Winter sea ice albedo variations in the Bohai Sea of China

Sea ice conditions in the Bohai Sea of China are sensitive to large-scale climatic variations. On the basis of CLARA-A1-SAL data, the albedo variations are examined in space and time in the winter（December, January and February） from 1992 to 2008 in the Bohai Sea sea ice region. Time series data of the sea ice concentration（SIC）, the sea ice extent（SIE） and the sea surface temperature（SST） are used to analyze their relationship with the albedo. The sea ice albedo changed in volatility appears along with time, the trend is not obvious and increases very slightly during the study period at a rate of 0.388% per decade over the Bohai Sea sea ice region.The interannual variation is between 9.93% and 14.50%, and the average albedo is 11.79%. The sea ice albedo in years with heavy sea ice coverage, 1999, 2000 and 2005, is significantly higher than that in other years; in years with light sea ice coverage, 1994, 1998, 2001 and 2006, has low values. For the monthly albedo, the increasing trend（at a rate of 0.988% per decade） in December is distinctly higher than that in January and February. The mean albedo in January（12.90%） is also distinctly higher than that in the other two months. The albedo is significantly positively correlated with the SIC and is significantly negatively correlated with the SST（significance level 90%）.

水下圆柱冲刷的时间演变

Temporal evolutions of scour at submerged circular cylinders were investigated.Flow visualization was carried out around the cylinders over plane,under developed and equilibrium scour holes.Video analysis technique was used to formulate the equations for determining the diameter of the horseshoe vortex around the submerged cylinders,which is also verified from the vector diagrams drawn using the velocity measurements.The scour process similar to live bed scour was noticed around the downstream cylinder.The diameter of the horseshoe vortex is found to depend on the diameter of respective cylinder,submergence ratio,spacing between the cylinders and skew angle.This formulation along with the dislodgement and transportation of a single sediment particle is further incorporated in the proposed model for determining the time variation of scour around the submerged cylinders.It is evident from the results that the upstream cylinder shelters the downstream cylinder and thereby reduces the scour at the downstream cylinder.Proposed model is further extended to incorporate the effect of non-uniformity of the sediment particles on the time variation of scour depth.The results indicate significant reduction of scour depth of around 6%and 35%for upstream and downstream cylinders respectively due to the formation of the armor layer.The model is also compared with the local scour component of field data around cylindrical bridge piers to establish the differences in the scour process around a partially submerged cylinder and fully submerged tandem and skewed cylinders.

Joint analysis of b-value and apparent stress before the 2011 M_(W)9.0 Tohoku-Oki, Japan earthquake

Detecting tempo-spatial changes of crust stress associated with major earthquakes has implications for understanding earthquake seismogenic processes.We conducted a joint analysis of b-value and apparent stress in the source region before the March 11,2011 MW9.0 TohokuOki,Japan earthquake.Earthquakes that occurred between January 1,2000 and March 8,2011 were used to estimate bvalues,while source parameters of events with magnitudes of Ms5.0–6.9 between January 1,1997 and March 8,2011 were used to calculate the apparent stresses.Our results show that the average b-value decreased steadily from 1.26 in 2003 to 0.99 before the Tohoku-Oki mainshock.This b-value decrease coincided with an increase in the apparent stress from 0.65 MPa to 1.64 MPa.Our results reveal a clear negative correlation between the decrease in b-value and increase in apparent stress,which lasted for approximately eight years prior to the 2011 mainshock.Additionally,spatial pattern results of the relative change in b-value show that the area associated with drastic b-value decreases(25%or greater)was concentrated near the 2011 mainshock epicenter.The joint analysis of b-value and apparent stress provides a promising method for detecting anomalies that could serve as potential indicators of large earthquakes.

Assessing Doppler velocities of Rankin Inlet F-region echoes

Doppler velocities observed by the Rankin Inlet （RKN） PolarDARN radar are assessed with a focus on data in the beams oriented roughly along the magnetic meridian. Hourly scatter plots for every month are built. They are shown to vary widely, with median values showing very clear magnetic local time variation with maximum magnitude during pre-noon and pre-midnight hours. The histograms contain a significant amount of very small velocity data that dominates at farther ranges and during the daytime. Near noon data show generally antisunward flows but at large ranges/magnetic latitudes and very close to noon, sunward flows occur for periods of positive IMF Bz. The reverse flows are stronger during spring equinox. The velocity magnitude was found to depend linearly on the IMF Be and interplanetary electric field. Velocities are often found to be smaller than those expected from the statistical convection model of Ruohoniemi and Greenwald -1996.

