Analysis on Precipitation Efficiency of the “21.7” Henan Extremely Heavy Rainfall Event

A record-breaking heavy rainfall event that occurred in Zhengzhou,Henan province during 19–21 July 2021 is simulated using the Weather Research and Forecasting Model,and the large-scale precipitation efficiency(LSPE)and cloud-microphysical precipitation efficiency(CMPE)of the rainfall are analyzed based on the model results.Then,the key physical factors that influenced LSPE and CMPE,and the possible mechanisms for the extreme rainfall over Zhengzhou are explored.Results show that water vapor flux convergence was the key factor that influenced LSPE.Water vapor was transported by the southeasterly winds between Typhoon In-Fa(2021)and the subtropical high,and the southerly flow of Typhoon Cempaka(2021),and converged in Zhengzhou due to the blocking by the Taihang and Funiu Mountains in western Henan province.Strong moisture convergence centers were formed on the windward slope of the mountains,which led to high LSPE in Zhengzhou.From the perspective of CMPE,the net consumption of water vapor by microphysical processes was the key factor that influenced CMPE.Quantitative budget analysis suggests that water vapor was mainly converted to cloud water and ice-phase particles and then transformed to raindrops through melting of graupel and accretion of cloud water by rainwater during the heavy precipitation stage.The dry intrusion in the middle and upper levels over Zhengzhou made the high potential vorticity descend from the upper troposphere and enhanced the convective instability.Moreover,the intrusion of cold and dry air resulted in the supersaturation and condensation of water vapor,which contributed to the heavy rainfall in Zhengzhou.

Fast 3D joint inversion of gravity and magnetic data based on cross gradient constraint

The gravity and magnetic data can be adopted to interpret the internal structure of the Earth.To improve the calculation efficiency during the inversion process and the accuracy and reliability of the reconstructed physical property models,the triple strategy is adopted in this paper to develop a fast cross-gradient joint inversion for gravity and magnetic data.The cross-gradient constraint contains solving the gradients of the physical property models and performing the cross-product calculation of their gradients.The sparse matrices are first obtained by calculating the gradients of the physical property models derived from the first-order finite difference.Then,the triple method is applied to optimize the storages and the calculations related to the gradients of the physical property models.Therefore,the storage compression amount of the calculations related to the gradients of the physical property models and the cross-gradient constraint are reduced to one-fold of the number of grid cells at least,and the compression ratio increases with the increase of the number of grid cells.The test results from the synthetic data and field data prove that the structural coupling is achieved by using the fast cross-gradient joint inversion method to effectively reduce the multiplicity of solutions and improve the computing efficiency.

Joint inversion of gravity and vertical gradient data based on modified structural similarity index for the structural and petrophysical consistency constraint

Joint inversion is one of the most effective methods for reducing non-uniqueness for geophysical inversion.The current joint inversion methods can be divided into the structural consistency constraint and petrophysical consistency constraint methods,which are mutually independent.Currently,there is a need for joint inversion methods that can comprehensively consider the structural consistency constraints and petrophysical consistency constraints.This paper develops the structural similarity index(SSIM)as a new structural and petrophysical consistency constraint for the joint inversion of gravity and vertical gradient data.The SSIM constraint is in the form of a fraction,which may have analytical singularities.Therefore,converting the fractional form to the subtractive form can solve the problem of analytic singularity and finally form a modified structural consistency index of the joint inversion,which enhances the stability of the SSIM constraint applied to the joint inversion.Compared to the reconstructed results from the cross-gradient inversion,the proposed method presents good performance and stability.The SSIM algorithm is a new joint inversion method for petrophysical and structural constraints.It can promote the consistency of the recovered models from the distribution and the structure of the physical property values.Then,applications to synthetic data illustrate that the algorithm proposed in this paper can well process the synthetic data and acquire good reconstructed results.

