Search

Your search keyword '"Chapagain, N. P."' showing total 30 results
Start Over Author "Chapagain, N. P."
30 results on '"Chapagain, N. P."'

6. Influence of the rainfall and temperature oscillation on air quality in Kathmandu valley: The wavelet analysis.

Author

Gautam, S. P., Silwal, A., Baral, B., Subedi, S., Lamichhane, N., Chapagain, N. P., and Adhikari, B.

Subjects
WAVELETS (Mathematics), RAINFALL, AIR quality, ATMOSPHERIC temperature, AIR quality indexes, NEPAL Earthquake, 2015
Abstract

In this study, wavelet analysis and traditional cross-correlation analysis (TCA) have been employed to explore the temporal characteristics of the Air Quality Index (AQI) (PM2.5) and its relationships with meteorological factors, air temperature, and rainfall in the capital city of Nepal, Kathmandu, during 2017 - 2020. The temporal variation of monthly averaged (AQI) (PM2.5) revealed that the air quality was unhealthy in winter, improved in summer, and subsequently became unhealthy again in autumn and spring. We also noticed that the lowest AQI (PM2.5) was recorded in 2020, which is due to the COVID-19 pandemic lockdown. By analyzing the time-frequency relationship of (AQI) (PM2.5) with air temperature and rainfall, using Cross Wavelet Transform (XWT), we observed the interannual, seasonal, and monthly common periodicity between them. The coherency of XWT is then tested by using Wavelet Transform Coherence (WTC), which showed a negative correlation of AQI (PM2.5) with rainfall and air temperature, while an anomaly was seen among AQI (PM2.5) and temperature as they were positively associated for a few months in 2017, 2018, and 2020. Moreover, the results of cross-correlation and multiresolution analysis (MRA) are consistent with wavelet analysis, indicating the driving effect of air temperature and rainfall on (AQI) (PM2.5). [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

27. Airglow observations and modeling of F region depletion zonal velocities over Christmas Island

Author

Chapagain, N. P., Taylor, Michael J., Nielsen, K., Jarvis, M. J., and American Geophysical Union

Subjects
zonal velocities, F region depletion, Physics, Physical Sciences and Mathematics, modeling, airglow, Christmas Island
Abstract

We report image measurements of plasma depletions in the equatorial F region ionosphere over Christmas Island (2.1°N, 157.4°W; dip latitude 2.8°N) in the central Pacific Ocean. The observations were made during the equinox period, September‐October 1995, using a Utah State University CCD imaging system filtered to observe thermospheric O I (630.0 nm) airglow emissions centered at ∼280 km altitude. Well‐defined magnetic field‐aligned depletions were observed on 18 nights during the campaign, including strong postmidnight fossilized structures, enabling detailed measurements of their morphology and dynamics. The number of depletions was influenced by their initial onset times and their persistence. The separations between adjacent depletions ranged from ∼150 to ∼250 km in good agreement with prior observations from other sites. However, measurements of their eastward zonal drift speeds indicated normal behavior peaking around 90–100 m/s prior to local midnight, with exceptionally high velocities, ∼80 m/s during the postmidnight period that persisted until dawn. These results differ markedly from optical measurements at similar equatorial latitudes but at different longitude sectors, suggesting that the zonal drift velocities can have a significant longitudinal dependence. Model drift velocities calculated using a simple electric field model with winds defined by the horizontal wind model (HWM‐07) produced an eastward drift throughout the night, but their postmidnight magnitudes were much smaller than observed. Using a modified HWM‐07 wind field, a basic nighttime trend similar to the Christmas Island trend was successfully obtained.

Published
2011

28. Climatology of early night equatorial spread F over Jicamarca

Author

Chapagain, N. P. and Fejer, Bela G.

Subjects
early, night, spred F, Jicamarca, Physics, Physics::Space Physics, Astrophysics::Solar and Stellar Astrophysics, climatology, Astrophysics::Earth and Planetary Astrophysics, equatorial, Physics::Atmospheric and Oceanic Physics, equator
Abstract

[1] We use radar observations from 1996 to 2006 to study the climatology of postsunset equatorial 3-m spread F irregularities over Jicamarca during all seasons. We show that the spread F onset times do not change with solar flux and that their onset heights, which occur near the altitude of the evening F region velocity vortex, increase linearly from about 260 to 400 km from solar minimum to solar maximum. Higher onset heights generally lead to stronger radar echoes. During the equinox, spread F onset occurs near vertical drift evening reversal times, while during the December solstice, they occur near the drift reversal times close to solar minimum and near the time of the prereversal velocity peak for high solar flux conditions. On average, radar plume onset occurs earlier with increasing solar flux in all seasons. Plume onset and peak altitudes increase with solar activity, and the peak heights are generally highest during the equinox. The F region upward drift velocities that precede spread F onset increase from solar minimum to solar maximum and are approximately proportional to the maximum prereversal drift peak velocities.

Published
2009

Catalog

Books, media, physical & digital resources
See catalog results