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We have performed an analysis of reprocessed GPS/MET data spanning 1995–1997 generated by the COSMIC Data Analysis and Archive Center (CDAAC) in 2007. CDAAC developed modified dual-frequency processing methods for the encrypted data (anti-spoofing (AS)-on) during 1995–1997. We compared the CDAAC data set to the Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) reanalysis, separately for AS-on and AS-off, focusing on the altitude range 10–30 km. MERRA-2 did not assimilate GPS/MET data in the period 1995–1997. To gain insight into the CDAAC data set, we developed a single-frequency data set for GPS/MET , which is unaffected by the presence of encryption. We find excellent agreement between the more limited single-frequency data set and the CDAAC data set: the bias between these two data sets is consistently less than 0.25 % in refractivity, whether or not AS is on. Given the different techniques applied between the CDAAC and the new data set presented here (designated JPL), agreement suggests that the CDAAC AS-on processing and the single-frequency processing are not biased in an aggregate sense greater than 0.25 % in refractivity, which corresponds approximately to a temperature bias less than 0.5 K. Since the profiles contained in the new single-frequency data set are not a subset of the CDAAC profiles, the combination of the CDAAC data set, consisting of 9579 profiles, and the new single-frequency data set, consisting of 4729 profiles, yields a total number of 11 531 unique profiles from combining the JPL and CDAAC data sets. All numbers are after quality control has been applied by the respective processing activities. [ABSTRACT FROM AUTHOR]

Significant polar topside total electron content (topTEC) enhancement (PTTE) above 1,336 km altitude is reported for the first time. The results are based on GPS measurements during 2008–2019 from NASA's Jason‐2 satellite with zenith‐oriented antennas. The observations show increasing topTEC toward the southern polar cap at geomagnetic latitudes poleward of 65°S, where TEC values are normally very low. A case study for the 2013 St. Patrick's Day storm indicates that the enhancement can exceed 5.5 TEC units above the dayside ambient state, corresponding to 78% increase. Comparisons with COSMIC/FORMOSAT‐3 topTEC measurements above 800 km altitude confirm that PTTE events are observed from both Jason‐2 and COSMIC on the same day. Our statistical analysis of the Jason‐2 data in the southern polar region reveals that PTTE mostly occurs on the dayside, with a seasonal preference of southern summer, and preferentially during geomagnetically disturbed days but can also occur during quiet days. PTTE during storm days shows increased occurrence, magnitude, and deviation from the mean in the cusp region compared with quiet days. Our case analysis indicates that PTTE is observed simultaneously with the effect of tongue of ionization. This suggests that the during storms, dayside F region plasma moving poleward following the antisunward plasma convection may also be part of the PTTE source, and the plasma upflow driven by the polar wind may act to cause PTTE. Plain Language Summary: Significant polar topside total electron content (topTEC) enhancement (PTTE) above 1,336 km altitude is reported for the first time. The results are based on GPS measurements from NASA's Jason‐2 satellite during 2008–2018. The observations show increasing topside TEC toward the southern polar cap where TEC values are normally very low. Comparisons with COSMIC/FORMOSAT‐3 topside TEC measurements confirm that PTTE events are observed from both Jason‐2 and COSMIC on the same day. Our statistical analysis reveals that PTTE mostly occurs in the southern cusp and dayside polar cap, with a seasonal preference of summer, and preferentially during geomagnetically disturbed days but can also occur during quiet days. PTTE during storm days shows increased occurrence, magnitude, and deviation from the mean in the cusp region compared with quiet days. Our case analysis indicates that PTTE is observed simultaneously with the effect of tongue of ionization. This suggests that the during storms, dayside F region plasma moving poleward following the antisunward plasma convection may also be part of the PTTE source, and the plasma upflow driven by the polar wind may act to cause PTTE. Key Points: NASA's Jason‐2 satellite zenith‐viewing GPS total electron content (TEC) measurements spanning 2008–2018 are analyzedSignificant increases of TEC above 1,336 km altitude in the southern polar region are reported for the first timeThe polar topside TEC enhancement (PTTE) appears preferentially during geomagnetic storms and during summer [ABSTRACT FROM AUTHOR]

