Constellation Observing System For Meteorology, Ionosphere, And Climate Measurements Research Articles

A regional ionospheric assimilation study with GPS and COSMIC measurements using a 3D-var algorithm (IDA4D)

The Ionospheric Data Assimilation Four-Dimension (IDA4D) is, developed by Bust et al. (2007) , a continuous time and three-dimension variational (3D-Var) algorithm that can optimally estimate the ionosphere from a model and measured data. In this study, we utilized three different data types into IDA4D for a regional ionosphere estimation: slant total electron contents (STEC) obtained from a Global Positioning System (GPS) network, NmF2 (peak electron density of the F2 layer) and STEC from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellite. These multiple type data were assimilated into a background model, the International Reference Ionosphere (IRI – 2016). To evaluate the effect of each data type, the assimilation was performed on the following data combinations (cases): (1) GPS-STEC’s only; (2) GPS-STEC’s and NmF2′s from COSMIC; (3) GPS-STEC’s and COSMIC-STEC’s; and (4) all three data types. For each case computed foF2′s (F2 layer critical frequency) from IDA4D were compared with measured values from five ionosondes (I-Cheon, Jeju, Okinawa, Kokubunji, and Wakkanai) in the region of Korea and vicinities for the test periods of March, June, September and December in 2015. The comparison shows that computed foF2′s for all cases have higher correlation coefficients (CC) and less root mean square errors (RMSE) from measured values than IRI estimated values. In Cases 2, 3 and 4, IDA4D performance progressively improved in areas where GPS measurements were not covered but COSMIC STEC and NmF2 data were available. Furthermore, the IDA4D assimilation yields better results for electron density profiles and TEC values in comparison with observed values than the IRI model does. Thus, our study suggests that the IDA4D model with multiple data types can provide a reliable estimation of the regional ionosphere over the Korean Peninsula and vicinities.

An application of artificial intelligence for investigating the effect of COVID-19 lockdown on three-dimensional temperature variation in equatorial Africa

We present interesting application of artificial intelligence for investigating effect of the COVID-19 lockdown on 3-dimensional temperature variation across Nigeria (2°–15° E, 4°–14° N), in equatorial Africa. Artificial neural networks were trained to learn time-series temperature variation patterns using radio occultation measurements of atmospheric temperature from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). Data used for training, validation and testing of the neural networks covered period prior to the lockdown. There was also an investigation into the viability of solar activity indicator (represented by the sunspot number) as an input for the process. The results indicated that including the sunspot number as an input for the training did not improve the network prediction accuracy. The trained network was then used to predict values for the lockdown period. Since the network was trained using pre-lockdown dataset, predictions from the network are regarded as expected temperatures, should there have been no lockdown. By comparing with the actual COSMIC measurements during the lockdown period, effects of the lockdown on atmospheric temperatures were deduced. In overall, the mean altitudinal temperatures rose by about 1.1 °C above expected values during the lockdown. An altitudinal breakdown, at 1 km resolution, reveals that the values were typically below 0.5 °C at most of the altitudes, but exceeded 1 °C at 28 and 29 km altitudes. The temperatures were also observed to drop below expected values at altitudes of 0–2 km, and 17–20 km.

Global Monitoring of Geomagnetic Storm‐Induced Ionosphere Anomalies Using 3‐D Ionospheric Modeling With Multi‐GNSS and COSMIC Measurements

