Tidally induced variations of polar mesospheric cloud altitudes and ice water content using a data assimilation system

Abstract

[1] A variety of spaceborne experiments have observed polar mesospheric clouds (PMC) since the late 20th century. Many of these experiments are on satellites in Sunsynchronous orbits and therefore allow observations only at fixed local times (LT). Temperature oscillations over the diurnal cycle are an important source of PMC variability. In order to quantify long-term natural or anthropogenic changes in PMCs, it is therefore essential to understand their variation over the diurnal cycle. To this end, we employ a prototype global numerical weather prediction system that assimilates satellite temperature and water vapor observations from the ground to ∼90 km altitude. We assemble the resulting 6 hourly high-altitude meteorological assimilation fields from June 2007 in both LT and latitude and use them to drive a one-dimensional PMC formation model with cosmic smoke serving as nucleation sites. We find that there is a migrating diurnal temperature tide at 69°N with a variation of ±4 K at 83 km, which controls the variation of PMC total ice water content (IWC) over the diurnal cycle. The calculated IWC is normalized to observations at 2300 LT by the Solar Occultation for Ice Experiment and allowed to vary with temperature over the diurnal cycle. We find that the IWC at 69°N has a single maximum between 0700 and 0800 LT and a minimum between 1900 and 2200 LT and varies by at least a factor of 5. The calculated variation of IWC with LT is substantially larger at 57°N, with a single prominent peak near 0500 LT.Citation: Stevens, M. H., et al. (2010), Tidally induced variations of polar mesospheric cloud altitudes and ice water content using a data assimilation system,

Quantitative relation between PMSE and ice mass density

“…The IWC at the 05:00-07:00 LT maximum in the daily cycle is higher than the minimum values in the afternoon-evening sector by a factor 4-10. The daily variation of ice mass densities in our proxy is consistent with the few available observations of diurnal variations in NLC and PMC occurrence rates, and with modelling results for IWC for the Northern Hemisphere (Stevens et al, 2010). In particular, the modelling results show similar maxima and minima in the mid-morning and evening sectors, respectively, and a factor 5-10 between minimum and maximum.…”

“…A recent study by Stevens et al (2010) has used assimilation of satellite temperature and water vapour observations into a global numerical model to determine the daily variation of conditions at the summer mesopause. This has been used to drive a microphysical model of PMC formation for the Northern Hemisphere summer of 2007, using IWC measured by SOFIE at 23:00 LT as a constraint to adjust the parameters of the microphysical modelling.…”

Simultaneous observations of a Mesospheric Inversion Layer and turbulence during the ECOMA-2010 rocket campaign

“…It shows measurements of zonal winds, meridional winds and temperatures in the top, middle and lower panels, respectively. These measurements reveal pronounced downward phase progression which is most probably associated with tides Hoffmann et al (2008); Stevens et al (2010); Hultgren et al (2011). Since lidar measurements are weather dependent and there was no luck to have long enough measurements for proper tidal analysis, we further consider wind measurements done by the Saura MF radar which is located close to the launch site (see Sect.…”

Solar and lunar tides in noctilucent clouds as determined by ground-based lidar

“…NLC variability during solar day was also investigated by models (e.g., Stevens et al, 2010Stevens et al, , 2017Schmidt et al, 2017). In general, maximum values for occurrence and brightness are found in the first half of the solar day, which is attributed to temperature tides and tidal variations in background water vapor.…”