Latitudinal, solar, and vertical variability of higher-order ionospheric effects on atmospheric parameter retrievals from radio occultation measurements

Abstract

[1] During Global Positioning System radio occultations (GPS/RO), the GPS signals always travel, at least partially, through the Earth's ionosphere. Hence, all GPS/RO measurements include ionospheric signatures that degrade the GPS signal quality, limiting the accuracy of GPS/RO measurements and of their derived products. Since the ionospheric effects are frequency-dependent, they can partially be removed, to the first order, by linearly combining dual-frequency GPS/RO measurements; small residual effects still remain and influence the accuracy of GPS/RO-derived products. In our study, we show how the first-order ionospheric residual effect, due to geometrical raypath splitting of the GPS signals, and the second-order ionospheric residual effect impact the estimation of GPS/RO-derived atmospheric parameters. Using 40 randomly selected GPS/RO events from the Challenging Minisatellite Payload (CHAMP) during periods of low (Rz12 = 2; 2008), moderate (Rz12 = 49; 2004), and high (Rz12 = 114; 2002) solar activity, we examine the variability of the ionospheric residual effects as function of altitude, latitude, and solar activity. We show that the first-order ionospheric residual effect introduces a maximum negative temperature systematic bias of about 0.1K at 50 km, which decreases with decreasing altitude. The second-order ionospheric residual effect attains values of about −2 mm, which leads to a minimum and maximum temperature systematic bias of about −0.5K at 5 km and +2.0K at 50 km, respectively. We also observe that the magnitude of the second-order ionospheric residual effect increases with increasing latitude and solar activity, in both hemispheres, following a sinusoidal pattern. Heading to Solar Cycle 24-expected to peak in May 2013 with a Rz12 ∼90-we conclude that it is necessary that the first-and second-order ionospheric residual effects be considered in GPS/RO data processing methodologies to enhance the current atmospheric models.Citation: Vergados, P., and S. D. Pagiatakis (2011), Latitudinal, solar, and vertical variability of higher-order ionospheric effects on atmospheric parameter retrievals from radio occultation measurements,

Performance of the Ionospheric Kappa‐Correction of Radio Occultation Profiles Under Diverse Ionization and Solar Activity Conditions

“…The remaining higher‐order residual ionospheric errors (RIE) in the RO data are of increasing importance with increasing altitude (above about 35 km); furthermore they vary (mainly) with the diurnal and solar cycle (Danzer et al., 2013; Liu et al., 2013, 2015, 2018; Mannucci et al., 2011; Syndergaard, 2000). Earlier approaches for higher‐order ionospheric corrections exist (Hoque & Jakowski, 2008; Kedar et al., 2003; Syndergaard, 2002; Vergados & Pagiatakis, 2010, 2011), however, they are usually in need of additional background information, such as the total electron content (TEC).…”

Systematic residual ionospheric errors in radio occultation data and a potential way to minimize them

“…The usual approach is to perform a first order ionospheric correction, as discussed below, but there are also attempts for a reduction of the ionospheric residual by taking the second order term into account (e.g., Kedar et al, 2003;Petrie et al, 2011;Vergados and Pagiatakis, 2011). A disadvantage of the second order approximation is that it is model dependent and requires further information, such as, the electron density in the vicinity of the ray path or the geomagnetic field.…”

Upper Atmospheric Responses to Surface Disturbances: An Observational Perspective

“…Schematic of the radio occultation geometry. The dotted red line represents the propagation path of the dual‐frequency transmitted GNSS signals as they enter the Earth's ionosphere (gray spherical cell) and neutral atmosphere (cyan spherical cell) (from Vergados & Pagiatakis, ).…”