Upper Atmosphere Physics

This area considers the final stage of the Sun-Earth connection, concerned with the dynamical interactions between the thermosphere, which is directly influenced by space plasma processes, and the climate system below.  Over the past ten years we have identified a number of important mechanisms which couple these regions.  To allow us to make further progress on these complex, but strategically important issues, we have developed strong links with partners both within the UK and internationally to enable us to amplify our activity in this area.  Above the mesopause, solar-terrestrial phenomena can be readily observed to drive the neutral atoms and molecules.  However, much of the mesosphere is transport dominated – meaning that wave motions play a more significant role than radiative processes.  For example, the amplitudes of gravity waves propagating through the middle atmosphere grow as the density diminishes and ultimately break in the mesosphere.  The energy and momentum lost from the wave accelerates the background winds and so induces a global-scale torque which in turn drives a circulation from the summer hemisphere to the winter.  Hence the summer mesopause is the coldest part of the atmosphere.  Numerical models are an essential tool in our efforts to interpret the often conflicting observations that have sought to demonstrate the link between space plasma processes and climate.

At Leicester, Dr Arnold and Professor Robinson have pioneered the use of coupled middle/upper atmosphere models which include atmospheric planetary waves and gravity waves, as well as ionized phenomena in the upper atmosphere, to investigate solar/middle atmosphere relations.  Building on the insights gained by Dr Arnold spending ~2 years working with Professor Hines at Goddard Space Flight Center on parameterizations of atmospheric gravity waves, we have concluded that transport processes play an important role in enabling solar-driven changes in the upper atmosphere to impact on the middle atmosphere (especially during the Northern Hemisphere stratospheric winter months).

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