The pressure-induced broadening and shift of CO spectral lines has been measured at room and liquid-nitrogen temperatures, using He and H2 as perturber gases. The R(2), P(8), and R(14) rovibrational transitions for the fundamental vibrational band were studied, which absorb in the 5 μm region of the infrared. A novel heterodyne spectrometer operating near 5 μm wavelengths has been used for these measurements. The local oscillator (LO) for the spectrometer was a frequency-doubled CO2 laser, with CdGeAs2 as the nonlinear crystal. This LO was step tunable and could be frequency stabilized to better than 0.5 MHz absolute accuracy. A spectral resolution of 20 MHz was achieved. The CO–He line-broadening measurements were accurate enough (∼2%–3% absolute accuracy) to distinguish between two proposed intermolecular potential models for this system. Also, a measured increase in the broadening coefficient as a function of rotational quantum number j was observed for CO–He at temperatures of 80 K. This is not easy to explain in the context of so-called ‘‘sudden approximations’’ which have been used to interpret pressure-broadening data for this system. The shift measurements are the first reported for the fundamental vibrational band of CO with He or H2. For H2, there appears to be a decrease of the shift with the rotational state j of the transition. For both He and H2, there is a pronounced temperature dependence of the shift for the P(8) transition, the shift becoming ‘‘redder’’ (toward lower frequency) as the temperature decreases from 298 to 80 K. [ABSTRACT FROM AUTHOR]

We construct a 9-year data record (2007-2015) of the tropospheric specific humidity using Global Positioning System radio occultation (GPS RO) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission. This record covers the ±40° latitude belt and includes estimates of the zonally averaged monthly mean specific humidity from 700 up to 400 hPa. It includes three major climate zones: (a) the deep tropics (±15°), (b) the trade winds belts (±15- 30°), and (c) the subtropics (±30-40°). We find that the RO observations agree very well with the European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim), the Modern-Era Retrospective Analysis for Research and Applications (MERRA), and the Atmospheric Infrared Sounder (AIRS) by capturing similar magnitudes and patterns of variability in the monthly zonal mean specific humidity and interannual anomaly over annual and interannual timescales. The JPL and UCAR specific humidity climatologies differ by less than 15% (depending on location and pressure level), primarily due to differences in the retrieved refractivity. In the middle-to-upper troposphere, in all climate zones, JPL is the wettest of all data sets, AIRS is the driest of all data sets, and UCAR, ERA-Interim, and MERRA are in very good agreement, lying between the JPL and AIRS climatologies. In the lower-to-middle troposphere, we present a complex behavior of discrepancies, and we speculate that this might be due to convection and entrainment. Conclusively, the RO observations could potentially be used as a climate variable, but more thorough analysis is required to assess the structural uncertainty between centers and its origin. [ABSTRACT FROM AUTHOR]

In this brief note we explore the role of the neutral atmosphere in magnetosphere–ionosphere coupling. We analyze momentum balance in the ion rest frame to form hypotheses regarding the role of neutral momentum in the lower ionosphere during geomagnetic storms. Neutral momentum that appears in the ion rest frame is likely the result of momentum imparted to ionospheric ions by solar wind flow and the resultant magnetospheric dynamics. The resulting ionneutral collisions lead to the existence of an electric field. Horizontal electron flow balances the momentum supplied by this electric field. We suggest a possible role played by the neutral atmosphere in generating field-aligned currents due to local auroral heating. Our physical interpretation suggests that thermospheric neutral dynamics plays a complementary role to the high-latitude field-aligned currents and electric fields resulting from magnetospheric dynamics. [ABSTRACT FROM AUTHOR]

We construct a 9-year data record (2007-2015) of the tropospheric specific humidity (SH) using Global Positioning System radio occultation (GPS RO) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission. This record covers the ±40° latitude belt and includes estimates of the zonally averaged monthly mean SH from 700 hPa up to 400 hPa. It includes three major climate zones: a) the deep tropics (±15°), b) the trade winds belts (±15-30°), and c) the subtropics (±30-40°). Our objective is to compare the RO observations with the European Center for Medium-range Weather Forecasts Re-Analysis Interim (ERA-Interim), the Modern-Era Retrospective analysis for Research and Applications (MERRA), and the Atmospheric Infrared Sounder (AIRS) to examine the consistency among the data sets. We present RO SHs from both JPL and UCAR processing centers to provide an estimate of the structural uncertainty of the RO SH products. The results show that the RO observations capture the seasonal and interannual SH variability as all other data sets. On average, the JPL-RO SH agrees with both reanalyses to within 10 %, is overall larger than all data sets, having maximum differences with AIRS by ~ 10-30 %, and is almost twice as wet as all other data sets in the middle-to-upper troposphere at the subtropics. The UCAR-RO SH also agrees with both reanalyses and AIRS, but is systematically drier than all other data sets. Provided the estimated differences between the RO observations and the rest of the data sets, together with the retrieval uncertainty of the SH products from all data sets, we conclude that RO observations are a valuable independent observing system, which could augment independent reanalyses and satellite platforms. We anticipate that the COSMIC-2 mission will increase the observational sampling; thus, improving the coverage and quality of the observed SH climatology. [ABSTRACT FROM AUTHOR]

