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

Temperature Fusion of TIMED/SABER Data and COSMIC Data in Stratosphere

AbstractThe acquisition of accurate stratospheric temperature data is of great significance for the research on global climate system and numerical weather forecasting. To obtain high‐precision stratospheric temperature, the three‐dimensional variational assimilation method, combined with kriging interpolation, was applied for data fusion of the Thermosphere, Ionosphere, Mesosphere Energetics, and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature data and the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) radio occultation temperature data. As a sample, the two data sets of TIMED/SABER and COSMIC, during the time range from 5 December 2009, 09:00 to 5 December 2009, 15:00, were used to construct global stratospheric temperature field of 5 December 2009, 12:00. The cross‐validation results showed that temperature distribution from the variational fusion method was consistent with COSMIC observations at the height range of 15–35 km, which the mean deviations and standard deviations were within a range of −1 to 1 and 3 to 4 K, respectively. At the height range from 35 to 40 km, the temperature distribution from the variational fusion method was more consistent with TIMED/SABER observations. The mean deviations were within 0 and 0.5 K, and the standard deviations were between 1.8 and 2 K. Overall, the temperature field after variational fusion combines the high‐precision advantage of SABER observations around 40 km and the high‐precision advantage of COSMIC observations at the height range of 15–30 km, the effect of the variational fusion method is significant.

The parameters of internal gravity waves in the atmosphere from the amplitude fluctuations of radio occultation signals

We develop a method for the reconstruction of the statistical parameters of internal gravity wave (IGW) in the atmosphere from the amplitude fluctuations of signals acquired in radio occultation observations. We discuss the choice of the model of the IGW spatial spectrum, derive the relationships between the IGW spectra and the amplitude fluctuation spectra, develop the reconstruction algorithm and estimate its uncertainties. The IGW spectrum parameters to be retrieved are the outer (dominant) scale and the structure characteristic, the latter determining the power of saturated IGW. The method was tested on the COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) observations acquired in the winter and summer seasons 2011. The IGW parameters were reconstructed in the height range from the upper boundary of the tropopause to 28 km. We show the altitude-latitudinal distributions of the IGW parameters and two integral characteristics: the variances of the temperature fluctuations and the IGW potential energy. We perform a detailed comparison of our results with those obtained from radiosonde and radio occultation observations. The developed method can be applied for the global monitoring of IGW parameters and activity in the middle atmosphere.

Assessment of IRI-2016 hmF2 model options with digisonde, COSMIC and ISR observations for low and high solar flux conditions

The attempt of this work is to evaluate the three options (BSE-1979, AMTB-2013, SHU-2015) embedded in IRI-2016 for the F2 layer peak height (hmF2) estimation under low and high solar flux levels. We compare the model hmF2 with digisonde observations from Qaanaaq, Milllstone Hill, Ramey, Jicamarca and Port Stanley as well as Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data over the five stations spanning from northern hemisphere to southern hemisphere. In the case of Millstone Hill, we also use incoherent scatter radar (ISR) measurements. For the comparison with digisonde data, SHU-2015 is the most accurate option for reproducing hmF2 at low and middle latitude stations (Milllstone Hill, Ramey, Jicamarca) with the smallest Root-Mean-Square-Error and the highest correlation with observations. At high latitude (Qaanaaq and Port Stanley), BSE-1979 becomes the best option. This is true for both low and high solar flux conditions. Similar results are obtained for the comparison between ISR and IRI-2016 hmF2 model options over Millstone Hill, where SHU-2015 option has the smallest deviations from the observation data in both low and high solar activity conditions. As for the comparison with COSMIC data, SHU-2015 edges out the other two options under low solar activity level with better performance at three stations. There is no optimal option under high solar activity level, which is to our surprise, cause SHU-2015 was developed based on a large amount of radio occultation data. At Jicamarca, all options show dramatic deviations from COSMIC observations, showing even negative correlations. We propose that the performance of the three options do not vary much with solar condition, while they differ a lot with location, for example, latitude.

