Spatiotemporal Dynamics of Fine Particulate Matter (PM2.5) over Different Locations of Andhra Pradesh, India Harikrishna Shanmugam Sridhar, Nulu Satya Manga Pushpa Latha Devi, Gouthu Uma, Auromeet Saha, Yen-Hsyang Chu, Potula Sree Brahmanandam Sustainability Switzerland, 2026 Most air pollution research in India has predominantly focused on the Indo-Gangetic Plain (IGP) owing to its high pollution levels and dense populations, leaving peninsular India comparatively undercharacterized. In contrast, South India remains underexplored because of its relatively limited long-term monitoring and more favorable meteorology. This geographical imbalance restricts a comprehensive national understanding of particulate matter (PM) dynamics. Addressing this gap, the present study delivers a multi-scale (hourly to interannual) spatiotemporal assessments of PM2.5 across eight monitoring stations in Andhra Pradesh, a South Indian State, for the period 2020–2024. The analysis reveals pronounced seasonal variability, with persistent winter and post-monsoon maxima. Although overall concentrations are low compared to northern India, urban–industrial centers such as Visakhapatnam and Rajahmahendravaram frequently exceeded both the National Ambient Air Quality Standards (NAAQS) and World Health Organization (WHO) guidelines. Notably, Amaravati, a non-industrial and low-lying inland site, exhibited anomalously moderate PM2.5 levels, with ~11.58% of hourly values surpassing 60 µg m−3. The COVID-19 lockdown period further offered a natural experiment, revealing substantial reductions (30–65%) in PM2.5 and PM10 at major urban sites while concurrent ozone enhancements (up to ~50%) at Tirupati and Rajahmundry exposed complex photochemical sensitivity under reduced NOx conditions. Satellite-based MERRA-2 estimates corroborated inter-annual variability and the short-lived improvement in air quality. This study demonstrates that air quality dynamics in the state of Andhra Pradesh are governed by region-specific meteorological controls, episodic processes, and localized emission characteristics, necessitating expanded long-term monitoring infrastructure and improved satellite–ground calibration frameworks.
FIRST-TIME OBSERVATIONS OF FINE PARTICLE MATTER (PM2.5) AT A RURAL SITE IN SOUTH INDIA – A CASE STUDY H. S. Sridhar, N.S.M.P. Latha Devi, G. Uma, A. Saha, P. S. Brahmanandam, et al. Proceedings on Engineering Sciences, 2024 For the first time, atmospheric fine particulate matter (PM2.5) concentrations were measured using a low-cost particulate sensor in Bhimavaram (16.55oN; 81.52oE; 17 m above MSL), a rural site and coastal station in the southern state of Andhra Pradesh, India. The study utilized preliminary data collected between April and May 2023. Throughout this period, PM2.5 concentrations exhibited notable temporal variations, with daily mean levels fluctuating between 5 and 60 μg/m3. Additionally, there were instances of hourly concentrations reaching as high as 100 μg/m3. The diurnal pattern of PM2.5 concentrations revealed a distinct morning peak, a mid-afternoon minimum, and a broad secondary peak in the late evening. The temporal and diurnal variations in PM2.5 concentrations are associated with the local sources (traffic, residential sources), local meteorology, and boundary-layer dynamics. This study provides valuable preliminary data on PM2.5 concentrations in Bhimavaram, highlighting the need for further research to understand the sources, dynamics, and health impacts of air pollution in rural locations.
Doppler Sodar Measured Winds and Sea Breeze Intrusions over Gadanki (13.5° N, 79.2° E), India Potula Sree Brahmanandam, G. Uma, K. Tarakeswara Rao, S. Sreedevi, N. S. M. P. Latha Devi, Yen-Hsyang Chu, Jayshree Das, K. Mahesh Babu, A. Narendra Babu, Subrata Kumar Das, V. Naveen Kumar, K. Srinivas Sustainability Switzerland, 2023 Doppler sodar measurements were made at the tropical Indian station, i.e., Gadanki (13.5° N, 79. 2° E). According to wind climatologies, the wind pattern changes from month to month. In July and August, the predominant wind direction during the monsoon season was the southwest. In September, it was the northwest and south. While the winds in November came from the northeast, they came from the northwest and southwest in October. The winds in December were out of the southeast. The diurnal cycle of winds at 60-m above the ground was visible, with disturbed wind directions in September and October. This may be connected to the Indian subcontinent’s southeastern monsoon recession. To better understand the monsoon circulation on a monthly basis, the present work is innovative in that it uses high-resolution winds measured using the Doppler sodar at the atmospheric boundary layer. The convergence of a sea breeze and the background wind might result in a sudden change in wind direction, and forecasting such a chaotic atmospheric event is crucial in the aviation sector. As a result, the wind shear that is produced may pose a serious threat to airplanes that are landing. In the current study, we present a few cases of sea breeze intrusions. The physics underlying these intrusions may help modelers better understand these chaotic wind structures and use them as inputs in their models. Based on surface-based atmospheric characteristics, there have been two reports of deep sea breeze intrusions that we report in this research. The sea breeze days were marked by substantial (moderate) drops in temperature (dewpoint temperatures) and increased wind speed and relative humidity. The India Meteorological Department (IMD) rainfall data showed a rise in precipitation over this location on 23 July (4.8 mm) and 24 July (9.5 mm) when sea breeze intrusions over Gadanki were noticed. Sea breeze intrusions could have brought precipitation (intrusion-laden precipitation) to this area due to conducive meteorological conditions. A simple schematic model is proposed through a diagrammatic illustration that explains how a sea breeze triggers precipitation over adjacent locations to the seacoast. The skew-T log-P diagrams have been drawn using the balloon-borne radiosonde measured atmospheric data over Chennai (a nearby location to Gadanki) to examine the thermodynamic parameters to gain insights into the underlying mechanisms and meteorological conditions during sea breeze intrusion events. It is found that the convective available potential energy (CAPE), which is presented as a thermos diagram, was associated with large values on 23 July and 24 July (898 J/kg and 1250 J/kg), which could have triggered thunderstorms over Chennai.
