Climatology and Characteristics of Medium‐Scale F Region Ionospheric Plasma Irregularities Observed by COSMIC Radio Occultation Receivers

Abstract

Medium-scale ionospheric ionization structures are a persistent global feature of the Earth's ionosphere. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation measurements are well suited to address the incomplete global observational picture of plasma density irregularities, including the global climatology in both bottomside and topside F region layers, and their structure in the vertical dimension. A climatological database of F region ionospheric irregularities and their characteristics has been developed through detection of total electron content perturbations by Global Positioning System receivers onboard COSMIC satellites. This paper presents global occurrence rates and detailed characteristics of equatorial to midlatitude medium-scale irregularities under quiet geomagnetic conditions. The study covers 4 years, two during solar minimum (2008)(2009) and two during the ascending phase of solar cycle 24 (2012)(2013). Irregularities were found to occur frequently at high latitudes and during nighttime in equatorial to midlatitude regions in both bottom and topside F region layers. Longitudinal-seasonal occurrence trends at equatorial and midlatitudes are consistent with previous irregularity climatology, which reaffirms that localized enhancements in plasma instability growth rates contribute to irregularity occurrence. Seasonal occurrence patterns also indicate a high occurrence of irregularities in regions corresponding to the solar terminator, confined primarily to altitudes below~300 km. The local time-altitude distributions of equatorial and midlatitude irregularity occurrence, amplitude, and scale size provide further insight into irregularity generation mechanisms, and include features consistent with "spread F" irregularities and traveling ionospheric disturbances.

Climatology of the Equatorial Plasma Bubbles Captured by FORMOSAT‐3/COSMIC

“…Multiple sources can excite gravity waves, such as the intertropical convergence zone (ITCZ) (Tsunoda, 2010a), latent heat release of deep convections (Chou, Lin, Yue, et al, 2017; Lay, 2018), and the solar terminator (Huang et al, 2013; Watson & Pedatella, 2018). Gravity waves with higher frequency and larger vertical wavelength usually can propagate to higher altitude from their sources in the troposphere (Vadas & Fritts, 2005).…”

“…The TEC observations have a 1 Hz temporal resolution and are available from the podTec files in the group of level1b of the COSMIC Data Analysis and Archive Center (CDAAC; http://cdaac-www.cosmic.ucar.edu) database. To extract the vertical fluctuations related to EPBs, a fifth‐order Butterworth filter with a band pass of 50 mHz to 0.1 Hz is applied to remove the background TEC variations for identifying the EPB structure with vertical scales between 5 and 50 km (e.g., Coïsson et al, 2015; Watson & Pedatella, 2018).…”

“…We select TEC observations instead of the electron density profiles because the spherical symmetry assumption of Abel inversion (Schreiner et al, 1999) would result in significant retrieval errors in the bottomside ionosphere (e.g., Liu et al, 2010; Pedatella et al, 2015), especially in the nighttime ionosphere (Chou, Lin, Tsai, & Lin, 2017). Using the TEC observations for EPB detection instead of the S4 index (e.g., Carter et al, 2013) also advances the comprehension of the relation between the atmospheric waves and EPBs in the bottomside ionosphere (e.g., Watson & Pedatella, 2018).…”

Topside Ionospheric Disturbances Detected Using Radio Occultation Measurements During the August 2017 Solar Eclipse

“…For irregularity analysis, COSMIC measurements were subjected to the same detrending procedure applied to GAP-O measurements shown in Figure 1b. Dynamic power spectra of COSMIC STEC were calculated using the S-Transform, while an irregularity detection algorithm (Watson & Pedatella, 2018) was applied in order to identify spectral components that correspond to STEC variations larger than a predefined threshold. Figure 3 shows the occurrence rate of irregularities detected in COSMIC STEC measurements at thresholds of 0.05 (a and d), 0.01 (b and e), and 0.20 TECU (c and f), for tangent point altitude ranges of 300-500 km (a-c) and 500-700 km (d-f), respectively.…”

Ionospheric Peak Parameters Retrieved from FY-3C Radio Occultation: A Statistical Comparison with Measurements from COSMIC RO and Digisondes Over the Globe

“…Since the 1960s, more than 20 low Earth orbit (LEO) satellites equipped with GNSS RO receivers have been launched, including the Challenging Minisatellite Payload (CHAMP) [7], the Gravity Recovery and Climate Experiment (GRACE) [8], the Constellation Observing System for the Meteorology, Ionosphere, and Climate (COSMIC) [9], MetOp-A, MetOp-B [10], Feng-Yun 3C (FY-3C) [11,12], and so on. The observation data provided by these GNSS RO missions contribute much to space environment monitoring [6,13] and were applied in ionospheric climate studies [14][15][16].…”