Inter-annual variations in vegetation and their response to climatic factors in the upper catchments of the Yellow River from 2000 to 2010

To understand the variations in vegetation and their correlation with climate factors in the upper catchments of the Yellow River, China, Normalized Difference Vegetation Index（NDVI） time series data from 2000 to 2010 were collected based on the MOD13Q1 product. The coefficient of variation, Theil–Sen median trend analysis and the Mann–Kendall test were combined to investigate the volatility characteristic and trend characteristic of the vegetation. Climate data sets were then used to analyze the correlation between variations in vegetation and climate change. In terms of the temporal variations, the vegetation in this study area improved slightly from 2000 to 2010, although the volatility characteristic was larger in 2000–2005 than in 2006–2010. In terms of the spatial variation, vegetation which is relatively stable and has a significantly increasing trend accounts for the largest part of the study area. Its spatial distribution is highly correlated with altitude, which ranges from about 2000 to 3000 m in this area. Highly fluctuating vegetation and vegetation which showed a significantly decreasing trend were mostly distributed around the reservoirs and in the reaches of the river with hydropower developments. Vegetation with a relatively stable and significantly decreasing trend and vegetation with a highly fluctuating and significantly increasing trend are widely dispersed. With respect to the response of vegetation to climate change, about 20–30% of the vegetation has a significant correlation with climatic factors and the correlations in most areas are positive： regions with precipitation as the key influencing factor account for more than 10% of the area; regions with temperature as the key influencing factor account for less than 10% of the area; and regions with precipitation and temperature as the key influencing factors together account for about 5% of the total area. More than 70% of the vegetation has an insignificant correlation with climatic factors.

Variation of the earth's rotation derived from timing records of solar eclipse in ancient China

In the study of variation of the earth’s rotation based on the records of some ancientastronomical events, the timing records of ancient astronomical events and phenomena, suchas solar and lunar eclises and lunar occultation, are important components of the data.The reliable records, especially those from the countries and regions with advanced an-cient astronomy and timing technology, contain valuable information on the variation

Applicability Assessment of the 1998–2018 CLDAS Multi-Source Precipitation Fusion Dataset over China

Traditional hourly rain gauges and automatic weather stations rarely measure solid precipitation, except for those stations with weighing-type precipitation sensors. Microwave remote sensing has only a low ability to retrieve solid precipitation. In addition, there are no long-term, high-quality precipitation data in China that can be used to drive land surface models. To address these issues, in the China Meteorological Administration(CMA) Land Data Assimilation System(CLDAS), we blended the Climate Prediction Center(CPC) morphing technique(CMORPH) and Modern-Era Retrospective analysis for Research and Applications version 2(MERRA2) precipitation datasets with observed temperature and precipitation data on various temporal scales using multigrid variational analysis and temporal downscaling to produce a multi-source precipitation fusion dataset for China(CLDAS-Prcp). This dataset covers all of China at a resolution of 6.25 km at hourly intervals from 1998 to 2018. We performed dependent and independent evaluations of the CLDAS-Prcp dataset from the perspectives of seasonal total precipitation and land surface model simulation. Our results show that the CLDAS-Prcp dataset represents reasonably the spatial distribution of precipitation in China. The dependent evaluation indicates that the CLDAS-Prcp performs better than the MERRA2 precipitation, CMORPH precipitation, Global Land Data Assimilation System version 2(GLDAS-V2.1) precipitation,and CLDAS-V2.0 winter precipitation, as compared to the meteorological observational precipitation. The independent evaluation indicates that the CLDAS-Prcp dataset performs better than the Global Precipitation Measurement(GPM) precipitation dataset and is similar to the CLDAS-V2.0 summer precipitation dataset based on the hydrological observational precipitation. The simulated soil moisture content driven by CLDAS-Prcp is slightly better than that driven by the CLDAS-V2.0 precipitation, whereas the snow depth simulation driven by CLDAS-Prcp is much better than that driven by the CLDAS-V2.0 precipitation. This is because the CLDAS-Prcp data have included solid precipitation. Overall, the CLDAS-Prcp dataset can meet the needs of land surface and hydrological modeling studies.

Motion of photons in a gravitational wave background

Photon motion in a Michelson interferometer is re-analyzed in terms of both geometrical optics and wave optics. The classical paths of the photons in the background of a gravitational wave are derived from the Fermat principle, which is the same as the null geodesics in general relativity. The deformed Maxwell equations and the wave equations of electric fields in the background of a gravitational wave are presented in a fiat-space approximation. Both methods show that even the envelope of the response of an interferometer depends on the frequency of a gravitational wave, but it is almost independent of the frequency of the mirror＇s vibrations.