Abstract: Scientific knowledge is acquired in geophysics generally without the benefit of controlled experiments. In this paper, we discuss how scientific inference based on observations occurs in geophysical contexts. We develop a specific approach that uses approximate simultaneity of proposed cause and effect phenomena to infer causality. The approach applies equally well to effect phenomena that follow the cause with a known time delay. We find that, in general, establishing a causal relationship between two phenomena based on simultaneity requires knowledge of how often simultaneity of these phenomena occurs in the absence of causality. We then extend the discussion to using numerical simulations in the scientific inference process. Numerical simulations of physical processes, because they can simulate the values of observations, are often used to infer what physical processes are occurring in nature. We discuss agreement between model output and observations as a basis for inferring the physical processes underlying the observations. We find that an important factor to consider, which we here call the “confusion factor,” is how often it may occur that insufficient model representations of the physical processes nevertheless lead to agreement between model computations and observations. We suggest that models of intermediate or low complexity may have a significant role to play when using geophysical simulations to reach scientific conclusions. [ABSTRACT FROM AUTHOR]

We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high-latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E-layer-dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the Southern, less sunlit, Hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50- magnetic latitude for signatures of precipitation in the E region. For 9 days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012 the precipitation tended to be somewhat more equatorward than the climatology (by about 5-10° latitude) and equatorward of the auroral boundary data acquired from the SSUSI sensor onboard the F18 DMSP satellite. We conclude that, if analyzed appropriately, high-latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region. [ABSTRACT FROM AUTHOR]

The spatial variability of the tropical tropospheric relative humidity (RH) throughout the vertical extent of the troposphere is examined using Global Positioning System Radio Occultation (GPSRO) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission. These high vertical resolution observations capture the detailed structure and moisture budget of the Hadley Cell circulation. We compare the COSMIC observations with the European Center for Medium-range Weather Forecast (ECMWF) Reanalysis Interim (ERA-Interim) and the Modern-Era Retrospective analysis for Research and Applications (MERRA) climatologies. Qualitatively, the spatial pattern of RH in all data sets matches up remarkably well, capturing distinct features of the general circulation. However, RH discrepancies exist between ERA-Interim and COSMIC data sets that are noticeable across the tropical boundary layer. Specifically, ERA-Interim shows a drier Intertropical Convergence Zone (ITCZ) by 15-20% compared to both COSMIC and MERRA data sets, but this difference decreases with altitude. Unlike ECMWF, MERRA shows an excellent agreement with the COSMIC observations except above 400 hPa, where GPSRO observations capture drier air by 5-10 %. RH climatologies were also used to evaluate intraseasonal variability. The results indicate that the tropical middle troposphere at ±5-25° is most sensitive to seasonal variations. COSMIC and MERRA data sets capture the same magnitude of the seasonal variability, but ERA-Interim shows a weaker seasonal fluctuation up to 10% in the middle troposphere inside the dry air subsidence regions of the Hadley Cell. Over the ITCZ, RH varies by maximum 9% between winter and summer. [ABSTRACT FROM AUTHOR]

We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At night 10 time local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E layer dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms, that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the southern, less sunlit, hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For nine days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012, the precipitation tended to be somewhat more equator ward than predicted by the climatology (by about 5-10° latitude). We conclude that, if analyzed appropriately, high latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region. [ABSTRACT FROM AUTHOR]