AbstractIonosphere is a significant component of the solar‐terrestrial space environment. Geomagnetic storm induces global ionospheric disturbances, severely affect radio communications and human space activities, e.g., earth observation, deep space exploration, and space weather monitoring and prediction. Monitoring ionospheric anomalies are critical to improve the performance of Global Navigation Satellite System (GNSS) positioning, navigation and timing (PNT) and provide early‐warning of disaster service during the extreme space weather event. The spatial and temporal variation of ionospheric electron density (IED) is utilized to characterize the ionospheric anomalies respond to storm. Thus, the global‐scale three‐dimensional (3‐D) ionospheric model is constructed by computerized ionospheric omography (CIT) technique combine multi‐GNSS(GPS/GLONASS/BDS/Galileo) and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) measurements. As ground‐based multi‐GNSS and space‐based Low Earth Orbit (LEO)/GNSS observation networks expand gradually, massive measurements are employed in ionospheric inversion in high temporal‐spatial resolution. Hence, the Open Multi‐Processing (OpenMP) parallel computing method is applied to improve the efficiency of imaging 3‐D ionosphere. The processing time reduces to within 10 mins, thus 3‐D ionospheric model updates in near real‐time is achievable. Moreover, the 3‐D IED model is applied to monitor the ionosphere dynamically during storms and the storm‐induced ionospheric anomalies are observed. This contribution suggests our reconstructed 3‐D model is capable of reflecting the ionospheric anomalies during storm in global‐scale, also it reveals the characteristics of the ionosphere respond to the storm and its evolution.

Evaluation of the performance of ionospheric models at solar maximum using COSMIC slant TEC measurements

AbstractWe report the results of a model validation study that assessed how well several ionospheric models captured the slant total electron content, especially at low latitudes near the equatorial ionization anomaly, where horizontal and vertical density gradients are large. We assessed NeQuick, IRI‐2007, IRI‐2012, SAMI‐3, and the Utah State University version of the Global Assimilation of Ionospheric Measurements (GAIM) model. We used slant total electron content measurements made by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) constellation during 5 May to 20 June 2012 to test GAIM, NeQuick, IRI‐2007, and IRI‐2012 and during 1 October 2011 to 31 December 2011 to test SAMI‐3, as the SAMI‐3 model runs were not available for the 2012 time frame. We found that the GAIM data assimilation model showed the lowest biases, although all of the models typically agreed with the COSMIC measurements to ~8% in the worst case. One area of concern with all of the models was that the mean percentage difference between the COSMIC measurements and the calculated total electron content (TEC) showed significant scatter, >15% at the 1 sigma level; this was attributed to all of the models not capturing the density gradients near the equatorial ionization anomaly (EIA). All of the models underestimated the topside electron density and thus also the ionospheric slab thickness. Since ionospheric models are often validated using near‐vertical TEC measurements and the vertical TEC is the product of the electron density at the F region peak and the slab thickness, our results suggest that the peak density values in the models may be too high.

Data assimilation of plasmasphere and upper ionosphere using COSMIC/GPS slant TEC measurements

AbstractIncreasing total electron content (TEC) measurements from the low Earth orbiting satellites to Global Positioning System satellites flourish the exploration of the ionosphere and plasmasphere for decades. This paper indicates a method that 3‐D Var is applied to assimilate precise orbit determination antenna TEC measurements of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites into the background global core plasma model (GCPM). The slant TEC data archived in the COSMIC Data Analysis and Archive Center from 500 km to 20,200 km are used to reconstruct a new electron density model. This model has a temporal resolution of 2 h and spatial resolutions of 2.5° in geomagnetic latitude, 5° in longitude, 50 km in the upper ionosphere, and several hundred kilometers in the plasmasphere. Preliminary results show that the data assimilation modifies the initial GCPM forecast to be better coincident with actual COSMIC measurements in internal quality check. Furthermore, independent validation with upper ionosphere‐retrieved electron density and TEC of global ionosphere maps implies a reasonable improvement in the estimation of plasmaspheric electron density after the assimilation.

