Statistical Investigation of the relationship between the occurrences of
AGW, ESF and ESF types in the American sector
Abstract
Equatorial Spread F (ESF), a manifestation of nighttime irregularities
in the equatorial ionosphere has been linked to Atmospheric Gravity
Waves (AGW) by different authors. However, there have not been much
study to ascertain the extent of the relationship between the occurrence
of AGW and the generation and occurrence of ESF. This study investigates
the correlation between AGW and ESF occurrences during the year 2016,
using data obtained with the aid of satellite borne Atmospheric Infrared
Sounder (AIRS) and ionogram obtained with the aid of Digisonde Portable
Sounder (DPS-4) located at Jicamarca, (geog. Lat. 11.95, Long. 76.87 and
geomagnetic Lat. 9.28, Long.-7.92), an equatorial station in the
Peruvian sector. During this period, 72.9% of AGW occurrence was
observed between 18:00UT and 00:00UT (post-sunset period) while the
remaining 27.1% occurrence was observed between 00:00 and 04:00UT
(post-midnight period) coinciding with the period of occurrence of ESF.
Results from the study reveal that the occurrences of ESF and AGW are
independent of each other. An insignificant correlation (0.39) was found
between the days of occurrence of the two phenomena. While ESF
occurrence is a regular daily occurrence with local time dependence, AGW
propagation is not dependent on local time. For Jicamarca, we found that
ESF occurrence is greater during the solstice months than equinox. The
probability of AGW reaching the bottomside F-layer depends on the
properties of the wave. In this study, AGW was able to penetrate
ionospheric heights on only six occasions. The results also show that
AGW occurrence can only influence the conditions that trigger ESF rather
than triggering ESF altogether. The occurrence of AGW tends to influence
the occurrence of MSF type of ESF which is predominantly a post sunset
phenomenon in preference to the other two types. Coefficient of
correlation between AGW and MSF ranged between