A new model describing Forbush Decreases at Mars: combining the heliospheric modulation and the atmospheric influence

Forbush decreases are depressions in the galactic cosmic rays (GCRs) that are caused primarily by modulations of interplanetary coronal mass ejections (ICMEs) but also occasionally by stream/corotating interaction regions (SIRs/CIRs). Forbush decreases have been studied extensively using neutron monitors at Earth;recently, for the first time, they have been measured on the surface of another planet, Mars, by the Radiation Assessment Detector (RAD) on board the Mars Science Laboratory’s (MSL) rover Curiosity. The modulation of GCR particles by heliospheric transients in space is energy-dependent;afterwards, these particles interact with the Martian atmosphere, the interaction process depending on particle type and energy. In order to use ground-measured Forbush decreases to study the space weather environment near Mars, it is important to understand and quantify the energy-dependent modulation of the GCR particles by not only the pass-by heliospheric disturbances but also by the Martian atmosphere. Accordingly, this study presents a model that quantifies both at the Martian surface and in the interplanetary space near Mars the amplitudes of Forbush decreases at Mars during the pass-by of an ICME/SIR by combining the heliospheric modulation of GCRs with the atmospheric modification of such modulated GCR spectra. The modeled results are in good agreement with measurements of Forbush decreases caused by ICMEs/SIRs based on data collected by MSL on the surface of Mars and by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft in orbit. Our model and these findings support the validity of both the Forbush decrease description and Martian atmospheric transport models.

THE INFLUENCE OF THE COSMIC RAY FORBUSH DECREASE ON THE LOW IONOSPHERE IN THE POLAR REGION

Used the ionization theory of the cosmic ray charged particles in the polar ionosphere, the influence of the cosmic ray Forbush decrease on the low ionosphere in the polar region is studied in this paper. The relationship between the Forbush decrease and the cosmic noise absorption during the polar night is analysed based on the data recorded by a Riometer at Antarctic Zhongshan Station (69° 22'24'S, 76°22'40'E). The relation of between the cosmic ray Forbush decrease and the cosmic noise absorption is well interpreted by means of the ionizaiotn theory.

Analysis of Forbush decreases observed using a muon telescope in Antarctica starting on 21 June 2015

A cosmic-ray muon telescope the telescope was built in the Zhongshan has been collecting data since the end Station of Antarctica. The telescope of 2014, which was shortly after is the first observation device to be built by Chinese scientists in Antarctica. The pressure change is very strong in Zhongshan station. The count rate of the pressure correction results shows that the large variations in the count rate are likely caused by pressure fluctuations. During the period from 18 June to 22 June 2015, four halo coronal mass ejections （CMEs） were ejected from the Sun. These CMEs initiated a series of Forbush decreases （FD） when they reached the Earth. We conducted a comprehensive study of the intensity fluctuations of galactic cosmic rays recorded during FDs. The intensity fluctuations used in this study were collected by cosmic ray detectors of multiple stations （Zhongshan, McMurdo, South Polar, and Nagoya）, and the solar wind measurements were collected by ACE and WIND. The profile of the FD of 22 June demonstrated a four-step decrease. The traditional one- or two-step FD classification method does not adequately explain the FD profile results. The interaction between the faster CME that occurred on 21 June 2015 and the two slow CMEs of the earlier few days should be considered. The cosmic ray intensities of the South Pole, McMurdo, and Zhongshan stations have similar hourly variations, whereas the galactic cosmic rays recorded between polar and non-polar locations are distinct. The FD pre-increase of 22 June 2015 for the Nagoya ninon telescope （non-polar location） lags those of the McMurdo and Zhongshan stations （polar locations） by 1 h. The FD onset of 22 June 2015 for the Nagoya muon telescope lags those of the polar locations by 1 h.

Latitudinal Distribution of Solar Flares and Their Association with Coronal Mass Ejections

Major solar flare events have been utilised to study the latitudinal frequency distribution of solar flares in northern and southern hemispheres for the period of 1986 to 2003. A statistical analysis has been performed to obtain the correlation between Coronal Mass Ejections (CMEs) and Forbush decrease (Fds) of cosmic ray intensity. Almost the same flares distribution in both hemispheres is found in association with CMEs. In a further analysis, it is noted that a larger number of CME-associated solar flares located in the northern hemisphere are found to be more effective in producing Forbush decreases.

The Neutron Flux Variation in the Earth’s Atmosphere Depending on the Solar Proton Flux

The Earth is continually exposed to the cosmic radiation of both solar and galactic origin. Solar eruption and solar ac- tivity may affect cosmic radiation flux density which has a secondary effect on the flux of particles in the atmosphere as well. Such one event was recorded in the last week of October 2003, where the measured dose rate of the cosmic radia- tion in the aircraft ATR 42 was 1.8 times higher than the average value of the other measurements. Later we found the data on an unusual solar activity in the mentioned time interval. Analysis of the increasing solar proton flux during the solar flare, as well as the decreasing neutron flux in the atmosphere (representing the galactic radiation), on May 14 and 15, 2005, showed a nonlinear correlation with the exponential equation of regression;this one described galactic ray modulation by solar flux during the short term variation of cosmic radiation.