All systems on the AIM spacecraft continue to operate well and as expected. We completed the January CIPS Southern Hemisphere Flat Field observations on February 3 and transitioned back to autonomous spacecraft operations via the On Orbit Mission Planner or OOMP. The CIPS February Flat Field observations are planned for February 28 – March 3 and will be transmitted to the spacecraft once we have bitlock.
SOFIE continued to operate nominally until the AIM transition to Contingency Mode on January 4th. SOFIE returned to science data collection on January 7th. All status flags remain GREEN, and all engineering parameters are well within tolerance. The first PMC cloud of the 2010-2011 winter hemisphere PMC season was seen on December 7. We have finished analyzing the on-orbit data from the special calibration that performed full elevation scans across the solar disk. From this data, we were able to characterize the off axis wings for each FOV function and the relative angular offset between the SOFIE channels. We have implemented these calibration results together with several other improvements in preparation for the next software release. Another significant improvement is to the bending angle conditioning.
AIM is currently observing its eighth PMC season, with four seasons in the Northern Hemisphere (NH) and four in the Southern Hemisphere. The figures below summarize the SOFIE observations, showing time series of ice occurrence frequency, ice water content (IWC), mesopause temperature, and water vapor (at 0.0055 hPa pressure, roughly the height of maximum PMC brightness). NH seasons are generally characterized by longer duration, greater ice frequency, and lower year-to-year variability, than in the SH (Figures a-b). The notable exception is the SH 2009-10 season when PMCs appeared earlier than all other NH and SH seasons. The other extreme example is the SH 2010-2011 SH season when PMC appeared ~10 days later than in 2007-08 or 2008-09. The early onset of PMCs in the 2009-10 SH can be linked to colder temperatures and enhanced water vapor (Figures d and f), while the late appearance of PMCs in 2010-11 is associated with warm temperatures and low water vapor.
Investigations of SOFIE inter-hemispheric differences in PMCs and their environment are ongoing and a paper is in preparation. SOFIE results indicate that PMCs are more frequent and brighter in the north, differences that are attributed primarily to colder temperatures in the north because water vapor is similar in both hemispheres.
Investigations of meteoric smoke composition using SOFIE observations at three wavelengths suggest that smoke is consistent with olivine particles. The results indicate that the smoke composition may be different within the ablation zone (above 70 km altitude) than below, although this result is still under investigation.
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CIPS continues to operate nominally.
Like SOFIE, the CIPS measurements are showing intriguing interannual and hemispheric differences. It has long been thought that PMCs in the southern hemisphere (SH) occur less frequently than in the northern hemisphere (NH). That seems to be true for most times and latitudes that CIPS has observed thus far. But the SH 2009-2010 season was different: Relative to the summer solstice, this season started earlier than any other season observed by CIPS.
The figure below shows CIPS PMC frequencies vs. time (measured as days from solstice) and latitude for all AIM seasons. CIPS shows PMCs poleward of about 70°S by DFS -25 in the SH 2009-2010 season, earlier than in any other SH or NH season. In just the opposite sense, the current SH season was very slow to start: It was not until the solstice that we began regularly observing clouds; and the frequencies appear to be quite low compared to all other seasons. We are currently investigating the causes of these anomalies, and believe they are due to atmospheric phenomena in other regions of the atmosphere, both far below the clouds and even in the other hemisphere.