| Understanding the Earth’s climate system and how it responds to changes is one of the largest
challenges faced by society. Being able to understand past climate and to better predict how
the Earth’s climate will change in the future requires good understanding of both natural and
anthropogenic sources of climate forcing. In addition to solar irradiance, energetic particle
forcing from the Sun can have a significant impact on the atmosphere, with the effect
being focused on the polar regions. This presentation will focus on this type of solar
forcing and discuss the influence of energetic particle precipitation (EPP) on the polar
atmosphere.
During solar storms the level of particle precipitation into the atmosphere can increase by
several orders of magnitude, and some level of EPP is nearly continuously present. In the
atmosphere EPP causes ionisation in the middle atmosphere (20-100 km). This effect is
confined to polar regions, where particles are guided by the geomagnetic field. In the
atmosphere enhanced ionisation leads to increased production of NOx and HOx. These are
gases, which participate in catalytic ozone destruction. HOx has a short-lived effect on
the atmosphere; NOx on the other hand is mainly destroyed by photodissociation.
Hence during polar winter, when little or no sunlight is present, NOx impact on the
atmosphere can be long lasting. For example, following a series of solar storms
in 2003, a 60% ozone depletion in the Arctic upper stratosphere was observed a
month after the storms. Consequently, the EPP effect on the atmosphere has the
potential to be long lasting (months to years). Dynamical coupling mechanisms
between atmospheric layers can further provide coupling between this form of
space weather and lower atmosphere and thus have indirect implications to polar
climate.
Recently, the analysis of meteorological data and chemistry-climate model
results have indicated that during the winter season polar surface temperatures show
variability depending on the level of NOx produced by EPP. Understanding this link
between particle forcing from the Sun and climate requires a close examination
of the dynamical and chemical coupling mechanisms connecting particle forcing
driven changes in the atmosphere to changes in climate variables. In addition, the
characteristics of EPP, particularly the energy spectrum and precipitation fluxes of
electrons, crucial in determining the initial impact on atmosphere, are not well known. |