HAO Colloquium - Huixin Liu, Kyushu University

Thermospheric gravity wave activity in the bottomside F region and equatorial plasma bubbles

Equatorial plasma bubbles (EPBs) are plasma irregularities in the nightside equatorial ionosphere, which present a challenge for ionosphere modelling and serious problems for modern communication and global navigation. A long-standing mystery in EPBs formation is what seeds/initializes the instability that generates them. Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to be one likely candidate. But the characteristics of such GWs was rarely examined due to the lack of direct measurements of the neutral atmosphere at this height. 

In this talk, I will first present a systematic survey of the medium-scale (150~620 km) GWs at this critical altitude, utilizing in-situ measurements of neutral density and wind from the GOCE satellite. The analysis reveals pronounced features on GW’s global distribution and seasonal variability, which turn out to resemble those of EPBs in spatial distribution but not in seasonality. This may imply that GW is necessary to seed EPBs, but stronger GW activity does not always lead to more EPBs.  

Next, I will present some preliminary results from a numerical experiment that quantitively tests the role of GWs in seeding EPBs using a 3-D high-resolution bubble model (0.002°) (Yokoyama 2014). It shows that a vertical wind perturbation can generate EPBs in the absence of initial plasma perturbation, and shorter wavelength appears to be more effective. However, a quick survey of simultaneous observations of GWs and EPBs shows no clear difference in the GW wavelength between days with single bubble and those with multi-bubbles. These model-observation discrepancies make GW’s role in EPB generation remain inconclusive. The GOLD observation, with its neutral and plasma observations, may make a step forward on this issue, hopefully.

Date and time: 
Wednesday, March 20, 2019 - 2:00pm to 3:00pm