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Objectives: With the ultra-high precision time and frequency signals provided by space high precision time and frequency system, series of space-to-ground time and frequency transfer and fundamental physics experiments can be carried out to support high precision validation of relativity and related theories. Methods: First, theoretical derivation and simulation analysis are conducted on the time and frequency transfer algorithm of space laser links. Theoretical formula of space-to-ground laser two way time transfer are reviewed, and the advantages and disadvantages of X-type and Lambda-type approaches are compared and analyzed. Then, the impact of relativistic effects on the conversion between proper time and coordinate time is discussed for the specific orbital height of China space station. Finally, the impact of space-to ground time and frequency transfer discontinuity on the stability evaluation of high-precision atomic clocks onboard space stations is discussed. Results: The results show that: (1) Lambda-type two-way time transfer based on satellite laser ranging can make up the distance difference of first-order Doppler effect on the uplink and downlink, and increase of Sagnac effect can be ignored. (2) The relativistic effect of the conversion between proper time and coordinate time for satellite ground time transfer makes high demands on the velocity accuracy of space station positions, in order to achieve 1×10-18 frequency transfer accuracy, geocentric distance accuracy of 1 dm and speed accuracy of 0.1 mm/s of space station is required; (3) Influenced by the visibility of space stations to the ground, it is not possible to evaluate the medium term stability of atomic clocks with only the observation data of domestic stations satellite for space-to-ground links. Conclusions: High precision navigation solution is important to ensure high-precision time and frequency transfer between space and ground. How to optimize navigation algorithms and use various payloads onboard to achieve high-precision position and velocity solution is a key issue that needs to be studied. [ABSTRACT FROM AUTHOR]

The Harbin Engineering University, the People's Republic of China, multifrequency multiple‐path coherent radio system operates continuously and provides data for post analysis. The data collected during the solar eclipse of 21 June 2020 have been chosen for this study with the objectives to interpret the variations in the Doppler spectra, Doppler shift, and in the reflected radio wave amplitudes that are associated with the solar eclipse, establish the magnitude and find physical significance of these variations, determine the reduction in the electron density caused by the solar eclipse, and to estimate an increase in wave activity in the ionosphere. The eclipse was accompanied by Doppler spectrum diffuseness resulting from an increase in the number of rays, the temporal variations in the Doppler shift were observed to be bi‐polar, asymmetrical, and anomalously small, with extreme Doppler shift magnitudes varying from −11 to −40 mHz and from 22 to 56 mHz. The duration of processes with negative Doppler shifts varied from 50 to 80 min, and the duration of processes with positive Doppler shifts changed from 30 to 80 min. The multi‐hop propagation (from two to five hops) took place along all propagation paths, with a 360 to 560‐km one‐hop length, due to the anomalous radio wave propagation via the sporadic‐E layer present about 80% of the time on 21 June 2020. The Doppler shift exhibited 4–18‐min period quasi‐sinusoidal variations with 20–10‐mHz amplitudes. Plain Language Summary: In the past, the study of the influence of eclipses on the ionosphere seemed to be a rather simple subject because a solar eclipse seemed to be just mimicking night, although over a shorter time interval. Subsequently, the movement of the solar terminators has been discovered to generate atmospheric gravity waves, which is also true for eclipses. Recent advances in instrumentation and measurement techniques have facilitated the revelation of unusual and interesting phenomena that do not necessarily belong to nighttime conditions. For example, in this study, we have discovered, along with the determination of specific changes in the atmospheric and radio wave parameters, that temporal variations in the Doppler shift were bi‐polar, asymmetrical, and anomalously small. Key Points: Doppler shift variations were bi‐polar, asymmetrical, and anomalously small, with extremes varying from −11 to −40 MHz and from 22 to 56 MHzMulti‐hop propagation (from two to five hops) took place along all propagation paths, with a length of one hop varying from 360 to 560 kmAn electron density decrease was determined to vary from –(12–16)% to –(20–26)% along different propagation paths [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide (CO2) is recognized as the most important component of the greenhouse gases, the concentration of which has increased rapidly since the pre-industrial era due to anthropogenic emissions of greenhouse gases (GHG). The accurate monitoring of carbon dioxide is essential to study the global carbon cycle and radiation budget on Earth. The Aerosol and Carbon Detection Lidar (ACDL) instrument onboard the Atmospheric Environmental Monitoring Satellite (AEMS) was successfully launched in April 2022, which allows a new perspective to quantify the global spatial distribution of atmospheric CO2 with high accuracy. In this work, the impact of the Doppler shift on CO2 measurements for an integrated-path differential absorption (IPDA) light detection and ranging (lidar) system was evaluated to meet the weighted column-averaged mixing ratio of carbon dioxide (XCO2) measurement requirements of less than one part per million (ppm). The measurement uncertainties due to the Doppler shift were first evaluated in airborne IPDA observations. The result shows that most of the Doppler shift is in the range of 6–8 MHz, resulting in 0.26-0.39 ppm deviations in the XCO2 results. The deviations between the XCO2 retrievals and in situ measurements decreased to 0.16 ppm after the correction of the Doppler shift from 11:28:29 to 11:28:49 in the flight campaign. In addition, the online Doppler shift accounts for 98% of the deviations between XCO2 retrievals and in situ measurements. Furthermore, the impact of the Doppler shift on ACDL measurements is also assessed. The differences between the XCO2 retrievals with and without Doppler shift are used to quantify measurement uncertainties due to the Doppler effect. The simulations reveal that a pointing misalignment of 0.067 mrad can lead to a mean bias of about 0.30 ppm (0.072%) in the CO2 column. In addition, CO2 measurements are more sensitive to the Doppler shift at high altitudes for IPDA lidar, so the largest differences in the CO2 columns are found on the Qinghai–Tibet Plateau in China. [ABSTRACT FROM AUTHOR]