The spatial variability of the tropical tropospheric relative humidity (RH) throughout the vertical extent of the troposphere is examined using Global Positioning System Radio Occultation (GPSRO) observations from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) mission. These high vertical resolution observations capture the detailed structure and moisture budget of the Hadley Cell circulation. We compare the COSMIC observations with the European Center for Medium-rangeWeather Forecast (ECMWF) Re-Analysis Interim (ERA-Interim) and the Modern-Era Retrospective analysis for Research and Applications (MERRA) climatolo gies. Qualitatively, the spatial pattern of RH in all data sets matches up remarkably well, capturing distinct features of the general circulation. However, RH discrepancies exist between ERA-Interim and COSMIC data sets, which are noticeable across the tropical boundary layer. Specifically, ERA-Interim shows a drier Inter Tropical Convergence Zone (ITCZ) by 15-20% compared both to COSMIC and MERRA data sets, but this difference decreases with altitude. Unlike ECMWF, MERRA shows an excellent agreement with the COSMIC observations except above 400 hPa, where GPSRO observations capture drier air by 5-10 %. RH climatologies were also used to evaluate intraseasonal variability. The results indicate that the tropical middle troposphere at ±5-25° is most sensitive to seasonal variations. COSMIC and MERRA data sets cap ture the same magnitude of the seasonal variability, but ERA-Interim shows a weaker seasonal fluctuation up to 10% in the middle troposphere inside the dry air subsidence regions of the Hadley Cell. Over the ITCZ, RH varies by maximum 9% between winter and summer. [ABSTRACT FROM AUTHOR]

This short paper presents phase and coherence data from the cross-wavelet transform applied on longitudinally separated very high frequency (VHF) equatorial ionospheric scintillation observations over Christmas Island. The phase and coherence analyses were employed on a pair of scintillation observations, namely, the east-looking and westlooking VHF scintillation monitors at Christmas Island. Our analysis includes 3 years of peak season scintillation data from 2008, 2009 (low solar activity), and 2011 (moderate solar activity). In statistically significant and high spectral coherence regions of the cross-wavelet transform, scintillation observations from the east-looking monitor lead those from the west-looking monitor by about 20 to 60 (40±20) min (most frequent lead times). Using several years (seasons and solar cycle) of lead (or lag) and coherence information of the cross-wavelet transform, we envisage construction of a probability model for forecasting scintillation in the nighttime equatorial ionosphere. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the impact of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals. A climatological model of the ionosphere and an ionospheric data assimilation model comparing quiet and geomagnetically disturbed conditions is provided. The study suggests that monitoring ionospheric conditions is critical for long-term climate observation with RO. Also, it indicates that orbit altitude has a significant impact on the bias.

The article presents a study which examines the effects of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals of atmospheric parameters including temperature and refractivity. The study compares quiet and geomagnetically disturbed conditions using an ionospheric data assimilation model and a climatological model of ionosphere. It is found out that satellites in higher altitude orbits have lower retrieval bias.

Abstract: In the coming years, opportunities for remote sensing of electron density in the Earth’s ionosphere will expand with the advent of Galileo, which will become part of the global navigation satellite system (GNSS). Methods for accurate electron density retrieval from radio occultation data continue to improve. We describe a new method of electron density retrieval using total electron content measurements obtained in low Earth orbit. This method can be applied to data from dual-frequency receivers tracking the GPS or Galileo transmitters. This simulation study demonstrates that the method significantly improves retrieval accuracy compared to the standard Abel inversion approach that assumes a spherically symmetric ionosphere. Our method incorporates horizontal gradient information available from global maps of Total Electron Content (TEC), which are available from the International GNSS Service (IGS) on a routine basis. The combination of ground and space measurements allows us to improve the accuracy of electron density profiles near the occultation tangent point in the E and F regions of the ionosphere. [Copyright &y& Elsevier]

The four-dimensional Global Assimilative Ionospheric Model (GAIM) is applied to a study of ionospheric disturbances. The investigation is focused on disturbance features, particularly in the altitude and latitude dimensions, at low latitudes during a geomagnetic storm on 7 August 2006, under solar minimum conditions. The modeling of storm-time ionospheric state (electron density) is conducted by assimilating an unprecedented volume of line-of-sight TEC data collected by the Global Positioning System (GPS) occultation receivers on board six FORMOSAT-3/COSMIC satellites and geodetic-quality GPS receivers at two hundred globally-distributed ground tracking stations. With a band-limited Kalman filter technique to update the ionospheric state, the assimilative modeling reveals a pronounced enhancement in the equatorial anomaly in the East Asia sector during dusk and evening hours. The disturbance characteristics, obtained by comparing with the quiet conditions prior to the storm also modeled in this study through data assimilation, include lifted F layer and reduced electron density in the equatorial region, enhanced density at the magnetically conjugate anomaly latitudes, and tilted feature of density increase towards higher altitudes at lower latitudes. The characteristics are attributed to the enhanced plasma fountain effect driven by an enhanced eastward zonal electric field. These results enable us to distinguish the storm-time electric field perturbations clearly from other sources during the storm. The possible origins of electric field perturbations are also discussed, including penetration of the magnetospheric electric field and wind dynamo disturbances. [ABSTRACT FROM AUTHOR]

