Investigation of the variability of night‐time equatorial thermospheric winds over Nigeria, West Africa

2021 ◽  
Author(s):  
A. B Rabiu ◽  
D. I Okoh ◽  
Q Wu ◽  
O. S Bolaji ◽  
R. B Abdulrahim ◽  
...  
Keyword(s):  
West Africa ◽  
Night Time ◽  
Thermospheric Winds

scholarly journals Investigation of the variability of night-time equatorial thermospheric winds over Nigeria, West Africa

2020 ◽  
Author(s):  
Daniel Izuikedinachi Okoh ◽  
A. Babatunde Rabiu ◽  
Qian Wu ◽  
Bolaji O S ◽  
R. B. Abdulrahim ◽  
...  
Keyword(s):  
West Africa ◽  
Night Time ◽  
Thermospheric Winds

Temporal and Spatial Distribution of Savanna Fires in Senegal and the Gambia, West Africa, 1989-90, Derived From Multi-Temporal AVHRR Night Images

1992 ◽  
Vol 2 (1) ◽  
pp. 21 ◽  
Author(s):  
S Langaas
Keyword(s):  
West Africa ◽  
Satellite Image ◽  
Fire Detection ◽  
Fire Regimes ◽  
The Gambia ◽  
Time Data ◽  
Night Time ◽  
Temporal And Spatial Distribution ◽  
Seasonal Periodicity ◽  
Fire Activity

Quantitative data on fire regimes from the world's savannas have previously been difficult to obtain due to logistical and scientific reasons. This study addresses the issue for Senegal and The Gambia, West Africa. A bispectral satellite image based method for fire detection has recently been improved and made semi-automatic to provide information on fire regimes of savannas. The method uses thermal night time data from the Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atrnospheric Administration (NOAA) series of weather satellites. Twenty-six near cloud-free AVHRR images have been classified using this method. Though they constitute a small temporal sample, some features of the seasonal periodicity and spatial variations of the region are suggested. Variations in firectivity at the four daily NOAA satellite passing times were recorded from a small field survey in The Gambia, and compared to data from the satellite images. Established relationships between reiative fire activity and data from the various NOAA passes have been used to estimate the maximum daily fire activity at the afternoon passing time. The seasonal variations for the whole study area and regions within are suggested by the estimated maximum values at the twenty-two dates. The locations of fire events in relation to locations of human activities and fuel loadings are examined and a brief summary of the main factors that regulate burning and fire regimes is given.

Daytime F2-layer positive storm effect at middle and lower latitudes

1995 ◽  
Vol 13 (5) ◽  
pp. 532-540 ◽  
Author(s):  
A. V. Mikhailov ◽  
M. G. Skoblin ◽  
M. Förster
Keyword(s):  
Background Level ◽  
Gas Composition ◽  
Night Time ◽  
Model Calculations ◽  
Plasma Drift ◽  
Neutral Gas ◽  
Storm Effect ◽  
Thermospheric Winds ◽  
Time Sector ◽  
Composition Changes

Abstract. Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N2] absolute concentrations, while (N2/O)storm/(N2/O)quiet\\approx1 at F2-layer heights, are shown to contribute largely to the background NmF2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional NmF2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N2] concentrations.

scholarly journals Comparing high-latitude thermospheric winds from Fabry–Perot interferometer (FPI) and challenging mini-satellite payload (CHAMP) accelerometer measurements

2019 ◽  
Vol 37 (6) ◽  
pp. 1095-1120
Author(s):  
Anasuya Aruliah ◽  
Matthias Förster ◽  
Rosie Hood ◽  
Ian McWhirter ◽  
Eelco Doornbos
Keyword(s):  
High Latitude ◽  
Auroral Oval ◽  
Horizontal Wind ◽  
Night Time ◽  
Champ Satellite ◽  
Fabry Perot ◽  
University College London ◽  
Wind Velocities ◽  
Thermospheric Winds ◽  
The University

Abstract. It is generally assumed that horizontal wind velocities are independent of height above the F1 region (> 300 km) due to the large molecular viscosity of the upper thermosphere. This assumption is used to compare two completely different methods of thermospheric neutral wind observation, using two distinct locations in the high-latitude Northern Hemisphere. The measurements are from ground-based Fabry–Perot interferometers (FPI) and from in situ accelerometer measurements onboard the challenging mini-satellite payload (CHAMP) satellite, which was in a near-polar orbit. The University College London (UCL) Kiruna Esrange Optical Platform Site (KEOPS) FPI is located in the vicinity of the auroral oval at the ESRANGE site near Kiruna, Sweden (67.8∘ N, 20.4∘ E). The UCL Longyearbyen FPI is a polar cap site, located at the Kjell Henriksen Observatory on Svalbard (78.1∘ N, 16.0∘ E). The comparison is carried out in a statistical sense, comparing a longer time series obtained during night-time hours in the winter months (DOY 300–65) with overflights of the CHAMP satellite between 2001 and 2007 over the observational sites, within ±2∘ latitude (±230 km horizontal range). The FPI is assumed to measure the line-of-sight winds at a height of ∼240 km, i.e. the peak emission height of the atomic oxygen 630.0 nm emission. The cross-track winds are derived from state-of-the-art precision accelerometer measurements at altitudes between ∼450 km (in 2001) and ∼350 km (in 2007), i.e. 100–200 km above the FPI wind observations. We show that CHAMP wind values at high latitudes are typically 1.5 to 2 times larger than FPI winds. In addition to testing the consistency of the different measurement approaches, the study aims to clarify the effects of viscosity on the height dependence of thermospheric winds.

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