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Atmospheric Electrical Activity and the Prospects for Improving short-term Weather Forecasting |
| Steven J. Goodman |
| How might lightning measurements be used to improve short-term (0-24
hr) weather forecasting? We examine this question under two different
prediction strategies. These include integration of lightning data into
short-term forecasts (nowcasts) of convective (including severe) weather
hazards and the assimilation of lightning data into cloud-resolving numerical
weather prediction models. In each strategy we define specific metrics
of forecast improvement and a progress assessment. We also address the
conventional observing system deficiencies and potential gap-filling information
that can be addressed through the use of the lightning measurement. |
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Variability of Lightning Activity as a Function of Tropical Easterly Wave Phase |
| Walter A. Petersen Dennis J. Boccippio |
| Three-to-Five day Tropical Easterly Waves (TEWs) significantly modulate the occurrence of tropical cyclogenesis and convection. It is therefore likely that TEW signals also exist in both lightning flash frequency data, and statistics describing the vertical structure of convection. Therefore, we pose the following question: <I>Can lightning data reliably indicate changes in mean convective vertical structure and latent heating as a function of easterly wave-phase</I>? To address this question we have examined space borne (TRMM-LIS, PR, TMI) and ocean-based lightning and radar observations of TEWs, partitioned by wave phase. Analysis of ocean-based data collected in the tropical E. Pacific (EPIC-2001 field campaign) suggests that lightning flash density, convective vertical development, and conditional mean rain rates all vary systematically with TEW phase. More specifically, CG flash counts, convective vertical structure, areas of heavy rain rate, and CAPE were all observed to reach maximum (minimum) values just prior to (after) the passage of TEW troughs. Conversely, convective echo coverage and areas of light rain were an order of magnitude larger <I>after</I> TEW trough passage. As a whole, these trends suggest changes in the diabatic heating structure across the phases of a TEW. To examine the global validity of the EPIC TEW results, we are in the process of analyzing space-borne lightning and radar observations (TRMM-LIS, PR) for multiple warm seasons (June-October, 1998-2001) across numerous regions in the tropics, including continental W. Africa, a region associated with both prolific lightning and TEW activity. For this analysis LIS view-time biases have been mitigated by compositing the data by wave phase, resulting in equal percentages of view-time in each hour of the day for each phase. Preliminary results from the analysis of TRMM-LIS data (June-October, 1998/1999) suggest that: a) lightning activity is significantly more prolific in the ridge and pre-trough phases of African TEWs over the continent; b) the diurnal cycle of lightning in the ridge and pre-trough periods peaks later in the day than its trough and post-trough counterpart. These trends in lightning activity are likely accompanied by similar changes in convective vertical structure, and identifiable changes in synoptic scale wave dynamics. To verify this, we are currently examining TRMM PR and TMI data, together with a matched database of NCEP Reanalysis variables. This comparison will result in an unprecedented study of the lightning and convective structure characteristics of TEWs as they relate to easterly wave dynamics across the global tropics. |
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The influence of local environmental conditions upon supercell kinematics, microphysics, electrification, and lightning. |
| Matthew S. Gilmore,
Ph.D. Alexandre Fierro (Univ. of Oklahoma), Edward R. Mansell, (CIMMS/Univ. of Oklahoma), Louis J. Wicker (National Severe Storms Laboratory), |
| Results will be presented illustrating the impact that sudden increases in environmental convective available potential energy (CAPE), 0-3 km vertical wind shear, and boundary-layer moisture can have upon the intensification of simulated supercell thunderstorms. Changes in the local environment will be related to changes in thunderstorm updraft strength, cloud temperature, cloud water content, and riming accretion rate. These kinematic and microphysical changes will then be related to changes in thunderstorm electrification, charge structure, and dominant cloud-to-ground (CG) lighting polarity. The environments to be studied were observed in the West Texas Panhandle on 2 June 1995 during the Verifications of the Origins of Rotation in Tornadoes Experiment (VORTEX). The simulations will be compared to the CG lightning characteristics and radar observations documented in Gilmore and Wicker (2002). The experiments will be conducted using the NSSL Collaborative Model for Multiscale Atmospheric Simulation (NCOMMAS). NCOMMAS is a non-hydrostatic thunderstorm model that includes 12 hydrometeor categories, a choice of the Takahashi (1984) or Saunders et al. (1991)/Saunders and Peck (1998) non-inductive charging parameterizations, the inductive charging parameterization of Ziegler et al. (1991), and the lightning parameterization from MacGorman et al. (2001) as modified by Mansell et al. (2002). |
