Distributions of TEC Fluctuations and Losses of Lock Associated with Equatorial Plasma Bubbles

Details Distributions of TEC Fluctuations and Losses of Lock Associated with Equatorial Plasma Bubbles Distributions of TEC Fluctuations and Losses of Lock Associated with Equatorial Plasma Bubbles

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa51b1217n&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SA51B-1217

Physics

[2415] Ionosphere / Equatorial Ionosphere, [2439] Ionosphere / Ionospheric Irregularities, [6964] Radio Science / Radio Wave Propagation, [7944] Space Weather / Ionospheric Effects On Radio Waves

Scientific paper

Equatorial plasma bubbles (EPBs) are local depletions of the electron density in the ionosphere. Due to field-aligned irregularities (FAIs) with various spatial scales, EPBs affect wide-band radio waves and cause scintillations in GPS navigation system. Strong scintillation can cause a GPS receiver to lose lock on GPS signals because of rapid variations of signal amplitude and phase, and limit the availability of carrier phase measurements. Since the scintillation is caused by Fresnel diffraction, the spatial scale of FAIs that causes the scintillation of GPS signals is about 2-300 m. Therefore, loss of phase lock (LOL) on GPS signals is a reference of hundred-meter-scale FAIs. As EPBs are also associated with fluctuations of the total electron content (TEC), the enhancement of Rate of TEC change index (ROTI) occurs around EPBs. Assuming that the altitude of the ionosphere is about 400 km, the velocity of the pierce point of the GPS radio wave at the ionospheric altitude is approximately 70 m/s around the zenith. Thus, ROTI averaged during 5 minutes is a reference of ten-kilometer-scale fluctuations. In this study, we analyzed LOL and 5-min. ROTI associated with EPBs to examine the spatial and temporal scales of electron density disturbances associated with EPBs. We selected 11 EPBs from 630-nm airglow images obtained by all-sky imager at Sata, Japan, in 2001. LOL and ROTI are obtained from GPS data from GPS Earth Observation Network (GEONET) of Japan, which consists of more than 1000 GPS receivers. As a result, it is shown that both LOL and the enhancement of ROTI are observed in 8 events out of 11 events. The distributions of LOL are approximately consistent with the areas in which the ionospheric electron density is depleted. The enhancements of ROTI are observed in the vicinities of EPBs. The enhancement of ROTI expands especially in the west side of EPBs. After the EPBs pass through, therefore, LOLs are vanished but the enhancements of ROTI last a while. This result shows that the hundred-meter-scale irregularities are distributed within EPBs while the ten-kilometer-scale disturbances are located around EPBs. Such huge EPBs as to be observed in Japan will appear in solar maximum periods. Therefore it is important to prepare against the next solar maximum by examining characteristics of the EPBs. Fortunately, LOL and the enhancement of ROTI are treated as indicators of these huge EPBs since most of the EPBs are associated with them. Examinations of these EPBs must be progressed further.

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