Nikolaos Bartsotas

Natural and anthropogenic aerosols in the Eastern Mediterranean and Middle East: Possible impacts

The physical and chemical properties of airborne particles have significant implications on the microphysical cloud processes. Maritime clouds have different properties than polluted ones and the final amounts and types of precipitation are different. Mixed phase aerosols that contain soluble matter are efficient cloud condensation nuclei (CCN) and enhance the liquid condensate spectrum in warm and mixed phase clouds. Insoluble particles such as mineral dust and black carbon are also important because of their ability to act as efficient ice nuclei (IN) through heterogeneous ice nucleation mechanisms. The relative contribution of aerosol concentrations, size distributions and chemical compositions on cloud structure and precipitation is discussed in the framework of RAMS/ICLAMS model. Analysis of model results and comparison with measurements reveals the complexity of the above links. Taking into account anthropogenic emissions and all available aerosol-cloud interactions the model precipitation bias was reduced by 50% for a storm simulation over eastern Mediterranean.

Using High-Resolution Numerical Weather Forecasts to Improve Remotely Sensed Rainfall Estimates: The Case of the 2013 Colorado Flash Flood

AbstractThe September 2013 flash flood–triggering rainfall event in Colorado highlighted the strong underestimation of remote sensing techniques over mountainous terrain. In this work, the use of high-resolution rainfall forecasts for adjusting weather radar– [Multi-Radar Multi-Sensor (MRMS) quantitative precipitation estimation (Q3)] and satellite-based [CPC morphing technique (CMORPH) and TRMM 3B42RT] rainfall estimates is examined. Evaluation of the adjustment procedures is based on the NCEP Stage IV product. Results show that 1-km-grid-resolution rainfall forecasts provided by a numerical weather prediction model [Regional Atmospheric Modeling System and Integrated Community Limited Area Modeling System (RAMS-ICLAMS)] adequately captured total rainfall amounts during the event and could therefore be used to adjust biases in radar and satellite rainfall estimates. Two commonly used adjustment procedures according to 1) mean field bias and 2) probability density function matching are examined. Findings ...

Moving toward Subkilometer Modeling Grid Spacings: Impacts on Atmospheric and Hydrological Simulations of Extreme Flash Flood–Inducing Storms

AbstractFlash floods develop over small spatiotemporal scales, an attribute that makes their predictability a particularly challenging task. The serious threat they pose for human lives, along with damage estimates that can exceed one billion U.S. dollars in some cases, urge toward more accurate forecasting. Recent advances in computational science combined with state-of-the-art atmospheric models allow atmospheric simulations at very fine (i.e., subkilometer) grid scales, an element that is deemed important for capturing the initiation and evolution of flash flood–triggering storms. This work provides some evidence on the relative gain that can be expected from the adoption of such subkilometer model grids. A necessary insight into the complex processes of these severe incidents is provided through the simulation of three flood-inducing heavy precipitation events in the Alps for a range of model grid scales (0.25, 1, and 4 km) with the Regional Atmospheric Modeling System–Integrated Community Limited Are...

The Role of Aerosols in Low and Upper Atmospheric Layers Condensation

Airborne particles of anthropogenic and/or natural origin have certain direct and indirect effects in the atmosphere. Radiative transfer is the category of processes related to aerosols and clouds (direct effects). Indirect effects are always associated with condensates at various atmospheric layers. Condensation within the tropospheric layers is mainly related to aerosol physical and chemical properties, thermodynamical and dynamical processes. As it was found in various studies, there is a strong relationship between aerosols and extreme weather events such as deep convection and extreme rainfall. Low-level condensation is associated with low-cloud formation and fog. In this presentation we will discuss the condensation processes within the lower and upper troposphere and how they are affected by the various types of aerosols. New model development related to nucleation processes and condensation at different levels is discussed. The model used for development and application is the fully-coupled atmospheric modeling system RAMS/ICLAMS. Model simulations have been performed for selected cases related to (i) extreme precipitation events and (ii) low-level condensation and fog formation in the Euro-Mediterranean and Arabian Peninsula. The sensitivity tests showed that the explicit activation of aerosols as CCN and IN causes changes in the precipitation distribution as well as in its spatiotemporal patterns. Fog formation near the coastline and low-cloud formation mechanisms are controlled by the thermal cooling and moisture evaporation by the surface. The accurate simulation of the microphysical processes involved in formation and dissipation of fog depends on several variables.

The Dust Cycle in the Arabian Peninsula and Its Role in the Urban Air Quality

The dust cycle plays an important role in the atmospheric processes. The levels of dust concentration in the Arabian cities are quite high, a fact that affects air quality. A better understanding of this phenomenon may lead in reduced impacts. Towards this direction, an integrated modeling approach has been selected and applied in SW Saudi Arabia. More specifically, we discuss the characteristics of the dust production processes using the RAMS/ICLAMS multiscale model. A series of very high resolution simulations have been performed and potential mitigation actions are discussed. A reduction in dust concentration is evident by changing the landscape characteristics. Extreme dust events affect the study areas despite the tested activities and changes. A characteristic example is the “haboobs”.

The Role of Aerosol Properties on Cloud Nucleation Processes

The clouds that develop in maritime or polluted environments have significant differences in their properties. A number of modeling sensitivity tests have been performed to describe the physical processes related to aerosol – cloud interactions at various stages of cloud development. Precipitation amounts and cloud structure were found to be very sensitive to changes in the size distribution and number concentrations of the aerosols. Certain combinations of CCN/IN properties and atmospheric properties may lead to significant enhancement of convection and precipitation. These interactions are not linear and it is the synergetic effects between meteorology and atmospheric chemistry that are responsible for the variation of precipitation.

An Integrated Weather and Sea State Forecasting System for the Arabian Peninsula (WASSF)

Saudi Aramco is the oil industry of the Kingdom of Saudi Arabia with several activities related to the environment. In order to optimize daily operations and minimize environmental risks a forecasting system has been employed and setup in operations. The objectives of the system include prevention and mitigation of environmental problems, as well as early warning of local conditions associated with extreme weather events. The management and operations part is related to early warning of weather and dust storms that affect operations of various facilities, whereas the environmental part is mainly focused on air quality and desert dust levels in the atmosphere.