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An altitude and distance correction to the source fluence distribution of TGFs.

Nisi RS, Østgaard N, Gjesteland T, Collier AB - J Geophys Res Space Phys (2014)

Bottom Line: We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and World Wide Lightning Location Network spheric measurements to determine the distance.The study is made possible by the increased number of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) TGFs found in the second catalog of the RHESSI data.The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Technology, University of Bergen Bergen, Norway ; Birkeland Center for Space Science Bergen, Norway.

ABSTRACT

The source fluence distribution of terrestrial gamma ray flashes (TGFs) has been extensively discussed in recent years, but few have considered how the TGF fluence distribution at the source, as estimated from satellite measurements, depends on the distance from satellite foot point and assumed production altitude. As the absorption of the TGF photons increases significantly with lower source altitude and larger distance between the source and the observing satellite, these might be important factors. We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and World Wide Lightning Location Network spheric measurements to determine the distance. The study is made possible by the increased number of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) TGFs found in the second catalog of the RHESSI data. One find is that the TGF/lightning ratio for the tropics probably has an annual variability due to an annual variability in the Dobson-Brewer circulation. The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

No MeSH data available.


Related in: MedlinePlus

The difference between the expected number of TGFs and the measured TGFs from the first RHESSI catalog. The blue colors denote a lesser amount of TGFs than expected, and the red colors denote a bigger amount of TGFs than expected. The figure reveals a lack of TGFs in Africa compared to the expected and an excess of TGFs in Asia and America. This is the same pattern as presented in Smith et al. [2010].
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fig07: The difference between the expected number of TGFs and the measured TGFs from the first RHESSI catalog. The blue colors denote a lesser amount of TGFs than expected, and the red colors denote a bigger amount of TGFs than expected. The figure reveals a lack of TGFs in Africa compared to the expected and an excess of TGFs in Asia and America. This is the same pattern as presented in Smith et al. [2010].

Mentions: Since our tropopause pressure is generally slightly lower than the tropopause from Smith et al. [2010], our probability of transmission will be higher; but because the shape of the two curves in Figure 6 is about the same, the relative difference will be fairly similar. In Figure 7, we show the difference between the first RHESSI catalog TGFs and the expected relative difference estimated from the lightning data, the exposure/efficiency and transmission. The map shows the same features as in Figure 5d of Smith et al. [2010], with the main discrepancies being the greater lack of TGFs in northern India and less negative values in Africa. The figure shows a similar global pattern as the inverse flash rate, duration, and radiance of LIS [Beirle et al., 2014]


An altitude and distance correction to the source fluence distribution of TGFs.

Nisi RS, Østgaard N, Gjesteland T, Collier AB - J Geophys Res Space Phys (2014)

The difference between the expected number of TGFs and the measured TGFs from the first RHESSI catalog. The blue colors denote a lesser amount of TGFs than expected, and the red colors denote a bigger amount of TGFs than expected. The figure reveals a lack of TGFs in Africa compared to the expected and an excess of TGFs in Asia and America. This is the same pattern as presented in Smith et al. [2010].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497453&req=5

fig07: The difference between the expected number of TGFs and the measured TGFs from the first RHESSI catalog. The blue colors denote a lesser amount of TGFs than expected, and the red colors denote a bigger amount of TGFs than expected. The figure reveals a lack of TGFs in Africa compared to the expected and an excess of TGFs in Asia and America. This is the same pattern as presented in Smith et al. [2010].
Mentions: Since our tropopause pressure is generally slightly lower than the tropopause from Smith et al. [2010], our probability of transmission will be higher; but because the shape of the two curves in Figure 6 is about the same, the relative difference will be fairly similar. In Figure 7, we show the difference between the first RHESSI catalog TGFs and the expected relative difference estimated from the lightning data, the exposure/efficiency and transmission. The map shows the same features as in Figure 5d of Smith et al. [2010], with the main discrepancies being the greater lack of TGFs in northern India and less negative values in Africa. The figure shows a similar global pattern as the inverse flash rate, duration, and radiance of LIS [Beirle et al., 2014]

Bottom Line: We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and World Wide Lightning Location Network spheric measurements to determine the distance.The study is made possible by the increased number of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) TGFs found in the second catalog of the RHESSI data.The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Technology, University of Bergen Bergen, Norway ; Birkeland Center for Space Science Bergen, Norway.

ABSTRACT

The source fluence distribution of terrestrial gamma ray flashes (TGFs) has been extensively discussed in recent years, but few have considered how the TGF fluence distribution at the source, as estimated from satellite measurements, depends on the distance from satellite foot point and assumed production altitude. As the absorption of the TGF photons increases significantly with lower source altitude and larger distance between the source and the observing satellite, these might be important factors. We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and World Wide Lightning Location Network spheric measurements to determine the distance. The study is made possible by the increased number of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) TGFs found in the second catalog of the RHESSI data. One find is that the TGF/lightning ratio for the tropics probably has an annual variability due to an annual variability in the Dobson-Brewer circulation. The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

No MeSH data available.


Related in: MedlinePlus