Seasonal variation of the quasi 5 day planetary wave: Causes and consequences for polar mesospheric cloud variability in 2007

Abstract

We have investigated the 5 day wave in both temperature and water vapor in the stratosphere and mesosphere as seen in the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics High Altitude (NOGAPS‐ALPHA) analysis fields for summer 2007. We have compared these fields and the derived saturation ratios with polar mesospheric cloud (PMC) measurements from the AIM satellite. We find that the 5 day wave is variable in both time and space, with significant amplitudes in the temperature wave in August (up to ∼6 K). By contrast, the 5 day wave–induced water vapor anomalies remain at a near‐constant level throughout the season. During August, the 5 day wave in the NOGAPS‐ALPHA saturation ratio and in the occurrence of clouds in the AIM data shows a clear anticorrelation with bright PMCs forming in the trough of the temperature wave. The analysis shows that the August enhancement in the 5 day wave amplitude acts to extend the PMC season past the time when zonal mean temperatures are saturated with respect to ice. The increased wave amplitude in August is attributed to in situ wave generation and amplification due to baroclinic instability of mean winds at around 0.1–0.01 hPa. The late‐season extension of cloud occurrence due to the 5 day wave may explain previous ground‐based reports of bright noctilucent cloud displays in August.

Consequences of recent Southern Hemisphere winter variability on polar mesospheric clouds

“…greater than 150-155 K). This relationship is also particularly surprising since the NOGAPS-ALPHA analyzed temperatures and saturation were previously shown to be a good qualitative indicator of the occurrence of bright clouds seen by SOFIE in the troughs of the 5-day wave in late summer at higher latitudes (Nielsen et al, 2010).…”

Comparison of co‐located independent ground‐based middle atmospheric wind and temperature measurements with numerical weather prediction models

“…Compared to the observations, the variability at shorter time scales is lacking in both weather and climate models. While relatively small at 1 hPa, planetary wave activity is substantial in the mesosphere [Nielsen et al, 2010]. Underestimating the~5 day amplitude of upward propagating planetary waves in the models could explain part of the disagreements noted at upper levels (60-70 km).…”

Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

“…In the MLT they can reach large amplitudes and are important because they can modulate the amplitude of atmospheric tides (e.g., Teitelbaum and Vial, 1991;Mitchell et al, 1996;Palo et al, 1999;Pancheva et al, 2004), influence the transport and photochemistry of minor species (e.g., Kulikov, 2007), modulate the fluxes of gravitywave momentum that drives the planetary-scale circulation of the upper middle atmosphere (e.g., Forbes et al, 1991;Miyahara and Forbes, 1991;Thayaparan et al, 1995;Nakamura et al, 1997;Manson et al, 2003) and cause perturbations in temperatures that can modulate the occurrence of Polar Mesospheric Clouds (e.g., Espy and Witt, 1996;Merkel et al, 2003Merkel et al, , 2008Nielsen et al, 2010) and Polar Mesospheric Summer Echoes (e.g., Morris et al, 2009). A major component of the planetary-wave field in the MLT is the so-called normal modes that manifest as the 2-, 5-, 10-and 16-day planetary waves (e.g., Salby, 1981a,b).…”