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- Title
Variations in the peak electron density of the Venus ionosphere: some new insights using Akatsuki Radio Science measurements.
- Authors
Tripathi, K. R.; Ambili, K. M.; Choudhary, R. K.; Imamura, T.; Ando, H.
- Abstract
Radio occultation is simple yet an unique technique using which the altitude profiles of temperature, pressure, and electron density of a planetary medium are derived unambiguously. It relies on the principle that the phase of a radio signal, propagating from a satellite to the ground station, gets perturbed when it crosses through the planetary atmosphere or ionosphere [1]. This perturbation leads to changes in the frequency of radio signal which is known as atmospheric residual (atmospheric Doppler). By calculating Newtonian Doppler and subtracting from total Doppler we obtain atmospheric residual. Assuming that there is no abrupt changes in earth ionosphere in preceding a few minutes before occultation, basic parameters (temperature, pressure, neutral number density and electron density of ionosphere etc.) of planetary atmosphere are retrieved using standard procedures [2]. Since 2016, Radio Science (RS or radio occultation, RO) experiments are being carried out using Akatsuki satellite to study Venus atmosphere, and ionosphere [3]. As per MOU between ISRO, and JAXA, the RO measurements are being conducted at IDSN, Bangalore as well. Orbital geometry of this spacecraft provides rare opportunities to probe Venusian ionosphere-atmosphere in equatorial region with single X band (8410932002.0 Hz) radio signal. We used geometrical optics (GO) method to retrieve electron density profile of Ionosphere from raw data collected at IDSN, India and UDSC, Japan [2]. Fresnel zone for Xband signal in ionosphere limited the vertical resolution of electron density between 400-700 meter [3]. Retrieved electron density profiles show direct correlation with the solar zenith angle (SZA). As the SZA increases, the peak electron density of V2 layer (nmV2) decreases while the peak height of V2 layer (hmV2) increases. The peak electron density of V2 layer varies from 5*105/cc to 1*104/cc for corresponding changes in SZA from 0 to 90 degree (SZA 00 stand for Sun on overhead). For higher SZA (>1200), the ionosphere becomes too thin to get any discernible profile. The highlight of Akatsuki measurements are the electron density profiles from the low latitude ionospheric regions. There are about 18 profile for which the solar zenith angle is less than 850. All the profile was simulated using an in-house developed one-dimensional photo chemical model (1DPCM) [4]. We note that though the model is able to reproduce the height of the V2 layer in most of the cases, there are a few cases when model overestimates the peak density of V2 layer. We will discuss about reasons for such overestimates and also describe characteristic features of V2 layer of Venus ionosphere as observed by the Akatsuki Orbiter.
- Subjects
BENGALURU (India); ELECTRON density; ELECTRON distribution; INDIAN Space Research Organisation; IONOSPHERE; RADIO measurements; VENUSIAN atmosphere
- Publication
LPI Contribution, 2021, p1
- ISSN
0161-5297
- Publication type
Article