Atmospheric Chemistry and Physics The effects of mineral dust particles, aerosol regeneration and ice nucleation parameterizations on clouds and precipitation (original) (raw)
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Atmospheric Chemistry and Physics, 2012
This study focuses on the effects of aerosol particles on the formation of convective clouds and precipitation in the Eastern Mediterranean Sea, with a special emphasis on the role of mineral dust particles in these processes. We used a new detailed numerical cloud microphysics scheme that has been implemented in the Weather Research and Forecast (WRF) model in order to study aerosol-cloud interaction in 3-D configuration based on 1 • × 1 • resolution reanalysis meteorological data. Using a number of sensitivity studies, we tested the contribution of mineral dust particles and different ice nucleation parameterizations to precipitation development. In this study we also investigated the importance of recycled (regenerated) aerosols that had been released to the atmosphere following the evaporation of cloud droplets.
Atmospheric Chemistry and Physics, 2011
This report addresses the effects of pollution on the development of precipitation in clean ("pristine") and polluted ("hazy") environments in the Eastern Mediterranean by using the Integrated Community Limited Area Modeling System (ICLAMS) (an extended version of the Regional Atmospheric Modeling System, RAMS). The use of this model allows one to investigate the interactions of the aerosols with cloud development. The simulations show that the onset of precipitation in hazy clouds is delayed compared to pristine conditions. Adding small concentrations of GCCN to polluted clouds promotes early-stage rain. The addition of GCCN to pristine clouds has no effect on precipitation amounts. Topography was found to be more important for the distribution of precipitation than aerosol properties. Increasing by 15% the concentration of hygroscopic dust particles for a case study over the Eastern Mediterranean resulted in more vigorous convection and more intense updrafts. The clouds that were formed extended about three kilometers higher, delaying the initiation of precipitation by one hour. Prognostic treatment of the aerosol concentrations in the explicit cloud droplet nucleation scheme of the model, improved the model performance for the twenty-four hour accumulated precipitation. The spatial distribution and the amounts of precipitation were found to vary greatly between the different aerosol scenarios. These results indicate the large uncertainty that remains and the need for more accurate description of aerosol feedbacks in atmospheric models and climate change predictions.
Predicting cloud ice nucleation caused by atmospheric mineral dust
Dust aerosols are very efficient ice nuclei important for heterogeneous cloud glaciation even in regions distant from desert sources. A new generation of ice nucleation parameterizations, including dust as ice nucleation agent, opens the way towards a more accurate treatment of cold cloud formation in atmospheric models. Using such parameterizations, we have developed a regional dust-atmospheric modelling system capable to predict in real-time conditions dust-induced ice nucleation. We executed the model with added ice nucleation component over the Mediterranean region, exposed to moderate Saharan dust transport over two periods lasting 15 and 9 days, respectively. Model results are validated against satellite and ground-based cloud-ice-related measurements, provided by SEVIRI (Spinning Enhanced Visible and InfraRed Imager) and by the CNR-IMAA Atmospheric Observatory CIAO in Potenza, South Italy. Predicted ice nuclei concentration shows reasonable level of agreement when compared against observed spatial and temporal patterns of cloud ice water. The developed methodology permits to use ice nuclei as input into cloud microphysics schemes of atmospheric models, expecting that this approach could improve predictions of cloud formation and associated precipitation. 1 Introduction Aerosol acting as ice nucleating particles () enhances the heterogeneous glaciation of cloud water making it to freeze earlier and at higher temperatures than otherwise. Insoluble particles such as dust and biological particles are known
Atmospheric Chemistry and Physics, 2016
Dust aerosols are very efficient ice nuclei, important for heterogeneous cloud glaciation even in regions distant from desert sources. A new generation of ice nucleation parameterizations, including dust as an ice nucleation agent, opens the way towards a more accurate treatment of cold cloud formation in atmospheric models. Using such parameterizations, we have developed a regional dust-atmospheric modelling system capable of predicting, in real time, dustinduced ice nucleation. We executed the model with the added ice nucleation component over the Mediterranean region, exposed to moderate Saharan dust transport, over two periods lasting 15 and 9 days, respectively. The model results were compared against satellite and ground-based cloud-icerelated measurements, provided by SEVIRI (Spinning Enhanced Visible and InfraRed Imager) and the CNR-IMAA Atmospheric Observatory (CIAO) in Potenza, southern Italy. The predicted ice nuclei concentration showed a reasonable level of agreement when compared against the observed spatial and temporal patterns of cloud ice water. The developed methodology permits the use of ice nuclei as input into the cloud microphysics schemes of atmospheric models, assuming that this approach could improve the predictions of cloud formation and associated precipitation.
