Development of a web application for monitoring solar activity and cosmic radiation
aa r X i v : . [ phy s i c s . s p ace - ph ] J a n Development of a web application for monitoring solar activityand cosmic radiation
D. Pelosi ( ) , N. Tomassetti ( ) , M. Duranti ( ) ( ) Dipartimento di Fisica e Geologia, Universit`a degli Studi di Perugia, Italy ( ) INFN - Sezione di Perugia - Perugia, Italy
Summary. — The flux of cosmic rays (CRs) in the heliosphere is subjected toremarkable time variations caused by the 11-year cycle of solar activity. To helpthe study of this effect, we have developed a web application (Heliophysics VirtualObservatory) that collects real-time data on solar activity, interplanetary plasma,and charged radiation from several space missions or observatories. As we will show,our application can be used to visualize, manipulate, and download updated data onsunspots, heliospheric magnetic fields, solar wind, and neutron monitors countingrates. Data and calculations are automatically updated on daily basis. A nowcastingfor the energy spectrum of CR protons near-Earth is also provided using calculationsand real-time neutron monitor data as input.
1. – Introduction
During their motion inside the heliosphere, cosmic rays (CRs) experience the effectsof heliospheric forces, commonly known as solar modulation. Specifically, the solar windand its embedded magnetic field constantly reshape their energy spectra. The solar mod-ulation effect is caused by several processes such as convection, drift motion, diffusion,and adiabatic cooling, although investigations are underway on defining the associatedparameters [1]. As a result, the energy spectrum of CRs observed near-Earth is signif-icantly different from that in the surrounding interstellar medium, the so-called LocalInterstellar Spectrum (LIS). Furthermore, solar modulation is known to be energy- andtime-dependent. In fact, the effect is more evident for CRs with kinetic energies be-low ∼
10 GeV and shows a clear correlation with solar activity. This implies that solarmodulation inherits the quasi-periodical behavior of solar activity. More specifically, themonthly SunSpot Number (SSN) observed on the Sun’s photosphere, widely used as agood proxy for solar activity, varies with a period of 11 years, known as solar cycle. Adeep investigation of the solar modulation phenomenon is of crucial importance to achievea full understanding of the dynamics of charged particles in the heliospheric turbulence,as well as to accurately predict the radiation dose received by electronics and astronauts.Forecasting the CR fluxes near-Earth and in the interplanetary space is essential, given D. PELOSI ETC. the ever-growing number of satellites orbiting around Earth and human space missionsto Moon and Mars planned in the next decades. For this purpose, several analytic andnumerical models of solar modulation have been proposed [1, 2, 3, 4]. Recent progressin this field has been possible thanks to time-resolved data on CRs fluxes released frommany space missions such as EPHIN/SOHO (since 1995 to 2018) [5], PAMELA (2006-2016) [6], AMS-02 (since 2011 and still operative for all ISS lifetime) [7], along withthe direct LIS data from the Voyager probes in the interstellar space [8]. The temporalvariations of CRs fluxes are also measured, with some caveats, with the ground-basednetwork of Neutron Monitors (NMs) whose data are collected in since 1951 [9]. A NMdetector is an energy-integrating device whose count rate ( N ) is defined (for each speciesof CR) as an integral, above the local geomagnetic rigidity cutoff, of a product of thenear-Earth CR flux and the specific yield function of the detector. Models also need solardata such as SSN (in different time resolutions) provided by the SILSO/SIDC databaseof the Royal Observatory of Belgium [10], polar field strength and tilt angle values of theheliospheric current sheet (HCS) monthly provided by the
Wilcox Solar Observatory [11]and heliospheric data about radial speed and proton density of solar wind, monthly dis-tributed by NASA missions WIND and ACE [12]. We have developed the
HeliophysicsVirtual Observatory (HVO) in order to make data-access easier and faster. HVO is aweb application that collects all the data mentioned above in a unique tool providing adaily automatic update. This tool gives users the functionalities of visualizing, manipu-lating and downloading updated data. We also present a simplified real-time model ofnear-Earth proton flux integrated into a specific section of HVO.
