 |
| Titel |
On the characteristics of 150-km echoes observed in the Brazilian longitude sector by the 30 MHz São Luís radar |
| VerfasserIn |
F. S. Rodrigues, E. R. Paula, J. L. Chau |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 10 ; Nr. 29, no. 10 (2011-10-28), S.1905-1916 |
| Datensatznummer |
250017114
|
| Publikation (Nr.) |
 copernicus.org/angeo-29-1905-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| We present long-overdue details about the intensity and spectral
characteristics of 150-km echoes observed by the São Luís radar in
Brazil. The São Luís observations show that the echoes usually come from
multiple scattering layers that descend in altitude before local noon, and
ascend during afternoon hours, similar to what has been found in observations
made in other longitude sectors. The layers are usually 3–5 km thick and
located, mostly, between 130 and 170 km altitude. The measurements also show
variations in echo intensity that are similar to observations made at other
equatorial and off-equatorial sites. Analysis of observations made during
2008 shows significant (>37%) monthly occurrence rates for every month.
Reduced occurrence rates were observed around March Equinox. We associate
this reduction in occurrence rate, however, to a non-geophysical factor. An
increase in the daytime sky noise in the months around March Equinox causes a
decrease in the signal-to-noise ratio (SNR) of the echoes, which makes them
less distinguishable in our analysis. A higher occurrence of weaker echoes
around March Equinox was confirmed by an statistical analysis of the seasonal
variation of echo intensities. Strong, long-lasting and, therefore, more
noticeable echoing layers, however, were observed between June and early
September compared to other months in 2008. Spectral analyses show that most
of the echoes have negative mean Doppler shifts indicating upward velocities.
The echoes also have narrow spectral widths of only a few m s−1. Finally, we
also found that the mean Doppler shift of the observed echoes can vary
noticeably with altitude at times. Using spaced antenna measurements we show
that this is caused by the wide field-of-view of the radar and the spatial
distribution of the scatterers within the radar beam. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|