Impact of Very Large Solar Particle Events on the Mesosphere and Stratosphere

Solar Particles during certain Extreme Space Weather Events caused large impacts on the Earth's atmosphere. In particular, the protons during these Solar Particle Events (SPEs) penetrated deep into the atmosphere and caused direct changes in the mesosphere and stratosphere. The protons in extremely large SPEs occurring in 1972, 1989, 2000, 2001, and 2003 initiated long-lasting atmospheric changes. The highly energetic solar protons produced odd hydrogen (HOx: H, OH, HO2) and odd nitrogen (NOy: N, NO, NO2, NO3, N2O5, HNO3, HO2NO2, ClONO2, BrONO2). The short-lived HOx constituents led to brief (days) ozone decreases, whereas the long-lived NOy enhancements led to prolonged (months) ozone variations. The very large July 2000 SPE occurred fairly recently, is well-studied, and was the third largest in the past fifty years, when comparing NOy production. This SPE led to observations and computations of short-lived HOx-caused polar mesospheric ozone decreases >70% as well as calculations of long-lived NOy-caused polar upper stratospheric ozone decreases >20%. Curiously, our global model also simulated SPE-caused polar lower stratospheric ozone increases >10% in the Southern Hemisphere due to the July 2000 SPE. These impacts were due to interference by enhanced NOy constituents with the chlorine and bromine catalytic cycles for ozone, leading to a long-lived increase in ozone several months after the very large event. Other very large SPEs in 1972(August), 1989(August,October), 2000(November), 2001(September, November), and 2003(October,November) led to similar polar atmospheric effects. Polar total ozone depletions up to 3% were simulated in both hemispheres for extended periods of time (several months) as a result of the NOy enhancements due to the very large SPEs in 1972, 1989, 2000, 2001, and 2003. Although such changes are small and are not observable in the total ozone record, they need to be understood and quantified in order to calculate the magnitude of the ongoing anthropogenically-caused ozone changes due to chlorine and bromine.