We acquired measurements of four observable parameters of refracted signals received from the ionosphere (Doppler shift, Doppler spectrum, number of rays, and signal amplitude) with the oblique HF Doppler technique in the city of Harbin during the super typhoon Lekima event of 4–12 August 2019. The ionospheric response was observed by the Harbin Engineering University multifrequency multiple path coherent radio system in the People's Republic of China. The maximum distortion of radio‐wave characteristics and ionospheric disturbances were observed to occur during the day when the super typhoon Lekima energy gained a maximum value and when the super typhoon approached close to the ionospheric part of the radio‐wave propagation paths. The magnitude of the ionospheric disturbances decreased with the distance between the super typhoon and propagation path midpoints. Both aperiodic (chaotic) and quasi‐sinusoidal disturbances were observed to accompany the action of the super typhoon in the ionosphere. The action of the typhoon was often accompanied by up to ±1.5 Hz broadening of the Doppler spectra, 10–30 dBV variations in the signal amplitude, and quasi‐sinusoidal variations in the Doppler shift with 0.10‐ to 0.40‐Hz amplitudes and periods of 20–30 to 70–80 min. The quasi‐sinusoidal variations in the signal amplitude with a ∼24‐min period, T, are due to focusing and defocusing of rays by wavelike disturbances in the electron density. The periods of the quasi‐sinusoidal disturbances were observed to be ∼12–24 min. Such periods pertain to atmospheric gravity waves. The atmospheric gravity waves generated by the super typhoon gave rise to quasi‐sinusoidal variations in the electron density with relative amplitudes of ∼3%–∼19%. Plain Language Summary: Typhoons pertain to high‐energy sources that are capable of giving rise to perturbations in all geospheres. The disturbances produced in the atmosphere and geospace make a significant contribution to the state of space weather, whereas the ionospheric perturbations have a drastic effect on the propagation of HF radio waves. We have used super typhoon Lekima, which took place during the 4–12 August 2019 period, to demonstrate some of the many disturbing influences that typhoons have on the state of space weather and the propagation of HF radio waves. The multifrequency multi path observations have been taken by the coherent radio system located at the city of Harbin (People's Republic of China). Key Points: Atmospheric gravity waves launched by the typhoon Lekima produced ∼3%–∼19% quasi‐sinusoidal electron density variationsSpectrum broadening attained ±1.5 Hz, and Doppler shift varied with 0.10–0.40‐Hz amplitudes and 20–30‐ to 70–80‐min periodsThe action of the super typhoon Lekima was accompanied by 10–30 dBV variations in the signal amplitude [ABSTRACT FROM AUTHOR]

