Spatial correlations in time and frequency domains between chlorophyll-a concentration and environmental factors in the Bohai Sea

Based on the reconstructed MODIS data and ECMWF reanalysis data from 2003 to 2021,spatial correlations between chlorophyll a(Chl a)and sea surface temperature(SST),photosynthetically available radiation(PAR),aerosol optical thickness(AOT),and wind speed(WS)in the Bohai Sea were analyzed from the perspective of time domain and frequency domain.Results indicate that the frequency domain analysis was more conducive to revealing the correlations between Chl a and environmental factors.The spatial pattern of time-domain correlations was similar to the isobaths of the Bohai Sea,which was positive in shallow waters and negative in deep waters for SST,PAR,and AOT,and was reversed for WS.Frequency-domain correlations were obtained by performing Fourier Transform and were higher than correlations in time domain.The spatial distributions indicated that the effects of SST and PAR on Chl a were greater than AOT and WS in the Bohai Sea.Additionally,cross-spectrum analysis was applied to explore the response relationships.A depth-dependent pattern was shown in correlations and time lags,indicating that the influential mechanism of environmental factors on Chl-a concentration is related to seawater depth.

Evolution of cavity size and energy conversion due to droplet impact on a water surface

The deformation characteristics of the cavity due to droplet impact on a water surface are experimentally investigated.Dimensional analysis shows that the characteristic values of time,depth,and horizontal diameter can be taken as 10^(-3)times the ratio of surface tension to the product of viscosity coefficient and gravitational acceleration,the maximum depth,and the maximum horizontal diameter,respectively.The evolutions of the dimensionless cavity sizes for different values of Weber number(We)coincide for 220<We<686.A partial-sphere model of cavity is established based on experimental observations.Energy models are then derived,and the energy conversions are calculated to identify the relationship between these conversions and cavity deformation.It is found that the kinetic energy model established under the hypothesis proposed by Leng is no longer applicable when the dimensionless time t^(*)<3.5,owing to deviations from the geometric model.