Multi-wavelength Radar Observations of Wintertime Thunder Clouds Related to the Polarity of the Lightning Discharges |
| Yasuyuki Maekawa,
Shinsuke Ogata, Yoshiaki Shibagaki,
Yasuo Sonoi, Michihiro Teshiba, Hiroyuki
Hashiguchi and Shoichiro Fukao, Yasuyuki Maekawa |
| Along the coast of the Sea of Japan, thunders peculiar to wintertime frequently occur as strong northerly or westerly seasonal winds approach the coast. The wintertime thunder clouds are characterized by a relatively low cloud top and frequent occurrence of positive-current cloud-to-ground strokes. Compared with the summertime thunder clouds, however, very little is yet known about the wintertime thunder clouds. In this study, a C-band (5.27 GHz) weather radar of the Kansai Electric Power Company and a millimeter-wave (34.75 GHz) radar of Kyoto University were both used to observe the wintertime thunder clouds at Mikuni in Fukui Prefecture, Japan. The millimeter-wave radar was recently developed especially to observe fine spatial structure and distribution of cloud droplets. From December 2001 to February 2002, the Millimeter-wave radar was located at Mikuni, and it observed several thunderstorm events simultaneously with the C-band Kusuya radar. The time, location, and polarity of each cloud-to-ground lightning stoke are obtained from the LLP system of the Kansai Electric Power Company.In the event on December 30 2001, more than 100 cloud-to-lightning strokes were detected. Negative-current strokes with magnitudes of less than 50 kA successively occurred almost every minute at the developing and matured stages of the thunder clouds. To contrast, positive-current strokes occurred less frequently at a rate of once in 5-10 min, with much larger amplitudes that sometimes exceeded 100 kA. Detailed height profiles of the millimeter-wave radar echoes suggest that some of them occurred near the core at higher levels of around 4 km and therefore came down directly from the cloud top. Also, convergence of horizontal velocities detected by the millimeter-wave Doppler radar may support possible ascending air flows near the lightning strokes. |
Climatology of Thunderstorm Activity over the Indian Region: I. A Study of East-West Contrast |
| G. K. Manohar A. P. Kesarkar |
| Based on the latest data (I. M. D., 1999) of monthly number of station
thunderstorm days (Thn) and mean maximum surface air temperatures (Tmax)
of 276 Indian stations, an important and a long pending (Rao et. al.,
1971) issue of East-West contrast in the frequencies of occurrence of
thunderstorms over India is resolved in substantial details in this study.
On the premise of nearly equal land areas, and density of the station
network, and location of ITCZ; India is divided in two regions: Eastern
Region (ER) and Western Region (WR) across the 79° E latitude line
over India. Results pertaining to the contrasting features of Thn over
ER and WR are presented (Fig 1(a, b)). Our analysis showed that the annual
total Thn over the ER are 4763, and over the WR are 3194. The prominent
difference in Thn is observed to be associated with monsoon season months
over the ER and WR. The Tmax sensitivity of occurrence of Thn showed (Fig
2 (a, b and c)) that thunderstorms respond exponentially to modest increment
in Tmax on the semi-annual and annual time-scales in both the regions
but with clear contrast (nearly twice) in their sensitivity over ER. This
result is in good agreement with the results cited in Williams, 1997 and
many other studies mentioned in this status report, where relationship
between global tropical surface air temperatures and GEC parameters are
investigated. Our analysis suggests that the hot and humid extensive land
region of the ITCZ of the ER is more suitable and responsible for the
development of thunderstorms. Further, results showing higher values of
Table 1: Monthly Mean Maximum Wet-Bulb Potential Temperature
(
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| Last Update : June 3,
2003 |
Full
program for Monday
and CAPE (table 1) over the ER are discussed
to explain the E-W pronounced contrast in the thunderstorm activity. It
is believed that the results presented in this study will be useful. 
