Statistically analyzing the effect of ionospheric irregularity on GNSS radio occultation atmospheric measurement

The Global Navigation Satellite System (GNSS) atmospheric radio occultation (RO) has been an effective method for exploring Earth's atmosphere. RO signals propagate through the ionosphere before reaching the neutral atmosphere. The GNSS signal is affected by the ionospheric irregularity including the sporadic E (Es) and F region irregularity mainly due to the multipath effect. The effect of ionospheric irregularity on atmospheric RO data has been demonstrated by several studies in terms of analyzing singe cases. However, its statistical effect has not been investigated comprehensively. In this study, based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO data during 2011–2013, the failed inverted RO events occurrence rate and the bending angle oscillation, which is defined as the standard deviation of the bias between the observed bending angle and the National Center for Atmospheric Research (NCAR) climatology model bending angle between 60 and 80 km, were used for statistical analysis. It is found that at middle and low latitudes during the daytime, the failed inverted RO occurrence and the bending angle oscillation show obvious latitude, longitude, and local time variations, which correspond well with the Es occurrence features. The F region irregularity (FI) contributes to the obvious increase of the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime over the geomagnetic equatorial regions. For high latitude regions, the Es can increase the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime. There also exists the seasonal dependency of the failed inverted RO event and the bending angle oscillation. Overall, the ionospheric irregularity effects on GNSS atmospheric RO measurement statistically exist in terms of failed RO event inversion and bending angle oscillation. Awareness of these effects could benefit both the data retrieval and applications of RO in the lower atmosphere.

Strip-like plasma bulges at lower-middle latitudes over a wide range of longitude during 8~9 September 2017 geomagnetic storm

<p>During the geomagnetic storm on 8~9 September 2017, a new kind of ionospheric irregularity is persistently captured in lower-middle latitudes at multiple local times, based on Swarm and DMSP satellites observations. This irregularity is observed as the conjugate strip-like bulge, which extends larger than 150° in longitude but only 1°~5° in latitude. The strip-like bulges can be categorized into sharp and blunt types depending on the sharpness of the density peaks. The blunt type is short-lived and appears earlier than the sharp type in the afternoon-sunset sector. The sharp type is long-lived and appears at all the observed local times. Both two types of strip-like bulges are dominated by the ion composition of the H<sup>+ </sup>/He<sup>+</sup>. This is the first evidence that the plasmaspheric particles are involved in forming the ionospheric structure at such low latitude. Moreover, the latitude/L-shell of the bulges decreased synchronously with the plasmaspheric compression. Also, these two types of strip-like bulges show different longitudinal dependencies controlled by the magnetic declination. We suggest that the combined effect from the plasmaspheric downwelling and disturbance neutral wind is responsible for the appearance of the strip-like bulges.</p>

Statistical analyzing the effect of ionospheric irregularity on GNSS radio occultation atmospheric measurement

The Global Navigation Satellite System (GNSS) atmospheric radio occultation (RO) has been an effective method for Earth’s atmosphere exploring. RO signals propagate through ionosphere before reaching the neutral atmosphere. The GNSS signal is affected by the ionospheric irregularity including the sporadic E (Es) and the F region irregularity due to mainly multipath effect. The effect of ionospheric irregularity on atmospheric RO data has been demonstrated by several studies in terms of cases. However, its statistical effect has not been investigated comprehensively. In this study, based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO data during 2011–2013, the failed inverted RO events occurrence rate and the bending angle oscillation, which is defined as the standard deviation of the bias between the observed bending angle and the National Center for Atmospheric Research (NCAR) climatology model bending angle between 60 and 80 km, were used for statistical analysis. It is found that in middle and low latitudes during the daytime, the failed inverted RO occurrence and the bending angle oscillation show obvious latitude, longitude, and local time variations, which correspond well with the Es occurrence features. The F region irregularity (FI) contributes to the obvious increase of the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime over the geomagnetic equatorial regions. For high latitude regions, the Es can increase the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime. There also exists the seasonal dependency of the failed inverted RO event and the bending angle oscillation. Overall, the ionospheric irregularity effects on GNSS atmospheric RO measurement exist in terms of failed RO event inversion and bending angle oscillation statistically. Awareness of these effects could benefit both the data retrieval and applications of RO in the lower atmosphere.