Assessment of IRI-2016 hmF2 model predictions with COSMIC observations over the African region

With significant advancement in the climatological nature of the International Reference Ionosphere (IRI) through a series of editions, the ionospheric community now focuses on possible improvements in the IRI Real-Time Assimilative Model (IRTAM) for describing the real-time weather conditions in the ionosphere. In line with the focuses of the global research community, the present study intends improving the critical ionospheric electron density height (hmF2) predictions in the latest version of the IRI model (IRI-2016) through a comparative analysis with the hmF2 derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric occultation profiles over the African region under various solar and geomagnetic conditions. As the existing operational ionosondes (only five in number) are not evenly distributed across the African region, the dense COSMIC soundings offer an excellent opportunity for assessing the IRI hmF2 model performance over the region. The study includes a comparative study of observed COSMIC hmF2 values with IRI-2016 predictions, almost covering the whole solar cycle (2007 to 2017). The comparison is based on statistical model validation metrics for datasets under various solar and geomagnetic conditions. The average performance of the IRI hmF2 model over Africa is similar during quiet geomagnetic conditions under both low and high solar activity periods. However, the average performance declines during disturbed geomagnetic conditions and for night-time values, while the best average performance is noticed in the daytime hmF2 predictions. The SHU-2015 model option in IRI-2016 manifests the least prediction error, best model efficiency, and correlation with the COSMIC hmF2 values, justifying the use of a large number of COSMIC profiles in the development of the SHU-2015 model. Finally, the study suggests the suitability of the SHU-2015 IRI hmF2 option over the African region when and where there are no or limited COSMIC profiles. Additionally, the research work suggests further improvements in the IRI hmF2 predictions, especially for night-time values over the African region.

Perturbations in Earth’s Atmosphere over An Indian Region during the Total Solar Eclipse on 22 July 2009

During a total solar eclipse (TSE) on 22 July 2009, atmospheric perturbations were monitored from the surface to thermosphere to understand TSE’s impact on the meteorological (temperature, relative humidity, wind speed, and wind direction) and chemical (O3 and NOx) parameters around Kadapa (14.28°N, 78.42°E), a tropical semi-arid region of India. For this purpose, an experiment was conducted at Yogi Vemana University Campus, Kadapa, India, to measure the temperature, wind speed, wind direction, and concentrations of ozone (O3), NO, NO2, and NOx by using the automatic weather station (AWS) and O3 analyzer. On the eclipse day (22 July 2009), the surface observations at Kadapa showed a reduction in temperature (about 1.1°C) because of the solar insulation. Comparison of the thermal, dynamical (wind), and chemical parameters on the TSE day with control days [preceding (21 July 2009) and succeeding (23 July 2009) the TSE] illustrated the influence of solar eclipse. During the eclipse period, the O3 mixing ratio decreased, while NO2 and NOx increased; however, NO remained unchanged. In addition, radio occultation (RO) temperature profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosat Satellite Mission (FORMOSAT-3) and Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) satellites were utilized to understand the impact of TSE on dynamics of the middle and upper atmosphere from tropopause to the thermosphere. High vertical resolution COSMIC observations revealed that during the solar eclipse, tropopause was cooler with twin peaks (double tropopause). The lower thermosphere between 110 and 130 km became warmer during the TSE, which might be caused by the dynamical response of the atmosphere in this region to the solar eclipse. The experimental data have provided very fine-scale variations of the atmospheric parameters both in time and height and also constituted a new set of results on TSE for further research.

