On the Relationship between Meteorological Variables, Dst Index, Solar Wind Speed, Solar Radio Flux, and Cosmic Rays and COVID-19 Cases

This study aims to determine the influential role of the meteorological, solar, and geophysical factors and cosmic rays on the transmission of COVID-19 in Riyadh, Saudi Arabia. The meteorological factors were air temperature, relative humidity, wind speed, and atmospheric pressure. The solar radio flux, Dst index, and solar wind speed were utilized as representatives of the solar and geophysical variables. The association between these variables and the COVID-19 pandemic cases from 3 April 2020 to 1 August 2021 was investigated using the Spearman and Kendall rank correlation tests. The obtained results showed that the air temperature and average wind speed are positively associated with the daily number of reported COVID-19 cases. On the other hand, the mean values of relative humidity and atmospheric pressure are inversely correlated with the number of COVID-19 cases in Riyadh. Moreover, the results showed that the Dst index and cosmic rays are positively correlated with the COVID-19 cases. Contrarily, solar wind speed and radio flux at 10.7 cm have negative correlations with the COVID-19 cases. The obtained results will help the epidemiologists to understand the behavior of the virus against meteorological, solar, and geophysical variables and can be considered as a useful supplement to help national and international organizations and healthcare policymakers in the process of strategizing to combat COVID-19.


Introduction
The spread of epidemics and pandemics depends on several factors, such as individual, social, economic, physiological or immunological, as well as environ-DOI: 10.4236/acs.2022.123030 518 Atmospheric and Climate Sciences mental influences such as meteorological and/or cosmo-geophysical factors (e.g., [1] [2]).
Since the first known identified case was reported in Wuhan, China, in December 2019, the Coronavirus (COVID-19) disease has spread worldwide and developed into a global pandemic, becoming one of the most significant global health threats in a century (WHO, 2020) [3].
Immediately afterward, several research studies around the world were conducted to investigate the association between COVID-19 and a wide range of factors to understand their influence in contributing to the spread of  and to reduce the ongoing threat of the pandemic. These include the population density, socio-economic factors, healthcare, and the like (e.g., [4] [5]).
Furthermore, a large number of investigations have been conducted to investigate the effects of meteorological conditions on COVID-19 transmission in several places in the world (e.g., [6]- [11]).
Given the large and effective role that the sun plays in influencing the Earth and thus, our lives, any slight change in the sun's activity will have an impact on the Earth depending on the strength and intensity of this change or event [12] [13]. Extraterrestrial factors mainly affected by solar disturbances, such as the fluctuation of the Earth's magnetic field (Earth-ionosphere cavity/Schumann resonances), geomagnetic activity, variation of cosmic ray (CR) intensity, and electromagnetic changes, contribute to the nature of the virus, acquired hosts, virus-host interactions, and spread of infectious diseases outbreaks (e.g., [1] [14] and references therein).
Over the last 20 years, numerous studies have been carried out, and the evidence suggests that space weather activity has a broad range of adverse effects on human health [15]- [23].
It is imperative to explore the potential effects of these factors on the current COVID-19 pandemic to help national and international organizations and healthcare policymakers in the process of strategizing to combat COVID-19. To the best knowledge of the authors, there is no study that examines the relationship between solar, CRs, geophysical parameters, and the spread of COVID-19 cases.

Data
The data used in this study covers the period from 3 April 2020 to 1 August 2021  [24].
Pressure-corrected CR observations for CR neutrons and muons were obtained from the KACST neutron detector and CARPET detectors located at the same location as the weather sensors: the KACST main building. The neutron monitor consists of an outer paraffin wax reflector (9.5 cm) surrounded by a lead producer. The inner two-cm-thick paraffin wax moderator was also surrounded by a neutron producer made of lead. The multiplied and decelerated neutrons reach the 63 cm-long LND2043 counter, filled with BF 3 gas at a pressure of 933 hPa. An interface unit was developed for logging and storing the data at a resolution of 1 ms.
The CARPET detector consists of 120 Geiger counters (type STS-6) located on a platform of ~1.5 × 1.5 m. The 120 counters were divided into groups of 60 upper and 60 lower counters, separated by an aluminum absorber with a thickness of 7 mm. The detector records data from three channels with a time resolution of 1 ms, (Up, Down, and Telescope or Tel). The CR muons are recorded by the telescope channel that registers the total number of particles that simultaneously cross the Up and Down layers of the counters. In this study, CR muons recorded by telescope channel will be used.
The technical details and calibration procedures of the detectors have been discussed in several research articles [25] [26].
Three solar and geophysical variables were used in this study: the solar wind speed, Dst index, and solar radio flux at 10.7 cm. The daily mean values of these variables were obtained from the OMNI NASA database (http://omniweb.gsfc.nasa.gov).
The Dst index monitors the variations of the globally symmetrical ring current, which encircles the Earth close to the magnetic equator in the Van Allen (or radiation) belt of the magnetosphere.
The 10.7-cm solar radio flux (F 10.7 ) is one of the most widely used indices of solar activity. It measures the total emissions at a wavelength of 10.7 cm from all sources present on the solar disk.
The solar wind is a stream of charged particles with the solar magnetic field embedded in it; it continuously flows outward from the solar corona and consists of electrons, protons, and alpha particles in a state known as plasma. The solar wind varies in density, temperature, and speed over time and over solar la-