The Jet Propulsion Laboratory (JPL) develops JPL-GIM, a software for generating global ionospheric maps (GIMs) of total electron content (TEC) using measurements from multiple Global Navigation Satellite System (GNSS) constellations. Within this overview paper, we delve into the current state and the most recent enhancements of JPL-GIM. An adaptable Kalman filter provides maps with user-defined temporal and spatial resolutions, while concurrently delivering essential covariance data for uncertainty assessment. Furthermore, multiple shell models offer a versatile framework to balance accuracy and computational efficiency. We present the five operational JPL GIM products (JPLG, JPRG, JPLI, JPLD, JPRT), highlighting JPLG and JPRG, our products routinely delivered to the International GNSS Service (IGS), and introduce a new near-real-time product (JPRT). As an added demonstration of JPL-GIM’s capabilities, we present a very-high-resolution (2-minute, multi-GNSS, 1000-station) configuration to showcase JPL-GIM’s ability to resolve long-lasting effects of the 2022 Hunga Tonga-Hunga Ha’apai eruption. Validations using independent datasets confirm the accurate reproduction of ionospheric variations across all latitudinal bands. [ABSTRACT FROM AUTHOR]

Comments on a study which compared the data acquired from heterodyne spectroscopy of carbon monoxide lines perturbed by hydrogen and helium. Details of theoretical values obtained through coupled states approximation; Information on molecular scattering calculations; Comparison of theoretical and experimental pressure broadening cross sections.

The ionospheric weather Vσ index maps are generated from GIM-TEC produced at the Jet Propulsion Laboratory (JPL) with the denser grids of 1 × 1° in latitude and longitude, respectively. Using sliding-window statistical analysis, moving TEC median μ for 15 preceding days with estimated variance bounds is obtained for each grid pixel of GIM-TEC. The ionosphere variability index, Vσ, is ΔTEC deviation from the median normalized by the standard deviation σ. Vσ index segmentation is introduced specifying TEC storm if an instant TEC is outside the bound of μ±2σ. Comparisons of Vσ variability of 1 × 1° GIM-TEC maps with normal GIM-TECs of 2.5 × 5° in latitude and longitude demonstrates the greater TEC storm activity with denser grids maps. The superposed epoch analysis is performed for 77 intense storms (Dst ≤ −100 nT) and 246 moderate storms (−100 < Dst ≤ −50 nT) during 2000–2017, with zero time, t 0 , at Dst storm peak. The probabilities of TEC storm occurrence both positive (Vσp index) and negative (Vσn) are evaluated for 24 h prior to t 0 and 48 h after t 0 for global scale and three specified latitude zones: North High (NH) magnetic latitudes λ > 50°, South High (SH) λ < −50°, and Equatorial Ionization Anomaly (EIA) Band between ±35° magnetic latitudes. The equinoctial positive Vσp index shows the maxima on March and September, Dst intensity peaks on April and October, and the negative Vσn peaks on May and November. The amplitude of Vσp for the intense storms exceeds that for the moderate storm by 2 times and exceeds the amplitude of Vσn by 1.5 times. Storm Enhanced Density (SED) is evident with the largest amplitude of Vσp at EIA Band exceeding Vσp for NH and SH zones by 3 times. The negative Vσn occurrence observed for selected zones during the intense storms is decreased by 5 times for the moderate storms. The normalized cross-correlation function is used to define lag (time delay) between peak of Vσp and Vσn and t 0 of Dst peak. The majority of positive Vσp indices (57.5%) are observed prior to Dst storm (lag varies from −1 to −6 h with Dst from −50 to −400 nT) so the TEC enhancement can serve as a precursor of Dst storm. The time delay for the negative Vσn is inversely related with Dst storm intensity (lag varies from 11 to 8 h with Dst from −50 to −400 nT). • Superiority of denser global TEC maps (1 × 1 deg grids) over standard IONEX GIM-TECs is demonstrated. • Hourly-seasonal hierarchy is established with the positive TEC storms preceeding Dst storm echoed by the negative TEC storm. • Storm Enhanced Density is dominant at Equatorial zone over North and South high latitude zones. • Intensity of ionosphere storms is dropped by 3–5 times from intense to moderate Dst storms. [ABSTRACT FROM AUTHOR]