We have acquired HF Doppler measurements and studied the dynamics of the ionosphere in the ∼100–300 km altitude range during the 1–10 September 2019 period of typhoon activity near the People's Republic of China (PRC). The multifrequency multiple path system located at the Harbin Engineering University campus, the PRC, and probing the ionosphere at oblique incidence was used to identify the effects from the typhoons. The response of the ionosphere to the Typhoon Lingling was detected along three adjacent radio‐wave propagation paths where chaotic and quasiperiodic variations in the Doppler shift and a significant (from −1 to 1 Hz or greater) Doppler spectrum broadening were observed to occur. The Doppler spectrum chaotic variations are due to plasma turbulence generated by typhoons in the ionosphere, and the Doppler shift quasiperiodic variations along the main ray are due to infrasound and atmospheric gravity waves (AGWs) launched by the typhoons. The relative amplitude of quasiperiodic variations in the electron density in the field of the infrasound wave reached several percent, and in the field of the AGW attained from ten to a few tens of percent. The effects of the Typhoon Faxai during 9/10 and 10/11 September 2019 nights were accompanied by a 27% decrease in the electron density in the ionospheric E and F regions. At the closest approach of the Typhoon Faxai to the ionosonde during 8/9 September 2019 night, when it had the largest energy, a 56% increase was detected in the ionospheric F region electron density. Key Points: Measurements utilized up to twelve 5–10 MHz propagation paths to observe the ionospheric response to the Typhoons Lingling and FaxaiUp to ±1–1.5 Hz Doppler spectrum broadening was detected, and up to ±1 Hz Doppler shift variations were seenUnder the action of the typhoons, the periods of the aperiodic and quasiperiodic disturbances in the ionosphere were observed to be 5–60 min [ABSTRACT FROM AUTHOR]

We demonstrate by theoretical analysis that periodically distributed viaduct piers of high-speed rail result in the Doppler effect in the seismic wavefield of high-speed rail at specific frequencies and analyze the Doppler effect's influence on the wavefield's spectrum feature. We further verify our theoretical prediction by using observational data of the high-speed rail seismic wavefield in Rongcheng, Hebei Province, China. We find that the wavefield component with a noticeable Doppler effect vibrates in the propagation direction and only has a unique apparent wave speed, indicating that P-wave is dominant. Furthermore, we propose a speed measurement method based on the Doppler effect and measure the wave speed of the medium along the rail. Measurement results are highly stable and consistent. [ABSTRACT FROM AUTHOR]

Traffic radar-based speed meter (TRSM) is an important measuring instrument for measuring the speed of target vehicle based on the radar Doppler effect, and has been legally used in road vehicle speeding enforcement for more than 30 years in China. TRSM with target position determination (TRSM-TPD) is a new generation of TRSM with the advantages of speeding enforcement by lane, high accuracy of speed measurement and target position determination, high efficiency, low cost, etc. This paper proposes a new verification method for TRSM-TPD in road vehicle speeding enforcement. The proposed verification method includes the simulated speed calibration method for initial verification in the laboratory, and the online speed and position calibration method for subsequent verification in the field. The range of simulated radial speed is up to (1∼400) km/h and the maximum permissible error is within ±0.03 km/h, which can satisfy the full-range and high-accuracy speed calibration requirements for TRSM-TPD. The uncertainty of the reference facility in actual traffic is 0.12% within the speed range of (60∼250) km/h, where coverage factor k = 3. The simulated and online calibration results validate the effectiveness of the proposed verification method and the feasibility of the realized target speed simulator and the established reference facility. [ABSTRACT FROM AUTHOR]

A brief description of the multipath coherent radio technique installation is presented. Its goal is continuous monitoring of the dynamical processes in the ionosphere caused by space weather variations and the impact of high-energy sources in the Earth–atmosphere–ionosphere–magnetosphere system. The variations of radio-wave characteristics (the Doppler spectra and signal amplitudes) in the HF range and the ionospheric parameters over China during the ionospheric storm of August 26, 2018, are described. An ∼50–100 km ascent in the radio-wave reflection region and its oscillations with an amplitude of ∼30–40 km were observed many times during the storm on all paths. The ascents were followed by descents of the radio-wave reflection region by many tens of kilometers. The ascents and descents of the reflection region were caused by a decrease in the electron concentration by a factor of 1.5–2 and its increase by a few times, respectively. The maximal increase in the electron concentration in the E and F regions reached a factor of 1.5 and 3, respectively. The relative amplitude of oscillations in the electron concentration reached many tens of percent. The amplitude of oscillations of frequency Doppler shift was several times lower on the reference days. The observed oscillations in the frequency Doppler shift were apparently caused by generation of the atmospheric gravity waves and their subsequent propagation to the latitudes of the means of observation. The velocity of wave disturbances was ∼275–480 m/s, whereas their period was ∼60 min. The ionospheric disturbances of August 27, 2018, were insignificant despite the repeated magnetic storm. [ABSTRACT FROM AUTHOR]

