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.

/pdf/changes-in-precipitation-with-climate-change-3ofcyuiy76.pdf

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

Following the theory of Kusuda and Alpert (Part I), expressions for the eccentricity and tilt angle of the surface-wind hodograph at different latitudes are derived as functions of the amplitude and phase shift of the horizontal thermal force and also of some reasonable frictional parameter. Further, analyses of 47 hodographs in Washington, Oregon and California give the observed tilt angles, eccentricities and senses of rotation. The tilt angle is nearly linearly dependent on latitude. Eccentricities are in general high (0.9–1) and higher friction leads usually to higher eccentricity. However, eccentricity may sometimes be very small giving a circular hodograph) even with high friction and also very high with low friction; the latter case is primarily due to a phase shift between the horizontal thermal forces. It is shown that although in general the frequency of ACR (anticlockwise rotation) hodographs decrease northward in the Northern Hemisphere, lower friction may lead to a minimum in ACR fre...

Anticlockwise Rotation, Eccentricity and Tilt Angle of the Wind Hodograph. Part II: An Observational Study

Detecting and adjusting artificial biases of long-term temperature records in Israel

Three major modifications to the treatment of land surface processes in the Pennsylvania State University‐ National Center for Atmospheric Research mesoscale model MM5, are tested in a matrix of eight model experiments. Paired together in each dimension of the matrix are versions of the code with and without one of the changes. The three changes involve 1) a sophisticated land surface model [the Parameterization for Land‐ Atmosphere Convective Exchange (PLACE)], 2) the soil moisture and temperature initial conditions derived from running PLACE offline, and 3) a 1.5-order turbulent kinetic energy (TKE) turbulence boundary layer. The code without changes, defined as the control code, uses the most widely applied land surface, soil initialization, and boundary layer options found in the current MM5 community code. As an initial test of these modifications, a case was chosen in which they should have their greatest effect: conditions where heterogeneous surface forcing dominates over dynamic processes. The case chosen is one with widespread summertime moist convection, during the Convection and Precipitation Electrification Experiment (CaPE) in the middle of the Florida peninsula. Of the eight runs, the code with all three changes (labeled TKE-PLACE) demonstrates the best overall skill in terms of biases of the surface variables, rainfall, and percent and root-mean-square error of cloud cover fraction for this case. An early, isolated convective storm that formed near the east coast, at the downwind edge of a region of anomalous wet soil, and within the dense cluster of CaPE mesoscale observation stations, is correctly simulated only by TKE-PLACE. It does not develop in any of the other seven runs. A factor separation analysis shows that a successful simulation requires the inclusion of the more sophisticated land surface model, realistic initial soil moisture and temperature, and the higher-order closure of the planetary boundary layer (PBL) in order to better represent the effect of joint and synergistic (nonlinear) contributions from the land surface and PBL on the moist convection.

http://www.dgf.uchile.cl/~rmunoz/docs/MWR2001_Lynnetal_PLACE.pdf

Improved Simulation of Florida Summer Convection Using the PLACE Land Model and a 1.5-Order Turbulence Parameterization Coupled to the Penn State–NCAR Mesoscale Model

/pdf/on-the-urban-orographic-rainfall-anomaly-in-jerusalem-a-53tl9z9gxw.pdf

On the urban orographic rainfall anomaly in jerusalem--a numerical study

. Some strong natural fluctuations of climate in the Eastern Mediterranean (EM) region are shown to be connected to the major tropical systems. Potential relations between EM rainfall extremes to tropical systems, e.g. El Nino, Indian Monsoon and hurricanes, are demonstrated. For a specific event, high resolution modelling of the severe flood on 3-5 December 2001 in Israel suggests a relation to hurricane Olga. In order to understand the factors governing the EM climate variability in the summer season, the relationship between extreme summer temperatures and the Indian Monsoon was examined. Other tropical factors like the Red-Sea Trough system and the Saharan dust are also likely to contribute to the EM climate variability.

/pdf/tropical-tele-connections-to-the-mediterranean-climate-and-4jvv8yxzas.pdf

Pinhas Alpert

Papers

Anticlockwise Rotation, Eccentricity and Tilt Angle of the Wind Hodograph. Part II: An Observational Study

Detecting and adjusting artificial biases of long-term temperature records in Israel

Improved Simulation of Florida Summer Convection Using the PLACE Land Model and a 1.5-Order Turbulence Parameterization Coupled to the Penn State–NCAR Mesoscale Model

On the urban orographic rainfall anomaly in jerusalem--a numerical study

Tropical tele-connections to the Mediterranean climate and weather