Characteristics of sprite and gravity wave convective sources present in satellite IR images during the SpreadFEx 2005 in Brazil F. T. São Sabbas1, V. T. Rampinelli1, J. Santiago1, P. Stamus2, S. L. Vadas2, D. C. Fritts2, M. J. Taylor3, P. D. Pautet3, G. Dolif Neto4, and O. Pinto1 1National Institute for Space Research – INPE, São José dos Campos, São Paulo, Brazil 2Northwest Research Associates, CoRA Division, Boulder, CO, USA 3Utah State University, Logan, Utah, USA 4Center of Weather Forecast and Climate Studies/INPE, Cachoeira Paulista, São Paulo, Brazil
Abstract. We developed a technique to identify and estimate the size, intensity, and
Tropopause overshoot of thunderstorm convective cores expected to be significant sources
of gravity waves. The work was based on GOES IR images of South America on the night of
30 September to 1 October and 25–26 October 2005, as part of the Spread F
Experiment (SpreadFEx) in Brazil in 2005. We also characterized, for the first time, the convective activity of three
small TLE producing thunderstorms that yielded 11 TLEs on 25–26 October 2005. The campaign occurred during the dry to wet
season transition in central Brazil, marked by the presence of
extra-tropical cyclogenesis over the Atlantic Ocean, and cold fronts
penetrating inland. The Tropopause temperature was typically −76°C
with a corresponding altitude of ~15 200 m. Vigorous convective cores
capable of generating strong gravity waves were located in convective regions having
areas with cloud top temperatures ≤−76°C. They had typical cloud-top temperature deficits of ΔT−2.0°C to −8.0°C from the average surroundings, implying
overshoot heights of 200 to 3100 m, which are within the typical range.
Fast vertical development and high horizontal growth rates were associated
with a large number of simultaneously active vigorous convective
cores, indicating that their dynamics may have determined the
spatial-temporal development of the thunderstorms analyzed.
Moderate convective cores were also present in areas with cloud top
−76°C≤T≤−70°C. They had
ΔT of −1.9°C to −5.3°C producing overshoots between 80–300 m.
All convective cores had typical diameters of 5–20 km and their
size tended to increase with ΔT, there was a 57% correlation
between the two parameters. Analysis of the relationship of cloud
top T with positive and negative cloud-to-ground lightning (+/−CG)
occurrence rate and with peak current showed that lighting activity may provide an independent way
to identify convective cores and measure their intensity, since they were
characterized by a high incidence of low peak current −CGs that forms the
bulk of the −CG population.
Citation: São Sabbas, F. T., Rampinelli, V. T., Santiago, J., Stamus, P., Vadas, S. L., Fritts, D. C., Taylor, M. J., Pautet, P. D., Dolif Neto, G., and Pinto, O.: Characteristics of sprite and gravity wave convective sources present in satellite IR images during the SpreadFEx 2005 in Brazil, Ann. Geophys., 27, 1279-1293, doi:10.5194/angeo-27-1279-2009, 2009.