The UT Variation of the Polar Ionosphere Based on COSMIC Observations

AbstractMean polar electron content (mPEC) is used to analyze the polar ionosphere in both the Antarctic and Arctic. The mPEC is calculated over the polar region covering geographic latitudes higher than 60° from the global distributed vertical total electron contents based on electron density profiles observed by Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). Using this parameter, the universal time (UT) variation of the polar ionosphere is quantitatively characterized. This UT variation exists an opposite phase (i.e., a 12‐hr phase difference) between them. The mPEC standard deviation (SD) in the Antarctic is larger in summer and autumn (being 1.37 and 0.78 TECu, respectively) and smaller in winter (0.29 TECu) and spring (0.61 TECu). The SD in the Arctic, however, is the largest in winter (0.14 TECu). In other seasons, the SD is less than 0.1 TECu. (being 0.07 TECu in spring, 0.05 TECu in summer, and 0.08 TECu in autumn, respectively). We use SD over the mean value to describe relative intensity of mPEC variations. This relative intensity is larger in winter for both Antarctic and Arctic regions. The UT variation in intensity is much stronger in the Antarctic than in the Arctic. These characteristics are attributed to the fact that the separation of the geomagnetic pole and geographic pole is dihedral and the angle is larger in the Antarctic. The larger angle causes more electrons transported into the polar region when the geomagnetic pole is on the dayside and fewer electrons transported into the polar region when the geomagnetic pole is on the nightside.

Effect of Cloud Fraction on Arctic Low-Level Temperature Inversions in AIRS Observations Over Both Land and Ocean

The low-level temperature inversions have significant impacts on Arctic climate change feedbacks. The Atmospheric Infrared Sounder (AIRS) can extract the inversions over both land and ocean, and it is, however, sensitive to the presence of clouds. In this paper, we evaluate the effect of cloud fraction (CF) on AIRS inversions over both land and ocean. First, the AIRS inversions under clear-sky conditions are compared with the results from the microwave-based Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations in 2007–2013. Results show that despite the COSMIC and AIRS inversions appearing to be deeper and stronger in winter than in autumn, spring, and summer, the former is generally shallower and stronger than the latter in all seasons over both land and ocean. Time-series analysis of the mean monthly inversions from COSMIC and AIRS observations in 2007–2013 under both clear-sky and cloudy conditions further indicates that their differences are systematic and can be effectively mitigated after calibration under all sky conditions. Taking the calibrated COSMIC inversions as references, the AIRS inversion depths can be estimated with a root mean square (rms) of less than about 86 and 135 m, and the AIRS inversion strength can be obtained with an rms of better than about 1.7 °C and 1.3 °C under cloudy conditions over land and ocean, respectively. Moreover, while the AIRS inversion depths are insensitive to CF variations over both land and ocean, the inversion strengths are more sensitive to the CF variations over land than ocean.

Pre-seismic ionospheric anomalies of the 2013 Mw = 7.7 Pakistan earthquake from GPS and COSMIC observations

The seismo-ionospheric anomalies may provide some insights about the earthquake. However, pre-seismic ionospheric anomalies are still challenging. In this paper, seismo-ionospheric anomalies are investigated before the September 24, 2013 (Mw = 7.7) Awaran (Pakistan) earthquake from GPS TEC (Total Electron Content) and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) data. The TEC data are showing anomalies on September 21, 2013. The abnormality detected in the temporal data is about 10 TECU beyond the 30-day running median. The percentage deviation of the TEC anomaly on September 21, is 30% above the upper confidence interval. The anomalies prevail 5° in Latitude and 10° in Longitude over the epicenter. The spatial and temporal data of TEC showed anomalies in TEC from UT = 08 to UT = 12. In addition, the enhancement on September 21, 2013 is also very significant in COSMIC data. The results of COSMIC completely agreed with GPS TEC anomalies on September 21, 2013. The percentage deviation of the peak plasma frequency on September 21 is 5% of the normal distribution. The storm indices are quiet before and after the earthquake. The pre-sesimic ionospheric anomalies are most probably associated with the 2013 Mw = 7.7 Awaran (Pakistan) earthquake.

