Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Black carbon in soot is an efficient absorbing agent of solar irradiation that is preferentially emitted in the tropics and can form atmospheric brown clouds in mixture with other aerosols. These factors combine to make black carbon emissions the second most important contribution to anthropogenic climate warming, after carbon dioxide emissions.

Global and regional climate changes due to black carbon

There is a direct influence of global warming on precipitation. Increased heating leads to greater evaporation and thus surface drying, thereby increasing the intensity and duration of drought. However, the water holding capacity of air increases by about 7% per 1°C warming, which leads to increased water vapor in the atmosphere. Hence, storms, whether individual thunderstorms, extratropical rain or snow storms, or tropical cyclones, supplied with increased moisture, produce more intense precipitation events. Such events are observed to be widely occurring, even where total precipitation is decreasing: 'it never rains but it pours!' This increases the risk of flooding. The atmo- spheric and surface energy budget plays a critical role in the hydrological cycle, and also in the slower rate of change that occurs in total precipitation than total column water vapor. With modest changes in winds, patterns of precipitation do not change much, but result in dry areas becoming drier (generally throughout the subtropics) and wet areas becoming wetter, especially in the mid- to high latitudes: the 'rich get richer and the poor get poorer'. This pattern is simulated by climate mod- els and is projected to continue into the future. Because, with warming, more precipitation occurs as rain instead of snow and snow melts earlier, there is increased runoff and risk of flooding in early spring, but increased risk of drought in summer, especially over continental areas. However, with more precipitation per unit of upward motion in the atmosphere, i.e. 'more bang for the buck', atmo- spheric circulation weakens, causing monsoons to falter. In the tropics and subtropics, precipitation patterns are dominated by shifts as sea surface temperatures change, with El Nino a good example. The volcanic eruption of Mount Pinatubo in 1991 led to an unprecedented drop in land precipitation and runoff, and to widespread drought, as precipitation shifted from land to oceans and evaporation faltered, providing lessons for possible geoengineering. Most models simulate precipitation that occurs prematurely and too often, and with insufficient intensity, resulting in recycling that is too large and a lifetime of moisture in the atmosphere that is too short, which affects runoff and soil moisture.

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Changes in precipitation with climate change

Climate change projections for the Mediterranean region

Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.

A satellite view of aerosols in the climate system

Meridional distribution of aerosol optical thickness (AOT) over the ocean was analyzed by using the eight-year MISR and MODIS-Terra data sets, from March 2000 to February 2008, as well as the five-year MODIS-Aqua data set, from July 2002 to June 2007. The three independent sensors show that there was a pronounced meridional aerosol asymmetry. It was found that there were strong seasonal variations in the hemispheric aerosol asymmetry: it was pronounced during the half-year period, from March to August (the most pronounced asymmetry was observed from April to July). There was no noticeable asymmetry during the season from September to December. Not only has the Northern hemisphere, where the main sources of aerosols are located, but also the Southern hemisphere contributed to the formation of noticeable aerosol asymmetry. The increase in AOT, averaged over the Northern hemisphere during the season of pronounced hemispheric aerosol asymmetry, was accompanied by a decrease in AOT, averaged over the Southern hemisphere. In both hemispheres, amplitudes of seasonal AOT variations decreases from mid-latitudes (60N - 30N and 30S - 60S) to low latitudes (30N - 0 and 0 - 30S) respectively, indicating that the contribution of AOT averaged over mid-latitudes to the formation of pronouncedmore » meridional hemispheric asymmetry and its seasonal variations is more significant than the contribution of AOT averaged over low latitudes. For the season of prominent hemispheric aerosol asymmetry, from April to July, during the eight-year period under consideration, a declining long-term tendency of AOT prevailed at latitudes between 30oN and 60oN, suggesting brightening over the cloud-free ocean.« less

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Variations of meridional aerosol distribution and solar dimming