Water storage changes and balances in Africa observed by GRACE and hydrologic models

Continental water storage plays a major role in Earth's climate system.However,temporal and spatial variations of continental water are poorly known,particularly in Africa.Gravity Recovery and Climate Experiment(GRACE)satellite mission provides an opportunity to estimate terrestrial water storage(TWS)variations at both continental and river-basin scales.In this paper,seasonal and secular variations of TWS within Africa for the period from January 2003 to July 2013 are assessed using monthly GRACE coefficients from three processing centers(Centre for Space Research,the German Research Centre for Geo-sciences,and NASA's Jet Propulsion Laboratory).Monthly grids from Global Land Data Assimilation System(GLDAS)-I and from the Tropical Rainfall Measuring Mission(TRMM)-3B43 models are also used in order to understand the reasons of increasing or decreasing water storage.Results from GRACE processing centers show similar TWS estimates at seasonal timescales with some differences concerning inter-annual trend variations.The largest annual signals of GRACE TWS are observed in Zambezi and Okavango River basins and in Volta River Basin.An increasing trend of 11.60 mm/a is found in Zambezi River Basin and of 9 mm/a in Volta River Basin.A phase shift is found between rainfall and GRACE TWS GRACE TWS is preceded by rainfall by 2-3 months in parts of south central Africa.Comparing GLDAS rainfall with TRMM model,it is found that GLDAS has a dry bias from TRMM model.

Evaluation of regional ionospheric grid model over China from dense GPS observations

The current global or regional ionospheric models have been established for monitoring the ionospheric variations. However, the spatial and temporal resolutions are not enough to describe total electron content（TEC） variations in small scales for China. In this paper, a regional ionospheric grid model（RIGM） with high spatial-temporal resolution（0.5 0.5 and 10-min interval） in China and surrounding areas is established based on spherical harmonics expansion from dense GPS measurements provided by Crustal Movement Observation Network of China（CMONOC） and the International GNSS Service（IGS）. The correlation coefficient between the estimated TEC from GPS and the ionosonde measurements is 0.97, and the root mean square（RMS） with respect to Center for Orbit Determination in Europe（CODE） Global Ionosphere Maps（GIMs） is 4.87 TECU. In addition, the impact of different spherical harmonics orders and degrees on TEC estimations are evaluated and the degree/order 6 is better. Moreover, effective ionospheric shell heights from300 km to 700 km are further assessed and the result indicates that 550 km is the most suitable for regional ionospheric modeling in China at solar maximum.

Water storage variations in the Poyang Lake Basin estimated from GRACE and satellite altimetry

The Gravity Recovery and Climate Experiment（GRACE） satellite mission provides a unique opportunity to quantitatively study terrestrial water storage（TWS） variations. In this paper,the terrestrial water storage variations in the Poyang Lake Basin are recovered from the GRACE gravity data from January 2003 to March 2014 and compared with the Global Land Data Assimilation System（GLDAS） hydrological models and satellite altimetry. Furthermore, the impact of soil moisture content from GLDAS and rainfall from the Tropical Rainfall Measuring Mission（TRMM） on TWS variations are investigated. Our results indicate that the TWS variations from GRACE, GLDAS and satellite altimetry have a general consistency. The TWS trends in the Poyang Lake Basin determined from GRACE, GLDAS and satellite altimetry are increasing at 0.0141 km^3/a, 0.0328 km^3/a and 0.0238 km^3/a,respectively during the investigated time period. The TWS is governed mainly by the soil moisture content and dominated primarily by the precipitation but also modulated by the flood season of the Yangtze River as well as the lake and river exchange water.

Pre-seismic ionospheric anomalies of the 2013 Mw=7.7 Pakistan earthquake from GPS and COSMIC observations

The seismo-ionospheric anomalies may provide some insights about the earthquake.However,preseismic ionospheric anomalies are still challenging.In this paper,seismo-ionospheric anomalies are investigated before the September 24,2013(Mw=7.7)Awaran(Pakistan)earthquake from GPS TEC(Total Electron Content)and COSMIC(Constellation Observing System for Meteorology,Ionosphere and Climate)data.The TEC data are showing anomalies on September 21,2013.The abnormality detected in the temporal data is about 10 TECU beyond the 30-day running median.The percentage deviation of the TEC anomaly on September 21,is 30% above the upper confidence interval.The anomalies prevail 5 in Latitude and 10 in Longitude over the epicenter.The spatial and temporal data of TEC showed anomalies in TEC from UT=08 to UT=12.In addition,the enhancement on September 21,2013 is also very significant in COSMIC data.The results of COSMIC completely agreed with GPS TEC anomalies on September 21,2013.The percentage deviation of the peak plasma frequency on September 21 is 5% of the normal distribution.The storm indices are quiet before and after the earthquake.The pre-sesimic ionospheric anomalies are most probably associated with the 2013 Mw=7.7 Awaran(Pakistan)earthquake.