An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean

Abstract. The global positioning system (GPS) radio occultation (RO) method is a relatively new technique for taking atmospheric measurements for use in both weather and climate studies. As such, this technique needs to be evaluated for all parts of the globe. Here, we present an extensive evaluation of the performance of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS RO observations of the Southern Ocean boundary layer. The two COSMIC products used here are the "wetPrf" product, which is based on 1-D variational analysis with European Centre for Medium-Range Weather Forecasts (ECMWF), and the "atmPrf" product, which contains the raw measurements from COSMIC. A direct comparison of temporally and spatially co-located COSMIC profiles and high resolution radiosonde profiles from Macquarie Island (54.62° S, 158.85° E) highlights weaknesses in the ability of both COSMIC products to identify the boundary layer structure, as identified by break points in the refractivity profile. In terms of reproducing the temperature and moisture profile in the lowest 2.5 km, the "wetPrf" COSMIC product does not perform as well as an analysis product from the ECMWF. A further statistical analysis is performed on a large number of COSMIC profiles in a region surrounding Macquarie Island. This indicates that, statistically, COSMIC performs well at capturing the heights of main and secondary break points. However, the frequency of break points detected is lower than the radiosonde profiles suggest, but this could be simply due to the long horizontal averaging in the COSMIC measurements. There is also a weak seasonal cycle in the boundary layer height similar to that observed in the radiosonde data, providing some confidence in the ability of COSMIC to detect an important boundary layer variable.

Validation of COSMIC ionospheric peak parameters by the measurements of an ionosonde chain in China

Abstract. Although the electron density profiles (EDPs) from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) measurement have been validated by ionosonde data at a number of locations during the solar minimum period, the performance of COSMIC measurements at different latitudes has not been well evaluated, particularly during the solar maximum period. In this paper the COSMIC ionospheric peak parameters (peak electron density of the F region – NmF2; peak height of the F region – hmF2) are validated by the ionosonde data from an observation chain in China during the solar maximum period of 2011–2013. The validations show that the COSMIC measurement generally agrees well with the ionosonde observation. The error in NmF2 from COSMIC and ionosonde measurements varies with latitude. At midlatitude stations, the differences between COSMIC NmF2s and those of ionosondes are very slight. However, COSMIC NmF2 overestimates (underestimates) that of the ionosonde at the north (south) of the equatorial ionization anomaly (EIA) crest. The relative errors of hmF2s are much lower than those of NmF2s at all stations, which indicates the EDP retrieval algorithm of the COSMIC measurement has a better performance in determining the ionospheric peak height. The root mean square errors (RMSEs) of NmF2s (hmF2s) are higher (lower) during the daytime than during the nighttime at all stations. Correlation analysis shows that the correlations for both NmF2s and hmF2s are comparably good (correlation coefficients > 0.9) at midlatitude stations, while correlations of NmF2 (correlation coefficients > 0.9) are higher than those of hmF2 (correlation coefficients > 0.8) at low-latitude stations.

Validation of the IRI-2012 model with GPS-based ground observation over a low-latitude Singapore station

The ionospheric total electron content (TEC) in the low-latitude Singapore region (geographic latitude 01.37° N, longitude, 103.67° E, geomagnetic latitude 8.5° S) for 2010 to 2011 was retrieved using the data from global positioning system (GPS)-based measurements. The observed TEC from GPS is compared with those derived from the latest International Reference Ionosphere (IRI)-2012 model with three options, IRI-Nequick (IRI-Neq), IRI-2001, and IRI-01-Corr, for topside electron density. The results showed that the IRI-Neq and IRI-01-Corr models are in good agreement with GPS-TEC values at all times, in all seasons, for the year 2010. For the year 2011, these two models showed agreement at all times with GPS-TEC only for the summer season, and for the period 11:00 to 24:00 UT hours (19:00 to 24:00 LT and 00:00 to 08:00 LT) during the winter and equinox seasons. The IRI-2012 model electron density profile showed agreement with constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultation (RO)-based measurements around 250 to 300 km and was found to be independent of the options for topside density profiles. However, above 300 km, the IRI-2012 model electron density profile does not show agreement with COSMIC measurements. The observations (COSMIC and GPS) and IRI-2012-based data of TEC and electron density profiles were also analyzed during quiet and storm periods. The analysis showed that the IRI model does not represent the impact of storms, while observations show the impact of storms on the low-latitude ionosphere. This suggests that significant improvements in the IRI model are required for estimating behavior during storms, particularly in low-latitude regions.

