ROCSAT Observations of Meso-Scale Density and Flow Undulations in Conjunction with Intermediate-Scale Density Irregularities at Midlatitude Topside Ionosphere

Details ROCSAT Observations of Meso-Scale Density and Flow Undulations in Conjunction with Intermediate-Scale Density Irregularities at Midlatitude Topside Ionosphere ROCSAT Observations of Meso-Scale Density and Flow Undulations in Conjunction with Intermediate-Scale Density Irregularities at Midlatitude Topside Ionosphere

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsa22a..01s&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SA22A-01

Other

2437 Ionospheric Dynamics, 2439 Ionospheric Irregularities, 2443 Midlatitude Ionosphere, 2481 Topside Ionosphere

Scientific paper

ROCSAT-1 orbiting at 600 km topside ionosphere has observed many meso-scale (~50 to 1000 km) ion density and flow undulation events at low- to mid-latitudes. During the 8 January 2000 event, noticeable intermediate- scale (0.1 to 50 km) density irregularities were observed in conjunction with meso-scale undulations in many consecutive ROCSAT orbits. The meso-scale undulations indicate in-phase variations of outward and westward flow with the density enhancement. The derived electric-field perturbations point mostly to the northeast direction at about 45 degree in azimuth. The onset locations of the meso-scale disturbances observed from consecutive ROCSAT orbits also indicate a frontal structure alignment from northwest to southeast in geographic coordinate. The disturbances cover a large geographic area from 120 degree to 300 degree in longitude and from latitude 20 degree up to the ROCSAT turn-around latitude at 35 degree. Since the onset of meso-scale undulation is preceded by a sudden enhancement of a southeast directed background flow which can be induced by a southwest pointed electric field, the cause of meso-scale undulation is identified as the Perkins instability [Perkins, 1973]. The intermediate-scale density irregularities that are observed to co-exist within the meso-scale undulation can be explained from a secondary instability process in the non-uniform density variation inside the meso-scale undulations as derived from two different ROCSAT observations made at the same location separated by three hours. On the other hand, it is difficult to explain the stand-alone intermediate-scale irregularities that appear alone in time and space without meso-scale undulations. One possible explanation is from the mapping process from E region or lower F region irregularity structures. However, theoretical model of the energy cascading process in the instability structure or the mapping process is not available at the moment. These need to be further investigated in the future.

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