Results obtained from observations of ionospheric disturbances over the People's Republic of China during the course of the geospace storm of 14 May 2019, one of the largest storms in 2019, are presented. The Harbin Engineering University operates the multi-frequency multipath radio wave diagnostics employing software defined technology and continuously monitoring dynamic process acting in the ionosphere at oblique incidence since April 2018. The basic premise upon which this instrument operation is based is that the digital re-sampling remains coherent with radio frequency for each propagation path, which permits Doppler spectra and signal amplitudes to be calculated along each of the 14 propagation paths. UT dependences of the Doppler spectra, the main mode Doppler shifts of frequency, and signal amplitudes that were measured on the day of the ionospheric storm and on the reference days of 13 and 15 May 2019 have been analyzed. After the magnetic storm onset, the Doppler shift of frequency exhibits an abrupt –1-Hz decrease, indicating the ionospheric storm onset. In addition, quasi-periodic variations in the Doppler shift of frequency, with 5-, 15-, 20-, and 30-min periods and the amplitudes in the range from 0.05 Hz to 0.15 Hz, occur in the course of the storm. These variations are due to modulation by infrasound (5-min period oscillation) and atmospheric gravity waves (15-, 20-, and 30-min period oscillations). In the electron density, the corresponding waves have amplitudes equal to 0.7% and 4–8%, respectively. [ABSTRACT FROM AUTHOR]

This article studies both experimentally and numerically the backscattering radar cross section (RCS) and Doppler spectrum characteristics from 2-D linear and nonlinear time-varying sea-like surface at UHF band under low grazing incidence. The small slope approximation and choppy wave model are applied to solve rough surface scattering and generate nonlinear sea waves, respectively. A coherent Doppler radar operating at 340 MHz was deployed at the tip of Huangqi peninsula in the southeast coast of China to measure the echo spectrum from the actual sea surfaces. At the same time, an ocean buoy was placed in the radar coverage to monitor the sea states. The RCS and Doppler spectrum are analyzed and compared comprehensively between radar measurements and numerical predictions. After compensating the influence of wind direction, the responses of radar echo power and numerical predicted RCS to wind speed are basically consistent and are more sensitive in low sea states. The correlation of Doppler spectra between radar measurements and numerical simulations exceed 0.96 during the whole experiment. The intensity of the high-order peaks increases rapidly with the wind speed, while the intensity of the Bragg peak decreases slightly. Doppler spectrum will be shifted by an amount proportional to radial surface current. [ABSTRACT FROM AUTHOR]

We present the observational evidence of $E$ - and $F$ -region field-aligned irregularities (FAIs), nighttime medium-scale traveling ionospheric disturbances (MSTIDs), and a sporadic $E$ ($E_{\text {S}}$)-layer using the Wuhan very-high-frequency (VHF) coherent scatter radar, Wuhan Global Navigation Satellite System (GNSS) network, and Wuhan ionosonde. We observed simultaneously E and F FAIs by VHF radar and the $E_{\text {S}}$ -layer and spread- $F$ by Wuhan ionosonde. We also observed MSTIDs using the Wuhan GNSS network in a southwestward direction of propagation and horizontal propagation velocity of less than 180 m/s, for a period of ~33 min. Simultaneous observations of an $E_{\text {S}}$ -layer and FAIs in the $E$ -region and FAIs in the $F$ -region suggested the existence of an electrodynamic coupling between the $E$ and $F$ regions in the mid- and low-latitude nighttime ionosphere. A polarized electric field associated with nighttime MSTIDs can generate the uplift movements of the $F$ -region’s electron density. This uplift effect consequently can excite the gradient drift instability (GDI) with an accompanying enhanced vertical gradient of the $F$ -layer’s electron density. Our results indicated that the $F$ -region MSTIDs excited by Perkins instability might be further modulated by the $E \times B$ effect and subsequently can evolve to spread-F like FAIs. Our observational investigation provided the first evidence of the full dynamics and links among different ionospheric disturbances in a mid- and low-latitude nighttime region of China. [ABSTRACT FROM AUTHOR]