[1] Moisture budget components over a rectangular region defined by the longitudes 6.0°W–36.0°E and latitudes 30.0°N to 45.0°N, with an area of about 6.08 × 106 km2 over the Mediterranean (Med) Basin, are studied by the use of the Japan Meteorological Agency super-high-resolution (20 km) GCM monthly mean data. The research time periods are 1979–2007 for current run and 2075–2099 for future run. Six rainy months of October to March with a total of 168 months for the current run and 144 months for the future run were selected. The rain months have been categorized into five groups of months based on the mean monthly rainfall amounts where the five groups are P < 1.0, 1.0 ≤ P < 1.5, 1.5 ≤ P < 2.0, 2.0 ≤ P < 2.5, and 2.5 mm/d ≤ P. We found that generally, over the Mediterranean, the outflow-inflow is balancing the independently calculated evaporation-precipitation quite well with a correlation coefficient of about 0.89. The present seasonal (October-March) precipitation simulated from the 20 km GCM showed a quite reasonable agreement with the CRU. The seasonal area mean precipitation and evaporation are 1.85 mm/d and 2.44 mm/d, respectively. The largest two precipitation categories contribute over 50% of the total seasonal rainfall. The evaporation varies positively with the precipitation for all precipitation categories. Also, the relatively high mean recycling ratio (55%) indicates that the local Med evaporation has a central role in the local precipitation. Another important finding is that the decreasing trend of recycling ratio with the rising of the precipitation category implies that the outside moisture inflow role increases with the increase of the precipitation category. For all the precipitation categories, the total outflow is larger than the total inflow, indicating that the Med area is an important source of moisture. Individual boundary moisture flux shows that the main moisture comes from the west boundary and contributes 59% of the total inflow, while the main outflow is through east boundary and is responsible for 46% of total outflow. Analysis of monthly precipitation indicates that the October and November have the two largest amount of precipitation over the research region. The moisture budget study separated for the east and the west Med shows that the area mean precipitation for the east and the west Med are 2.14 and 2.29 mm/d, while the evaporation are 4.48 and 3.59 mm/d. The plausible reason for the differences between these two basins has been discussed. The moisture supplies to the east Med is mainly from the west boundary, while for the west Mediterranean, the north boundary inflow also plays an important role along with the west boundary. The future moisture budget components over Med suggest that the precipitation is decreasing from 1.85 to 1.62 mm/d and the evaporation is increasing from 2.44 to 2.56 mm/d between current and future. Another finding is that the largest precipitation number of months decreases from 12% to only 6% of the total number of months, while the intensity of the precipitation in this category enhances in the future.

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Climatological relationships among the moisture budget components and rainfall amounts over the Mediterranean based on a super‐high‐resolution climate model

SUMMARY A meso y-scale (Ax = 1 km) model for orographic rainfall was used to investigate the dependence of orographic enhancement on wind speed and direction and on detailed topography. Applying the model to cases reported in south Wales, high sensitivity to wind direction and the corresponding upwind topographical cross-sections-factors neglected in some previous studies-was found. This suggests that studies of highresolution orographical rainfall characteristics (such as orographic enhancement as function of wind speed) or model verification should account for detailed interaction of the wind vector with the high-resolution topography. Comparison with microphysical models illustrates that the effect of detailed wind-topography interaction is at least of similar magnitude to that due to microphysical processes.

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Role of detailed wind-topography interaction in orographic rainfall

A computerized system for mapping an atmospheric phenomenon in a geographic region. Multiple free-space electromagnetic communications links are previously distributed in the geographic region. The system includes an interface to monitoring mechanisms attached respectively to the free-space electromagnetic communications links. The monitoring mechanisms respectively monitor attenuation levels of the free-space electromagnetic communications links. A processor simultaneously processes the attenuation levels, and maps in the geographic region the atmospheric phenomenon. The simultaneous processing preferably applies a non-linear model which relates the attenuation levels the atmospheric phenomenon, and solves a tomographic problem based on the non-linear model and the attenuation levels. The tomographic problem is preferably solved by an interactive algorithm based on consecutive fefinenment and linear inversion at each iteration. Alternatively, an interpolation is performed based on respective inverse distance from the communications links. Preferably, the interpolation is further based on respective lengths of communications links. A data interface preferably provides to subscribers temporal information related to the atmospheric phenomenon within portions of the geographic region.

Pinhas Alpert

Papers

Variations of meridional aerosol distribution and solar dimming

Climatological relationships among the moisture budget components and rainfall amounts over the Mediterranean based on a super‐high‐resolution climate model

Role of detailed wind-topography interaction in orographic rainfall

Monitoring and Mapping of Atmospheric Phenomena

A physical model to complement railfall normals over complex terrain