using parameterizations that relate the depth of convective clouds to lightning frequencies. The model's simulations of lightning distributions in time and space show good agreement with available observations. The model's annual mean climatology shows a global lightning frequency of 77 flashes per second, with cloud-to-ground lightning making up 25% of the total. The maximum lightning activity in the GCM occurs during the Northern Hemisphere summer, with approximately 91% of all lightning occurring over continental and coastal regions.

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Colin Price and David Rind

Abstract

Future climate change could have significant repercussions for lightning-caused wildfires. Two empirical fire models are presented relating the frequency of lightning fires and the area burned by these fires to the elective precipitation and the frequency of thunderstorm activity. One model deals with the seasonal variations in lightning fires, while the second model deals with the interannual variations of lightning fires. These fire models are then used with the Goddard Institute for Space Studies General Circulation Model to investigate possible changes in fire frequency and area burned in a 2 × CO2 climate. In the United States, the annual mean number of lightning fires increases by 44%, while the area burned increases by 78%. On a global scale, the largest increase in lightning fires can be expected in untouched tropical ecosystems where few natural fires occur today.

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Judah Cohen and David Rind

Abstract

Large-scale snow cover anomalies are thought to cause significant changes in the diabatic heating of the earth's surface in such a way as to produce substantial local cooling in the surface temperatures. This theory was tested using the GISS 3-D GCM (General Circulation Model). The results of the GCM experiment showed that snow cover caused only a short term local decrease in the surface temperature. In the surface energy budget, reduction in absorbed shortwave radiation and the increased latent heat sink of melting snow contributed to lower temperatures. However, all the remaining heating terms contribute to increasing the net heating over a snow covered surface. The results emphasize the negative feedback which limits the impact of snow cover anomalies over longer time scales.

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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 Rind and Nambath K. Balachandran

Abstract

Results Of experiments with a GCM involving changes in UV input (±25%, ±5% at wavelengths below 0.3 µ) and simulated equatorial QBO are presented, with emphasis on the tropospheric response. The QBO and UV changes alter the temperature in the lower stratosphere/upper troposphere, altecting tropospheric/stratospheric vertical stability. When the extratropical lower stratosphere/upper troposphere warms, tropospheric eddy energy is reduced, leading to extratropical tropospheric cooling of some 0.5°C on the zonal average, and surface temperature changes up to ±5°C locally. Opposite effects occur when the extratropical lower stratosphere/upper troposphere cools. Cooling or warming of the comparable region in the Tropics decreases/increase static stability, accelerating/decelerating the Hadley circulation. Tropospheric dynamical changes are on the order of 5%.

The combined UV/QBO effect in the troposphere results from its impact on the middle atmosphere. in the QBO east phase, more energy is refracted to higher latitudes, due to the increased horizontal shear of the zonal wind, but with increased UV, this energy propagates preferentially out of the polar lower stratosphere, in response to the increased vertical shear of the zonal winds; therefore, it is less effective in warming the polar lower stratosphere. Due to their impacts on planetary wave generation and propagation, all combinations of UV and QBO phase affect the longitudinal patterns of tropospheric temperatures and potential heights. The modeled perturbations often agree qualitatively with observations and are of generally similar orders of magnitude.

The results are sensitive to the forcing employed. In particular, the nature of the tropospheric response depends upon the magnitude (and presumably wavelength) of the solar irradiance perturbation. The results of the smaller UV variations (±5%) are more in agreement with observations, showing clear differences between the UV impact in the cast and west QBO phase. However, since the UV magnitudes have been exaggerated relative to observed solar UV variations during the last solar cycle, the results cannot be used to prove an actual solar forcing of the troposphere. The results will also likely be sensitive to the model, particularly its planetary longwave energy, and may be influenced by other processes that have not been included, such as changes in stratospheric ozone.

The dynamical changes are accompanied by changes in cloud cover and snow cover that differ between maximum and minimum UV, and affect the radiative balance of the planet. As these influences do not cancel in the extreme phases of the UV variations, a net radiative forcing may result from solar cycling in conjunction with the QBO. An assessment of the solar impact on climate change must include these dynamically driven forcings.

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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 VITO PAGNOTTI

Abstract

The relationship between midtropospheric synoptic features and midstratospheric temperature in winter is investigated by examining averages of 5–10 yr of observations, monthly mean observations, and daily records. It is found that midstratospheric warm regions lie above midtropospheric troughs and subtropical ridges, while stratospheric cold regions occur above high-latitude tropospheric ridges. Thus, at high latitudes, an inverse correlation exists between 500-mb height and 10-mb temperatures; this correlation seems to be simultaneous in nature. The implications of these results are discussed with relation to the general circulation of the stratosphere, and in particular to the relative importance of hydrostatic adjustment, planetary wave propagation, and tidal energy.

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Gary L. Russell and David Rind

Abstract

The GISS coupled atmosphere–ocean model is used to investigate the effect of increased atmospheric CO2 by comparing a compounded 1% CO2 increase experiment with a control simulation. After 70 yr of integration, the global surface air temperature in the 1% CO2 experiment is 1.43°C warmer. In spite of this global warming, there are two distinct regions, the northern Atlantic Ocean and the southern Pacific Ocean, where the surface air temperature is up to 4°C cooler. This situation is maintained by two positive feedbacks: a local effect on convection in the South Pacific and a nonlocal impact on the meridional circulation in the North Atlantic. The poleward transport of latent energy and dry static energy by the atmosphere is greater in the 1% CO2 experiment, caused by warming and therefore increased water vapor and greater greenhouse capacity at lower latitudes. The larger atmospheric transports tend to reduce upward vertical fluxes of heat and moisture from the ocean surface at high latitudes, which has the effect of stabilizing the ocean, reducing both convection and the thermohaline circulation. With less convection, less warm water is brought up from below, and with a reduced North Atlantic thermohaline circulation (by 30% at time of CO2 doubling), the poleward energy transport by the oceans decreases. The colder water then leads to further reductions in evaporation, decreases of salinity at high latitudes, continued stabilization of the ocean, and maintenance of reduced convection and meridional overturning. Although sea ice decreases globally, it increases in the cooling regions, which reduces the overall climate sensitivity, especially in the Southern Hemisphere. Tropical warming has been observed over the past several decades; if modeling studies such as this and others that have produced similar effects are valid, these processes may already be beginning.

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