• A transmitter with bandwidth of 40–100 MHz at 100-kilowatt level was cross-verified through three-dimensional (3D) simulations and experiments. • New phenomenons of high frequency oscillation between the short strip inductor and the shield cavity was found in the input simulation results. • The simulation can provide both the electric field energy and the surface current distribution of the structure of the entire amplifier at a particular power. • The amplifier installed with the new tetrode DB968 achieved the design objectives in the test experiment with 150 and 110 kW power outputs at 48 and 100 MHz, respectively. A 1.5 MW final power amplifier is to be developed for ion cyclotron resonance heating (ICRH) system for the China fusion engineering testing reactor (CFETR) project. First, the feasibility of driver power amplifier with input matching circuit and output resonator cavity and a newly developed tetrode was cross-verified through three-dimensional (3D) simulations and experiments. A single coaxial cavity in parallel with the tetrode covered the frequency range of 40 to 100 MHz at a 100-kilowatt level. In contrast to the previous method of deducing matching parameters using RF circuit and transmission line theory, the use of 3D transmitter simulations provided more accurate matching parameters of tuning components at different operating frequencies. A new phenomenon of high frequency oscillation between the short strip inductor and the shield cavity was found in the input simulation results, which was subsequently verified by experiments. Specific reasons for dividing the output into two parts of high and low frequency were found through output circuit simulations. One is that the length of short stub decreases with the increase of operating frequency, thus decreasing the frequency resolution if all frequencies were using low frequency port. The other is that the coupling capacitor increases sharply with the increase of frequency due to parasitic effect in the low output. Further, the simulation facilitated the study of parasitic effects on matching parameters caused by strip-inductance, inter electrode capacitances of tetrode, and RF cavity. Thus, facilitating the design of final power amplifier in the future. Finally, the amplifier installed with the new tetrode DB968 achieved the design objectives in the test experiment with 150 and 110 kW power outputs at 48 and 100 MHz, respectively. [ABSTRACT FROM AUTHOR]

Composite reflectivity Doppler radar data from June to September of 2007-2010 were used to classify mesoscale convective systems (MCSs) over central east China into seven morphologies. The morphologies included one nonlinear mode (NL) and six linear modes: convective lines with no stratiform precipitation (NS), trailing stratiform precipitation (TS), leading stratiform precipitation (LS), parallel stratiform precipitation (PS), bow echoes (BE), and embedded lines (EL). Nonlinear and linear systems composed 44.7% and 55.3% of total MCSs, respectively, but there was no primary linear mode. All MCS morphologies attained their peak occurrence in July, except BE systems, which peaked in June. On average, TS and PS modes had relatively longer lifespans than did other modes. Significant differences in MCS-produced severe weather existed between dry and moist environments. High winds and hail events were mainly observed in dry environments, and in contrast, short-term intense precipitation occurred more frequently in moist environments. BE systems generated the most severe weather on average, while most TS systems were attendant with short-term intense precipitation and high winds. EL and PS systems were most frequently associated with extreme short-time intense precipitation (≥50 mm h−1) as these systems preferentially developed in moist environments. BE systems generally occurred under strong low-level shear and intermediately moist conditions. LS systems were observed in weak low-level shear, whereas EL systems often developed in relatively stable conditions and weak low- to middle-level shear. The largest instability was present in the environment for NS systems. The environmental parameters for TS systems featured the largest differences between the dry and moist cases. [ABSTRACT FROM AUTHOR]

Abstract: The transient thermal-hydraulic code THACOS is under development for analysis of China Demonstration Fast Reactor. Applying modular technology, the code contains the core module, the pump module, the sodium pool module and the heat exchanger module and each module could operate separately. It can provide one-dimensional thermal-hydraulic simulation for the primary sodium coolant loop. The point reactor kinetics equations with six-group delayed neutrons have been applied to calculate the core power considering reactivity feedbacks caused by the Doppler effect, coolant density, axial expansion of fuel rods and radial expansion of the core. Multiple-channel model is applied to depict the core. Compressible homogenous flow model is used for the two-phase flow of sodium. The calculated results show that sodium boiling will occur quickly under the ULOF accident without any shutdown rods insertion. While, with the insertion of three hydraulically suspended shutdown rods, the core could be shut down safely and boiling will not occur in a short period of time. Obviously, the passive hydraulically suspended shutdown rods could keep the core safe under ULOF accidents. [Copyright &y& Elsevier]