Statistical Tests
In this study, the relationships between the considered variables were examined according to the Spearman and Kendall rank correlation tests. Factors were considered to affect COVID-19 if significant differences were observed in both statistical tests.
Spearman's rank correlation coefficient is the nonparametric version of the Pearson product-moment and is used to examine the strength of the association between two variables (monotonic relationship). The formula for the Spearman rank correlation test is as follows (e.g., [23]): where ρ is the Spearman rank correlation coefficient; d i is the difference between the ranks of corresponding values xi and yi; and n is the number of x and y pairs.
The Kendall rank correlation, another non-parametric test, is used to assess statistical associations based on the ranks of the data and can be estimated as follows: ( ) where τ is the Kendall rank correlation coefficient while n c and n d represent the number of concordant and discordant pairs, respectively. Here, n represents the number of pairs.

General Trends
Since the first confirmed case of COVID-19 in Saudi Arabia on 2 March 2020, a total of 542,000 confirmed cases have been reported as of August 20, 2021. During our study period, from 3 April 2020 to 1 August 2021, a total of 103,729 confirmed that the locally-transmitted COVID-19 cases were identified in Riyadh.  The Kendall correlation coefficients between the number of COVID-19 cases and air temperature, RH, atmospheric pressure, and wind speed were 0.331, −0.324, −0.323, and 0.143, respectively. On the other hand, the Spearman correlation coefficient between the COVID-19 cases and air temperature was 0.507, between the cases and relative humidity was 0.494, and between the cases and atmospheric pressure was −0.456 and lower value of 0.219 with wind speed.

Non-Parametric Tests between Meteorological Variables and COVID-19 Cases
The obtained results, presented here, are in total agreement with some of the previously established studies and partly or totally contradicted several others conducted at several locations around the world. For instance, our finding of the positive effect of the mean temperature and wind speed and the number of COVID-19 cases was supported by the work of (e.g., [7] [11]). Auler [28] established that the mean temperature and average relative humidity are significant in enhancing the COVID-19 contamination rate in Brazil. Xie and Zhu [29] established that the humidity, wind speed, and temperature are inversely associated with the infection rate of COVID-19.

Non-Parametric Tests between Cosmic Rays, Cosmo-Geophysical Variables, and COVID-19 Cases
The results of Spearman and Kendall tests between the number of confirmed COVID-19 cases and the considered variables are presented in Table 2.
It is clear that all the variables have a significant association to the COVID-19 cases. However, the strength and the type of the association differ from one variable to another. The Dst, SWS and F10.7 are significantly correlated with the COVID-19 cases with a 95% confidence level, whereas the CR neutrons and muons have a significant relationship with the COVID-19 cases with a 99% confidence level. While the solar wind speed and radio flux (F10.7 cm) have negative correlations with the COVID-19 cases, the Dst index and the CR muons and neutrons are positively correlated with the COVID-19 cases. Spearman correlation coefficients were 0.14, −0.084, and −0.095 for Dst, SWS, and F10.7 respectively. For correlations between these variables and COVID-19 cases, the Kendall correlation coefficients were 0.072, −0.063, and −0.61 respectively. On the other hand, Spearman and Kendall tests showed stronger correlation coefficients (0.429 for NM and 0.405 for Muons) than the Kendall correlation coefficients

Conclusions
In this study, the effect of the meteorological variables, the solar and geophysical factors, and the cosmic rays on the number of the daily COVID-19 cases recorded in Riyadh, Saudi Arabia, for the period 3 March 2020 to 1 August 2021, was investigated using the Spearman and Kendall rank correlation tests. The meteorological factors were air temperature, relative humidity, wind speed, and atmospheric pressure. The solar and geophysical variables were the solar radio flux at 10.7 cm, Dst index, and solar wind speed. The analysis results showed the following conclusions: 1) The considered meteorological variables air temperature, relative humidity, air pressure, and wind speed, which cover all the atmospheric conditions experienced in Riyadh, have a significant impact on the number of COVID-19 cases.
2) Air temperature and wind speed correlated positively with the COVID-19 cases.
3) Relative humidity and air pressure are inversely correlated with the COVID-19 cases.
4) The Dst index is correlated with the COVID-19 cases.