This paper presents the Intertropical Convergence Zone (ITCZ) as the possible source mechanism of... more This paper presents the Intertropical Convergence Zone (ITCZ) as the possible source mechanism of the medium-scale traveling ionospheric disturbances (MSTIDs) propagating to the southeast direction over the South American region. Using the data collected by the GNSS dual-frequency receivers network from January 2014 to December 2019, detrended TEC maps were generated to identify and characterize 144 MSTIDs propagating southeastward over the South American low-latitude and equatorial region. We also used images from the Geostationary Operational Environmental Satellite (GOES) 13 and 16 in the infrared (IR) and water vapor (WV) channel, and reanalisys data from the National Centers for Environmental Prediction (NCEP) of the National Oceanic and Atmospheric Administration (NOAA) to study the daily features and seasonal migration of ITCZ. In the winter, when ITCZ migrates to the northern hemisphere around 10–15° N, 20 MSTIDs propagated southeastward. During summer, when the ITCZ lies wi...
Using COSMIC-2 and METOP radio occultation measurements during the years 2020 and 2021, the study... more Using COSMIC-2 and METOP radio occultation measurements during the years 2020 and 2021, the study presents the first direct and independent relationship between the potential energy (Ep) in the stratosphere, precipitable water vapour (PWV), tropopause heights, and cold-point heights over South America. The South American continent comprises the tropical region, the Andes Mountain range, and the mid-latitude climates. The seasonal mean of the potential energy (Ep), the PWV, and the tropopause parameters height (TPH and CPH) were obtained to investigate the relationship between the SGW Epand the tropospheric parameters (PWV, TPH, and CPH). Around the Andes Mountains to the east, there is significantly less water vapour (PWV < 10 mm) and relatively high gravity wave Ep(Ep>8 kJ kg− 1). A good correlation of variability was found between the PWV and the lower stratospheric gravity wave (SGW) Epin summer over the tropical region (± 20◦). Our result affirmed the possibility that conv...
Este projeto estudou as observacoes de longo prazo de ondas gravitacionais de media escala sobre ... more Este projeto estudou as observacoes de longo prazo de ondas gravitacionais de media escala sobre a regiao equatorial brasileira. Como parte deste objetivo, 11 anos (2000 a 2010) medicoes de imagens de todas as imagens celestes de ondas de gravidade mesosfericas foram feitas com sucesso a partir de Sao Joao do Cariri (7.40oS, 36.50oW) do equador magnetico. A observacao a longo prazo forneceu medicoes continuas das estruturas caracteristicas das ondas de gravidade em escala media a serem analisadas. A analise de Keograms foi utilizada para determinar os parâmetros de 537 ondas gravitacionais de media escala observadas na emissao OH a 87km de altitude. As caracteristicas foram estudadas, bem como a seansonalidade da direcao de propagacao da fase e a evolucao dos MSGWs segundo o ciclo solar . O comprimento de onda horizontal maximo, o periodo observado e a velocidade da fase foram concentrados entre 100 a 150km, 20 a 40m / se 60 a 80 minutos, respectivamente. A anisotropia total da dire...
Using data collected by the GNSS dual-frequency receivers network, de-trended TEC maps were gener... more Using data collected by the GNSS dual-frequency receivers network, de-trended TEC maps were generated to identify and characterize the medium-scale traveling ionospheric disturbances (MSTIDs) over the South American equatorial region (latitude: 0∘ to 15∘ S and longitude: 30∘ to 55∘ W) during solar cycle 24 (from January 2014 to December 2019). A total of 712 MSTIDs were observed during quiet geomagnetic conditions. The Frequency of occurrence of MSTID is high during the solar maximum and low in the minimum phase. This might be due to the solar cycle dependence of gravity wave activity in the lower atmosphere and gravity wave propagation conditions in the thermosphere. The predominant daytime MSTIDs, representing 80% of the total observations, occurred in winter (June-August season in the southern hemisphere) with the secondary peak in the equinox; while the evening time MSTIDs, representing 18% of the entire events, occurred in summer (December to February season) and equinox (March...
Large Scale Wave Structures (LSWS) in the equatorial ionospheric F‐region were observed by measur... more Large Scale Wave Structures (LSWS) in the equatorial ionospheric F‐region were observed by measuring spatial and temporal variations within detrended total electron content (dTEC) data obtained by ground‐based GNSS receivers over the South American continent. By using dTEC‐maps, we have been able to produce, for the first‐time, two‐dimensional representations of LSWS. During the period from September to December, the LSWS frequently occurred starting a few hours prior to Equatorial Plasma Bubble (EPB) development. From 17 events of LSWS observed in 2014 and 2015, wave characteristics were obtained: the observed wavelengths, periods, and the phase speeds are respectively, ~900 km, ~41 min and ~399 m/s; the waves propagated from the northeast to southeast. In some cases the front of the oscillation was meridionally aligned, extending to more than 1600 km, the first time such large extension of the wavefront has been reported. From F‐layer bottom height oscillation data, measured by ionosonde, LSWS exhibit two different vertical phase propagation modes, in‐phase and downward phase. The former mode indicates the presence of a polarization electric field in the F‐layer bottom side; the latter suggests propagation of atmospheric gravity waves. The presence of LSWS near the solar terminator, followed by the development of EPBs, suggests that the upwelling of the F‐layer bottom height produces a condition favorable to the development of Rayleigh–Taylor instability.