In the upper troposphere (UT), Global Navigation Satellite System (GNSS) Radio Occultations (ROs) provide accurate air temperatures (<0.5 K) every ∼200 m vertically. We use RO observations from 01/2002 until 12/2018 at 300, 250, and 200 hPa to quantify the tropical upper tropospheric amplification (defined as the ratio of temperature trends in the UT relative to the surface). We compare the RO‐derived results against Atmospheric Infrared Sounder (AIRS), Coupled Model Intercomparison Project Phase 6 (CMIP6) Atmospheric Model Intercomparison Project (AMIP) models, Modern‐Era Retrospective Analysis for Research and Applications version 2 (MERRA‐2), and European Center for Medium‐range Weather Forecasts Re‐Analysis Interim (ERA‐Interim) data. We find that CMIP6 AMIP models show excellent agreement with independent AIRS and RO observations on the magnitude of the UT warming and show warming that is significantly faster than both reanalyses above 250 hPa. Additionally, AIRS and CMIP6 AMIP present excellent agreement with the RO‐measured tropical tropospheric amplification. Plain Language Summary: In the upper troposphere, Global Navigation Satellite System Radio Occultations (GNSS‐RO) measure the air's refractive index, which depends primarily on the air's temperature. We use these GNSS‐RO temperatures from 01/2002 until 12/2018 at 200, 250, and 300 hPa in the tropics (where the atmosphere experiences the largest amplification in response to surface warming). Routinely, climate models are used to simulate how much the upper atmosphere has warmed in response to surface warming. However, there appears to be a disagreement between observations and models, which today we try to understand. The GNSS‐RO observations have a unique feature of being able to measure the air temperature every 200 m, and show us that that climate models are in close agreement with the GNSS‐RO and other infrared observations. In other words, GNSS‐RO observations show that the upper atmosphere warms faster and the amplification due to surface warming is stronger than what current reanalysis estimate. Independent infrared observations of the Earth's upper troposphere also support the GNSS‐RO findings and are also in very close agreement with the climate models. Interestingly, the reanalysis indicates that at 200 hPa there is no warming observed, contrary to what GNSS‐RO, infrared, and climate models reveal. Key points: Coupled model intercomparison project phase 6 (cmip6) atmospheric model intercomparison project (AMIP) models agree with independent radio occultation and infrared data on the magnitude of the tropical upper tropospheric temperature trendsRadio occultations reveal faster tropical upper tropospheric warming than both modern‐era retrospective analysis for research and applications version 2 (MERRA‐2) and European Center for Medium‐Range Weather Forecasts Re‐Analysis Interim (ERA‐Interim) (above 250 hPa) reanalysesERA‐Interim presents decreasing tropical upper troposphere amplification with altitude, unlike the amplification shown by radio occultations [ABSTRACT FROM AUTHOR]

We study solar wind-ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) - 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and midlatitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10-22 October 2003, was analyzed for comparative purposes, with daytime lowlatitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008-2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008-2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~3.3 × 1010W and 2.7 × 1010W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind-ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind-ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals. [ABSTRACT FROM AUTHOR]

Launched in 2006, the Formosa Satellite Mission 3-Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) was the first constellation of microsatellites carrying global positioning system (GPS) radio occultation (RO) receivers. Radio occultation is an active remote sensing technique that provides valuable information on the vertical variations of electron density in the ionosphere, and temperature, pressure, and water vapor in the stratosphere and troposphere. COSMIC has demonstrated the great value of RO data in ionosphere, climate, and meteorological research and operational weather forecasting. However, there are still challenges using RO data, particularly in the moist lower troposphere and upper stratosphere. A COSMIC follow-on constellation, COSMIC-2, was launched into equatorial orbit in 2019. With increased signal-to-noise ratio (SNR) from improved receivers and digital beam steering antennas, COSMIC-2 will produce at least 5,000 high-quality RO profiles daily in the tropics and subtropics. In this paper, we summarize 1) recent (since 2011 when the last review was published) contributions of COSMIC and other RO observations to weather, climate, and space weather science; 2) the remaining challenges in RO applications; and 3) potential contributions to research and operations of COSMIC-2. [ABSTRACT FROM AUTHOR]