First Results From the Ionospheric Extension of WACCM‐X During the Deep Solar Minimum Year of 2008

AbstractNew ionosphere and electrodynamics modules have been incorporated in the thermosphere and ionosphere eXtension of the Whole Atmosphere Community Climate Model (WACCM‐X), in order to self‐consistently simulate the coupled atmosphere‐ionosphere system. The first specified dynamics WACCM‐X v.2.0 results are compared with several data sets, and with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM), during the deep solar minimum year. Comparisons with Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite of temperature and zonal wind in the lower thermosphere show that WACCM‐X reproduces the seasonal variability of tides remarkably well, including the migrating diurnal and semidiurnal components and the nonmigrating diurnal eastward propagating zonal wavenumber 3 component. There is overall agreement between WACCM‐X, TIE‐GCM, and vertical drifts observed by the Communication/Navigation Outage Forecast System (C/NOFS) satellite over the magnetic equator, but apparent discrepancies also exist. Both model results are dominated by diurnal variations, while C/NOFS observed vertical plasma drifts exhibit strong temporal variations. The climatological features of ionospheric peak densities and heights (NmF2 and hmF2) from WACCM‐X are in general agreement with the results derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data, although the WACCM‐X predicted NmF2 values are smaller, and the equatorial ionization anomaly crests are closer to the magnetic equator compared to COSMIC and ionosonde observations. This may result from the excessive mixing in the lower thermosphere due to the gravity wave parameterization. These data‐model comparisons demonstrate that WACCM‐X can capture the dynamic behavior of the coupled atmosphere and ionosphere in a climatological sense.

Longitudinal variation in the ionosphere‐plasmasphere system at the minimum of solar and geomagnetic activity: Investigation of temporal and latitudinal dependences

AbstractWe use the Global Self‐consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) as the first‐principle calculation of the physical system state, the quick‐run ionospheric electron density model (NeQuick) as the climatology background, and the International Reference Ionosphere‐based Real‐Time Assimilative Model for a global view of the ionospheric weather during a quiet period of the December 2009 solstice. The model computations are compared to the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation profiles, CHAMP and Gravity Recovery and Climate Experiment in situ densities, and GPS total electron content (TEC). It is shown that the plasma density in the ionosphere is generally larger in the American/Atlantic longitudinal sector at any local time. The high‐latitude density enhancements are visible in the GSM TIP output at different altitudes but are not reproduced by the NeQuick empirical model. Given that observational data confirm an existence of the high‐latitude areas where ionospheric densities are elevated in the altitude range between 300 and 480 km, we conclude that the NmF2 maximum in the GSM TIP output can be trusted. Indeed, such high‐latitude NmF2, ionospheric electron content, and TEC maxima in the American longitude sector form on the proper places as shown by the GSM TIP data, COSMIC and GPS observations. According to our results, the high‐latitude maximum of NmF2 (1) manifests itself only when the integration over LT or UT of the global maps for 22 December 2009 includes nighttime, i.e., supporting an argument of its close association with the Weddell Sea Anomaly, and (2) also appears in the Ne distribution at altitudes above the F2 peak.

Remote sensing of tropospheric turbulence using GPS radio occultation

Abstract. Radio occultation (RO) measurements are sensitive to the small-scale irregularities in the atmosphere. In this study, we present a new technique to estimate tropospheric turbulence strength (namely, scintillation index) by analyzing RO amplitude fluctuations in impact parameter domain. GPS RO observations from the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites enabled us to calculate global maps of scintillation measures, revealing the seasonal, latitudinal, and longitudinal characteristics of the turbulent troposphere. Such information are both difficult and expensive to obtain especially over the oceans. To verify our approach, simulation experiments using the multiple phase screen (MPS) method were conducted. The results show that scintillation indices inferred from the MPS simulations are in good agreement with scintillation measures estimated from COSMIC observations.

