All systems on AIM are functioning nominally. Also, in order to mitigate the effects of the solar eclipse which occurred on October 23rd, AIM was transitioned to its backup attitude control mode (TMON/RTS Control) prior to the eclipse, and transitioned back to OOMP (the normal control mode) on the evening of October 24th.
The CIPS instrument continues to perform well, with no health issues. We are gearing up for the start of the Southern Hemisphere (SH) season, which should begin later in November or early December. We previously suggested that interhemispheric teleconnections triggered by planetary wave activity in the SH winter stratosphere led to a rapid decrease in PMCs in the Northern Hemisphere (NH) that began about 40 days from solstice (DFS). The PMCs recovered significantly after reaching a minimum near DFS 45, peaking near DFS 53; the season ended shortly thereafter. See the first figure below, which shows the daily PMC frequency at 80°N latitude for all NH PMC seasons observed by AIM; the red curve shows 2014.
Recent analyses suggest that the recovery around DFS 53 was caused by significant planetary wave activity in the NH summer mesopause region. To demonstrate this, the second plot is a Hovmöller plot, which shows mesopause temperatures at 83 km vs. longitude and time at 75°N (color contours) from the NASA Microwave Limb Sounder instrument. Note that time proceeds from top to bottom (15 July 2014 through 20 August 2014). Superimposed are dots wherever the CIPS PMC frequency exceeded 40%. The peak warming at 75°N occurred between 5 August and 10 August, and corresponded to very low CIPS cloud frequencies. When the atmosphere cooled down slightly after this, PMC frequencies increased in troughs of the 5-day planetary wave. In the second figure here, the wave is apparent from the diagonal bands of alternating warm and cold regions; note that the longitudes where PMC frequencies exceeded 40% in August all correspond to the cold wave troughs. This is consistent with the findings of Nielsen et al. , which showed that the PMC season could be prolonged by the presence of planetary waves. The 2014 data are exceptional in that the wave activity enabled the PMCs to recover after the early August decline, which otherwise would have led to the end of the season.
Reference: Nielsen, K., D. E. Siskind, S. D. Eckermann, K. W. Hoppel, L. Coy, J. P. McCormack, S. Benze, C. E. Randall, and M. E. Hervig (2010), Seasonal variation of the quasi 5 day planetary wave: Causes and consequences for polar mesospheric cloud variability in 2007, J. Geophys. Res., 115, D18111, doi:10.1029/2009JD012676.
Figure 1. CIPS PMC frequencies at 75°N latitude for all NH seasons observed by AIM.
Figure 2. Hovmöller contour plot of MLT temperature at 75°N, 83 km. Black dots indicate PMC frequencies that exceed 40%.
The SOFIE instrument continues to operate nominally, and is collecting high quality data on the state of the middle atmosphere. Observations of the Northern Hemisphere (NH) 2014 season are complete and relevant data files and figures are available on the SOFIE and AIM web pages. The recent 2014 PMC season was the warmest NH season to date, and consequently was associated with the lowest ice mass and ice occurrence frequencies. Part of this is likely due to a slight equator-ward progression of the SOFIE measurement latitudes (about 4 degrees) compared to previous years, but also may be due to a slight increase in solar activity during the 2014 summer. The SOFIE team has begun production of the latest data version (V1.3), and is in the process of validating the new data. The validation effort is comparing the results to the previous version (V1.2), and also redoing some of the comparisons of SOFIE to other measurements that were previously published. The V1.3 results indicate colder temperatures near the summer mesopause, compared to V1.3. This change is due to new signal drift corrections and to using SABER oxygen in the NLTE temperature retrievals. Once the team has vetted the new SOFIE V1.3 data it will be prepared for public release.