AE42A-01 10:20h
VHF Broadband Digital Interferometer on Panel Extension Satellite
{\br INTRODUCTION} The usefulness of thunderstorm observations from space has been shown by Tropical Rainfall Measuring Mission (TRMM) satellite. As one of the principal organizations of Lightning Imaging Sensor (LIS) on TRMM, {\it Lightning Research Group of Osaka University} (LRG-OU) demonstrates the universal power-five law between lightning activity and thunderstorm snow depth. _eSnow depth_f means the height of cloud top from the freezing level, and it is unveiled to be a key index of the thunderstorm activity. LRG-OU also demonstrates less lightning activity over East asia during El Ni\~{n}o period than the ordinary period. Los Alamos Science Team is concerned with VHF observations by Fast On-orbit Recording of Transient Events (FORTE) satellite. LRG-OU concludes that the combination of optical observations and VHF ones is complementary each other, and join the {\br {\it SOHLA Satellite Project}} . This is a preliminary report how our team plans the VHF observations from space. {\br VHF BROADBAND DIGITAL INTERFEROMETRY} LRG-OU has been developing a VHF Broadband Digital Interferometer (DITF) to image precise lightning channels and monitor lightning activity widely. The feature of broadband DITF is its bandwidth (from 25MHz to 100MHz). The principle of the DITF is direction-of-arrival (DOA) estimation for electromagnetic (EM) wave caused by lightning discharges from the phase differences between EM signals captured by antenna array. This procedure is applied to all Fourier components of VHF broadband EM pulses. In other words, a few tens Fourier components are contribute to obtain one VHF source location, and this _e{\br implicit redundancy}_f is the noticeable superiority to any other source location techniques. It is well known that one lightning flash emits a few thousands of VHF impulses, and imaging VHF source train could give us the development of lightning discharges. According to the previous observations and numerical calculations the accuracy of 0.01 radians may be feasible. It is noticed that a few meters base line may present the sufficient accuracy for source locations. The time resolution is also enough to discriminate the branching of the lightning channel. Because of the advantage of the DITF it may be cleaver to equip on a satellite. {\br PETSAT AND VHF BROADBAD DITF} Panel Extension Satellite (PETSAT) may consist of ten and a few of independent panels. Each panel will be designed to own individual function and the configuration of PETSAT is adjustable depending on the objectives. Since it is shown that the short baseline of DITF could accomplish the high time and space resolutions for VHF source locations, we can reach an idea of VHF broadband DITF operation on PETSAT. PETSAT is planed to be a low altitude satellite about several hundred kilometers from the ground, and the locations accuracy of 0.01 radians may provide us the sufficient and unique opportunity to discriminate between the active thunderclouds from non active ones by satellite observations. We are expecting to launch PETSAT by 2007.
AE42A-02 10:35h
Satellite Observations of Small Ice Crystals and Lightning
Lightning is well known to require strong updrafts, but the reasons for this---and the charge transfer mechanism that produces electrification---have been the subject of intense debate. Here, pan-tropical satellite observations of lightning flash rate and near-infrared cloud scattering are used to show that lightning is facilitated by a broad ice size distribution that includes numerous, small ice particles in the upper part of the anvil. The abundance of small ice particles, rather than lofted graupel or supercooled water, appears to be the main control on lightning flash rate in tropical systems. We use an explicit microphysical cloud model to support our interpretation of the satellite data and to argue that enchanced CCN aerosol concentrations will generate the required particles, implicating aerosols in enhancing tropical lightning. Strong updrafts can also enhance CCN nucleation, helping to explain the observed correlation between updraft speed and electrification. We examine the implications of these empirical results for various microphysical charging mechanisms that have been examined in laboratory studies.
AE42A-03 10:50h
An orbital "virtual radar" from TRMM passive microwave and lightning observations
The retrieval of vertical structure from joint passive microwave and lightning observations is demonstrated. Three years of data from the TRMM (Tropical Rainfall Measuring Mission) are used as a training dataset for regression and classification neural networks; the TMI (TRMM Microwave Imager) and LIS (Lightning Imaging Sensor) provide the inputs, the PR (Precipitation Radar) provides the training targets. Both vertical reflectivity profile categorization (into 9 convective, 7 stratiform, 2 mixed and 6 anvil types) and geophysical parameters (surface rainfall, vertically integrated liquid [VIL], ice water content [IWC] and echo tops) are retrieved. Retrievals are successful over both land and ocean surfaces. The benefit of using lightning observations as inputs to these retrievals is quantitatively demonstrated; lightning essentially provides an additional convective/stratiform discriminator, and is most important for isolation of midlevel (tops in the mixed phase region) convective profile types (this is because high frequency passive microwave observations already provide good convective/stratiform discrimination for deep convective profiles). This is highly relevant as midlevel convective profiles account for an extremely large fraction of tropical rainfall, and yet are most difficult to discriminate from comparable-depth stratiform profile types using passive microwave observations alone. The retrievals proceed as follows: A principal components analysis (PCA) is performed on 33 "raw" inputs (lightning, nine passive microwave frequency/polarization brightness temperature variants, physically-based linear and nonlinear combinations of them, and metrics derved from texture analyses of them). The first 25 PCs are retained, accounting for 99.9% of the variance in the original observations. These are then used as inputs to a regression neural network (i.e., nonlinear multivariate continuous regression) for the geophysical parameters listed above, and a separate classification neural network (i.e., a nonlinear multivariate categorical regression) for the 25 different profile types (previously identified from cluster analysis of a large sample of PR data). The networks are trained with "oversampled" TMI data (i.e., at the PR pixel level), and hence incorporate TMI subpixel convective/stratiform variability effects into their predictions. The resulting classification network is shown to be unbiased with respect to profile type, and not overfitted (more than adequate training data exist for even very complex, nonlinear NNs). The preliminary predictions are then used to "cross-train" and refine the estimates (a new regression NN is trained using both the TMI/LIS PCs and the classification predictions as inputs; a new classification NN is trained using both the TMI/LIS PCs and the geophysical predictions as inputs). In addition to the predicted geophysical quantities, the profile type retrievals can be used to reconstruct a full volumetric radar reflectivity field, hence the term "virtual radar". This allows computation of reflectivity-based products other than the subset of geophysical parameters that are explicitly retrieved. The quality of retrieved fields is sufficient for data assimilation purposes, which is highly important, as data assimilation modules trained on volumetric radar data can thus be directly applied to a number of past, current and future orbital passive microwave sensors/platforms (SSM/I, TMI, AMSR-E, NPOESS, GPM, etc.). Similarly, "conventional" radar-based warning products familiar to operational decision-makers can be dervied from sensors on these platforms.