Tropical tropopause layer cirrus and its relation to tropopause

This study examines the spatial and temporal patterns of tropical tropopause layer (TTL) cirrus clouds (i.e., clouds with bases higher than 14.5km) and their relationship to tropical tropopause including both cold point tropopause (CPT) and lapse rate tropopause (LRT). We use eight years (2006–2014) data from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) measurements. In addition to the CALIPSO cloud layer product, the clouds included in the current CALIPSO dataset as stratospheric features have been considered by separating clouds from aerosols, which are important in the TTL cloud analysis. It is also shown that the temporal variation of the stratospheric aerosols matches well with the volcanic eruption events. The TTL cloud fraction and the tropical tropopause temperature both have pronounced annual cycles and are strongly negatively correlated both temporally and spatially. The examination of the TTL cloud height relative to tropopause from collocated CALIPSO and COSMIC observations indicates that the tropopause plays a critical role in constraining the TTL cloud top height. We show that the probability density function of TTL cloud top height peaks just below the CPT while the occurrence of TTL clouds with cloud tops above the CPT could be largely explained by observed tropopause height uncertainty associated with the COSMIC vertical resolution.

Observational study of ionospheric irregularities and GPS scintillations associated with the 2012 tropical cyclone Tembin passing Hong Kong

AbstractThis study presents the ionospheric responses observed in Hong Kong to a Typhoon, namely, Tembin, from the aspects of the occurrence of ionospheric irregularities and scintillations, using Global Positioning System (GPS) observations from a ground‐based GPS scintillation monitoring station in Hong Kong and from GPS receivers on board the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. The ionospheric irregularities and scintillations are characterized by the rate of total electron content variation index (ROTI) and the amplitude scintillation index S4, respectively. The typhoon Tembin formed over the western North Pacific during 18–30 August 2012 and approached Hong Kong during 24–27 August 2012 with the closest distance 290 km from Hong Kong at around 17 universal time (UT) on 25 August 2012. The ground‐based observations indicate that in the nighttime period of 20:00–02:00 local time (LT = UT + 8 h) on 26 August when Tembin passed closely to Hong Kong, the ionospheric irregularities and scintillations of GPS signals were observed in the south of Hong Kong, over the area of 13°N ~ 23°N in latitude and 110°E ~ 120°E in longitude. From the COSMIC observations, it shows that the number of radio occultation scintillation events peaks on 26 August 2012 during the passage of Tembin. Without the presence of strong geomagnetic or solar activity, it is suspected that gravity waves might be generated in the lower atmosphere and likely seed the formation of ionospheric plasma irregularities. This work for the first time from Hong Kong observes the sign of coupling between the lower atmosphere and ionosphere in a tropical cyclone event, combining both ground‐ and space‐based GPS observation data.

Short‐term nonmigrating tide variability in the mesosphere, thermosphere, and ionosphere

AbstractThe intraseasonal variability of the eastward propagating nonmigrating diurnal tide with zonal wave number 3 (DE3) during 2007 in the mesosphere, ionosphere, and thermosphere is investigated using a whole atmosphere model reanalysis and satellite observations. The atmospheric reanalysis is based on implementation of data assimilation in the Whole Atmosphere Community Climate Model (WACCM) using the Data Assimilation Research Testbed (DART) ensemble Kalman filter. The tidal variability in the WACCM+DART reanalysis is compared to the observed variability in the mesosphere and lower thermosphere (MLT) based on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) observations, in the ionosphere based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations, and in the upper thermosphere (∼475 km) based on Gravity Recovery and Climate Experiment (GRACE) neutral density observations. To obtain the short‐term DE3 variability in the MLT and upper thermosphere, we apply the method of tidal deconvolution to the TIMED/SABER observations and consider the difference in the ascending and descending longitudinal wave number 4 structure in the GRACE observations. The results reveal that tidal amplitude changes of 5–10 K regularly occur on short timescales (∼10–20 days) in the MLT. Similar variability occurs in the WACCM+DART reanalysis and TIMED/SABER observations, demonstrating that the short‐term variability can be captured in whole atmosphere models that employ data assimilation and in observations by the technique of tidal deconvolution. The impact of the short‐term DE3 variability in the MLT on the ionosphere and thermosphere is also clearly evident in the COSMIC and GRACE observations. Analysis of the troposphere forcing in WACCM+DART and simulations of the Global Scale Wave Model (GSWM) show that the short‐term DE3 variability in the MLT is not related to a single source; rather, it is due to a combination of changes in troposphere forcing, zonal mean atmosphere, and wave‐wave interactions.

