Abstract:Accurate and objective forecasts of thunderstorm, short-time severe rainfall, thunderstorm gale and hail are meaningful for extending the validation of warnings and taking targeted preventive measures. This paper introduces the framework and implementation ways of the objective forecasting system combining physical understanding and fuzzy logic artificial intelligence. This system, developed by the National Meteorological Centre (NMC), can provide short-term probability forecasts of thunderstorm, short-time severe rainfall, thunderstorm gale, and hail. The key predictors used for the four different convective weather phenomena, the methods for obtaining the membership functions, and the weighting sets of predictors are discussed. The property for the wide applicability of the combination method of physical understanding and fuzzy logic artificial intelligence is further investigated. It is concluded that the combination of the two can cover and reveal the key characteristics of the ever-changing environmental features favorable for a specific convective weather phenomenon.

Abstract:In this paper, the operational forecasts of the rapid intensification (RI) of Typhoon Lekima (1909) by the Tropical Regional Atmosphere Model for the South China Sea of China Meteorological Administration (CMA-TRAMS) and the high-resolution products of the ECMWF atmospheric model （HRES） are analyzed. Numerical sensitivity experiments are designed and carried out from the perspectives of horizontal resolution, initial and boundary conditions, and physical parameterization schemes. It is found that CMA-TRAMS and HRES both can predict the strengthening of Tyhpoon Lekima to some extent, but the predicted strengthening speed is obviously lower than observation. The two models both fail to meet the 24 h and 12 h RI standards, but can reach the 6 h RI standard. The experiment using 3 km horizontal resolution produces better forecasts of track and intensity of Lekima than that using 9 km resolution based on CMA-TRAMS, but it cannot improve the RI forecast. Nevertheless, the prediction of typhoon RI is significantly improved if the scheme has 3 km resolution nested to 9 km resolution. The experiment using the MRF boundary layer parameterization scheme generally performs better in forecasting typhoon track, intensity and RI than that using the YSU scheme. When the initial and boundary conditions with higher vertical resolution are used, combined with the sea surface temperature (SST) parameterization scheme, the RI forecast is obviously improved in the frequency and maximum speed. Analyses indicate that the SST parameterization scheme increases the difference between sea and air temperature, affecting the heat transport and exchange significantly. The enhancement of sensible heat flux from the ocean to the atmosphere and the enhancement of latent heat flux in the inner-core section of typhoon increase the temperature and humidity and magnify the negative tendency of pressure.

Abstract:The paper discusses the coordinate influence of CODAS-SST and the assimilated FY-4A temperature profiles on sea fog simulation with WRF model around the Yellow-Bohai Sea. The analyses show that the high-resolution CODAS-SST can significantly improve the results of sea fog simulation with WRF model around the Yellow-Bohai Sea, which makes the range and intensity of simulated fog more reasonable. By analyzing the sensitivity of various elements in the foggy area to change in SST, we have clarified that the 2 m temperature and specific humidity, as well as the sensible heat, latent heat, and water vapor fluxes at the sea-air interface, exhibit varying degrees of positive correlation with SST, while the liquid water content shows a significant negative correlation with SST. The assimilation of FY-4A vertical sounding data can further optimize the vertical distribution of specific humidity and wind speed in the boundary layer of WRF model, improving the vapor transport and liquid water content. Therefore, the coordinate assimilation of FY-4A vertical sounding data and CODAS-SST can better simulate the mesoscale characteristics of fog area, which indicates the high-precision and high-resolution ocean observation data are beneficial for improving the numerical simulation capability of sea fog.

