ICAE International Commission on Atmospheric Electricity

ICAE 2003 Versailles

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Benjamin Franklin

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Friday 11th June



Session F1 Global Lightning and Climate I

8:30 E. Williams
Keynote: A review

Z. Kawasaki, T. Ushio, S. Yoshida and Y. Satoh
What we have learned by TRMM/PR and LIS

9:15 H.J.Christian
Global Lightning Activity
9:30 A. R. Jacobson and G. Molinie
Relationship between lightning-storm characteristics, and both power and rate of lightning-discharge RF emissions observed by FORTE
9:45 A. M. Blyth, H. J. Christian, Alan Gadian and John Latham
Derivation of Thundercloud Ice Hydrometeor Characteristics from Satellite Observations of Lightning
10:00 C. Price and M. Asfur
Global Lightning and Climate Variability
10:15 D. M. Mach, R. J. Blakeslee, J.C. Bailey, W. M. Farrell, R. A. Goldberg, M. D. Desch and J. G. Houser
Optical Pulse and Electric Field Lightning Statistics from Storm Overflights During the Altus Cumulus Electrification Study



E.R. Williams
Massachusetts Institute of Technology, Cambridge, MA USA

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Global Lightning Activity

H. J. Christian
National Space Science and Technology Center
Huntsville, Alabama


Our knowledge of the global distribution of lightning has improved dramatically since the 1995 launch of the Optical Transient Detector (OTD), followed in 1997 by the launch of the Lightning Imaging Sensor (LIS). Together, these instruments have generated a continuous seven-year record of global lightning activity. These lightning observations have provided a new global perspective on total lightning activity. For the first time, total lightning activity (CG and IC) has been observed over large regions with high detection efficiencies and accurate geographic location. This has produced new insights into lightning distributions, times of occurrence and variability. It has produced a revised global flash rate estimate (46 flashes per second) and has lead to a new realization of the significance of total lightning activity in severe weather.

Accurate flash rate estimates are now available for large areas of the earth (+/- 72o latitude). Ocean-land contrasts as a function of season are clearly revealed, as are orographic effects and seasonal and interannual variability. The data set indicates that air mass thunderstorms, not large storm systems dominate global activity.

The ability of LIS and OTD to detect total lightning has lead to improved insight into the correlation between lightning and storm development. The relationship between updraft development and lightning activity is now well established and presents an opportunity for providing a new mechanism for remotely monitoring storm development. In this concept, lightning would serve as a surrogate for updraft velocity. It is anticipated that this capability could lead to significantly improved severe weather warning times and reduced false warning rates.

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Relationship between lightning-storm characteristics, and both power and rate of lightning-discharge RF emissions observed by FORTE

Abram R. Jacobson, Gilles Molinie
Space and Atmospheric Sciences Group, Mail Stop D466, Los Alamos, New Mexico 87545, U. S. A.


Prior studies have noted a strongly nonlinear enhancement of lightning flash rates with increasing cloud height.

First we report a related observation, of a tendency for increasing intracloud-discharge radiofrequency (RF)-emission power for increased height of the electrified cloud. The FORTE satellite's radio-frequency-receiver payload has performed extensive recordings of electromagnetic emissions of lightning discharges. The most commonly occurring such emission arises from intracloud electrical breakdown and is usually recognizable by a pulse followed by a delayed echo from the ground reflection. We have used other systems of lightning monitors to provide source locations for an extended dataset of FORTE intracloud-discharge signals. The interpulse separation within each pulse pair yields the discharge height above the reflective ground. The storm in which the pulse occurs usually provides many (at least 50) recorded events. From the pattern of these events' heights, we can usually infer a capping height which serves as an upper bound on the lightning-discharge heights for that storm. We find that there is a strong statistical increase of effective radiated power of intracloud discharges, for increasing capping height of the parent storm. Thus a future satellite-based lightning monitor which triggers on only the most intense radiofrequency emissions will be strongly selective for electrified storms with very deep vertical development. Such storms are also indicated in severe convective weather.

Second we report on initial results in relating storm characteristics to the "flash rate" as seen by FORTE. This requires correction of the bias that is caused by the finite trigger threshold of the FORTE RF payload, and of the bias that is caused by the distance from the storm to the satellite.