Impact of the semidiurnal lunar tide on the midlatitude thermospheric wind and ionosphere during sudden stratosphere warmings

AbstractVariability of the midlatitude ionosphere and thermosphere during the 2009 and 2013 sudden stratosphere warmings (SSWs) is investigated in the present study using a combination of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations and thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) simulations. Both the COSMIC observations and TIME‐GCM simulations reveal perturbations in the F region peak height (hmF2) at Southern Hemisphere midlatitudes during SSW time periods. The perturbations are ∼20–30 km, which corresponds to 10–20% variability of the background mean hmF2. The TIME‐GCM simulations and COSMIC observations of the hmF2 variability are in overall good agreement, and the simulations can thus be used to understand the physical processes responsible for the hmF2 variability. Through comparison of simulations with and without the migrating semidiurnal lunar tide (M2), we conclude that the midlatitude hmF2 variability is primarily driven by the propagation of the M2 into the thermosphere where it modulates the field‐aligned neutral winds, which in turn raise and lower the F region peak height. Though there are subtle differences, the consistency of the behavior between the 2009 and 2013 SSWs suggests that variability in the Southern Hemisphere midlatitude ionosphere and thermosphere is a consistent feature of the SSW impact on the upper atmosphere.

NmF2 enhancement during ionospheric F2 region nighttime: A statistical analysis based on COSMIC observations during the 2007–2009 solar minimum

AbstractIn this paper the global features of NmF2 enhancement occurring during ionospheric F2 region nighttime (the period when the sunlight is occulted by the Earth in the altitudinal range of ionospheric F2 region) and lasting for more than 2 h were investigated based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) measurements during the 2007–2009 solar minimum. This nighttime enhancement of NmF2 mainly appears at the latitudes with dips larger than 45° in the winter hemisphere in solstice seasons. The magnitude of NmF2 enhancement reaches latitudinal maxima (minima) at the geomagnetic latitudes of about 40°–50° (60°–70°), with larger magnitudes in the northern winter hemisphere than in the southern winter hemisphere. The longitudinal variation of nighttime enhancement is also evident; especially the magnitude of NmF2 enhancement shows a significant longitudinal modulation in the southern winter hemisphere. The controlling factors of the spatial variations of NmF2 nighttime enhancement were analyzed. The longitudinal variation of NmF2 nighttime enhancement is suggested to be related to the longitudinal differences in background NmF2, thermospheric density, and interhemispheric plasma transport, and the latitudinal variation of NmF2 nighttime enhancement is possibly related to the latitudinal variations of geomagnetic inclination and the plasma storage in the topside ionosphere and the plasmasphere. The configuration of the geomagnetic field plays an important role in the longitudinal and latitudinal variations of NmF2 nighttime enhancement.

