Short- and medium-term atmospheric constituent effects of very large solar proton events

[摘要] Solar eruptions sometimes produce protons, which impact the Earth'satmosphere. These solar proton events (SPEs) generally last a few days andproduce high energy particles that precipitate into the Earth's atmosphere.The protons cause ionization and dissociation processes that ultimately leadto an enhancement of odd-hydrogen and odd-nitrogen in the polar cap regions(>60° geomagnetic latitude). We have used the Whole AtmosphereCommunity Climate Model (WACCM3) to study the atmospheric impact of SPEsover the period 1963–2005. The very largest SPEs were found to be the mostimportant and caused atmospheric effects that lasted several monthsafter the events. We present the short- and medium-term (days to a fewmonths) atmospheric influence of the four largest SPEs in the past 45 years(August 1972; October 1989; July 2000; and October–November 2003) ascomputed by WACCM3 and observed by satellite instruments. Polarmesospheric NO_x (NO+NO₂) increased by over 50 ppbvand mesospheric ozone decreased by over 30% during these very largeSPEs. Changes in HNO₃, N₂O₅, ClONO₂, HOCl,and ClO were indirectly caused by the very large SPEsin October–November 2003, were simulated by WACCM3, andpreviously measured by Envisat Michelson Interferometer for PassiveAtmospheric Sounding (MIPAS).WACCM3 output was also represented by sampling with theMIPAS averaging kernel for a more valid comparison.Although qualitatively similar,there are discrepancies between the model and measurement with WACCM3predicted HNO₃ and ClONO₂ enhancements being smaller than measuredand N₂O₅ enhancements being larger than measured.The HOCl enhancements were fairly similar in amounts and temporalvariation in WACCM3 and MIPAS.WACCM3 simulated ClO decreases below 50 km, whereas MIPASmainly observed increases, a very perplexing difference.Upper stratospheric and lower mesosphericNO_x increased by over 10 ppbv and was transported during polar nightdown to the middle stratosphere in several weeks past the SPE. The WACCM3simulations confirmed the SH HALOE observations of enhanced NO_xin September 2000 as a result of the July 2000 SPE and the NH SAGE IIobservations of enhanced NO₂ in March 1990 as a result ofthe October 1989 SPEs.

[学科分类] 大气科学