Atmospheric Research, 2014
An improved approach for cloud droplet activation process parameterization is proposed that can utilize the empirically determined hygroscopicity information and practically limit the sizes of newly activated droplets. With the implementation of the improved approach in a cloud model, the aerosol effects on ice microphysics in convective cloud and precipitation development under different thermodynamic conditions is investigated. The model is run for four different thermodynamic soundings and three different aerosol types, maritime (M), continental (C) and polluted (P). Warm rain suppression by increased aerosol (i.e., CCN) is clearly demonstrated when weakly convective warm clouds are generated but the results are mixed when relatively stronger convective warm clouds are generated. For one of the two soundings that generate strong convective cold clouds, the accumulated precipitation amount is larger for C and P than for M, demonstrating the precipitation enhancement by increased CCN. For the maritime cloud, precipitation is initiated by the warm rain processes but ice hydrometeor particles form fast, which leads to early but weak cloud invigoration. Another stronger cloud invigoration occurs later for M but it is still weaker than that for C and P. It is the delayed accumulation of more water drops and ice particles for a burst of riming process and the latent heat release during the depositional growth of rimed ice particles that invigorate the cloud strongly for C and P. For the other sounding where freezing level is low, ice particles form fast for all three aerosol types and therefore warm rain suppression is not clearly shown. However, there still is more precipitation for C and P than for M until the accumulated precipitation amount becomes larger for M than for C near to the end of the model run. The results demonstrate that the precipitation response to aerosols indeed depends on the environmental conditions.
Impact of mineral dust on cloud formation in a Saharan outflow region
Atmospheric Chemistry and Physics, 2012
We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. On both days dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation 5 we used the fully online coupled model WRF-chem.
Mineral dust altering cloud microphysics and precipitation, and exerting LW cooling effect
Multi-platform and multi-sensor observations are employed to investigate the impact of mineral dust on cloud microphysical and precipitation processes in mesoscale convective systems. For a given convective strength, small hydrometeors were more prevalent in the stratiform rain regions with dust than in those regions that were dust free. Evidence of abundant cloud ice particles in the dust sector, particularly at altitudes where heterogeneous nucleation of mineral dust prevails, further supports the observed changes of precipitation. The consequences of the microphysical effects of the dust aerosols were to shift the precipitation size spectrum from heavy precipitation to light precipitation and ultimately suppressing precipitation. In addition to microphysical changes in clouds and precipitation, changes in nucleation processes of ice cloud due to aerosols would result in substantial changes in cloud top distribution. We found that the ice cloud effective temperature increases with...
Journal of Geophysical Research, 2005
1] The size distribution and chemical composition of aerosol particles during a dust storm in the eastern Mediterranean are analyzed. The data were obtained from airborne measurements during the Mediterranean Israeli Dust Experiment (MEIDEX). The dust storm passed over the Mediterranean Sea and extended up to an altitude of about 2.5 km. The uniqueness of this dust storm is that approximately 35% of the coarse particles up to about 1 km in height were internally mixtures of mineral dust and sea salt. Just north of the dust storm, large convective clouds developed, and heavy rain was recorded by the radar on the Tropical Rainfall Measuring Mission satellite. The chemical and physical properties of the particles are used as initial conditions for conducting a sensitivity simulation study with the two-dimensional detailed spectral bin microphysical model of Tel Aviv University. The simulations show that ignoring the ice-nucleating ability of the mineral dust, but allowing the soluble component of the mixed aerosols to act as efficient giant cloud condensation nuclei (CCN), enhances the development of the warm rain process in continental clouds. In our simulations the rain amounts increased by as much as 37% compared to the case without giant CCN. Introducing similar coarse-mode particles into more maritime-type clouds does not have significant effect on the cloud or on the amount of rainfall. On the other hand, allowing the mineral dust particles to also act as efficient ice nuclei (IN) reduces the amount of rain on the ground compared to the case when they are inactive. The simulations also reveal that under the same profiles of meteorological parameters, maritime clouds develop precipitation earlier and reach lower altitudes than continental clouds. When the dust particles are active as both giant CCN and effective IN, the continental clouds become wider, while the effects on the more maritime clouds is very small. Citation: Levin, Z., A. Teller, E. Ganor, and Y. Yin (2005), On the interactions of mineral dust, sea-salt particles, and clouds: A measurement and modeling study from the Mediterranean Israeli Dust Experiment campaign,