Specifying the equatorial ionosphere using CINDI on C/NOFS, COSMIC, and data interpolating empirical orthogonal functions

Data Interpolating Empirical Orthogonal Functions (DINEOFs) are a data‐based method for determining a few orthogonal basis functions that optimally reproduce a given data set. This technique is applied to meridional drift measurements performed by the Coupled Ion Neutral Dynamics Investigation (CINDI) onboard the Communication/Navigation Outage Forecasting System (C/NOFS) as well as electron density profiles derived from GPS Radio Occulations (RO) performed by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The low densities of the equatorial ionosphere spanning 2009–2010 restricted quality drift measurements by CINDI to altitudes near perigee, limiting the local time coverage of measurements. Full local time descriptions may be obtained as perigee moves through all local times though this requires a minimum 67 day season. To increase the data coverage of the ionosphere, CINDI data are supplemented with COSMIC GPS RO data. DINEOFs are applied to median meridional drift measurements as well as COSMIC measurements spanning 2009–2010 and are used to make a best estimate of the equatorial ionosphere at locations not observed. The scattered distribution of COSMIC profiles as well as the physical relationship between meridional ion drifts and the distribution of density with altitude improves the quality of the reconstructions compared to using CINDI alone. The DINEOF reconstructions demonstrate that the annual anomaly of reduced ionospheric densities in June compared to December measured by COSMIC is coincident with a change in the meridional ion drifts at the geomagnetic equator measured by CINDI.

Characteristics of global precipitable water in ENSO events revealed by COSMIC measurements

Precipitable water (PW) retrievals from FORMOSAT‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) measurements were analyzed and compared with those derived from Special Sensor Microwave/Imager (SSM/I) and Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR‐E) during the El Niño‐Southern Oscillation (ENSO) events from 2007 to 2011. For the three ENSO events in 2007–2011, monthly mean binned COSMIC PW results are in a very high correlation (up to 0.98) with those of SSM/I and AMSR‐E over the ocean, generally with root‐mean‐square differences less than 4 mm. PW retrievals from the three satellites are also of similar latitudinal variations. However, the PW is slightly underestimated by GPS RO, in particular, in the tropical regions. This underestimate may be caused partially by the fact that not all RO measurements can reach the surface. Inter‐satellite PW anomaly comparisons for the winter months in the ENSO events, with respect to those during the neutral (non‐ENSO) months, show consistent ENSO signals with major PW anomaly near the central Pacific in the warm event and near the Indonesian region and east of Australia in the two cold events. However, the 2007/2008 La Niña is somewhat less correlated for COSMIC with AMSR‐E and SSM/I. For the stronger 2010/2011 La Niña, their PW anomalies are in higher correlations of about 0.8.

Comparisons of tropopause derived from COSMIC measurements at Nanjing since August 2006

Tropopause temperature (Tt) and pressure (pt) at Nanjing are derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) from August 2006 to December 2011. We compareTtandptamong the COSMIC, radiosonde provided by the Earth System Research Laboratory (ESRL) and reanalysis data sets from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) Reanalysis (NNR) on 10-day, seasonal and annual timescales. Ten-day meanTt andptof the COSMIC data are higher than that of radiosonde by 0.2°C and 5.3hPa and reanalysis by 1.0°C and 17.5hPa, respectively. Results of multiple comparisons demonstrate a significant difference forptbetween the NNR and COSMIC data. Systematic biases are more significant in low-pressure level than in high-pressure level for reanalysis and radiosonde in terms of seasonal average differences. As for annual mean difference pressure, the COSMIC is higher than ESRL and NNR data by 3.4hPa–6.5hPa and 10hPa, respectively. Besides, the COSMIC and other two data sets are in the best agreement forTtandptwith maximum number of occultation events in 2008. Lastly, quasi-biennial period of correlation coefficients between the ESRL and NNR data sets from 2007 to 2011 requests further verification.

