Writing by mustafa on Sunday, 15 of June , 2008 at 10:03 am
Hurricanes are Earth’s most deadly storms, causing tremendous devastation around the globe every year. While forecasters are quite successful in predicting the trajectories of hurricanes days in advance, hurricane intensification or weakening is less accurately predicted. In this paper we present evidence that the maximum sustained winds (and minimum pressures) in hurricanes are preceded by increases in lightning activity approximately one day before the peak winds. This is the first study to track lightning activity in 56 hurricanes around the globe, during their entire lifetimes. All these hurricanes showed highly significant positive correlations between lightning activity and maximum sustained winds, with a mean correlation coefficient of 0.82. We suggest that increases in lightning activity in hurricanes is related to enhanced convection that influences the rate of moistening of the lower troposphere, which in turn influences the intensification of hurricanes. Since lightning activity can now be monitored continuously in hurricanes at any location around the globe, lightning data may contribute to better hurricane forecasts in the future.
Category: Articles
Writing by mustafa on Tuesday, 22 of April , 2008 at 6:15 pm
Hurricanes in a Warmer World
Hurricanes, typhoons, and cyclones have always bedeviled coasts, but global warming may be making matters worse. Sea level is rising and will continue to rise as oceans warm and glaciers melt. Rising sea level means higher storm surges, even from relatively minor storms, which increases coastal flooding and subsequent storm damage along coasts. In addition, the associated heavy rains can extend hundreds of miles inland, further increasing the risk of flooding.
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Category: Articles
Writing by mustafa on Sunday, 2 of March , 2008 at 10:55 am
The relationship between global lightning frequencies and global climate change is examined in this thesis. In order to study global impacts of climate change, global climate models or General Circulations Models (GCMs) need to be utilized. Since these models have coarse resolutions many atmospheric phenomena that occur at subgrid scales, such as lightning, need to be parameterized whenever possible. (Read more…)
Category: Articles
Writing by mustafa on Saturday, 16 of February , 2008 at 10:07 am
The global electrical circuitThe Earth’s surface, ocean and solid, and the ionosphere are both highly conductive. The atmosphere conducts electricity because of the presence of positive and negative ions plus free electrons. Conductivity is poor near sea level but increases rapidly with height up to the ionosphere, also it is greater at polar latitudes than equatorial. The conductivity near sea level is low because there are fewer ions and those ions tend to become attached to the larger aerosol particles that are more common near the surface.
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Category: Articles
Writing by mustafa on Sunday, 10 of February , 2008 at 1:40 pm
When you think of lightning, you think of a thunderstorm. Many people also assume that hurricanes have a lot of lightning because they are made up of hundreds of thunderstorms.
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Category: Articles
Writing by mustafa on Sunday, 10 of February , 2008 at 1:35 pm
Atlantic hurricane activity has increased significantly since 1995 , but the underlying causes of this increase remain uncertain. It is widely thought that rising Atlantic sea surface temperatures have had a role in this, but the magnitude of this contribution is not known. Here we quantify this contribution for storms that formed in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico; these regions together account for most of the hurricanes that make landfall in the United States. We show that a statistical model based on two environmental variables—local sea surface temperature and an atmospheric wind field—can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005.
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Category: Articles
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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