Irina A. Mironova

Cosmic ray induced ionization model CRAC:CRII: An extension to the upper atmosphere

[1] A new version of the CRAC:CRII model computing ionization induced by cosmic rays in the atmosphere is presented, which is extended to the upper atmosphere and can be now applied to the entire atmosphere. The model is able to compute the ionization rate in the atmosphere at any given location and time provided the energy spectrum of incoming cosmic rays is known. It is discussed that the use of earlier models, either analytical or Monte Carlo, with the limited upper energy of 500 MeV, is well validated for the upper atmosphere (above a few g/cm 2 atmospheric depth, which corresponds to the altitude about 40 km) to study the effect of solar energetic particles but may lead to a significant underestimate of the background ionization due to galactic cosmic rays. The use of a full model accounting for the atmospheric cascade and full energy range of incoming cosmic rays, rather than earlier simplified models, is recommended to study the ionization effects of galactic cosmic rays in the upper atmosphere. On the other hand, transient strong effects of solar energetic particle events can be studied using truncated models.

What is the solar influence on climate? Overview of activities during CAWSES-II

This paper presents an overview of the main advances in the Key Questions identified by the Task Group ‘What is the Solar Influence on Climate’ by the SCOSTEP CAWSES-II science program. We go through different aspects of solar forcing from solar irradiance, including total solar irradiance (TSI) and solar spectral irradiance (SSI), to energetic particle forcing, including energetic particle precipitation (EPP) and cosmic rays (CR). Besides discussing the main advances in the timeframe 2009 to 2013, we also illustrate the proposed mechanism for climate variability for the different solar variability sources listed above. The key questions are as follows: What is the importance of spectral variations to solar influences on climate? What is the effect of energetic particle forcing on the whole atmosphere and what are the implications for climate? How well do models reproduce and predict solar irradiance and energetic particle influences on the atmosphere and climate?

Variations of aerosol optical properties during the extreme solar event in January 2005

[1] We present the results of analysis of the aerosol optical depth variations for January 2005 when an extreme solar energetic particle event occurred leading to a greatly enhanced flux of energetic particles penetrating into the atmosphere. An increase of the concentration of sulfate or nitrate aerosol was found on the second day after the solar energetic particle event in the south magnetic pole region with the maximum penetration of anisotropic solar cosmic rays. This suggests that an enhanced flux of solar energetic particles can lead to notable changes in the chemical and physical properties of the polar troposphere. A statistical test confirms that the observed change of the aerosol index is significant and is unlikely to be related to a spatial or temporal independent fluctuation of the aerosol content. Thus, the results of the present work provide evidence of a direct influence of cosmic rays on physical-chemical properties of the atmosphere. Citation: Mironova, I. A., L.

Possible effect of strong solar energetic particle events on polar stratospheric aerosol: a summary of observational results

This letter presents a summary of a phenomenological study of the response of the polar stratosphere to strong solar energetic particle (SEP) events corresponding to ground level enhancements (GLEs) of cosmic rays. This work is focused on evaluation of the possible influence of the atmospheric ionization caused by SEPs upon formation of aerosol particles in the stratosphere over polar regions. Following case studies of two major SEP/GLE events, in January 2005 and September 1989, and their possible effects on polar stratospheric aerosols, we present here the results of an analysis of variations of the daily profiles of the stratospheric aerosol parameters (aerosol extinction for different wavelengths, as well as Angstrom exponent) for both polar hemispheres during SEP/GLE events of July 2000, April 2001 and October 2003, which form already five clear cases corresponding to extreme and strong SEP/GLE events. The obtained results suggest that an enhancement of ionization rate by a factor of about two in the polar region with night/cold/winter conditions can lead to the formation/growing of aerosol particles in the altitude range of 10‐25 km. We also present a summary of the investigated effects based on the phenomenological study of the atmospheric application of extreme SEP events.

Computation of electron precipitation atmospheric ionization: updated model CRAC-EPII

A new model of the CRAC family, CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization) is presented. The model allows one to calculate atmospheric ionization induced by precipitating electrons. The model is based on pre-computed with highprecision ionization yield functions, which are obtained using full Monte Carlo simulation of electron propagation and interaction in the Earth’s atmosphere, explicitly considering all physical processes involved in ion production. The simulations were performed using GEANT 4 simulation tool PLANETOCOSMICS with NRLMSISE 00 atmospheric model. A quasi-analytical approach, which allows one to compute the ionization yields for events with arbitrary incidence is also presented. It is compared with Monte Carlo simulations and good agreement between Monte Carlo simulations and quasi-analytical approach is achieved.