AE42A-04 INVITED 11:05h
Emerging Applications of the LMA to Meteorology and Nowcasting
As Lightning Mapping Array (LMA) data become increasingly available to forecasters in real-time situations, the applications of total lightning measures to meteorology and nowcasting situations are beginning to emerge. Current integrations of the LMA data stream into forecasting environments are utilizing lightning source locations in plan view, and using the auxiliary 2-dimensional lightning data to compare against radar PPI scans. Forecasters are gauging storm severity with the additional parameter of lightning activity, and using the activity to discern between situations where radar reflectivity shows similar structure and magnitude; storms with higher lightning intensity are invariably the ones to watch more closely when other parameters show little difference. Additional characteristics in the 2-dimensional data can also aid in prediction: Lightning density cross-sections can show signs of rotation or lighting holes, often at the times of strong convection or just preceding tornado or funnel cloud formation. The next step is to utilize the full vertical information in the LMA data. By watching the temporal development of vertical structure in storms, episodes of increasingly high altitude lightning sources can be seen. These `convective surges' have been shown to be precursors to the onset of positive cloud-to-ground episodes in storms, tornadic onset, and lighting holes; all of which are strong indications of severity. As additional real-time implementations and techniques of analysis for the LMA data evolve and develop, the utility of using total lightning data continues to show great promise for facilitating and expediting severe weather prediction in nowcasting environments.
AE42A-05 11:25h
Lightning and Electric Field Structure of a Squall Line During TELEX
During the 2004 field program for the Thunderstorm Electrification and Lightning Experiment (TELEX), simultaneous electric field soundings, three-dimensional lightning mapping observations, high-resolution Doppler radar data, polarimetric radar data, and environmental soundings were acquired for several mesoscale convective systems, supercell storms, and non-severe thunderstorms. The overall data set was of particularly high quality for a squall line that produced frequent lightning in southern and central Oklahoma on the morning of 19 June 2004. A total of five balloon-borne electric field soundings were launched into the leading line of convection and into the trailing stratiform region. Two 5-cm wavelength mobile Doppler radars (SMART-R's) provided coordinated volume scans every 3 min throughout the period of operations. Furthermore, all operations were well within range of the 10-cm wavelength polarimetric radar and the three-dimensional lightning mapping array. This presentation will emphasize lightning mapping and electric field observations to characterize the electrical behavior of the convective line and the stratiform region.
AE42A-06 11:40h
Electrically Active Storms in the Appalachian Mountains
There is less lightning activity in the Appalachian Mountains than in other surrounding areas as indicated by several flash density studies. Some storms have demonstrated a characteristic coined as the Appalachian Lightning Jump where the lightning ends as it approaches the mountain range or continues on following the valleys in between the mountains instead of the mountain peaks as in other regions such as the Front Range of the Rocky Mountains. In certain storms, the lightning diverts around the higher elevations as if the storm may be experiencing some sort of a blocking effect such as cold air damming or the loss of low level convergence with the surface elevation changes. In this follow-on study to the Appalachian Lightning Jump presentation at the 2003 Annual AGU Meeting, the storms exhibiting this jumping characteristic are examined by including lightning data from the National Lightning Detection Network (NLDN) and measurements from the WSR-88D radars in the area to determine if there is a change in the structure of these storms. Comparisons with storms similar in nature, from a lightning perspective, are also examined to determine if the lightning jump is unique to more shallow systems that may lose their support when approaching the mountains or that may experience cold air damming.
AE42A-07 INVITED 11:55h
The Anthropogenic/Lightning Effects Around Houston: The Houston Environmental Aerosol Thunderstorm (HEAT) Project - 2005
A major field program will occur in summer 2005 to determine the sources and causes for the enhanced cloud-to-ground lightning over Houston, Texas. This program will be in association with simultaneous experiments supported by the Environmental Protection Agency (EPA) and the Texas Commission on Environmental Quality (TCEQ), formally the Texas Natural Resource Conservation Commission (TNRCC). Recent studies covering the period 1989-2002 document a 60 percent increase of cloud-to-ground lightning in the Houston area as compared to surrounding 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 (thermal hypothesis), and 2) the increasing levels of air pollution from anthropogenic sources producing numerous small cloud droplets and thereby suppressing mean droplet size (aerosol hypothesis). 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. 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. 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 (CG) lightning. Total lightning (intracloud (IC) and CG) will be measured using a lightning mapping system (LDAR II) to observe if there is an enhancement in intracloud lightning as well.