Evaluation of ocean tide loading effects on GPS-estimated precipitable water vapour in Turkey

Global Positioning System （GPS） has been widely used to estimate the total zenith tropo- spheric delay （ZTD） and precipitable water vapour （PWV） for weather prediction and at- mospheric research as a continuous and all-weather technique. However, estimations of ZTD and PWV are subject to effects of geophysical models with large uncertainties, particularly imprecise ocean tide models of inland seas in Turkey. In this paper, GPS data from Jan. 1, 2010 to Dec. 31, 2011 are processed using GAMIT/GLOBK at four co-located GPS stations （ISTN, ERZR, SAMN, and IZMI） with Radiosonde from the Turkish Met-Office together with several nearby IGS stations. Four widely used ocean tide models are adopted to evaluate their effects on GPS-estimated PWV, such as IERS recommended FES2004, NAO99b, CSR4.0 and GOT00. Five different strategies are taken without ocean tide model and with four ocean tide models, respectively, which are used to evaluate ocean tide models effects on GPS-estimated PWV through comparing with co-located Radiosonde. Results showed that ocean tide models have greatly affected the estimation of the pre- cipitable water vapour at stations near coasts. The ocean tide model FES2004 gave the best results when compared to Radiosonde with ＋2.12 mm in PWV at stations near coastline. While other ocean tides models agree each other at millimeter level in PWV. However, at inland GPS stations, ocean tide models have less effect on GPS-estimated PWV.

Sea level change along the Black Sea coast from satellite altimetry, tide gauge and GPS observations

Sea level change affects human living conditions, particularly ocean coasts. However, sea level change is still unclear along the Black Sea coast due to lack of in-situ measurements and low resolution satellite data. In this paper, sea level change along the Black Sea coast is investigated from joint satellite altimetry, tide gauge {TG） and Global Positioning System （GPS） observations. The linear trend and seasonal components of sea level change are estimated at 8 TG stations （Amasra, Igneada, Trabzon-II, Sinop, Sile, Poti, Tuapse, and Batumi） located along the Black Sea coast, which are compared with Satellite Altimetry and GPS. At the tide gauge stations with long-term records such as Poti （about 21 years） and Tuapse （about 19 years）, the results obtained from the satellite altimetry and tide gauge observations show a remarkably good agreement. While some big differences are existed between Satellite Altimetry and TG at other stations, after adding vertical motion from GPS, correlation coefficients of the trend have been greatly improved from 0.37 to 0.99 at 3 co-located GPS and TG stations （Trabzon-II, Sinop and Sile）.

Ionospheric disturbances following the March 2015 geomagnetic storm from GPS observations in China

When strong solar activities and geomagnetic storms happen, satellite communications and navigation system will be strongly disturbed. It is of great significance to monitor ionospheric disturbances,because empirical models cannot capture ionospheric anomalous disturbances well. Nowadays, dualfrequency GPS(Global Positioning System) observations can be used to estimate the ionospheric total electron content, correct the ionospheric delay and analyze the response of the ionosphere to geomagnetic storms. In this paper, the ionospheric response to the geomagnetic storm occurred in March 2015 is investigated using GPS observations provided by Crustal Movement of Observation Network of China. The result shows that this storm increases the electron density in the ionosphere quickly and disrupts the structure of the northern equatorial anomaly region at the beginning. In the main process stage, compared with that in the quite periods, the VTEC(Vertical Total Electron Content)around the longitude of 120°E decreases by 50% and the amount of depletion is larger in the high latitude region than that in the low latitude region. We also find the height of the peak electron density in F2 layer increases during the geomagnetic storm from the electron density profiles derived from GPS occultation mission.

