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.
(Read more…)
Category: Articles
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%.
(Read more…)
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…)
Category: Articles
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
Writing by mustafa on Sunday, 13 of January , 2008 at 11:18 am
Thunderstorms can be very destructive as a result of intense rainfall that occurs over short periods of time, often resulting in flash floods. While many countries in the developed world now have weather radar networks to track storms and precipitation, the majority of the world is not covered by radar observations. In addition, radar coverage is usually sparse and inadequate in mountainous regions – such as most coastal regions of the Mediterranean basin that are prone to flash floods. Infrared (IR) measurements from geostationary (GEO) satellites enable following storm development at the relevant space and time scales, but have limited applicability for quantitative precipitation measurement. Alternatively, microwave (MW) observations from low Earth orbiting (LEO) satellites provide more direct and reliable measurements of precipitation and cloud internal structure, but do not properly address the fundamental space-time scales of precipitation and storm evolution. Since thunderstorms usually develop within 1-2 hours, there is a need to use data having high temporal resolution and to develop methodologies to monitor intense rainfall continuously, especially in regions not covered by radar networks. Unlike radar observations of thunderstorms, lightning observations of storms can be carried out from thousands of kilometers away due to the propagation of low frequency electromagnetic waves emitted from lightning discharges (Volland, 1995). Therefore, lightning observations provide a possibility of monitoring regional thunderstorm activity continuously in remote regions of the Mediterranean and
Europe (Defer et al., 2005). Lightning activity also defines the convective core of thunderstorms where rainfall is normally the heaviest.
Category: Articles
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