An observational evidence of a unique plasma depletion event was captured by an O( 1 D) 630.0 nm airglow imager on 13 June 2018 over a transition region of geomagnetic low-mid latitude, Hanle, Leh Ladakh, India (32.77°N, 78.97°E; Mlat.~24. 1°N). The observed plasma depletion structures are tilted at an angle of 13°± 2°west of the geomagnetic north and drifted toward west. Collocated Global Navigation Satellite System-Total Electron Content measurements confirm that the structures are indeed associated with TEC depletions. Simultaneous ionosonde measurements from Delhi, India (28.70°N, 77.10°E; Mlat.~20.2°N) shows spread-F signatures confirming that these structures are associated with the ionospheric irregularities. Interestingly, radar observations over the geomagnetic low-latitude station Gadanki, India (13.5°N; 79.2°E; Mlat.~6.5°N) reveal the absence of equatorial plasma bubbles on this night. Therefore, these observations strongly suggest that the observed structures in the airglow images over Hanle are associated with mid-latitude spread-F (MSF). These MSF structures are possibly affected by the shear in the zonal plasma drift that forces the field aligned plasma irregularity structures to tilt toward west. These observations, for the first time, bring out the presence of MSF structures over geomagnetic low-mid latitude transition region. It is suggested that the plasma distribution over low latitudes plays an important role in the occurrence of MSF structures over this transition region. Understanding the source and characteristics of the plasma irregularity structures over this transition region can help in understanding the spatio-temporal evolution of global L-band scintillation in a better way.Plain Language Summary Understanding the spatio-temporal distribution of the ionospheric plasma irregularities is important in the operational forecasting of L-band scintillation and therefore has important ramifications in the satellite-based communication and navigation systems. Traditionally, plasma irregularities in the low and mid-latitudes had received focused attentions in the past with very less attention has been paid over the low to mid-latitude transition region. The present investigation provides an attempt toward that direction and proposes a mechanism on the relationship between the plasma distribution over low latitudes and the occurrence of the mid-latitude plasma irregularities over the geomagnetic low-mid latitude transition region. Comprehensive investigations are further needed in the future to understand and characterize the ionospheric plasma irregularity structures over this region.

With the increasing stress on water resources for a developing country like India, it is pertinent to understand the dominant streamflow patterns for effective planning and management activities. This study investigates the spatiotemporal characterization of streamflow of six unregulated catchments in India. Firstly, Mann Kendall (MK) and Changepoint analysis were carried out to detect the presence of trends and any abrupt changes in hydroclimatic variables in the chosen streamflows. To unravel the relationships between the temporal variability of streamflow and its association with precipitation and global climate indices, namely, Niño 3.4, IOD, PDO, and NAO, continuous wavelet transform is used. Cross-wavelet transform and wavelet coherence analysis was also used to capture the coherent and phase relationships between streamflow and climate indices. The continuous wavelet transforms of streamflow data revealed that intra-annual (0.5 years), annual (1 year), and inter-annual (2–4 year) oscillations are statistically significant. Furthermore, a better understanding of the in-phase relationship between the streamflow and precipitation at intra-annual and annual time scales were well-captured using wavelet coherence analysis compared to cross wavelet transform. Furthermore, our analysis also revealed that streamflow observed an in-phase relationship with IOD and NAO, whereas a lag correlation with Niño 3.4 and PDO indices at intra-annual, annual and interannual time scales.

This study evaluates the relationship between flow variability of unregulated and regulated streamflow stations and global climate indicators. Mann–Kendall and change-point analysis is applied to investigate the gradual and abrupt changes in streamflow data, followed by the investigation of multi-scale fluctuations in streamflow data using Continuous Wavelet Analysis. Linkages between streamflow and global climate indicators are examined using Cross-Wavelet and Wavelet Coherence Analysis. Results showed contrasting trend values for unregulated and regulated streamflow stations. Surprisingly, all unregulated stations experienced a significant abrupt shift in change point contrary to the regulated streamflow. Further, for unregulated stations, streamflow variability and hydroclimatic teleconnections were observed at a lower scale, indicating that variations in streamflow are more frequent and generally occur on an intra-annual to inter-annual scale. Contrary, regulated stations observed the streamflow variability and hydroclimatic teleconnections at a larger scale (8–10 years), indicating that all the fluctuations are smoothened out. Thus, unregulated stations cannot be used as a proxy for regulated stations in any given basin. Indeed, for better water resource planning and management, both regulated and unregulated streamflow should be investigated.

<p>With the increasing stress on water resources for a developing country like India, it is very much pertinent to study how the water resources are varying with time and investigate the dominant streamflow patterns for carrying effective planning and management activities. In this study, we attempt to investigate the spatiotemporal characterization of streamflow of six unregulated catchments in India and also quantify the impact of precipitation changes and four climate indices, namely, Niño 3.4, IOD, PDO and NAO on streamflow. Initial analysis of streamflow and precipitation was carried out using Mann Kendall and step change detection methods. Temporal variability of streamflow and its association with precipitation and climate indices was unraveled using continuous wavelet transform and Wavelet coherence respectively. Cross-wavelet transform was also used to capture the coherent relationships and phase relationships between streamflow and climate indices. The results of the study reveal an in-phase relationship between precipitation and streamflow. The analysis also considers that streamflow is mostly affected by Niño 3.4 and PDO indices. Based on the results of this work, better understanding of interrelationship between the streamflow and precipitation was well captured using Wavelet coherence when compared to Cross wavelet. It was observed that almost all basins had showed the effect of changes in precipitation on streamflow. Based on these observations, it is clear that WTC can be used for understanding interrelationship between variable when compared to XWT and gives better insights regarding the interrelationship</p>

<p>The interaction between the Sun and the Earth defines the space environment of the Earth. This interaction is complex and exhibits various time scales ranging from a  few seconds to years. The High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events are mainly the manifestations of the interactions of the corotating interaction regions (CIRs) with the terrestrial magnetosphere which continues for several days. The responses of two HILDCAA events are investigated by using solar wind observations at the L1 point, magnetospheric measurements at geosynchronous orbit, and changes in the global ionosphere. This study provides evidence of the existence of quasi-periodic oscillations (1.5-2hr) in the ionospheric electric field over low latitude, total electron content at high latitude, the magnetic field over the globe, energetic electron flux and magnetic field at geosynchronous orbit, geomagnetic indices (SYM-H, AE, and PC) and the Y-component of the interplanetary electric field (IEFy) during the HILDCAA events at all local times. Based on detailed wavelet and cross-spectrum analyses, it is shown that the periodic oscillations of 1.5-2hr in IEFy are the most effective one that controls the solar wind-magnetosphere-ionosphere coupling process during the  HILDCAA events for several days. Therefore, this investigation for the first time, shows that the  HILDCAA event affects the global magnetosphere-ionosphere system with a “resonant” mode of oscillation. These results are important not only to evaluate the solar wind-magnetosphere-ionosphere coupling process during the HILDCAA events but can also help to build up a forecasting strategy in the future.</p>