On the disappearance of noctilucent clouds during the January 2005 solar proton events

[1] A possible connection between the January 2005 solar proton events (SPEs) and the partial disappearance of Noctilucent clouds (NLCs) in the southern polar mesopause region is studied. Space-borne measurements of the NLC occurrence rate made with SCIAMACHY on Envisat as well as temperature measurements with MLS on Aura are employed. Immediately after the onset of the enhanced solar particle precipitation on January 16, 2005, we observe a severe decrease in the NLC occurrence rate. Between 70 degrees S-80 degrees S the NLC occurrence rate drops from about 80% to less than 20% within the period of enhanced solar proton fluxes. Throughout this period an anti-correlation between NLC occurrence rate and temperatures at NLC altitude is found, and the disappearance of NLCs is apparently caused by increasing temperatures. Potential mechanisms leading to the warming are discussed.