Abstract
Variation in solar irradiance is considered an important factor in natural climate forcing. Variations in the solar UV in particular are now regarded as a major source of decadal variability in the stratosphere, influencing surface climate through stratosphere-troposphere coupling.However, by analyzing meteorological re-analysis data we find that the magnitude of the solar controlled energetic particle forcing signal in stratospheric zonal mean zonal winds and polar temperatures is equivalent to those arising from solar irradiance variations during the Northern hemisphere polar winter months.We find that energetic particle forcing drives warmer polar upper stratospheric temperatures from early winter leading to an anomalously strong polar night jet via modulation of the vertical temperature gradient. By midwinter the stratosphere-troposphere coupling pathway becomes analogous to the solar UV impact at high latitudes. This not only highlights the importance of the energetic particle forcing contribution to stratospheric circulation, but enables us to understand the pathways responsible for the previously reported energetic particle forcing impacts on the troposphere in terms of the coupling of solar UV forcing to dynamics in the latter part of the winter.
Highlights
Understanding the role of the Sun and solar variability as a source of external forcing to the atmosphere has become increasingly important with the need to understand all factors, both natural and anthropogenic, contributing to the Earth’s climate
We present a mechanism of energetic particle forcing driving dynamical changes in the atmosphere that are as intense as those arising from the known solar irradiance variations
Our results show how these changes propagate through the stratosphere
Summary
Understanding the role of the Sun and solar variability as a source of external forcing to the atmosphere has become increasingly important with the need to understand all factors, both natural and anthropogenic, contributing to the Earth’s climate. The role of direct solar as well as solar activity controlled magnetospheric energetic particle forcing [4, 5] Forcing, this includes electrons of auroral to relativistic energies, i.e., tens of keV up to few MeV, as well as protons.), in the form of electron and proton precipitation into the atmosphere, has sparked interest due to it’s potential influence on stratospheric circulation [6,7,8,9,10,11]. The first idealized model study looking beyond stratospheric chemical changes arising from EPF [6] suggested that the impact on stratospheric and tropospheric temperatures, even on annual scales, might be comparable to those arising from solar UV variations between the solar maximum and solar minimum, but the physical mechanisms linking the EPF influence on chemical changes in the middle atmosphere www.frontiersin.org to stratospheric and tropospheric circulation and dynamics have remained elusive
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