Abstract
Abstract. We utilise hydroxyl observations from the MLS/Aura satellite instrument to study the latitudinal extent of particle forcing in the northern polar region during the January 2005 solar proton event. MLS is the first satellite instrument to observe HOx changes during such an event. We also predict the hydroxyl changes with respect to the magnetic latitude by the Sodankylä Ion and Neutral Chemistry model, estimating the variable magnetic cutoff energies for protons using a parameterisation based on magnetosphere modelling and the planetary magnetic index Kp. In the middle and lower mesosphere, HOx species are good indicators of the changes in the atmosphere during solar proton events, because they respond rapidly to both increases and decreases in proton forcing. Also, atmospheric transport has a negligible effect on HOx because of its short chemical lifetime. The observations indicate the boundary of the proton forcing and a transition region, from none to the "full" effect, which ranges from about 57 to 64 degrees of magnetic latitude. When saturating the rigidity cutoff Kp at 6 in the model, as suggested by earlier studies using observations of cosmic radio noise absorption, the equatorward boundary of the transition region is offset by ≈2 degrees polewards compared with the data, thus the latitudinal extent of the proton forcing in the atmosphere is underestimated. However, the model predictions are in reasonable agreement with the MLS measurements when the Kp index is allowed to vary within its nominal range, i.e., from 1 to 9 in the cutoff calculation.
Highlights
Solar proton events (SPE) correspond to solar coronal mass ejections during which a large amount of protons and heavier ions are emitted (Reames, 1999), sometimes toward the Earth
In this paper we study the latitudinal extent of solar proton forcing in the middle atmosphere by satellite observations of the atmospheric effects caused by the SPE which occurred in January 2005
We have studied the latitudinal extent of the solar proton event which occurred in January 2005
Summary
Solar proton events (SPE) correspond to solar coronal mass ejections during which a large amount of protons and heavier ions are emitted (Reames, 1999), sometimes toward the Earth. It becomes necessary to consider the time-varying geomagnetic cutoff energy, which we calculate using a method described by Rodger et al (2006) This method uses particle tracing studies by Smart and Shea (2003), who calculated the cutoff energies at a given International Geomagnetic Reference Fields (IGRF) McIlwain Lparameter at 450 km altitude using the Kp-dependent Tsyganenko magnetospheric field model (Tsyganenko, 1989), but with two modifications: 1) the rigidity cutoff is made to vary as 15.062×L−2 as observed by the SAMPEX instrument and 2) the upper limit for Kp index in the rigidity model is Kp=6, i.e. the exceeding values are forced to Kp=6 in the calculations. On 19 January the cutoff transition region at 74 km is clearly wider in latitude than on 21 January when the transition between 64◦ N and 65◦ N is very sharp
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