Abstract: A survey was conducted to examine river bedforms using side-scan sonar, sub-bottom profiler and an Acoustic Doppler Profiler in the middle–lower (mid-lower) Changjiang (Yangtze) River (downstream of Wuhan), China, during August 14–20, 2003 when the discharge was 27,000–36,000m3s−1. The results show bedforms of a range of sizes occur in the channel and their heights and lengths follow an exponential correlation below Flemming''s maximum line. Not all bedforms were formed under the flow conditions experienced during the survey, as shown by comparison to three existing models in the literature. Small-scale bedforms with a length <60m, defined as flat bed, mega-ripple and small dune in the present study, are mostly in equilibrium and are probably formed under the existing flow conditions. The large dunes with a length of >60m are not in equilibrium and are believed to be the relicts of previous large discharges now undergoing adjustment. Different bedform types occur in the five river reaches in this section of the Changjiang (Wuhan–Tianjiazhen, Tianjiazhen–Anqing, Anqing–Maanshan, Maanshan–Jiangyin and Jiangyin–estuary downstream). In the narrow and single channel reaches above Anqing, large/small dunes are limited to the channel with higher water surface slope where stream power is strong enough for riverbed sediments to be moved frequently. In the downstream reaches between Anqing and Jiangyin, characterized by anabranching channels, small-scale bedforms superimposed on large dunes occur widely due to intensive riverbed sediment transport from frequent diverging/converging flow during both floods and low-flow periods. Mega-ripples and flat beds prevail in the lowermost channel below Jiangyin where wider cross-sections result in dispersed stream power. [Copyright &y& Elsevier]

Abstract: Yellow River is the second longest river in China''s, and its mainstream passes four different tectonic provinces in North China from west to east. Here, we exploit the relationship between the fractal dimensions of Yellow River channel and the tectonic provinces it flows through. The fractal dimension series D i was obtained for the main channel of Yellow River by applying the successive shift divider method using several different scale ranges. The results show that the magnitude of D i values is related to the uplifting intensity and time of the tectonic provinces where the river channel is located. The intenser and younger the uplifting of the tectonic provinces, the larger the fractal dimension D i of the channel when the scale range is taken as 200 nodes (300km). Using the same scale range, the D i values also are calculated by applying a successive shift box method. The differences between results from both methods are discussed. [Copyright &y& Elsevier]

The Beijing 2008 Forecast Demonstration Project (B08FDP) included a variety of nowcasting systems from China, Australia, Canada, and the United States. A goal of the B08FDP was to demonstrate state-of-the-art nowcasting systems within a mutual operational setting. The nowcasting systems were a mix of radar echo extrapolation methods, numerical models, techniques that blended numerical model and extrapolation methods, and systems incorporating forecaster input. This paper focuses on the skill of the nowcasting systems to forecast convective storms that threatened or affected the Summer Olympic Games held in Beijing, China. The topography surrounding Beijing provided unique challenges in that it often enhanced the degree and extent of storm initiation, growth, and dissipation, which took place over short time and space scales. The skill levels of the numerical techniques were inconsistent from hour to hour and day to day and it was speculated that without assimilation of real-time radar reflectivity and Doppler velocity fields to support model initialization, particularly for weakly forced convective events, it would be very difficult for models to provide accurate forecasts on the nowcasting time and space scales. Automated blending techniques tended to be no more skillful than extrapolation since they depended heavily on the models to provide storm initiation, growth, and dissipation. However, even with the cited limitations among individual nowcasting systems, the Chinese Olympic forecasters considered the B08FDP human consensus forecasts to be useful. Key to the success of the human forecasts was the development of nowcasting rules predicated on the character of Beijing convective weather realized over the previous two summers. Based on the B08FDP experience, the status of nowcasting convective storms and future directions are presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper retrieves the three dimensional (3D) wind fields and studies the evolution of the 3D wind fields and the formation mechanism of the sudden heavy rainfall on Meiyu front on 26th–27th June 2003 in Huaihe river basin in China, using the volume scan data of the dual-Doppler radar located in Hefei and Maanshan cities. Due to the effect of the low level trough, low level jet and the convergence line at the low and medium levels, it produced a heavy precipitation in Anhui province. It shows clearly that the primary feature of this event is local, sudden and short timed. It is a convective-stratiform mixed cloud precipitation based on the radar echo analyses. The meso-β-scale convective system (MβCS) and the meso-γ-scale system located on the MβCS played an important role on this heavy rainfall. The meso-β-scale convective cloud has high precipitation efficiency. The dual-Doppler retrieved wind reveals that the heavy rainfall was caused by the meso-β-scale convergence lines at the low and the medium levels. The convergence line triggered and maintained the heavy rainfall. There were strong convergence and vorticity at the low and medium levels of the MβCS. The convergence line spread from west to east and the position of the convergence line at the medium levels is westward of the ones at the low levels. When the convergence line at the low and medium levels began to weak, the precipitation began to weak too. The intensity of the precipitation weakened remarkably when the convergence line dissipated. The 3D kinematic conceptual structure model of this heavy rainfall case is also given. [Copyright &y& Elsevier]

