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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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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 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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Nambath K. Balachandran and David Rind

Abstract

Results of experiments with a GCM involving changes in UV input (±25%, ±10%, ±5% at wavelengths below 0.3 µm) and simulated equatorial QBO are presented, with emphasis on the middle atmosphere response. The UV forcing employed is larger than observed during the last solar cycle and does not vary with wavelength, hence the relationship of these results to those from actual solar UV forcing should be treated with caution. The QBO alters the location of the zero wind line and the horizontal shear of the zonal wind in the low to middle stratosphere, while the UV change alters the magnitude of the polar jet and the vertical shear of the zonal wind. Both mechanisms thus affect planetary wave propagation. The east phase of the QBO leads to tropical cooling and high-latitude warming in the lower stratosphere, with opposite effects in the upper stratosphere. This quadrupole pattern is also wen in the observations. The high-latitude responses are due to altered planetary wave effect, while the model's tropical response in the upper stratosphere is due to gravity wave drag.

Increased UV forcing warms tropical latitudes in the middle atmosphere, resulting in stronger extratropical wen winds, an effect which peaks in the upper stratosphere/lower mesosphere with the more extreme UV forcing but at lower altitudes and smaller wind variations with the more realistic forcing. The increased vertical gradient of the zonal wind leads to increased vertical propagation of planetary warm altering energy convergences and temperatures. The exact altitudes affected depend upon the UV forcing applied.

Results with combined QBO and UV forcing show that in the Northern Hemisphere, polar warming for the east QBO is stronger when the UV input is reduced by 25% and 5% as increased wave propagation to high latitudes(east QB0 effect) is prevented from then propagating vertically (reduced UV effect). The model results are thus in general agreement with observations associated with solar UV/QBO variations, although the west phase is not absolutely warmer with increased UV. Questions remain concerning the actual variation of stratospheric winds with the solar cycle as the magnitude of the variations reported in some observations cannot be associated with UV variations in this model (but do arise in the model without any external forcing). The model results actually come closer to reproducing observations with the reduced magnitude of UV forcing due to the lower altitude of west wind response, despite the smaller wind variations involved. An evaluation of the reality of the reported effects of combined QBO and solar UV variations on the middle atmosphere requires the use of proper UV solar cycle forcing and should include possible ozone variations.

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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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Drew T. Shindell, David Rind, and Patrick Lonergan

Abstract

Parameterized stratospheric ozone photochemistry has been included in the Goddard Institute for Space Studies (GISS) GCM to investigate the coupling between chemistry and climate change for the doubled CO2 climate. The chemical ozone response is of opposite sign to temperature changes, so that radiative cooling in the upper stratosphere results in increased ozone, while warming reduces ozone in the lower stratosphere. The increased overhead column reduces the amount of UV reaching the lower stratosphere, resulting in further ozone decreases there. Changes of up to 15% are seen, including both photochemistry and transport. Good agreement is found between the authors’ results and those in other models for tropical latitudes where the stratospheric temperature responses are similar. However, in the extratropics, there are large differences between present results and those of the other models due to differences in tropospheric warming and tropospheric forcing of the stratospheric residual circulation. A net decrease in column ozone at midlatitudes is seen in this climate model, in contrast to the other models that showed an increase in column ozone everywhere. These ozone reductions lead to an increase of 10% in UV radiation reaching the surface at northern midlatitudes. The authors find significantly less of an increase in the high-latitude ozone column than in the other models.

When parameterized heterogeneous chemistry on polar stratospheric clouds is also included, while maintaining current chlorine loading, it is found that the Antarctic ozone hole becomes significantly larger and of longer duration. In addition, an ozone hole of approximately half the depth in percent of the current Antarctic ozone hole forms in the Arctic due to both chemistry and transport changes resulting from a reduction of sudden warmings seen in the doubled CO2 atmosphere.

