Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsa11a..03g&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SA11A-03
Physics
0342 Middle Atmosphere: Energy Deposition (3334), 3332 Mesospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342)
Scientific paper
The arctic stratosphere and mesosphere are dynamically altered throughout the winter months as wave activity and its interaction with the mean flow is a regular occurrence. An extreme interaction leads to polar vortex breakdown and a complete alteration in temperature from the lower stratosphere through the mesosphere. However, there are more regular occurrences where the dynamical interactions can alter just the upper stratosphere and mesosphere without modification to the lower stratosphere. We investigate these occurrences and their associated baroclinic conditions that can result in dramatic (50K) changes in upper stratosphere and mesosphere temperatures. Due to the flexible lower boundary, strong temperature gradients, and low air density, the circulation development of the arctic middle atmosphere is less well known than that below 30 km. Under certain conditions the wintertime polar vortex may become distorted and weakened, producing baroclinic conditions near the stratopause and into the lower mesosphere. Ageostrophic vertical circulations are enhanced during these times resulting in regions of adiabatic heating and cooling that further strenghten the baroclinic state . Events have been identified over the years where the stratopause warms by up to 50 K (and the mesosphere cooled by a similar magnitude) over nominal conditions. These heating/cooling events cannot be caused by advection and are based on the associated changing dynamical conditions. We propose that strong vertical circulation generates the required adiabatic heating and cooling. We have identified a number of these events over the past ten years in UKMO fields of the upper stratosphere and in middle atmosphere temperature measurements provided by the SABER instrument on the TIMED satellite. In order to determine the vertical circulations induced, we apply a technique used in tropospheric meteorology that requires only temperature and geopotential height fields known as the Q-vector analysis. The Q-vector allows us to qualitatively determine regions of ascending and descending air. The Q-vector analysis is well- suited to this region of the atmosphere as there are relatively few observational variables available. The UKMO assimilated data set provides the necessary fields up to approximately 2 hPa. Measurements from SABER/TIMED satellite instruments provide temperature measurements well into the mesosphere. Using these data sets, we identify these middle atmospheric baroclinic events and using Q-vector analysis show the vertical air motion induced.
Greer K. R.
Livingston John M.
Thayer Jeffrey P.
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