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Derivation of Thundercloud Ice Hydrometeor Characteristics from Satellite Observations of Lightning

A.M. Blyth,
School of Environment, University of Leeds,
Leeds, UK, LS2 9JT

H.J. Christian,
977 Explorer Blvd.,
Huntsville, AL 35806, USA

Alan Gadian,
Physics Dept., UMIST, Manchester,
UK, M60 1QD

John Latham,
MMM Division, NCAR,
PO BOX 3000, Boulder, CO 80307-3000, USA


Satellite-borne NASA/MSFC devices for the detection of global lightning (the OTD and the LIS) offer the opportunity to explore relationships between lightning frequency f and other thundercloud parameters: more specifically, to determine from measurements of f precipitating and non-precipitating ice fluxes. Computations predict that f is proportional to the product of the downward flux fg of graupel through the BODY of the thundercloud and the upward flux fi of ice crystals into its anvil. This raises the possibility of determining, on a global basis, values of fg and/or fi from the lightning measurements. An examination of data from LIS and the TRMM Microwave Imager suggests that thunderstorms with the highest frequency of total lightning also possess the most pronounced microwave scattering signatures at 37 and 85 GHz. A log-linear relationship was shown to exist (one for each frequency) between the number of optical lightning pulses produced by each storm and the corresponding microwave brightness temperatures. These relationships are consistent throughout the seasons in a wide variety of regimes, suggesting that global relationships exist between lightning activity and cloud ice content.


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Global Lightning and Climate Variability

Colin Price and Mustafa Asfur
Department of Geophysics & Planetary Sciences Tel Aviv University Ramat Aviv 69978 ISRAEL
tel: 972-3-6406029
fax: 972-3-6409282
e-mail: cprice@flash.tauac.il


One of the key factors related to future climate change is the possibility of changes in the variability of the earth's climate, and not just changes in the mean state. Studies in many regions have shown decreases in the mean rainfall, while the extreme rainfall events have increased over the past 50 years. In addition to thunderstorms themselves, other climatic parameters related to deep convection may also be changing due to climate change. One of these key parameters is upper tropospheric water vapor (UTWV). Small changes in UTWV have a much larger impact on the greenhouse effect than small changes in water vapor in the lower atmosphere. Recent observations indicate that UTWV may already be increasing. We present evidence showing the close link between regional/global lightning activity and UTWV variability. Integrated regional and global lightning activity can be continuously observed from a few locations on the earth's surface via the Schumann Resonance (SR). SR data from the Negev Desert, Israel, were compared with the National Oceanic and Atmospheric Administration (NOAA) National Center for Environmental Prediction (NCEP) reanalysis product of specific humidity (SH) at 300mb over the three main lightning regions of the globe (S. America, Africa and SE Asia). We have found that on a daily basis the regional and global SH is highly correlated with the SR observations in Israel. The agreement between the variability of SR intensities and global SH values suggests that single-station measurements of the Schumann resonance could supply a cheap, continuous, long-term measure of the variability of UTWV, thereby helping us further understand our global climate system. Furthermore, UTWV is likely to be closely linked to other processes important to climate change such as tropical cirrus clouds, stratospheric water vapor, and tropospheric chemistry.


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Optical Pulse and Electric Field Lightning Statistics from Storm Overflights During the Altus Cumulus Electrification Study

D. M. Mach
University of Alabama in Huntsville, Huntsville, AL 3599, U.S.A.

R. J. Blakeslee
NASA Marshall Space Flight Center, Huntsville, AL 35812, U.S.A.

J.C. Bailey
Raytheon ITSS, Huntsville, AL 35805, U.S.A.

W. M. Farrell, R. A. Goldberg, M. D. Desch and J. G. Houser
NASA Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A.


The Altus Cumulus Electrification Study (ACES) was conducted during the month of August, 2002 in an area near Key West, Florida. One of the goals of this study was to collect high resolution optical pulse and electric field data from thunderstorms. During our month long campaign, we acquired many hundreds of lightning generated optical pulses correlated with the associated electric field changes. Most of these observations were made while close to the top of the storms. We present relative amplitudes of the optical pulses and electric field changes due to both ground and cloud flashes. We also present statistics on the delay, rise-time, pulse width, and amplitude characteristics of the various types of optical pulses. The results of our pulse analysis will contribute to improved validation of the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS), as well as future satellite-based optical lightning sensors such as the geostationary Lightning Mapping Sensor. Pre-launch estimates of the flash detection efficiency were based on a small sample of optical pulse measurements associated with less than 350 lightning discharges collected by the NASA U-2 aircraft in the early 1980s with only 25 of them from confirmed ground flashes. Even preliminary analyses of our ACES measurements show that we have greatly increased the number of optical pulses available for validation of the LIS and other orbital lightning optical sensors. In addition, since the Altus was so close to the storms, many of the optical pulses will be from low- energy pulses. From these low-energy pulses, we can determine the fraction of optical lightning pulses below the thresholds of LIS, OTD, and future satellite-based optical sensors.  


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