2. – Real-time model
The propagation of CRs in the heliosphere is governed by the Parker equation: ∂f∂t = − ( C ~V + h ~v drift i ) · ∇ f + ∇ · ( K · ∇ f ) + 13 ( ∇ · ~V ) ∂f∂ ln R + q (1)The equation describes the temporal evolution of CR phase space density f = f ( t, R ),where R = p/Z is the CR rigidity, h ~v drift i is the averaged particle drift velocity, ~V is thesolar wind velocity, K is the symmetric part of CR diffusion tensor, and q is any localsource of CRs [1]. The Parker equation is often resolved within the so-called Force-Field(FF) approximation [2]. The FF model assumes steady-state conditions (i.e. negligibleshort-term modulation effects), radially expanding wind V ( r ), isotropic and separablediffusion coefficient K ≡ κ ( r ) · κ ( R ), negligible drift and loss terms. Despite theseassumptions are often violated, the FF approximation provides a useful way to describethe near-Earth CR flux evolution and it is frequently used thanks to its simplicity. Theresulting CR flux J ( t, R ) is related to f by J = R f . Writing the solution in terms ofkinetic energy per nucleon E , for a CR nucleus with charge number Z and mass number A , the near-Earth ( r = 1 AU) flux at the epoch t is given by: J ( E, t ) = ( E + M p ) − M p ( E + M p + ZA φ ( t )) − M p J LIS ( E + ZA φ ( t )) , (2)where φ is the modulation potential , it has the units of an electric potential, typically inthe range 0.1-1 GV. The parameter φ can be interpreted as the averaged rigidity lossof CRs in their motion from the edge of the heliosphere down to the Earth. Thus, the WEB APPLICATION FOR MONITORING SOLAR ACTIVITY AND COSMIC RADIATION implementation of this simplified model depends on the knowledge of two key elements:the time-series of φ and the LIS. In this work, we have used the new LIS models basedon the latest results from Voyager 1 and AMS-02 [13] and the values of the modulationpotential reconstructed by Usoskin et al. 2011 [14], from NM data on monthly basis,since 1964 to 2011. To set up the φ reconstruction after 2011 and to the present epoch,instead of repeating the Usoskin methodology (based on NM’s yield function), we proposea simplified method. For a given NM detector, the NM counting rate N ( t ) and φ ( t ) areanti-correlated and we can establish a quadratic relation between them: φ ( N ( t )) = A + B · N ( t ) + C · N ( t ) (3)We determined the coefficient A , B , and C as best-fit values using for several NM stationsthe Usoskin φ -values. This enable us to obtain an prediction of φ for any epoch t forwhich the NM rate N is known. Inserting the parameterization of LIS and the φ value atepoch t in Eq. 2 we obtain a real-time estimator for near-Earth CR flux. This simplifiedmodel has been integrated into HVO.
3. – The Heliophysics Virtual Observatory
The investigation of the solar modulation phenomenon requires a large variety ofheliospheric and radiation data. HVO [15] is a project developed under the CRISP sci-entific program of experimental study and phenomenological modeling of space weather,within the framework agreement between
Universit`a degli Studi di Perugia and
AgenziaSpaziale Italiana (ASI). HVO is a web application that daily extracts data with Pythonscripts from several databases (listed in Resources section), it visualizes and makes themavailable in a standardized format. HVO has been implemented with the JavaScript
ROOT package
JSROOT . It enables users to manipulate, directly from the web page, graphs anddownload data as text format or graphic objects with
ROOT extension. To date, HVOhas three main sections. The first one is dedicated to solar data such as SSN in daily,monthly, yearly, and smoothed formats extracted from SILSO/SIDC [10], observations ofthe Sun’s polar magnetic field strength and tilt angle of the HCS reconstructed with theclassic and radial model from the Wilcox Solar observatory [11]. The second section con-tains heliospheric data such as proton density and radial speed of the solar wind, monthlyupdated from WIND and ACE [12]. The third section contains cosmic radiation datafrom NMs and a real-time model for Galactic CR protons discussed in Sect. 2. An inter-active user interface provides the possibility to select one or more NM stations, choosethe time resolution of the rates (daily, monthly, yearly and by Carrington rotation), setthe proton energy and time interval. HVO provides, for each selected NM, the graph ofthe count rate N ( t ), the calculated time-series of φ from Eq. 3, and the estimated protonflux near-Earth J ( E ) from Eq. 2. Fig. 1 shows an example of the HVO functionality.
4. – Conclusions
In this work, we have presented a web application aimed at monitoring solar activityand cosmic radiation, as well as providing real-time calculation of the energy spectraof CR protons in proximity of the Earth. HVO is in its first development phase. Wecan propose possible improvements to realize a useful tool for the CR astrophysics andspace physics community. In particular, we can extend the real-time proton model toother charged species. HVO can be also integrated with improved numerical models of
D. PELOSI ETC.
Fig. 1. – Plots extracted from HVO: A) Monthly rate N ( t ) of the NEWK station (Newark, NJ,USA) in time interval 1/1/2004 - 1/1/2021. B) Monthly SSN in the time interval 1/1/2004 -1/1/2021. C) Calculated time-series of φ using the NEWK rates (1/1/2004 - 1/1/2021). D)Averaged tilt angle of the HCS measured with the classic model for any Carrington rotationbetween 1/1/2004 and 1/1/2021. E) Estimated near-Earth proton flux at E = 1 GeV using theNEWK rates (1/1/2004 - 1/1/2021). F) Solar wind speed for the period 1/1/2004 - 1/1/2021. CRs transport in the heliosphere [3, 4], that will enable us to forecast the CR radiationat an interplanetary level. Finally, we can include other relevant observations such as,e.g., data on solar energetic particle (SEP) events, solar flares and coronal mass ejections(CME) or other interplanetary disturbance phenomena. ∗ ∗ ∗
We acknowledge the support of Italian Space Agency under agreement ASI-UniPG2019-2-HH.0.
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