Characteristics of tropopause‐penetrating convection determined by TRMM and COSMIC GPS radio occultation measurements

AbstractDistribution and influence of convection in the upper troposphere and lower stratosphere have been investigated case by case or on regional to global scale. However, previous studies were limited by using proxies for convection or the bias of the tropopause data. Here the tropopause‐penetrating convection is investigated based on the sole use of observational products from Tropical Rainfall Measuring Mission (TRMM) precipitation radar data and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). The result shows that the frequency of precipitation‐top heights above the monthly mean tropopause in the tropics is reduced logarithmically if the cold‐point tropopause is adopted instead of the lapse‐rate tropopause. Using the collocated COSMIC and precipitation radar observations, the tropopause‐penetrating convection, i.e., the convection with the precipitation‐top height above the lapse‐rate tropopause, can be found over the summer monsoon regions and some continental regions. The averaged relative precipitation‐top heights of tropopause‐penetrating convective clusters are about 0.2–0.5 km without significant land‐ocean difference, while equivalent radii of clusters are 2.7–3.5 km over land and 0.2–0.5 km larger than those over ocean. These areal and vertical extents are smaller than those reported by previous studies. Furthermore, the collocated temperature profiles show that the tropopause‐penetrating convection generates warming in the upper troposphere and cooling near the lapse‐rate tropopause and in the lower stratosphere. Moreover, the tropopause‐penetrating convection leads to a rapid (within 20 min) lift of the lapse‐rate tropopause by the adiabatic lofting within the convection (within a 10 km radius).

On the comparisons of tropical relative humidity in the lower and middle troposphere among COSMIC radio occultations and MERRA and ECMWF data sets

Abstract. 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.

Structure and origins of the Weddell Sea Anomaly from tidal and planetary wave signatures in FORMOSAT‐3/COSMIC observations and GAIA GCM simulations

AbstractThe Weddell Sea Anomaly (WSA) is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime. In this study, tidal decomposition is applied to FORMOSAT‐3 (Formosa Satellite)/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) total electron content (TEC) and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the WSA region. Our results present some of the first three‐dimensional spaceborne analyses of the WSA from a tidal perspective over multiple years. We find that the features of the WSA can be reconstructed as the result of superposition between the dominant diurnal standing (D0), eastward wave number 1 (DE1), westward wave number 2 (DW2), and stationary planetary wave 1 (SPW1) components in TECs, producing the characteristic midnight WSA peak. The D0, DE1, DW2, and SPW1 components are found to be an interannually recurring feature of the southern midlatitude to high‐latitude ionosphere during the summer, manifesting as enhancements in electron density around 300 km altitude of the summer middle to high magnetic latitudes. The phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent, suggesting in situ generation, rather than upward propagation from below. However, the SPW1 signature shows some signs of an eastward tilt with altitude, suggesting possible downward propagation. The relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) general circulation model (GCM), connecting the tidal interpretation of the WSA to previously examined generation mechanisms.

Observations and simulations of the ionospheric lunar tide: Seasonal variability

AbstractThe seasonal variability of the ionospheric lunar tide is investigated using a combination of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations and thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) simulations. The present study focuses on the seasonal variability of the lunar tide in the ionosphere and its potential connection to the occurrence of stratosphere sudden warmings (SSWs). COSMIC maximum F region electron density (NmF2) and total electron content observations reveal a primarily annual variation of the ionospheric lunar tide, with maximum amplitudes occurring at low latitudes during December–February. Simulations of the lunar tide climatology in TIME‐GCM display a similar annual variability as the COSMIC observations. This leads to the conclusion that the annual variability of the lunar tide in the ionosphere is not solely due to the occurrence of SSWs. Rather, the annual variability of the lunar tide in the ionosphere is generated by the seasonal variability of the lunar tide at E region altitudes. However, compared to the observations, the ionospheric lunar tide annual variability is weaker in the climatological simulations which is attributed to the occurrence of SSWs during the majority of the years included in the observations. Introducing a SSW into the TIME‐GCM simulation leads to an additional enhancement of the lunar tide during Northern Hemisphere winter, increasing the lunar tide annual variability and resulting in an annual variability that is more consistent with the observations. The occurrence of SSWs can therefore potentially bias lunar tide climatologies, and it is important to consider these effects in studies of the lunar tide in the atmosphere and ionosphere.