COSMIC observations of dayside total electron content enhancements in response to moderate disturbances in the solar wind

[1] We have analyzed measurements from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites acquired during an 81 day interval in late 2007 to study total electron content (TEC) responses of the dayside ionosphere during three consecutive passes of a high-speed stream (HSS) in the solar wind by Earth. During the second encounter the HSS arrival was closely preceded by the arrival at the first Lagrange point L1 of an interplanetary coronal mass ejection (ICME). In all cases the corotating interaction region (CIR) at the HSS's leading edge was characterized by increases in both nSW and TP above predisturbance levels, and large-amplitude oscillations in all interplanetary magnetic field (IMF) components. The solar wind events induced moderate magnetic storm activity; the minimum Dst of −71 nT occurred during the second encounter. TEC enhancements appeared at low-magnetic to midmagnetic latitudes during the ICME/CIR-driven storm. Some increases exceeded quiet time values by factors of ∼110%. In the absence of local auroral electron precipitation to create new plasma in the magnetic latitude domain of COSMIC measurements, the detected TEC increases must reflect transport effects. The COSMIC main phase observations of dayside TEC enhancement are explained as being caused by an ionospheric storm time “fountain” effect driven by weak (<1 mV/m) penetration electric fields. Our observations suggest that penetration dawn-to-dusk electric fields cause plasma to drift upward and toward higher latitudes. Plasma and field measurements from the Advanced Composition Explorer (ACE) allow estimates of penetration electric fields that we mapped to the ionosphere to calculate plasma transport velocities. We argue that observed TEC dynamics reflect the interplay between storm time transport and the production/loss histories of plasma parcels as they rotate around Earth.

Assessment of radiosonde temperature measurements in the upper troposphere and lower stratosphere using COSMIC radio occultation data

Temperature profiles derived from Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission are compared with those from four types of radiosonde systems from 12 to 25 km to assess the performance of these radiosonde systems in the upper troposphere and lower stratosphere. Results show that temperature measurements from the Vaisala‐RS92 and Shanghai radiosonde systems agree well with those of COSMIC with a close‐to‐zero mean difference. Large temperature biases are shown for the MRZ and VIZ‐B2 radiosonde systems relative to COSMIC, which are probably caused by diurnal radiative effects. In addition, we show that the temperature measurements from a new Chinese radiosonde system are improved compared to those of an older system through a comparison with COSMIC measurements.

Global temperature estimates in the troposphere and stratosphere: a validation study of COSMIC/FORMOSAT-3 measurements

Abstract. This paper mainly focuses on the validation of temperature estimates derived with the newly launched Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC)/Formosa Satellite 3 (FORMOSAT-3) system. The analysis is based on the radio occultation (RO) data samples collected during the first year observation from April 2006 to April 2007. For the validation, we have used the operational stratospheric analyses including the National Centers for Environmental Prediction - Reanalysis (NCEP), the Japanese 25-year Reanalysis (JRA-25), and the United Kingdom Met Office (MetO) data sets. Comparisons done in different formats reveal good agreement between the COSMIC and reanalysis outputs. Spatially, the largest deviations are noted in the polar latitudes, and height-wise, the tropical tropopause region noted the maximum differences (2–4 K). We found that among the three reanalysis data sets the NCEP data sets have the best resemblance with the COSMIC measurements.

Midlatitude nighttime enhancement in F region electron density from global COSMIC measurements under solar minimum winter condition

Ionospheric electron density profiles retrieved from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites measurements from 6 November 2006 to 5 February 2007 are used to study the ionospheric nighttime electron density enhancements under winter, solar minimum, and geomagnetically quiet conditions. In this work, the peak electron densities of F2 layer (NmF2) derived from COSMIC measurements are found to be in reasonably good agreement with ionosonde observations during the night. Therefore the morphology of nighttime enhancements is investigated at geomagnetic midlatitudes (MLAT 20–60°) in the northern hemisphere using COSMIC observations. The enhancements of electron density are evident near the F2 layer peak at most latitudes and longitudes; however, significant variations in the latitudinal dependence of the occurrence time and net magnitudes of the enhancements are found in different regions. The characteristics of enhancements in the North Atlantic Ocean sector are distinctly different from those in the eastern part of the North American sector and also from those at longitudes from Europe to Asia, in the Pacific Ocean, and in the western part of the North American sectors. The longitudinal variations of the morphology of the electron density enhancements during nighttime are possibly caused by different downward plasma flux, meridional winds, and electric field drifts under the effect of the geomagnetic field.