This paper presents the Intertropical Convergence Zone (ITCZ) as the possible source mechanism of... more This paper presents the Intertropical Convergence Zone (ITCZ) as the possible source mechanism of the medium-scale traveling ionospheric disturbances (MSTIDs) propagating to the southeast direction over the South American region. Using the data collected by the GNSS dual-frequency receivers network from January 2014 to December 2019, detrended TEC maps were generated to identify and characterize 144 MSTIDs propagating southeastward over the South American low-latitude and equatorial region. We also used images from the Geostationary Operational Environmental Satellite (GOES) 13 and 16 in the infrared (IR) and water vapor (WV) channel, and reanalisys data from the National Centers for Environmental Prediction (NCEP) of the National Oceanic and Atmospheric Administration (NOAA) to study the daily features and seasonal migration of ITCZ. In the winter, when ITCZ migrates to the northern hemisphere around 10–15° N, 20 MSTIDs propagated southeastward. During summer, when the ITCZ lies wi...
Using COSMIC-2 and METOP radio occultation measurements during the years 2020 and 2021, the study... more Using COSMIC-2 and METOP radio occultation measurements during the years 2020 and 2021, the study presents the first direct and independent relationship between the potential energy (Ep) in the stratosphere, precipitable water vapour (PWV), tropopause heights, and cold-point heights over South America. The South American continent comprises the tropical region, the Andes Mountain range, and the mid-latitude climates. The seasonal mean of the potential energy (Ep), the PWV, and the tropopause parameters height (TPH and CPH) were obtained to investigate the relationship between the SGW Epand the tropospheric parameters (PWV, TPH, and CPH). Around the Andes Mountains to the east, there is significantly less water vapour (PWV < 10 mm) and relatively high gravity wave Ep(Ep>8 kJ kg− 1). A good correlation of variability was found between the PWV and the lower stratospheric gravity wave (SGW) Epin summer over the tropical region (± 20◦). Our result affirmed the possibility that conv...
Este projeto estudou as observacoes de longo prazo de ondas gravitacionais de media escala sobre ... more Este projeto estudou as observacoes de longo prazo de ondas gravitacionais de media escala sobre a regiao equatorial brasileira. Como parte deste objetivo, 11 anos (2000 a 2010) medicoes de imagens de todas as imagens celestes de ondas de gravidade mesosfericas foram feitas com sucesso a partir de Sao Joao do Cariri (7.40oS, 36.50oW) do equador magnetico. A observacao a longo prazo forneceu medicoes continuas das estruturas caracteristicas das ondas de gravidade em escala media a serem analisadas. A analise de Keograms foi utilizada para determinar os parâmetros de 537 ondas gravitacionais de media escala observadas na emissao OH a 87km de altitude. As caracteristicas foram estudadas, bem como a seansonalidade da direcao de propagacao da fase e a evolucao dos MSGWs segundo o ciclo solar . O comprimento de onda horizontal maximo, o periodo observado e a velocidade da fase foram concentrados entre 100 a 150km, 20 a 40m / se 60 a 80 minutos, respectivamente. A anisotropia total da dire...
Using data collected by the GNSS dual-frequency receivers network, de-trended TEC maps were gener... more Using data collected by the GNSS dual-frequency receivers network, de-trended TEC maps were generated to identify and characterize the medium-scale traveling ionospheric disturbances (MSTIDs) over the South American equatorial region (latitude: 0∘ to 15∘ S and longitude: 30∘ to 55∘ W) during solar cycle 24 (from January 2014 to December 2019). A total of 712 MSTIDs were observed during quiet geomagnetic conditions. The Frequency of occurrence of MSTID is high during the solar maximum and low in the minimum phase. This might be due to the solar cycle dependence of gravity wave activity in the lower atmosphere and gravity wave propagation conditions in the thermosphere. The predominant daytime MSTIDs, representing 80% of the total observations, occurred in winter (June-August season in the southern hemisphere) with the secondary peak in the equinox; while the evening time MSTIDs, representing 18% of the entire events, occurred in summer (December to February season) and equinox (March...
Large Scale Wave Structures (LSWS) in the equatorial ionospheric F‐region were observed by measur... more Large Scale Wave Structures (LSWS) in the equatorial ionospheric F‐region were observed by measuring spatial and temporal variations within detrended total electron content (dTEC) data obtained by ground‐based GNSS receivers over the South American continent. By using dTEC‐maps, we have been able to produce, for the first‐time, two‐dimensional representations of LSWS. During the period from September to December, the LSWS frequently occurred starting a few hours prior to Equatorial Plasma Bubble (EPB) development. From 17 events of LSWS observed in 2014 and 2015, wave characteristics were obtained: the observed wavelengths, periods, and the phase speeds are respectively, ~900 km, ~41 min and ~399 m/s; the waves propagated from the northeast to southeast. In some cases the front of the oscillation was meridionally aligned, extending to more than 1600 km, the first time such large extension of the wavefront has been reported. From F‐layer bottom height oscillation data, measured by ionosonde, LSWS exhibit two different vertical phase propagation modes, in‐phase and downward phase. The former mode indicates the presence of a polarization electric field in the F‐layer bottom side; the latter suggests propagation of atmospheric gravity waves. The presence of LSWS near the solar terminator, followed by the development of EPBs, suggests that the upwelling of the F‐layer bottom height produces a condition favorable to the development of Rayleigh–Taylor instability.
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Papers by Patrick Essien