Gravity wave activities in Tibet observed by COSMIC GPS radio occultation

The Gravity waves activities in the Tibetan Plateau are very complex with different effects and natures that are not clear due to the lack of high resolution data from space and also from ground. In this paper,using COSMICGPS radio occultation data from 2006 to 2014, the atmospheric gravity waves activities and climatologic behaviors in Tibetan stratosphere are studied and analyzed, which show different characteristics. Most of the gravity waves with potential energy(Ep) at altitude of 17-24 km are associated with mountain waves. A good correlation between gravity wave activities and zonal wind flow is found. The distribution of gravity wave(GW) activities in Tibet is strongly connected with zonal wind variation and topography. GW activities are enhanced in winter seasons and decreased in summer seasons since strong western winds persist at all heights of the Tibetan troposphere. The gravity waves generated in the Tibetan area are mostly related to the orography of the area. The vertical wavelengths of GWS are shorter.Gravity waves in the Northwest have different vertical wavelengths in the Southeastern part of Tibetan Plateau, and dominant wavelengths are 3-5 km in the Northwest and 2-3 km in the Southeast,respectively. In the summer, the Northwestern part is the main source of wave generation while in the winter the GW is generated almost from all peaks of the Tibetan Plateau. Gravity waves in the region are clearly related to deep convection, which can also be proved by the inverse relation of Outgoing long wave radiation(OLR) and potential energy(Ep).

Hydrological mass variations in the Nile River Basin from GRACE and hydrological models

Terrestrial water storage(TWS)change is a key component of the global water cycle and hydrologic cycle.Therefore,it is of significance to quantify TWS variations at large scale and understand how the climate changes affect in the water systems,particularly in the Nile River Basin.In this study,TWS variations in the Nile River Basin are estimated and investigated from January 2003 to August 2016 by using the Gravity Recovery and Climate Experiment(GRACE).Also,the Global Land Data Assimilation System(GLDAS)and Tropical Rainfall Measuring Mission(TRMM)are used to understand the causes of the TWS variations in the Nile River Basin(NRB).The peak of precipitation has happened in July and August.After one month the appearance of the influence of precipitation on soil moisture is clear.On the other hand,after two months the same effect of precipitation in TWS is clear.While the peak of soil moisture has occurred in August and September,the maximum of TWS has observed in September and October.The maximum annual TWS from GRACE measurements is 42.66 mm in NRB during September-November(autumn),and its minimum is-33.77 mm during March-May(spring).Also,the maximum annual soil moisture is 25.22 mm in NRB during September-November(autumn),and its minimum is-23.34 mm during March-May(spring)while the peak precipitation is 100.11 mm during June-August(summer)and its minimum is 14.62 mm during December-February(winter).The trend of TWS variations in NRB is 0.04 mm/yr from GRACE.Furthermore,the TWS variations are mainly dominated by the soil moisture in the Nile River Basin with the correlation coefficient of 0.88.In addition,the correlation factor between the non-seasonal TWS and ScPDSI is 0.60,indicating that GRACE-derived TWS well capture the most severe droughts occurred in 2006 and 2011.

Three-dimensional gravity inversion based on optimization processing from edge detection

Gravity inversion requires much computation,and inversion results are often non-unique.The first problem is often due to the large number of grid cells.Edge detection method,i.e.,tilt angle method of analytical signal amplitude(TAS),helps to identify the boundaries of underground geological anomalies at different depths,which can be used to optimize the grid and reduce the number of grid cells.The requirement of smooth inversion is that the boundaries of the meshing area should be continuous rather than jagged.In this paper,the optimized meshing strategy is improved,and the optimized meshing region obtained by the TAS is changed to a regular region to facilitate the smooth inversion.For the second problem,certain constraints can be used to improve the accuracy of inversion.The results of analytic signal amplitude(ASA)are used to delineate the central distribution of geological bodies.We propose a new method using the results of ASA to perform local constraints to reduce the non-uniqueness of inversion.The guided fuzzy c-means(FCM)clustering algorithm combined with priori petrophysical information is also used to reduce the non-uniqueness of gravity inversion.The Open Acc technology is carried out to speed up the computation for parallelizing the serial program on GPU.In general,the TAS is used to reduce the number of grid cells.The local weighting and priori petrophysical constraint are used in conjunction with the FCM algorithm during the inversion,which improves the accuracy of inversion.The inversion is accelerated by the Open Acc technology on GPU.The proposed method is validated using synthetic data,and the results show that the efficiency and accuracy of gravity inversion are greatly improved by using the proposed method.