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Barry H. Lynn, David Rind, and Roni Avissar

Abstract

A mesoscale atmospheric model was used to evaluate the impact of subgrid-scale landscape discontinuities on the vertical profiles of resolved temperature, moisture, and moist static energy in the planetary boundary layer (PBL) of GCMs. These profiles were produced with a 3D version of the model (using a horizontal grid resolution of 7.5 km and 13 vertical layers in the PBL) by averaging horizontally the various atmospheric variables over a 180×180 km2 domain-about the size of the horizontal domain represented by a single grid element in a GCM. They were compared to corresponding vertical profiles produced with a 1 D version of the model, which simulates the PBL, as in a GCM, over a single horizontal grid element. Differences obtained between the horizontally averaged atmospheric variables produced with the 3D situations and the 1 D simulations emphasize the impact of subgrid-scale landscape discontinuities on GCM-resolved variables. Various types of landscape discontinuities, characterized by horizontal contrasts of surface wetness and size of land patches, were simulated under various background-wind conditions. Differences of temperature, specific humidity, and moist static energy as large as 4 K, 6 g kg−1, and 10 kJ kg−1 were obtained in some cases. These differences were not affected significantly by moderate winds but were sensitive to the spatial distribution of surface wetness. Thew results emphasize the need to parameterize mesoscale processes induced by landscape discontinuities in GCMs.

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Tackseung Jun, Lalith Munasinghe, and David H. Rind

Abstract

Extreme monsoon rainfall in India has disastrous consequences, including significant socioeconomic impacts. However, little is known about the overall trends and climate factors associated with extreme rainfall because rainfall greatly varies across India and because few appropriate methods are available to measure extreme rainfall in the context of such heterogeneity. To provide a comprehensive assessment of extreme monsoon rainfall, the authors developed a metric using record rainfall data to measure the changes in the likelihood of extreme high and extreme low rainfall over time; this metric is independent of the characteristics of the underlying rainfall distributions. Hence, the metric is ideally suited to aggregate extreme rainfall information across heterogeneous regions covering India. The authors found that from 1930 to 2013, the likelihood of extreme high and extreme low rainfall increases 2-fold and 4-fold, respectively. These overall trend increases are driven by anomalous increases, particularly in the early 2000s; the likelihood of extreme high and extreme low rainfall increases 5-fold and 18-fold in 2005 and 2002, respectively. These findings imply a broadening of the underlying monsoon rainfall distribution over the past century. The authors also show that the time patterns of the likelihood of extreme rainfall in recent decades are correlated with El Niño–Southern Oscillation, especially when it is in the same phase with the Pacific decadal oscillation and Indian Ocean dipole.

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George Tselioudis, William B. Rossow, and David Rind

Abstract

The International Satellite Cloud Climatology Project (ISCCP) dataset is used to correlate variations of cloud optical thickness and cloud temperature in today's atmosphere. The analysis focuses on low clouds in order to limit the importance of changes in cloud vertical extent, particle size, and water phase. Coherent patterns of change are observed on several time and space scales. On the planetary scale, clouds in colder, higher latitudes are found to be optically thicker than clouds in warmer, lower latitudes. On the planetary scale, winter clouds are, for the most part, optically thicker than summer clouds. The logarithmic derivative of cloud optical thickness with temperature is used to describe the sign and magnitude of the optical thickness-temperature correlation. The seasonal, latitudinal, and day-to-day variations of this relation are examined for Northern Hemisphere clouds in 1984. The analysis is done separately for clouds over land and ocean. In cold continental clouds, optical thickness increase with temperature, consistent with the temperature variation of the adiabatic cloud water content. In warm continental and in almost all maritime clouds, however, optical thickness decreases with temperature. The behavior of the optical thickness-temperature relation is usually, though not always, the same whether the temperature variations are driven by seasonal, latitudinal, or day-to-day changes. Important exceptions are noted. Some explanations for the observed behavior are proposed.

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