Writing by mustafa on Saturday, 26 of January , 2008 at 11:23 am
The proximity in time and space of consecutive lightning flashes in thunderstorms was first studied by Mazur (1982) who termed the phenomenon “associated lightning discharges”. These flashes were reported to occur in multi-cell storms, where several electrically active cells (EACs) co-exist in the same mesoscale region. VHF radar observations showed that lightning echoes from discharges follow one another within a time interval typical of a multistroke cloud-to-ground (CG) flash, but are spaced in range by several km. Mazur (1982) used statistical methods to disprove the null hypothesis that these associated discharges were merely a pooled output of randomly occurring flashes. He concluded that an association between flashes is the triggering of one flash by another flash, separated spatially from it, and suggested that the interdependence of the electric field within neighboring EACs may be the responsible mechanism.
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Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:40 am
Recent years have shown the tremendous damage and loss of life that can be caused by Atlantic Basin hurricanes. The majority of these hurricanes start as African easterly waves (AEWs) over the African continent. In this paper we provide evidence showing the connection between lightning activity over eastern Africa, and the AEWs that leave the west coast of Africa, some of which develop into hurricanes. We have analyzed the 2005 and 2006 hurricane seasons, one a very active hurricane year (2005), and the other a very quiet year (2006). More than 90% of the tropical storms and hurricanes during these 2 years were preceded by periods of above average thunderstorm activity in eastern Africa. During the 2006 season not only was the east African lightning activity 23% lower than during 2005, but there was 36% less lightning activity over the entire African continent during 2006. We suggest the possibility that lightning activity in tropical Africa may represent an important precursor of Atlantic hurricane formation.
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Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:36 am
The Mediterranean Israeli dust experiment (MEIDEX) flew on-board the space shuttle in winter 2003, in a 39°-inclination orbit for 16 days, passing over the major thunderstorm regions on Earth. The primary science instrument of the MEIDEX payload is a Xybion IMC-201 image-intensified radiometric camera with six narrow band filters, boresighted with a wide-FOV color video camera. During the nightside of the orbit there will be dedicated observations toward the Earth’s limb above areas of active thunderstorms, in an effort to image transient luminous events (TLEs) from space. Optical observations from space will be conducted with the 665 nm filter that matches the observed wide peak centered at 670 nm that typifies red sprites, and also with the 380 and 470 nm filters for recording blue jets. Observations will consist of a continuous recording of the Earth’s limb, from the direction of the dusk terminator towards the nightside. Areas of high convective activity will be forecasted and uplinked to the crew before the observation. The astronaut will direct the camera toward areas with lightning activity, observed visually through the windows and on monitors in the crew cabin. Simultaneously with the optical observations from space, dedicated ground measurements will be conducted on a global scale. Two field sites in the Negev Desert in Israel will be used to collect electromagnetic data in the ELF and VLF frequency range. Additional ground stations in Germany, Hungary, USA, Antarctica, Chile, South Africa, Australia, Taiwan and Japan will also record Schumann resonance and VLF signals. The coordinated measurements from various locations on Earth and from space will enable us to triangulate the location and determine the polarity and charge moment of the parent lightning of the optically observed TLEs. The success of the campaign will further clarify the geographical distribution of Sprites, Elves and Jets.
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Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:28 am
Tropospheric water vapor is a key element of the earth’s climate. It has direct effects as a greenhouse gas, as well as indirect effects through the interaction with clouds, aerosols, and tropospheric chemistry. Small changes in upper tropospheric water vapor (UTWV) have a much larger impact on the greenhouse effect than small changes in water vapor in the lower atmosphere. Both climate models and observations support the idea that higher temperatures will increase the amount of UTWV. (Read more…)
Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:27 am
Sprites were observed over Asian continent and over oceans around Taiwan in the summer of 2001 (Geophys. Res. Lett. 29(4) 2002). In this article, we report some characteristic differences between the oceanic and the land sprites. Qualitatively, the oceanic sprites are tended to be brighter than the land sprites. Also some of the oceanic sprites have very peculiar forms, which do not match any of the existing types. In two of the recorded sprites, the diffuse hair region contains a distinct short streak. We suspect that they probably are tracks left behind by micrometeorites, which might also have helped in lowering the threshold of the electric field needed for sprite generation and produced exceptionally bright sprites.
