First observation of mesosphere response to the solar wind high‐speed streams

Abstract

We present a first analysis of 9 and 6.75 day periodic oscillations observed in the neutral mesospheric density in 2005 and 2006. Mesospheric densities near 90 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E; magnetic latitude, 74.6°S), Antarctica. Spectral analysis indicates that the pronounced periodicities of 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high‐speed streams and recurrent geomagnetic activity. Neutral mesospheric winds and temperatures, simultaneously measured by the Davis meteor radar, also exhibit 9 and 6.75 day periodicities. A Morlet wavelet analysis shows that the time evolution of the 9 and 6.75 day oscillations in the neutral mesosphere densities and winds are similar to those in the solar wind and in planetary magnetic activity index, Kp in 2005 and 2006. These results demonstrate a direct coupling between Sun's corona (upper atmosphere) and the Earth's mesosphere.

Estimation of Mesospheric Densities at Low Latitudes Using the Kunming Meteor Radar Together With SABER Temperatures

“…A harmonic fit of annual, semiannual, terannual, and quadrennial components for peak heights shows a maximum in midwinter (i.e., January) of approximately 90 km and minimum in midsummer (i.e., July) at around 88.6 km. The peak height can be used as a proxy for the height of a constant neutral atmospheric density surface (e.g., Clemesha & Batista, ; Lima et al, ; Liu et al, ; Stober et al, , ; Yi, Reid, Xue, Younger, Murphy, et al, ; Yi, Reid, Xue, Younger, Spargo, et al, ; Yi et al, ), and this will be discussed in below.…”

“…The results above show that the densities obtained from the KMMR and MSIS show similar annual variations; however, the KMMR densities exhibit more seasonal and intraseasonal variations than the MSIS model density. To determine whether KMMR‐derived densities are sufficiently reliable to study the climate and dynamics of the MLT region, we also compared KMMR densities with simultaneous observations of the meteor peak height by KMMR, which can be used to infer changes in neutral atmospheric density (e.g., Clemesha & Batista, ; Lima et al, ; Liu et al, ; Stober et al, , ; Yi, Reid, Xue, Younger, Murphy, et al, ; Yi, Reid, Xue, younger, Spargo, et al, ; Yi et al, ).…”

“…Recently, Yi, Reid, Xue, Younger, Murphy, et al () and Yi, Reid, Xue, Younger, Spargo, et al () reported the first observations of 6.75‐, 9‐, and 13.5‐day subharmonics of the solar rotational period (27 days) in neutral mesospheric density at 90 km. They estimated density using observations from the Davis meteor radar, Antarctica, and suggested these periodic variations were due to the modulation of periodic recurrent geomagnetic activity connected to corotating interaction regions in the solar wind high‐speed streams.…”

“…They estimated density using observations from the Davis meteor radar, Antarctica, and suggested these periodic variations were due to the modulation of periodic recurrent geomagnetic activity connected to corotating interaction regions in the solar wind high‐speed streams. These periodic variations of neutral mesospheric density caused by geomagnetic effects are relatively weak and may not be easily observed by satellite‐based instruments such as the Microwave Limb Sounder on the Aura satellite (see, Yi, Reid, Xue, Younger, Spargo, et al, ; Yi, Reid, Xue, Younger, Murphy, et al, ), but it appears that the meteor radar is more sensitive to these variations than the satellite measurements.…”

Comment on “First Observation of Mesosphere Response to the Solar Wind High‐Speed Streams” by W. Yi et al.

“…In response, Yi et al () have mentioned a Yi, Reid, Xue, Younger, Murphy, et al () paper which discussed a mechanism for the Yi, Reid, Xue, Younger, Spargo, et al () mesospheric effects. We agree with much of what Yi, Reid, Xue, Younger, Murphy, et al () have stated, but what is missing is that these are freshly injected ~10‐ to 100‐keV electrons into the magnetosphere (not trapped particles) and specifically ~20‐ to 50‐keV electron energies (not a “few kiloelectron volt to several megaelectron volt energies”).…”