158-161Lunar oscillation in the ionospheric absorption for the frequency 2•4 MHz at Kokubunji has... more 158-161Lunar oscillation in the ionospheric absorption for the frequency 2•4 MHz at Kokubunji has been computed using the data for the period 1957-68. It has been found that the lunar tide in absorption at Kokubunji behaves in a way opposite to that of the tide at an equatorial station like Colombo. The phase of the tide during E-months shows a reversal compared to the other two seasons of the year. The amplitude of the tide increases with the increase of solar activity. The maximum amplitude of the lunar tide in absorption takes place at stations within 20ᵒ±5ᵒdip latitude
The National MST (mesosphere-stratosphere-troposphere) Radar Facility (NMRF) has been set-up at G... more The National MST (mesosphere-stratosphere-troposphere) Radar Facility (NMRF) has been set-up at Gadanki (13.5 degreesN, 79.2 degreesE) near Tirupati, with a primary objective to study the atmospheric dynamical phenomena in the height region between similar to 5 and 100 km. The technical capabilities of the radar are briefly mentioned. Mesospheric observations and preliminary results using the Indian MST radar are presented. It is seen that the mesospheric echoes of the radar signals arise from two distinct height regions of 67-70 km and 72-76 km, with the latter being predominantly present. The turbulence centres responsible for enhanced radar backscatter signals from the mesosphere grow and decay with time periods of a few tens of minutes and with the typical occurrence periods of similar to 1 h. The spectral width and signal-to-noise ratio (SNR) are in general directly correlated, except for certain echoes which are very sharp and with very high SNRs generated from very thin layer...
Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper a... more Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by CO2, which photo-dissociates into [O] that plays a significant role, invoking stronger O 2 in Martian ionosphere. Initial measurements from NGIMS instrument on MAVEN estimated these crossover altitude between ≈225 km to 240 km during solar maximum with peak solar illuminations. The primary photo-dissociative species CO2, crossover its neutral abundance with [O] in the heterogeneous atmosphere with varying local solar conditions. MENCA sampled the neutral atmospheric species, below the exobase upto periareion of ≈160 km, under low solar active conditions during June 2018. Observations of partial pressures of CO2 and [O] in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where [O]/CO2 remain unity, alongside influences from temperature. The multi-spacecraft measurements o...
An overview of the development of the Indian Space Programme is given as implemented by the India... more An overview of the development of the Indian Space Programme is given as implemented by the Indian Space Research Organization ISRO. This programme involves meteorological, communications, and scientific spacecrafts and payloads, as well as a complete Launcher and Rocket development programme.
Details of the coordinated rocket and MST radar campaign for mesospheric turbulence studies carri... more Details of the coordinated rocket and MST radar campaign for mesospheric turbulence studies carried out during July 19-27 2004 are presented One RH-300 MK II rocket instrumented with a Langmuir probe and spherical probe was launched from SHAR 13 7 N 80 2 E at 1142 h IST on July 23 2004 when strong mesospheric echoes were observed by the
Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper a... more Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by $CO_2$, which photo-dissociates into $[O]$ that plays a significant role, invoking stronger $O_2^+$ in Martian ionosphere. Initial measurements from NGIMS instrument on MAVEN estimated these crossover altitude between $\approx$225 km to 240 km during solar maximum with peak solar illuminations. The primary photo-dissociative species $CO_2$, crossover its neutral abundance with $[O]$ in the heterogeneous atmosphere with varying local solar conditions. MENCA sampled the neutral atmospheric species, below the exobase upto periareion of $\approx$160 km, under low solar active conditions during June 2018. Observations of partial pressures of $CO_2$ and $[O]$ in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where $[O]/CO_2$ remain unity, alongside influences from temperatur...
Global and regional annual mean temperature data have been analysed by many groups to determine t... more Global and regional annual mean temperature data have been analysed by many groups to determine the linear trends of temperature over climatological time scales. The near consistent results generally show an increase of about 0.07 {\deg}C per decade during the 20th Century. But many basic questions including spatial and temporal data gaps, non-uniform distribution of observing sites, superposition of internal/natural variations at different scales with parametric feedbacks etc., still remain unresolved. This paper mainly deals with a detailed study of the climatological variations of surface-air temperatures over the Indian region using a well-tested, verified, researched and gridded (1{\deg}x1{\deg}) daily mean temperature data set for the period 1970-2009. The annual mean temperatures estimated with different spatial integration show linear trends with an increase of about 0.4 {\deg}C during this period. A detailed error analysis of the voluminous data shows that the statistical e...
Proceedings of the Indian Academy of Sciences - Section A, 1972
ConclusionThe comparison of X-ray flares observed in satellites and their manifestation in the fi... more ConclusionThe comparison of X-ray flares observed in satellites and their manifestation in the field-strength records of 164 kHz radio waves received at Ahmedabad from Tashkent show that almost all the flares between 0200–1200 hr U.T. during the period 27 October to 3 November, 1968, were able to influence the signal intensity. The starting time and peak time of the X-ray flare and the sudden changes in 164 kHz radio signal agreed within a few minutes. The flare effect on the signal strength persists for a longer time than the flare itself.The effects of even small X-ray flares on 164 kHz field-strength can be seen at Ahmedabad and Poona whereas only bigger flares show up at Delhi often with a pronounced initial dip. This suggests that the distance between the transmitter and receiver plays an important role in the observable effects on LF propagation; the longer the distance, the better is the effect observed. The details of the X-ray flux variations during a flare and the associated changes in radio signal intensities (164 kHz) at Ahmedabad and Delhi are under further study.