Atmospheric climate monitoring requires observations of high quality that conform to the criteria of the Global Climate Observing System (GCOS). Radio occultation (RO) data based on Global Positioning System (GPS) signals are available since 2001 from several satellite missions with global coverage, high accuracy, and high vertical resolution in the troposphere and lower stratosphere. We assess the consistency and long-term stability of multi-satellite RO observations for use as climate data records. As a measure of long-term stability, we quantify the structural uncertainty of RO data products arising from different processing schemes. We analyze atmospheric variables from bending angle to temperature for four RO missions, CHAMP, Formosat-3/COSMIC, GRACE, and Metop, provided by five data centers. The comparisons are based on profile-to-profile differences aggregated to monthly medians. Structural uncertainty in trends is found to be lowest from 8 to 25 km of altitude globally for all inspected RO variables and missions. For temperature, it is < 0.05 K per decade in the global mean and < 0.1 K per decade at all latitudes. Above 25 km, the uncertainty increases for CHAMP, while data from the other missions – based on advanced receivers – are usable to higher altitudes for climate trend studies: dry temperature to 35 km, refractivity to 40 km, and bending angle to 50 km. Larger differences in RO data at high altitudes and latitudes are mainly due to different implementation choices in the retrievals. The intercomparison helped to further enhance the maturity of the RO record and confirms the climate quality of multi-satellite RO observations towards establishing a GCOS climate data record. [ABSTRACT FROM AUTHOR]

Atmospheric climate monitoring requires observations of high-quality conforming to the criteria of the Global Climate Observing System (GCOS). Radio occultation (RO) data based on Global Positioning System (GPS) signals are available since 2001 from several satellite missions with global coverage, high accuracy, and high vertical resolution in the troposphere and lower stratosphere. We assess the consistency and long-term stability of multi-satellite RO observations for use as climate data records. As a measure of long-term stability, we quantify the structural uncertainty of RO data products arising from different processing schemes. We analyze atmospheric variables from bending angle to temperature for four RO missions, CHAMP, Formosat-3/COSMIC, GRACE, and Metop, provided by five data centers. The comparisons are based on profile-to-profile differences, aggregated to monthly means. Structural uncertainty in trends is found lowest from 8 km to 25 km altitude globally for all inspected RO variables and missions. For temperature, it is < 0.05 K per decade in the global mean and < 0.1 K per decade at all latitudes. Above 25 km, the uncertainty increases for CHAMP while data from the other missions are based on advanced receivers and are usable to higher altitudes for climate trend studies: dry temperature to 35 km, refractivity to 40 km, and bending angle to 50 km. Larger differences in RO data at high altitudes and latitudes are mainly due to different implementation choices in the retrievals. The intercomparison helped to further enhance the maturity of the RO record and confirms the climate quality of multi-satellite RO observations towards establishing a GCOS climate data record. [ABSTRACT FROM AUTHOR]

Comprehensive measurements of the Martian atmosphere, especially high-resolution temperature and pressure fields of the lower atmosphere, are needed for the characterization of scientifically important Martian weather and climate features such as wind, dust storms, atmospheric tides, and seasonal hydrogen escape. In addition, spatial information about the atmospheric state is necessary for planning of future aero braking events and for prediction of various aspects of the entry, descent, and landing of spacecraft.While the individual measurements obtained from sensors such as infrared radiometers, spectrometers or radio occultation payloads onboard Mars Odyssey, Mars Express, or Mars Reconnaissance Orbiter, are processed on a routine basis to derive detailed information about the atmospheric state, inter-technique comparisons are beneficial to understand the specific sensor characteristics and to reduce the risk for misinterpretations. We will show how the combination of measurements based on the tomography principle can improve the understanding of atmospheric processes on Mars, especially of those, which are characterized by distinct horizontal temperature and pressure gradients.In contrast to Earth, horizontal temperature and pressure gradients on Mars can be much more severe. Based on end-to-end simulations we will show how and under which conditions it is possible to reconstruct these gradients from radio occultation and Mars Climate Sounder measurements using tomography principles. Successfully applied to real observations, the enhanced temperature and pressure retrievals can provide crucial information for improving our understanding of atmospheric dynamics, especially over complex terrain, at the day-night terminator, or the Northern polar vortex. [ABSTRACT FROM AUTHOR]

