Measurement of thermospheric neutral wind and ion drift velocities by using chemical releases of Ba/Sr operated by CHI rocket experiment

Abstract:

A model of up-welling due to Joule heating of the ionospheric E layer in the cusp region causing atmospheric density enhancements above 400 km was suggested by Lühr et al. [2004]. In order to obtain the clue of the Joule heating, more quantitative measurements especially with small-scale electric field measurements are required. We observed neutral wind and ion drift with chemical release experiments of Ba/Sr using sounding rockets. In November 2014, Cusp Region Experiment 1 (C-REX-1) rocket was launched from Andøya Space Center, Norway, and released Ba/Sr from 10 out of 24 canisters, however, no signatures of the up-welling and small-scale electric field were observed at that experiment. In December 2019, Cusp Heating Investigation (CHI) rocket was launched from Svalbard Rocket Range, Norway, and released Ba/Sr from all 8 canisters. C-REX-2 was also planned at the same window of CHI, however, it was postponed due to the low magnetospheric activity and weather conditions.

In order to observe ion drift and neutral wind separately, we used cameras with specific band-pass filters for each observation. For the CHI and C-REX-2 observation, we newly developed 2 types of band-pass filters for ionized Ba (Ba⁺, 614.2 nm) and Sr (460.7 nm) with 6 nm bandwidth, with each wavelengths corresponding to the resonance scattering emission of Ba⁺/Sr, respectively. We successfully observed Ba⁺/Sr for about 30 minutes after the launch of CHI rocket from 2 ground observation sites in Svalbard: Longyearbyen and Ny-Ålesund.

A Ba⁺ image taken at Ny-Ålesund with a camera that equipped a 614.2 nm band-pass filter is shown in Figure 1. Figure 2 shows the path of the Ba⁺ clouds in the same filed of Figure 1. Assuming the release altitudes are nominal, and Ba⁺ clouds move only the horizontal direction in the thermosphere, the roughly estimated velocities of Ba⁺ are shown in Table 1 for each altitude. In addition, it is necessary to investigate the position of Ba⁺ clouds in the ionospheric convection in order to understand the meaning of ion drift velocity. In this paper, the results of ion drift and neutral wind velocities will be discussed.

References:
Lühr, H., M. Rother, W. Köhler, P. Ritter, L. Grunwaldt, Thermospheric up-welling in the cusp region: Evidence from CHAMP observations, Geophys. Res. Lett., 31, L06805, 2004.