158-161Lunar oscillation in the ionospheric absorption for the frequency 2•4 MHz at Kokubunji has... more 158-161Lunar oscillation in the ionospheric absorption for the frequency 2•4 MHz at Kokubunji has been computed using the data for the period 1957-68. It has been found that the lunar tide in absorption at Kokubunji behaves in a way opposite to that of the tide at an equatorial station like Colombo. The phase of the tide during E-months shows a reversal compared to the other two seasons of the year. The amplitude of the tide increases with the increase of solar activity. The maximum amplitude of the lunar tide in absorption takes place at stations within 20ᵒ±5ᵒdip latitude
The National MST (mesosphere-stratosphere-troposphere) Radar Facility (NMRF) has been set-up at G... more The National MST (mesosphere-stratosphere-troposphere) Radar Facility (NMRF) has been set-up at Gadanki (13.5 degreesN, 79.2 degreesE) near Tirupati, with a primary objective to study the atmospheric dynamical phenomena in the height region between similar to 5 and 100 km. The technical capabilities of the radar are briefly mentioned. Mesospheric observations and preliminary results using the Indian MST radar are presented. It is seen that the mesospheric echoes of the radar signals arise from two distinct height regions of 67-70 km and 72-76 km, with the latter being predominantly present. The turbulence centres responsible for enhanced radar backscatter signals from the mesosphere grow and decay with time periods of a few tens of minutes and with the typical occurrence periods of similar to 1 h. The spectral width and signal-to-noise ratio (SNR) are in general directly correlated, except for certain echoes which are very sharp and with very high SNRs generated from very thin layer...
Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper a... more Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by CO2, which photo-dissociates into [O] that plays a significant role, invoking stronger O 2 in Martian ionosphere. Initial measurements from NGIMS instrument on MAVEN estimated these crossover altitude between ≈225 km to 240 km during solar maximum with peak solar illuminations. The primary photo-dissociative species CO2, crossover its neutral abundance with [O] in the heterogeneous atmosphere with varying local solar conditions. MENCA sampled the neutral atmospheric species, below the exobase upto periareion of ≈160 km, under low solar active conditions during June 2018. Observations of partial pressures of CO2 and [O] in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where [O]/CO2 remain unity, alongside influences from temperature. The multi-spacecraft measurements o...
An overview of the development of the Indian Space Programme is given as implemented by the India... more An overview of the development of the Indian Space Programme is given as implemented by the Indian Space Research Organization ISRO. This programme involves meteorological, communications, and scientific spacecrafts and payloads, as well as a complete Launcher and Rocket development programme.
Details of the coordinated rocket and MST radar campaign for mesospheric turbulence studies carri... more Details of the coordinated rocket and MST radar campaign for mesospheric turbulence studies carried out during July 19-27 2004 are presented One RH-300 MK II rocket instrumented with a Langmuir probe and spherical probe was launched from SHAR 13 7 N 80 2 E at 1142 h IST on July 23 2004 when strong mesospheric echoes were observed by the
Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper a... more Mars Exospheric Neutral Composition Analyzer of Mars Orbiter Mission measures the neutral upper atmospheric constituents of Mars. Martian lower atmosphere predominated by $CO_2$, which photo-dissociates into $[O]$ that plays a significant role, invoking stronger $O_2^+$ in Martian ionosphere. Initial measurements from NGIMS instrument on MAVEN estimated these crossover altitude between $\approx$225 km to 240 km during solar maximum with peak solar illuminations. The primary photo-dissociative species $CO_2$, crossover its neutral abundance with $[O]$ in the heterogeneous atmosphere with varying local solar conditions. MENCA sampled the neutral atmospheric species, below the exobase upto periareion of $\approx$160 km, under low solar active conditions during June 2018. Observations of partial pressures of $CO_2$ and $[O]$ in subsequent orbits reveals that solar inputs are crucial in quantifying these crossing points, where $[O]/CO_2$ remain unity, alongside influences from temperatur...
Global and regional annual mean temperature data have been analysed by many groups to determine t... more Global and regional annual mean temperature data have been analysed by many groups to determine the linear trends of temperature over climatological time scales. The near consistent results generally show an increase of about 0.07 {\deg}C per decade during the 20th Century. But many basic questions including spatial and temporal data gaps, non-uniform distribution of observing sites, superposition of internal/natural variations at different scales with parametric feedbacks etc., still remain unresolved. This paper mainly deals with a detailed study of the climatological variations of surface-air temperatures over the Indian region using a well-tested, verified, researched and gridded (1{\deg}x1{\deg}) daily mean temperature data set for the period 1970-2009. The annual mean temperatures estimated with different spatial integration show linear trends with an increase of about 0.4 {\deg}C during this period. A detailed error analysis of the voluminous data shows that the statistical e...
Proceedings of the Indian Academy of Sciences - Section A, 1972
ConclusionThe comparison of X-ray flares observed in satellites and their manifestation in the fi... more ConclusionThe comparison of X-ray flares observed in satellites and their manifestation in the field-strength records of 164 kHz radio waves received at Ahmedabad from Tashkent show that almost all the flares between 0200–1200 hr U.T. during the period 27 October to 3 November, 1968, were able to influence the signal intensity. The starting time and peak time of the X-ray flare and the sudden changes in 164 kHz radio signal agreed within a few minutes. The flare effect on the signal strength persists for a longer time than the flare itself.The effects of even small X-ray flares on 164 kHz field-strength can be seen at Ahmedabad and Poona whereas only bigger flares show up at Delhi often with a pronounced initial dip. This suggests that the distance between the transmitter and receiver plays an important role in the observable effects on LF propagation; the longer the distance, the better is the effect observed. The details of the X-ray flux variations during a flare and the associated changes in radio signal intensities (164 kHz) at Ahmedabad and Delhi are under further study.
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Papers by Subhas Chakravarty