Ionospheric responses to the 21 August 2017 great American solar eclipse – A multi-instrument study G. Uma, P.S. Brahmanandam, V.K.D. Srinivasu, D.S.V.V.D. Prasad, V. Sai Gowtam, S. Tulasi Ram, Y.H Chu Advances in Space Research, 2020 Herein, we report on the ionospheric responses to a total solar eclipse that occurred on 21 August 2017 over the US region. Ground-based GPS total electron content (TEC) data along with ground-based measurements (Millstone Hill Observatory (MHO) and digital ionosondes) and space-based measurements (COSMIC radio occultation (RO) technique) allowed us to identify eclipse-associated ionospheric responses. TEC data at ~20°, ~30°, and ~40°N latitudes from the west to east longitudes show not only considerable depression but also wave-like characteristics in TEC both in the path of totality and away from it, exclusively on the day of eclipse. Interestingly, the observed depressions are associated with lesser (higher) magnitudes at stations over which the solar obscuration percentage was meager (significant), a clear indication of bow-wave-like features. The MHO observes a 30% reduction in F2-layer electron densities between 180 and 220 km on eclipse day. Ionosonde-scaled parameters over Boulder (40.4°N, 100°E) and Austin (30.4°N, 94.4°E) show a significant decrease in critical frequencies while an altitude elevation is seen in the virtual heights of the F-layer only during the eclipse day and that decreases are associated with wave-like signatures, which could be attributed to eclipse-generated waves. The estimated vertical electron density profile from the COSMIC RO-based technique shows a maximum depletion of 40%. Relatively intense and moderate depths of TEC depression, considerable reductions in the F2-layer electron densities measured by the MHO and COSMIC RO-measured densities at the F2-layer peak, and elevations in virtual heights and reduction in the critical frequencies measured by ionosondes during the eclipse day could be due to the eclipse-induced dynamical effects such as gravity waves (GWs) and their associated electro-dynamical effects (modification of ionospheric electric fields due to GWs).
A complete solar cycle (2006–2016) studies of scale heights derived using COSMIC radio occultation retrieved electron density profiles G. Uma, P.S. Brahmanandam, S. Tulasi Ram, K.-H. Wu, Y.H. Chu Journal of Atmospheric and Solar Terrestrial Physics, 2019 Various ionospheric vertical scale heights (VSH) including, the Chapman (Hm), VSH at upper ionosphere (VSHUP) and 500 km (VSH500) derived using COSMIC radio occultation (RO) retrieved electron density profiles during a complete solar cycle (2006–2016) are presented in this research. VSH show distinct latitudinal variations and solar-activity dependencies. VSH follow the geomagnetic equator with a longitudinal structure irrespective of the season and year, although mid and high latitudes show higher values and irregular variations in low (2006–2010) and moderate-to-high (2011–2016) sunspot years during the daytime hours (1300 LT-1500 LT). The longitudinal structure of VSH500 appears only in moderate-to-high sunspot years, which is an important observation reported for the first time in this communication. Diurnal variations of Hm at equatorial latitudes show higher values starting from ∼0400 LT to ∼2300 LT with a post-sunset peak. However, an absence of the post-sunset peak is seen in VSHUP and VSH500 which is probably due to the altitudinal gradients of vertical drifts that increase (decrease) below (above) the F-layer peak during evening pre-reversal enhancements. The reduced drifts above the F-layer peak thereby, suppresses the post-sunset peak in VSH. Concurrent and large-scale structures in VSH500 and VSHUP at mid and high latitudes in summer hemispheres during June and December solstice seasons are reported for the first time, which occurred possibly due to the long-duration exposure to the Sun's strong radiation during summer seasons. A one-to-one correlation exists between the Chapman scale heights and peak height of the F2 layer (hmF2) at equatorial latitudes in different seasons, while moderate correlation is seen between them away from the equatorial latitudes. These presented scale heights at a global scale are very significant, particularly, for future empirical modeling studies and the long-term availability of COSMIC RO retrieved electron density profiles allowed us to present these scale heights.
