Simultaneous observation of sporadic E with a rapid-run ionosonde and VHF coherent backscatter radar

Abstract

Abstract. During the SEEK 2 rocket campaign, ionograms were recorded every minute at the Yamagawa Radio Observatory at about 90 km west of the region monitored by a VHF (very high frequency) coherent backscatter radar. Sporadic E-layer parameters, which include the critical (foEs) and blanketing (fbEs) frequencies, the layer height (h Es), and the width of the range spread of sporadic E-traces, were compared with RTI (range-time-intensity) plots of VHF quasiperiodic (QP) and continuous coherent backscatter echoes. A close relationship was found between the appearance of QP echoes in the RTI plots and the level of spatial inhomogeneity in sporadic E plasma, signified here by the difference between foEs and fbEs. During QP echo events, foEs increased while fbEs decreased, so that the difference foEs-fbEs was enhanced, indicating the development of strong spatial structuring in electron density within a sporadic E-layer. On the other hand, increases in sporadic E range spreading also correlated with the occurrence of QP echoes but the degree of correlation varied from event to event. Continuous radar echoes were observed in association with low altitude sporadic E-layers, located well below 100 km and at times as low as 90 km. During the continuous echo events, both foEs and fbEs were less variable, and the difference foEs-fbEs was small and not as dynamic as in the QP echoes. On the other hand, the Es-layer spread intensified during continuous echoes, which means that some patchiness or corrugation in those low altitude layers is also necessary for the continuous backscatter echoes to take place.

Observational evidence of coupling between quasi-periodic echoes and medium scale traveling ionospheric disturbances

“…This is different from the postulated situation in the preceding E-F region coupling models, where both regions are perturbed at the same wave length Cosgrove and Tsunoda, 2004). The E s layer is known to be very inhomogeneous when QP echoes are observed (Ogawa et al, 2002;Maruyama et al, 2006). In our experiment, for example, when well-defined QP echoes were observed on 2 June 2006, the lowest electron density of the E s layer over the MU radar site was 6.0×10 10 m −3 (f b E s =2.2 MHz) which was less than 1/20 of the highest (1.4×10 12 m −3 , f o E s =10.5 MHz).…”

“…The ionosonde at the MU radar site, however, observed the strong and inhomogeneous E s layer 02:30-04:30 JST on 31 May 2005. f o E s and f b E s over the MU radar, which, respectively, correspond to the highest and lowest plasma density in E s layers, were 8.5 MHz (9×10 11 m −3 ) and 2 MHz (5×10 10 m −3 ). QP echoes are known to be closely related to large f o E s −f b E s (Ogawa et al, 2002;Maruyama et al, 2006). In fact, we find a few faint striations of E region echoes in this time period.…”

“…Two-dimensional structures of nighttime MSTIDs have been studied with optical (Mendillo et al , 1997;Garcia et al, 2000;Kubota et al, 2000) or radio techniques (Saito et al, 1998). They propagate southwestward with typical wavelengths of 100-500 km.…”

Phase and group velocity tracing analysis of projected wave packet motion along oblique radar beams – qualitative analysis of QP echoes

“…Accumulation of the E-region plasma into the layers is well explained by the shear of the neutral wind (Bernhardt et al, 2005;Larsen et al, 2005;Pfaff et al, 2005;Wakabayashi and Ono, 2005;Yokoyama et al, 2005). The Es-layers are spatially modulated by the motion of the neutral atmosphere (Maruyama et al, 2006), and then FAI echoes start to appear. The sources of the FAIs are the plasma-density gradient of Published by Copernicus GmbH on behalf of the European Geosciences Union.…”

HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam

“…Our observation that the E S layer echo intensity in different range bins is modulated by 5 to 20 min quasi periods both during day time and night time, and the QP echoes at 150 km are also observed during day time in low latitudes (Patra and Rao, 2006) is to be investigated in terms of the gravity wave modulation of the irregularities during different times of the day. Maruyama et al (2006) found a close relationship between the appearance of QP echoes in the RTI plot and the level of in-homogeneity in Sporadic E plasma, signified by the difference between f b E S and f o E S . During QP echo events, f o E S increased while f b E S decreased so that the difference between these two enhanced indicating the development of strong spatial structuring in electron density within the sporadic E layer.…”