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Writing by mustafa on Saturday, 26 of January , 2008 at 9:25 am
It is now well known that the majority of transient luminous events (TLEs) in the upper atmosphere, known as sprites, are associated with large positive cloud-to-ground lightning discharges. These positive lightning flashes produce extremely low frequency (ELF) and very low frequency (VLF) radiation that can be detected anywhere on the earth’s surface. During the STEPS2000 field program in the
United States, ELF/VLF transients associated with sprites were detected in the Negev Desert, Israel, some 11000 km away.
Using the VLF data to obtain the azimuth of the transients, and the ELF data to calculate the distance between the source and receiver, we were able to remotely determine the location of sprite-forming lightning events to an accuracy of 1.5%.
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Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:18 am
Global warming is becoming a reality, with growing evidence that anthropogenic activity on our planet is starting to influence our climate (IPCC, 2001). Due to the increase in significant weather-related disasters in recent years, new attention has been focused by the climate change community on the impact of global warming on extreme weather. In this paper we attempt to estimate the long term trends in lightning activity over tropical Africa during the past 50 years, using upper tropospheric water vapor as a proxy for regional lightning activity. (Read more…)
Category: Articles
Writing by mustafa on Saturday, 26 of January , 2008 at 9:12 am
Lightning activity in thunderstorms is closely related to the intensity of vertical updrafts in deep convective clouds that also transport large amounts of moisture into the upper troposphere. Small changes in the amount of upper tropospheric water vapor (UTWV) can have major implications for the Earth’s climate. We present new evidence showing a strong connection between the daily variability of tropical lightning activity and daily upper tropospheric water vapor concentrations from the NCEP/NCAR reanalysis. Our results over the African continent show that the NCEP upper tropospheric water vapor peaks one day after intense lightning activity in the tropics. (Read more…)
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Writing by mustafa on Sunday, 20 of January , 2008 at 1:10 pm
Lightning activity associated with Atlantic hurricanes has been investigated using the World Wide Lightning Location Network (WWLLN), a global ground-based VLF network that is sensitive only to the most intense cloud-to-ground (CG) lightning discharges. The lightning data are binned into 10×10 degree boxes around the center location of the hurricane. The data are accumulated daily, giving the daily lightning activity around the center of the hurricane, where the center location is taken at 1200UT every day. The results show highly significant correlations between lightning activity and maximum sustained winds within the hurricanes, however, with a lag of 1-2 days. In other words, the lightning activity peaks a day or two before the maximum hurricane intensity (both wind speed and pressure). These results imply that monitoring lightning continuously across the
Atlantic may provide important information for forecasting the intensification of hurricanes.
Category: Articles
Writing by mustafa on Monday, 14 of January , 2008 at 3:04 pm
Lightning activity associated with Atlantic hurricanes has been investigated using the World Wide Lightning Location Network (WWLLN), a global ground-based VLF network that is sensitive only to the most intense cloud-to-ground (CG) lightning discharges. The lightning data are binned into 10×10 degree boxes around the center location of the hurricane. The data are accumulated daily, giving the daily lightning activity around the center of the hurricane, where the center location is taken at 1200UT every day. The results show highly significant correlations between lightning activity and maximum sustained winds within the hurricanes, however, with a lag of 1-2 days. In other words, the lightning activity peaks a day or two before the maximum hurricane intensity (both wind speed and pressure). These results imply that monitoring lightning continuously across the
Atlantic may provide important information for forecasting the intensification of hurricanes.
Category: Articles
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