Background: Effect of meteorological factors such as air temperature, humidity, and sunlight exposure on transmission dynamics of novel coronavirus disease 2019 (COVID-19) remains controversial. We investigated the association of these factors on COVID-19 incidence in Japan.Methods: We analyzed data on reverse transcription polymerase chain reaction confirmed COVID-19 cases for each prefecture (total=47) in Japan and incidence rate was defined as the number of all reported cumulative cases from January 15 to March 17, 2020. Independent variables of each prefecture included three climatic variables (mean values of air temperature, relative humidity, and sunlight exposure), population elderly ratio, and the number of inbound travelers from China during February 2020. Multivariable-adjusted Poisson regression model was constructed to estimate COVID-19 incidence rate ratio (IRR) of independent variables.Results: There was a total of 702 cases during the study period in Japan (population=125, 900,000). Mean±standard deviation values of meteorological variables were 7.12°C±2.91°C for air temperature, 67.49%±7.63% for relative humidity, and 46.77±12.55% for sunlight exposure. Poisson regression model adjusted for climate variables showed significant association between the incidence and three climatic variables: IRR for air temperature 0.854 (95% confidence interval [CI], 0.804–0.907; P<0.0001), relative humidity 0.904 (95% CI, 0.864–0.945; P<0.0001), and sunlight exposure 0.973 (95% CI, 0.951–0.997; P=0.026).Conclusion: Higher values of air temperature, relative humidity and sunlight exposure were associated with lower incidence of COVID-19. Public health interventions against COVID-19 epidemic in a country should be developed by considering these meteorological factors.

In this paper, the flow fields of underexpanded impinging jet issued from rectangular nozzles of aspect ratio 1, 3 and 5 are numerically and experimentally studied. Two dimensional temperature and pressure distributions are measured by using infrared camera and the combination of a pressure scanning device and a stepping motor, respectively. The variation of the stagnation pressure on the impinging plate reveals that a hysteretic phenomenon exists during the increasing and decreasing of the pressure ratio for the aspect ratio of 3.0 and 5.0. It is also found that the nozzle of aspect ratio 1.0 caused the largest total pressure loss p c / p 0 = 0.27 at the pressure ratio of p 0 /p b = 6.5, where p c is the stagnation center pressure on the wall, p 0 the upstream stagnation pressure, p b the ambient pressure. The other two nozzles showed that the pressure loss p c / p 0 =0.52 and 0.55 were achieved by the nozzles of the aspect ratio 3,0 and 5.0, respectively. The comparison between the calculations and experiments is fairly good, showing the three dimensional streamlines and structures of the shock waves in the jets. However, the hysteresis of the pressure variations observed in the experiments between the pressure ratio of 3.5 and 4.5 cannot be confirmed in the calculations. K eywords: compressible flow, shock wave, under-expanded rectangular impinging jet, CFD. CLC number: O358 Document code: A

Twin underexpanded impinging jets are experimentally and numerically studied in this paper. The experiments were performed by two dimensional wall static pressure measurements and by the schlieren method. Numerical calculations were also conducted by solving three dimensional compressible Navier-Storkes equations in generalization curvilinear coordinate. The main parameters for the twin jets are the nondimensional distance between the two nozzle centers H/D covering 1.5 and 2.0, the nozzle to plate separation L/D 2.0 and 3.0 and the pressure ratio defined by p 0 /p b 2.5-5.0, where D is the diameter of each nozzle exit, p0 the stagnation pressure and p b the back pressure. It is found that, so called, a fountain flow which occurs at the middle position between the two jets breaks jets boundaries due to its unsteadiness. Comparison between the experiments and the calculations shows that in case of shorter distancce between two nozzle and higher pressure ratio, two jets interact before they reach the impinging wall causing clear pressure peak at the middle position between the jets.

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