Electron density and Neutral Wind (ENWi) probe and/or Langmuir probe were flown on three different rocket flights from equatorial station Thumba (8.5°N, 77°E), during daytime, eclipse time, and post sunset time respectively, of low solar activity period, to study ionization irregularities in the E region of the ionosphere. The spectral characteristics observed using the payloads were analyzed during the three different rocket flights. The 15 January 2010 solar eclipse event and “SOUREX 1” wind and electron density measurements confirm the validity of the wind shear theory for equatorial regions during the eclipse and post sunset periods, when electrojet is weak, using wind and electron density irregularity measurements from the same instrument (ENWi) for the first time. The spectral indices in the range of −1.2 to −1.78 and the strong wind shear due to gravity wave winds during the eclipse time as well as the post sunset time, confirm the role of neutral turbulence in the generation of irregularities in the 95–112 km altitude region. The spectral index of −2.0 to −2.7 and the presence of irregularities in the negative gradient regions establishes the role of wind-driven gradient drift instability (GDI) in generating irregularities during the SOUREX 1 post sunset flight for altitudes below 93 km. Further, the role of gradient drift instability in triggering ionization irregularities during the daytime on 14 January 2010 is unraveled by the spectral index of −2.03 and the presence of irregularities in the positive gradient regions alone.

Key Points

In situ measurements of electron density and neutral wind as well as spectral analysis of irregularities
Role of neutral turbulence in irregularity generation above 95 km during eclipse time and post sunset time unraveled
Role of wind-driven gradient drift instability in post sunset irregularity generation below 93 km is deduced

Plain Language Summary

The spectral characteristics of ionospheric plasma irregularities were studied using rocket-borne in situ measurements of electron density and neutral winds. The Electron density and Neutral Wind probe and/or Langmuir probe were flown during different geophysical conditions from equatorial station, Thumba. The validity of the wind shear theory for equatorial region and the role of neutral turbulence in the generation of irregularities were verified by the electron density and neutral wind measurements during daytime for the 15 January 2010 solar eclipse event and post sunset time for the “SOUREX 1” experiment. The presence of irregularities in the positive electron density gradient regions alone and the spectral index value of −2.03 together confirm the role of gradient drift instability in the generation of daytime E region irregularities. The irregularities generated through wind-driven GDI during post sunset time is characterized by the spectral index of −2.0 to −2.7 and the irregularities were present in the negative electron density gradient regions.

Open Research

Data Availability Statement

The ENWi payload based electron density and neutral wind data and LP probe derived electron density data along with HF radar data is available at https://spl.gov.in/SPLv2/index.php/spl-metadata.html under the heading Upper Atmosphere/Ionosphere and sub-heading Data- Ionospheric irregularity spectra. The COSMIC data used for N_e calibration is available at URL: https://cdaac-www.cosmic.ucar.edu/.

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Volume128, Issue11

November 2023

e2023JA031653

On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

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On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

Abstract

Key Points

Plain Language Summary

Open Research

Data Availability Statement

References

References

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PUBLICATION INFO