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Understanding the Effects of Aerosols On Cloud Microphysics in Coastal Urban Environments

Nathan Hosannah NASA-URC COSI Doctoral Student Dr. Jorge Gonzalez Cruz Mentor Department of Mechanical Engineering CCNY / Graduate Center CUNY.

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Understanding the Effects of Aerosols On Cloud Microphysics in Coastal Urban Environments

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  1. Nathan Hosannah NASA-URC COSI Doctoral Student Dr. Jorge Gonzalez Cruz Mentor Department of Mechanical Engineering CCNY / Graduate Center CUNY Understanding the Effects of Aerosols On Cloud Microphysics in Coastal Urban Environments

  2. Several studies have found evidence of warm-season rainfall increases over and downwind of major cities such as Atlanta, Phoenix, Mexico City, St. Louis, and Chicago. This precipitation has been predominately attributed to the induced updraft of warm air masses. Aerosols are abundant in urban environments, and it has been hypothesized that they play a role in the water balance of humid regions. High concentrations of cloud condensation nuclei (CCN) may induce precipitation in humid urban environments.  However, it is also noted that precipitation may also be reduced due to excess CCNs or by the presence of large aerosols, which are also known as giant cloud condensation nuclei (GCCN). The present research is directed towards improving our understanding of the role of aerosols in cloud processes in complex coastal urban environments through ground observations obtained from AERONET, LIDAR, and weather stations across the New York City and New Jersey region, and numerical analysis for the month of July 2007. Growth of particles from CCN to rain droplet sizes is explored for characteristic aerosol distributions obtained from these observations. The role of aerosols in precipitation is investigated through numerical analysis of cloud microphysics by implementing population growth by condensation, collision, and coalescence within the computational model. Condensation is the formation of liquid drops from water vapor. It is the process which creates clouds, and is therefore necessary for the formation of all types of precipitation. Coalescence is the merging of two or more water drops into a single larger drop after they collide with one another. Coalescence between colliding drops is affected by their impact energy, which tends to increase with the higher fall velocities of larger drops. A modified version of the Regional Atmospheric Model System (RAMS) will be investigated to determine whether it is beneficial to incorporate the new interpretation of cloud microphysics. The ultimate goal of this research is to discern between local precipitation attributed solely to the presence of atmospheric aerosols, and precipitation caused by convection. Abstract

  3. To improve our understanding of Cloud Condensation Nuclei (CCN) size distribution in coastal urban environments and its role in precipitation. To model cloud microphysics in regional coastal environments (i.e. RAMS and/or WRF). To generate a clear distinction between precipitation assisted by urban convection, and precipitation formed by aerosol/cloud interaction in coastal urban environments (i.e. through simulations & observations). Objectives

  4. Saturation ratio is defined as the ratio of the two previous pressure terms. (1) Growth of a droplet by diffusion depends on both thermal and mass vapor diffusion (Equations 2 & 3 respectively). (2) (3) Equation 9 enables us to determine growth of a CCN particle. (4) Computational Methods : Condensation Growth

  5. Collision efficiency between two droplets is given by: (15) The rate of change of the large droplet with regards to time is: (16) Finally for a small updraft, the rate of change of particle radius with respect to altitude is: (17)  Computational Methods:Collision & Coalescence (Cont.)

  6. Growth by Condensation and Coalescence

  7. Grid Resolution at 16K,4K, and 1K. RAMS Grids

  8. Weatherbug Stations Weatherbug stations across NYC/NJ which will be used to monitor precipitation patterns.

  9. Observations: July 2007 (Cont.)

  10. July 4th -8th Precipitation (Grid 1) Accumulated Precipitation over the Northeastern United States from July 4th at 12am, to July 8th at 12am. Vectors denote wind direction and magnitude.

  11. July 4th -8th Precipitation (Grid 3) Accumulated Precipitation over NYC from July 4th at 12am, to July 8th at 12am. Vectors denote wind direction and magnitude.

  12. RAMS vs. Observations

  13. Most researchers currently approximate aerosol particle size distribution as a uni-modal Gaussian distribution (in log space). Observations of actual particle size distribution taken from AERONET show that PSD can vary over time and across region. Lognormal Particle Size Distribution ingested into the MatLab code. Particle Size Distribution (PSD) Actual particle size distribution from observations.

  14. Get the proposal out to the committee and present Run summer-long simulations of RAMS, and configure it with AOT (need Daniel’s help) Three papers I. RAMS results for the summer of 2007 II. Ingestion of AOT into RAMS for NYC III. Role of Aerosols on Complex Urban Environments Goals

  15. 1) Saleeby, S. & Cotton, W. (2004). A Large-Droplet Mode and Prognostic Number Concentration of Cloud Droplets in the Colorado State University Regional Atmospheric Modeling System (RAMS). Part I: Module Descriptions and Supercell Test Simulations. Journal of Applied Meteorology, Volume 43, 182 – 195. 2) Sheperd, J., Peirce, H. & Negri, A. (2002). Rainfall Modification by Major Urban Areas: Observations from Space Bourne Rain Radar on the TRMM Satellite. Journal of Applied Meteorology, Volume 41, 689 – 701. 3) Comarazamy, D., Gonzalez, J., Tepley, C., Raizada, S. & Pandya V. (2006). The effects of Atmospheric Particle Concentration on Cloud Microphysics over Arecibo. 4) W. Grabowski (1999). Cloud Microphysics and the Tropical Climate: Cloud-Resolving Model Perspective. Journal of Climate, Volume 13, 2306 – 2322. 5) Sheperd, J., (2006). Evidence of urban-induced precipitation variability in arid climate regimes. Journal of Arid Environments, Volume 67, 607 – 628. 6) Huff, F.A., & Changnon, S.A. (1973). Precipitation modification by major urban areas. Bulletin American Meteoroligcal Society, Volume 54, 1220 – 1232. References

  16. 7) Otero, L.A., Fochesatto, G.J., Ristori, P.R., Flamant, P.H., Piacentini, R.D., Holben, B., Quel, E.J. (2002). Simple method to derive aerosol microphysical properties from AERONET multiwavelength direct solar measurements. Advances in Space Research, Volume 34, 2232 – 2235. 8) Stallins, J.A., Bentley, M.L., & Rose, L.S. (2006). Cloud-to-ground flash patterns for Atlana, Georgia (USA) from 1992 to 2003. Climate Research, Volume 30, 99 – 112. 9) www.wunderground.com 10) www.aeronet.gsfc.nasa.gov 11)http://www.globalchange.umich.edu/globalchange1/current/lectures/samson/aerosols/ References

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