Seismicity modulation by external stress perturbations in plate boundary vs.stable plate interior

Characterization of critically stressed seismogenic fault systems in diverse tectonic settings can be used to explore the stress/frictional condition of faults,along with its sensitivity for seismicity modulation by periodic stress perturbation.However,the process of seismicity modulation in response to external stress perturbation remains debated.In this paper,the characteristic difference in the seismicity modulation due to resonance destabilization phenomenon governed by rate-and-state friction is presented and val-idated with the globally reported cases of seismicity modulation in diverse tectonic settings.The rela-tively faster-moving plate boundary regions are equally susceptible for both shorter-period(e.g.,semi-diurnal,diurnal,and other small tidal constituents)and long-period(e.g.,semi-annual,annual,pole tide and pole wobble)seismicity modulation processes in response to stress perturbations from natural har-monic forcing,including tidal,semi-annual,annual,or multi-annual time scales.In contrast,slowly deforming stable plate interior regions and diffuse deformation zones appear to be more sensitive for long-period seismicity modulation of semi-annual,annual,or even multi-annual time scales but less sen-sitive for short-period seismicity modulation.This finding is also supported by the theoretical model pre-dictions from the resonance destabilization process and worldwide documented natural observations of seismicity modulation in diverse types of tectonic settings.

Thermospheric density responses to Martian dust storm in autumn based on MAVEN data

The unique seasonal surface dust storms on Mars have a significant impact on the Martian atmosphere.However,due to the lack of observations,semi-empirical models are difficult to simulate the density changes in the thermosphere with the existence of dust storms in detail.Data from multiple Mars probes now offer new opportunities to study the detailed response of Martian dust storms to the upper atmosphere.In this paper,we use MAVEN accelerometer and mass spectrometer to study the variations of the Martian thermosphere density in autumn between MY32 and MY34(The corresponding Earth dates:February 11,2015 to February 28,2019),and use the seasonal model with dust storm index to fit the annual data of the above three Martian years.The results show that the thermosphere density has a clear response to the surface dust storm activity.Furthermore,the spatial distribution of measured data in autumn(northern hemisphere)is compared with the atmospheric density distribution simulated by the general circulation model(GCM)under specific initial conditions.The model simulation results agree well with the thermospheric density distribution characteristics of each Martian year under the initial strong dust storm conditions.It proves the important role of global dust storm in changing the structure of the Martian thermospheric atmosphere.

Cassini's motions of the Moon and Mercury and possible excitations of free librations

On the basis of conditionally-periodic solutions of Hamiltonian systems at resonance of main frequencies Cassini’s motions, their stability, Cassini’s angle and periods of free librations of the Moon and Mercury have been recently studied and determined. The generalized formulations of Cassini’s laws for the motion of the Moon and Mercury, that are considered as absolutely rigid non-spherical bodies, have been determined. The study of the second approximation equations of the desired quasi-periodic solutions in the case of the Moon allows us to determine the constant components of the first order for six Andoyer variables and the constant component of the second order for the angular velocity of the Moon. These effects are caused by the influence of the third harmonic of selenopotential. In this paper, these effects are described by analytical formulas, the dynamic and geometric interpretations are given, and a new interpretation of Mercury’s motion under the generalized Cassini’s laws has been proposed. Predictions of the existence of free librations of significant amplitude in the Mercury longitude, that are confirmed by the radar measurements data of the Mercury angular velocity, and in its pole motion in the body and in space have been made. The mechanism describing free librations of celestial bodies and their pole oscillations has been proposed due to the forced relative oscillations and wobble of the core-mantle system of celestial bodies（Moon, Mercury, Earth and other bodies in the solar system） under gravitational action of the external celestial bodies. The paper shows that the ascending node of equator of Mercury（and the intermediate plane orthogonal to the angular momentum） of epoch 2000.0 on the ecliptic does not coincide with the ascending node of orbital plane of Mercury on the same plane, and is ahead of it at an angle 23°4’. Angular momentum vector of the rotational motion of Mercury forms a constant angle p;=4’1±1’1 with normal to the moveable plane of its orbit. The observed inclination of the angular velocity p;=2’1±0’1, can be considered as a possible evidence of a significant amplitude of the poles free motion of the Mercury rotation axis（c amplitude of about 2’-4’）.

