SUN and EARTH
The Sun, together with the Earth’s motion along its orbit, govern changes in the
solar–terrestrial environment on time scales ranging from minutes to glacial cycles.
The Sun continuously provides solar radiation to the Earth, and there is
considerable variation in the spectral density. This radiation is sporadically modified
by flare events that affect the magnetosphere, thermosphere, and ionosphere. The
quasi-steady flow of the solar wind is also modified by coronal mass ejections, which
accelerate energetic particles and cause geomagnetic storms during subsequent
impacts on Earth. The energetic particle precipitation leads to the modification of the
ionosphere and neutral atmosphere. In addition, galactic cosmic rays also impinge
into Earth’s environment. Observations have suggested that energetic particle forcing
may affect wave propagation, zonal mean temperatures, and zonal winds in the
Northern Hemisphere winter stratosphere.
However, the mechanisms by which these changes occur are still not known.
As changes in the Earth’s atmosphere occur, whether due to changes in solar forcing
or in response to enhanced anthropogenic activity and increased greenhouse gas
concentrations, the energy balance of the Earth’s atmosphere is altered and this
affects its dynamics. Specifically, changes can occur in the propagation of
atmospheric gravity waves, planetary waves, and tides, which play important roles in
driving the general circulation of the middle atmosphere.
