Water vapor is the most dominant greenhouse gas in the atmosphere and plays a critical role in Earth’s energy budget and hydrological cycle. This study aims to characterize the long-term seasonal variation of relative humidity (RH), convective available potential energy (CAPE), and convective inhibition (CIN) from surface and radiosonde observations from 1980–2020. The results show that during the monsoon season, very high RH values are depicted while low values are depicted during the pre-monsoon season. West Coast stations represent large RH values compared to other stations throughout the year. Irrespective of the season, the coastal regions show higher RH values during monsoon season. Regardless of season, the coastal regions have higher RH values during the monsoon season. During the pre-monsoon season, the coastal region has high RH values, whereas other regions have high RH values during the monsoon season. The rate of increase in RH in North-West India is 5.4%, followed by the West Coast, Central, and Southern parts of India.. An increase in water vapor leads to raised temperature, which alters the instability conditions. In terms of seasonal variation, our findings show that CAPE follows a similar RH pattern. CAPE increases sharply in Central India and the West Coast region, while it declines in South India. Opposite features are observed in CIN with respect to CAPE variability over India. The results of the study provide additional evidence with respect to the role of RH as an influencing factor for an increase in CAPE over India.

The carrier phase (CP) measurements should be unambiguous to achieve the enhanced accuracy of Global Navigation Satellite System (GNSS) services. However, all the real-time CP measurements are manipulated by different errors, namely, satellite and receiver clock error, ionosphere delay, troposphere delay, integer ambiguity, etc. Even after removing or minimizing all these errors, the CP measurements are influenced by multipath error and receiver hardware residual or bias. In this research article, a double difference (DD) method is proposed to estimate residual or bias in CP observations of Navigation with Indian Constellation (NavIC). The proposed method abolishes all the common errors and provides bias. However, the CP measurement with a bit of bias value can be considered a high-quality signal. Here, we investigate the quality of NavIC satellites L5 (1176.45 MHz) signal with real-time measurements obtained through zero base length (ZBL) and short base length (SBL) experiments conducted at Kurnool (15.79 N, 78.07 E), India. The results show that the CP measurement bias of the L5 signal is within the range ±0.338 and ±1.688 m, respectively, for stationary and moving receivers. The bias was enhanced to 3.71 m for the SBL measurements. The results also demonstrate that the bias is low when carrier to noise (C/No) is high, and its range is nearly the same for all the days. This research would be helpful to estimate the bias that improves accuracy of precise point positioning (PPP) applications.

This paper investigates the diurnal variations of modelled and observed Vertical Total Electron Content (VTEC) over the African region (40oN to + 40oS, 25oW to 65oE) obtained from ground-based Global Navigation Satellite System (GNSS) receivers. The investigations on ionospheric response during the super geomagnetic storm time (17 March 2015) is very crucial, especially over African low latitudes. Hence, the performance of ionospheric models has been evaluated in this paper. The VTEC predictability by regional/global ionospheric models (AfriTEC, IRI-2016, IRI-Plas 2017, GIM-CODE and Nequick-G) is evaluated by using root mean square error (RMSE) method and percentage deviation by comparing the GPS/GNSS-VTEC obtained from 10 IGS (International GNSS Service) stations with the modelled-VTEC values over African region. It is observed that peculiarity in VTEC values is evident during the superstorm sudden commencement when compared to the pre and post-storm periods. Northern hemisphere stations data showed/revealed a twin peak in the diurnal VTEC patterns. The enhanced VTEC values were observed over all the 10 IGS stations on the storm day than on other quiet days. Moreover, during the post-storm days (18–20 March 2015), these VTEC values decreased more than on quiet days over the IGS stations in southern hemisphere (MBAR, MAYG, HARB, SBOK). On the other hand, during the post-storm days (18–20 March 2015), the VTEC values remained high over the geomagnetic northern hemisphere (NOT1, SFER, MAS1, CPVG, NKLG). It is worth mentioning that three northern IGS stations (NOT1, SFER and MAS1) displayed a VTEC increase record of approximately 75–90%, which is due to the extension of Equatorial Ionization Anomaly (EIA) during the geomagnetic storm whereas the other northern stations at EIA trough region (CPVG, BJCO, NKLG) registered a VTEC increment of 7%, 26% and 25% respectively. Southern IGS stations registered an enhancement in VTEC of about 5%. The VTEC maps from AfriTEC, IRI-2016 and Nequick-G were able to predict the feature of Equatorial Ionospheric Anomaly (EIA) at around 200N/150S. The GPS-VTEC values at IGS stations located on the geomagnetic EIA crests (in both northern and southern hemispheres) and in the trough (equatorial stations) are higher than those of the IGS stations situated at midlatitudes. AfriTEC, which is a regional model, recorded lowest RMSE values over all the stations. The prediction results show that the regional model performance is better than the global ionospheric models (IRI-2016 and Nequick-G models) especially over EIA latitudes of African region.