[Table of Contents]

Abstract

Title: “The Houston Environmental Aerosol Thunderstorm (HEAT) Project”

Principal Investigators: Richard Orville, John Nielsen-Gammon, Renyi Zhang, and Don Collins (Texas A&M University)

Proposed Co-investigators and Interested Colleagues: Anne Thompson (NASA-Goddard), Danny Rosenfeld (Hebrew University), William Woodley (Woodley, Inc.), Earle Williams (MIT), John Helsdon, Paul Smith and Andy Detwiler (South Dakota Tech), Steven Rutledge (Colorado State), Paul Krehbiel (New Mexico Tech), Maribeth Stolzenburg and Tom Marshall (U. of Mississippi), Walt Lyons (FMA, Inc.), Ron Holle, Ken Cummins, Martin Murphy, and Nick Demetriades (Vaisala-Global Atmospherics, Inc.), Robert Maddox, David Rust, and Don MacGorman (National Severe Storms Laboratory), Bill Read and Steve Allen (National Weather Service, Houston), Daewon Byun (University of Houston), J. G. Hudson (Desert Research Institute, Nevada), J. Marshall Shepherd (NASA-Goddard), Gary Huffines (U.S. Air Force), Anne-Marie Schmoltner, Roddy R. Rogers, Steve Nelson, and Pam Stephens (NSF), Brigitte Baeuerle, Dave Carlson, Dick Dirks, Charles Knight, Jeff Stith, Tammy Weckwerth, and David Parsons (UCAR), Brandon Ely and Scott Steiger (Texas A&M University), Steve Burian (University of Arkansas), Dennis J. Boccippio, Steve Goodman, Hugh Christian, and Rich Blakeslee (NASA-MSFC), Larry D. Carey (North Carolina State University), Steve Rinard (NOAA), Jim Wilson (UCAR/NCAR-ATD), Mike Biggerstaff (University of Oklahoma), John Latham (NCAR), NCAR-MMM personnel to be determined

Lead Institutions: Texas A&M University and the National Center for Atmospheric Research (NCAR)

Project Period: Four years (2003-2007); field program (summer 2005)

Project Cost: (To be determined)

Project Summary:

            We propose a four-year experiment (one summer in the field, 2005) to determine the sources and causes for the enhanced cloud-to-ground lightning over Houston, Texas, in association with simultaneous experiments by the Environmental Protection Agency (EPA) and the Texas Natural Resource Conservation Commission (TNRCC).  Houston is the third most populous city in the United States and the region contains 50% of the petroleum refining capacity of the United States.  Recent studies covering the period 1989-2000 document a 50% increase of cloud-to-ground lightning in the Houston area as compared to background values, which is second in flash density only to the Tampa Bay, Florida area.  We suggest that the elevated flash densities could result from several factors, including, 1) the convergence due to the urban heat island effect and complex sea breeze, and 2) the increasing levels of air pollution from anthropogenic sources producing numerous small droplets and thereby suppressing mean droplet size.  The latter effect would enable more cloud water to reach the mixed phase region where it is involved in the formation of precipitation and the separation of electric charge, leading to an enhancement of lightning.

            Houston is a metropolitan area in which past and current studies are conducted to further our understanding of urban environments.  The Texas Air Quality Field Study of the ozone and particulate matter in Houston was completed in the summer of 2000 with the support of the TNRCC.  Further studies supported by the EPA for $3.5 million are beginning for a two-year period, 2003-2005, and will involve Texas A&M University, the University of Texas, and the University of Houston.  The goal of the EPA funded study is the development of joint multi pollutant air quality modeling facilities and air monitoring stations for the Houston-Galveston area.  Thus, this study will parallel the HEAT project and provide valuable air trajectory information not previously available to thunderstorm studies.

            The primary goals of HEAT are to examine the effects of (1) pollution, (2) the urban heat island, and (3) the complex coastline, on storms and lightning characteristics in the Houston area.  In a recent study by Rosenfeld (2000), it was found that increased concentrations of small aerosols suppress precipitation in clouds.  It has been proposed that the increased concentration of aerosols, such as in polluted urban areas, results in a narrower cloud droplet spectra, deeper mixed phase region in the cloud, additional charge separation in this region, and enhanced lightning downwind of the aerosol sources.  The HEAT project will examine several aspects of this hypothesis including the effects of background aerosol concentration on storm development and lightning enhancement.

            The effect of the urban heat island dynamics will be investigated.  Three hypotheses will be examined: 1) the urban heat island effects on thermodynamic instability, 2) urban heat island convergence in association with intensification and/or initiation of electrically active thunderstorms in the metropolitan area, and 3) urban heat island enhancement of convective updraft strength in relation to the frequency of lightning.

            Due to the proximity of Houston to the coast, effects on thunderstorm development and lightning enhancement in association with the irregular shape of the coastline and the sea breeze interaction must be considered.  Irregularities in the shape of the coast lead to localized areas of enhanced convergence along the sea breeze front.  Consequently, we will examine three aspects: 1) low level convergence associated with the complex coastline and the effect on convective initiation in the Houston area, 2) interaction of the sea breeze with the urban heat island and the effects on convective initiation and development, and 3) the effect of the sea breeze on convection intensity.  A list of objectives follows and is expanded in the main document.

            The transport of air pollutants by Houston thunderstorms will be investigated. In particular, the relative amounts of lightning-produced and convectively transported NOx into the upper troposphere will be determined, and a comparison of the different NOx sources in the urban area of Houston will be developed.

            The HEAT project is based on the observation that there is an enhancement in cloud-to-ground lightning.  Total lightning (intra-cloud (IC) and CG) will be measured using a lightning mapping system to observe if there is an enhancement in intra-cloud lightning as well.  Electrical field soundings will also be conducted to see how an urban environment affects a thunderstorm’s charge distribution. 

            The proposed research will be particularly cost effective.  We will take advantage of previous research conducted by the TNRCC in Houston (2000), the current EPA two-year study for the Houston area ($3.5 million) beginning in 2003, and the follow-up TNRCC 2005 program for a funding amount that is still to be determined.