Daytime VHF amplitude scintillations recorded at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during 1997–2003 G. Uma, P.S. Brahmanandam, V.K.D. Srinivasu, D.S.V.V.D. Prasad, P.V.S. Rama Rao Advances in Space Research, 2018 In this research, it is presented the daytime amplitude scintillations recorded at VHF frequency (244 MHz) at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during seven continuous years (1997–2003). Contrary to the nighttime scintillation seasonal trends, the occurrence of daytime scintillations maximizes during summer followed by winter and the equinox seasons. The fade depths, scintillation indices and the patch durations of daytime scintillations are meager when compared with their nighttime counterparts. A co-located digital high frequency (HF) ionosonde radar confirms the presence of sporadic (Es) layers when daytime scintillations are observed. The presence of daytime scintillations is evident when the critical frequency of the Es-layer (foEs) is ≥4 MHz and Es-layers are characterized by a highly diffuse range spread Es echoes as can be seen on ionograms. It is surmised that the gradient drift instability (GDI) seems to be the possible mechanism for the generation of these daytime scintillations. It is quite likely that the spread Es-F-layer coupling is done through polarization electric fields (Ep) that develop inside the destabilized patches of sporadic E layers, which are mapped up to the F region along the field lines as to initiate the daytime scintillations through the GDI mechanism. Further, the presence of additional stratification of ionosphere F-layer, popularly known as the F3-layer, is observed on ionograms once the Es-layers and daytime scintillations are ceased.
Ionosphere VHF scintillations over Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a latitude Indian station – A case study P.S. Brahmanandam, G. Uma, T.K. Pant Advances in Space Research, 2017 This research reports the 250 MHz amplitude ionosphere scintillations recorded at Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a low-latitude station in India. Though amplitude scintillations were recorded for four continuous days (05–08 November 2011), the presence of intense and long-duration scintillations on 06 November 2011 instigated us to verify the ionosphere background conditions. This research, therefore, is also used important databases including, diurnal variations of h′F (virtual height of the F-layer) and the vertical drifts as measured by an advanced digital ionosonde radar located at an Indian equatorial station i.e. Trivandrum (Geographic Latitude 8.5°N, Geographic Longitude 77°E, Dip 0.5°N), equatorial Electrojet (EEJ) ground strength measured using magnetometers and the total electron content (TEC) maps provided by the International GPS Service (IGS) to study the background ionosphere conditions. The interesting observations are higher E × B drifts, the occurrence of long-duration range-type spread F signatures at Trivandrum and, thereafter, intense scintillations over Vaddeswaram. It was found a secondary peak at around 1600 LT in EEJ strength followed by a higher upward drift velocity (more than 60 m/s) with a significant raise of the F region up to 470 km over the magnetic equator on 06 November 2011. The possible physical mechanisms of these important observational results are discussed in the light of available literature.
Long-term morphological and power spectral studies of VHF amplitude scintillations recorded over Waltair (17.7°N, 83.3°E), India Vadlamuri Kanaka Durga Srinivasu, Potula Sree Brahmanandam, Gouthu Uma, Dasari S. V. V. D. Prasad, Paluri Venkata Satya Rama Rao, Shyamoli Mukherjee Terrestrial Atmospheric and Oceanic Sciences, 2017 This research reports on recently recorded 250 MHz amplitude scintillations at Waltair (17.7°N, 83.3°E), a low-latitude station in India, using the signals radiated from a geostationary satellite (FLEETSAT, 73°E) during a six-year period (2008 2013), which covers extremely low and higher solar activity years (2008 and 2013). The morphological features in terms of local time, month, and season during different geophysical conditions are presented. The scintillation patches (segregated based on their occurrence durations) have shown an increasing trend with the increasing sunspot activity. The scintillation patches with 30-min duration show increasing trends with increasing sunspot activity, and their occurrence frequencies also show increasing trends with increasing sunspot activity. The scintillation activity during disturbed epochs (Kp index lies between 3+ and 9) is found to be less compared to its quiet day counterparts. The plausible mechanisms for these observational results are discussed. In addition, power spectral characteristics, including Fresnel frequency, upper role of frequency and spectral slope of scintillations are calculated and the salient results are presented. Article history: Received 15 May 2016 Revised 24 October 2016 Accepted 8 November 2016
Seasonal and diurnal variations of Convective Available Potential Energy (CAPE) measured with COSMIC Radio Occultation (RO) retrieved data products during 2007- 2012-first results International Journal of Applied Engineering Research, 2014
A comparative study on ionospheric parameter (h’F) measured with ionosonde and predicted using IRI – 2007 model at Japanese longitudes during low solar activity years International Journal of Applied Engineering Research, 2013