Among the single-Doppler radar wind analysis methods, the velocity–azimuth display (VAD), velocity–azimuth process (VAP), and uniform-wind (UW) methods are widely used because of their simplicity. This paper shows that the VAD, VAP, and UW methods can all be derived from the same relationship based on the azimuthal uniform-wind assumption. Using this assumption, an integrating VAP (IVAP) method is developed that can provide a smoother wind field than the VAP and UW methods and a higher resolution than the VAD method. Using the IVAP technique, the wind fields associated with a heavy rainfall case in Shanghai, China, are retrieved and compared with those from surface observations and wind-profiler data. [ABSTRACT FROM AUTHOR]

The 24 GHz continuous-wave (CW) Doppler radar sensor (DRS) is widely used for measuring the instantaneous speed of moving objects by using a non-contact approach, and has begun to be used in train-borne movable speed measurements in recent years in China because of its advanced performance. The architecture and working principle of train-borne DRSs with different structures including single-channel DRSs used for freight train speed measurements in railway freight dedicated lines and dual-channel DRSs used for speed measurements of high-speed and urban rail trains in railway passenger dedicated lines, are first introduced. Then, the disadvantages of two traditional speed calibration methods for train-borne DRS are described, and a new speed calibration method based on the Doppler shift signal simulation by imposing a signal modulation on the incident CW microwave signal is proposed. A 24 GHz CW radar target simulation system for a train-borne DRS was specifically realized to verify the proposed speed calibration method for a train-borne DRS, and traceability and performance evaluation on simulated speed were taken into account. The simulated speed range of the simulation system was up to (5~500) km/h when the simulated incident angle range was within the range of (45 ± 8)°, and the maximum permissible error (MPE) of the simulated speed was ±0.05 km/h. Finally, the calibration and uncertainty evaluation results of two typical train-borne dual-channel DRS samples validated the effectiveness and feasibility of the proposed speed calibration approach for a train-borne DRS with full range in the laboratory as well as in the field. [ABSTRACT FROM AUTHOR]

The Key Laboratory of Ocean Remote Sensing of the Ministry of Education of China, Ocean University of China, has developed the first mobile Doppler wind lidar in China. As an important component of meteorological services for the Good Luck Beijing 2007 Qingdao International Regatta, the mobile Doppler wind lidar was used to measure the sea surface wind (SSW) with 100 m*100 mspatial and 10-mintemporal resolution in Qingdao from 15 to 23 August 2007. We present the results from two aspects of this campaign. First, the lidar was operated in the fixed-direction mode and compared to SSW simultaneously measured by a collocated buoy. Second, we present lidar wind measurements throughout the regatta and show good agreement with the match situation of the International Regatta. In addition, we present a case study, accounting for the observation of sailboats stopped by the headwind. With considerable data accumulated, we have shown that the mobile Doppler wind lidar can indeed provide near real-time SSW in support of the sailing games. The lidar has also provided meteorological services for the 2008 Olympic sailing games from 8 to 22 August and Paralympics Sailing Games from 8 to 13 September 2008 in Qingdao. [ABSTRACT FROM AUTHOR]

Focuses on the acoustic Doppler-effect water current meters purchased by China's Environmental Protection Administration from U.S.-based RD Instruments Inc. as part of a river pollution monitoring program. Measure of flow rates and direction; Determination of current velocities; Software package RDI WinRiver.