We analyze the spatial‐temporal variability of the mesosphere/lower thermosphere (MLT) temperature at ±15N/S over 14 years, using measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. We report that during the Madden‐Julian Oscillation season (November–April) the MLT region exhibits temperature variations with dominant periodicities at 40 and 60 days with amplitudes as large as 5.0 K. These intraseasonal oscillations (ISOs) are expressed across all longitudes, having superimposed zonal wave‐like structures that resemble waves 3 and 4 with amplitudes as large as 5.0 K. The cold and warm ISO phases are ubiquitous and repeatable from year to year over the 14‐year satellite record. We show that the MLT ISO exhibits the characteristics of a propagating wave carrying the embedded zonal wave‐like structures. At 20 km an ISO signal also exists with similar characteristics as the MLT ISO, suggesting a potential connection with the lower atmosphere. Plain Language Summary: We find that the Earth's temperature in the low‐latitude mesosphere/lower thermosphere (MLT) region appears to increase and decrease by 5.0 K every 60 days. This behavior is present in every year from 2002 until 2016, and it affects all longitudes. Such an event was not possible before to observe, due to a limited number of ground‐based stations that monitor the Earth's MLT region. In our analysis, we used satellite observations from 2002 to 2016 that covered all longitudes. The instrument we used was the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Interestingly, superimposed within these intraseasonal oscillations (ISOs), the MLT region is noticed to also vary as a function of longitude. These variations represent waves that travel around the Earth's atmosphere increasing and decreasing the Earth's MLT region by 5.0 K. Interestingly, when such oscillations are present in the MLT region, the lower stratosphere presents similar variability at the same periodicities, which makes us to believe that there may be a potential influence of the lower to upper atmosphere. Our results provide a unique picture of the MLT's thermal structure as a function of longitude, which is important in model simulations of the dynamic structure of the MLT region. Key Points: The mesosphere/lower thermosphere (MLT) region displays intraseasonal oscillations (ISOs) at 40 and 60 days that are ubiquitous and repeatable from year to yearThe MLT ISO exhibits zonal variations that resemble wave 3 and 4 structures in the temperaturesWhen the MLT ISO is present, the lower stratosphere also shows ISOs with similar periodicities and longitudinal structures [ABSTRACT FROM AUTHOR]

Solar soft X-ray (XUV) radiation is highly variable on all time scales and strongly affects Earth’s ionosphere and upper atmosphere; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. Although there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the broad bands measured in the XUV range. In particular, the simple conversion of the XUV photometer signal into irradiance, in which a static solar spectrum is assumed, overestimates the flare variations by more than a factor of two as compared to the atmospheric response to the flares. To address this deficiency in the simple conversion, an improved algorithm using CHIANTI spectral models has been developed to process the XUV Photometer System (XPS) measurements with its broadband photometers. Model spectra representative of quiet Sun, active region, and flares are combined to match the signals from the XPS and produce spectra from 0.1 to 40 nm in 0.1-nm intervals for the XPS Level 4 data product. The two XPS instruments are aboard NASA’s Solar Radiation and Climate Experiment (SORCE) and Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) satellites. In addition, the XPS responsivities have been updated for the latest XPS data processing version. The new XPS results are consistent with daily variations from the previous simple conversion technique used for XPS and are also consistent with spectral measurements made at wavelengths longer than 27 nm. Most importantly, the XPS flare variations are reduced by factors of 2 – 4 at wavelengths shorter than 14 nm and are more consistent, for the first time, with atmospheric response to solar flares. Along with the details of the new XPS algorithm, several comparisons to dayglow and photoelectron measurements and model results are also presented to help verify the accuracy of the new XUV irradiance spectra. [ABSTRACT FROM AUTHOR]

Tracking of the radio signals broadcast by the Global Positioning System (GPS) satellites as they are occulted from a GPS receiver by the Earth's atmosphere can provide high resolution vertical profiles of atmospheric refractivity, temperature and water vapour. Most implementations of this radio occultation technique use two GPS frequencies to correct for ionospheric effects. However, during most soundings, one of the frequencies is degraded by the introduction of the so-called Anti-Spoofing (AS) encryption mode. A retrieval method is discussed in this work for periods when only one of the two frequency signals has good quality. This method uses only the frequency with higher signal-to-noise ratio. We illustrate the quality of the atmospheric profiles obtained from such single frequency retrievals using GPS/MET data from the periods where the AS was turned off and the two frequencies were available. The results enable us to ensure the quality of a climate record of thousands of radio occultations collected by GPS/MET during the period with AS encryption, and the data processing of future missions with similar constraints, like IOX, can be performed. [ABSTRACT FROM AUTHOR]

It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves. [ABSTRACT FROM AUTHOR]