Effect of lunar gravity models on Chang'E-2 orbit determination using VLBI tracking data

The precise orbit determination of ChanE-2 is the most important issue for successful mission and scientific applications, while the lunar gravity field model with big un- certainties has large effect on Chang＇E-2 orbit determination. Recently, several new gravity models have been produced using the latest lunar satellites tracking data, such as LP16SP, SGM1SOJ, GL0900D and GRGM900C. In this paper, the four gravity models mentioned above were evaluated through the power spectra analysis, admittance and coherence analysis. Effect of four lunar gravity models on Chang＇E-2 orbit determination performance is investigated and assessed using Very Long Baseline Interferometry （VLBI） tracking data. The overlap orbit analysis, the posteriori data residual, and the orbit prediction are used to evaluate the orbit precision between successive arcs. The LPI65P model has better orbit overlap performance than the SGM150J model for Chang＇E-2100 km x 100 km orbit and the SGM150J model performs better for Chang＇E-2100 km x 15 km orbit, while GL0900D and GRGM900C have the best orbit overlap results for the two types of Chang＇E-2 orbit. For the orbit prediction, GRGM900C has the best orbit prediction performance in the four models.

Remote sensing and its applications using GNSS reflected signals:advances and prospects

The Global Navigation Satellite Systems(GNSS),including the US’s GPS,China’s BDS,the European Union’s Galileo,and Russia’s GLONASS,offer real-time,all-weather,any-time,anywhere and high precision observations by transmitting L band signals continuously,which have been widely used for positioning,navigation and timing.With the development of GNSS technology,it has been found that GNSS-reflected signals can be used to detect Earth’s surface characteristics together with other signals of opportunity.In this paper,the current status and latest advances are presented on Global Navigation Satellite System-Reflectometry(GNSS-R)in theory,methods,techniques and observations.New developments and progresses in GNSS-R instruments,theoretical modeling,and signal processing,ground and space-/air-borne experiments,parameters retrieval(e.g.wind speed,sea surface height,soil moisture,ice thickness),sea surface altimetry and applications in the atmosphere,oceans,land,vegetation,and cryosphere are given and reviewed in details.Meanwhile,the challenges in the GNSS-R development of each field are also given.Finally,the future applications and prospects of GNSS-R are discussed,including multi-GNSS reflectometry,new GNSS-R receivers,GNSS-R missions,and emerging applications,such as mesoscale ocean eddies,ocean phytoplankton blooms,microplastics detection,target recognition,river flow,desert studies,natural hazards and landslides monitoring.

Geodetic study on earth surface loading with GNSS and GRACE

Ice,snow,and liquid water on the surface of the Earth exert downward force onto the solid earth and deform the lithosphere typically in seasonal timescale.Space techniques,such as Global Navigation Satellite System(GNSS),made it possible to directly measure subtle displacements caused by loading.We can also observe such loads with time-variable gravity using gravity recovery and climate experiment satellites.These techniques made surface loads an attracting scientific target of modern geodesy.In this paper we briefly review the history of geophysical studies of surface loads through geodetic observations of crustal deformation and time-variable gravity.We also review advanced topics such as short-term crustal deformation due to severe meteorological episodes and monitoring of terrestrial water storages.We also present a few related topics such as the change of the obliquity of the Earth due to loads and artificial crustal subsidence signals caused by snow accretion onto GNSS antenna radomes.

Present-day spreading motion of the mid-Atlantic ridge

Over a long period of time, the spreading rate of the mid-Atlantic ridge has been ascertained by the geological age of the magnetic stripe laid out on either side of the mid-ocean ridge in conjunction with the annals of the magnetic reversal history. Is the mid-Atlantic ridge still spreading today? How fast is it moving or are there any changes? All these questions remain unsolved. Based on the newest ITRF2000 velocity field published by the International Earth Rotation Service (IERS), the contemporary global plate motion model ITRF2000VEL is constructed, independent of any plate model hypothesis. Solutions for relative Euler’s vectors of plate pairs as North America-Eurasia, North America-Africa and South America-Africa are obtained, implying current spreading rates of the mid-Atlantic ridge. Comparing them with results from the NNR-NUVEL1A model displays the present-day motion characteristics of the mid-Atlantic ridge that the mid-ridge of the South Atlantic, whose spreading is slowing down, spreads