Abstract:Using observation data from Yantai S-band dual polarization Doppler weather radar, Rongcheng CINRAD/SA radar, radiosonde and surface meteorological stations, as well as the ERA5 (ECMWF reanalysis data) and the hail, and tornado information obtained from field surveys, this article analyzes a severe hailstorm and tornado that occurred on 1 October 2021 in the eastern part of Shandong Peninsula. The results are as follows. Compared to the climatic mean field, the 500 hPa northeast cold vortex responsible for this severe convective process was extremely strong, and at 850 hPa there was continuous southward water vapor transport from South China to the west of Northeast China. Under the abnormal circulation background, the atmospheric thermal and dynamic conditions, such as dry and cold in the upper troposphere, but wet and warm in the low troposphere, with strong 0-6 km 〖JP2〗vertical wind shear and convective available〖JP〗 potential energy (CAPE) on the eastern Shandong Peninsula, were very favorable for the occurrence of severe hailstorm and tornadoes. The features of pre-storm low pressure, thunderstorm high pressure, and cold pool were obvious near the surface. During the hail period, the supercell features were very typical, with distinct hook-shaped echo and inverted “V” anterior inflow gaps in the lower layers, and vertical profiles showed distinct bounded weak echo region (BWER) and differential reflectivity (ZDR) column characteristics. According to the large hail location and starttime information, the median values of reflectivity factor (ZH), ZDR and correlation coefficient (CC) were 48.7 dBz, 0.89 dB and 0.90 respectively. When tornado and severe hail appeared on the ground, the maximum storm-top 〖JP2〗divergent outflow reached 71.5 m·〖JP〗s-1. The cold pool airflow at the northern end of the rear flank gust front (RFGF) and the south inflow on the pre-storm side formed a strong vortex upward motion, resulting in an EF1-level tornado. The tornado occurred at the top of the hook-like echo, and large hailstones appeared on the north side of the inflow gap. About 5 min before the tornado, 〖JP2〗the radar detected the tornadic debris signature (TDS) features, with ZDR being as low as -0.1 dB〖JP〗 and CC as low as 0.81. About 11 min before the tornado genesis, the ZDR arc in the lower layer and the descending reflectivity core (DRC) in the rear flank side of the supercell was detected. Rongcheng and Yantai radars identified mesoscale cyclones and tornadic vortex signature (TVS) about 22 min and 5 min in advance, respectively. This can provide an important reference for tornado warning. Based on the observation analysis, the schematic diagram of the low-layer air flow field and the tornado and large hail-falling area of the supercell storm is summarized.

Abstract:In order to evaluate the performance of millimeter-wave radar in the case of typhoon, the millimeter-wave cloud radar data of Shanghai during the four typhoons in 2018 and 2019, and the data of disdrometer, satellite and S-band weather radar are studied to explore the feasibility of using the millimeter-wave radar to study the outer rainbands of typhoon. It is shown that the millimeter-wave radar has a good detection performance, and has certain application potential for detecting vertical structure of cloud and precipitation. Determination of cloud top height is more accurate when the 〖JP2〗rainfall rate is lower than 5 mm·〖JP〗h-1. A method for bright band determination is proposed, and the results of application are found to be in good agreement with the sounding. Comparison of the retrieval of rainfall intensity by millimeter-wave radar and S-band radar shows feasibility of retrieving rainfall rate profile by taking advantage of the millimeter-wave radar attenuation. In the situation of significant growth of raindrops, it is necessary to revise the retrieval algorithm. This research could provide a reference for millimeter-wave radar detection of typhoon outer rainbands.

Abstract:Using the Doppler weather radar and cloud-to-ground (CG) lightning observation data in Jiangxi Province from March to September in 2013-2020, we carried out a statistical analysis on the distribution characteristics of lightning and its relationship with the main features of radar. The results show that the CG lightning frequency in Jiangxi Province gradually decreases from the northeast to the southwest, and the Poyang Lake Plain in the north is the area with high CG lightning frequency. The CG lightning frequency has obvious seasonal and diurnal variation characteristics, and the total CG lightning frequency reaches the peak of one day at 16:00 BT. The relationship between CG lightning frequency and the low-level (3 km) radar echo intensity can be described by a logarithmic fitting equation. The number of CG lightning frequency is positively correlated to the variation trend of the low-level (3 km) radar echo area, and the stronger the echo, the stronger the correlation. However, there is a phase difference between the two, and the increase of the CG lightning frequency precedes the increase of the echo area by about 57%-60%. In most cases, the increase in both of CG lightning frequency and echo area can be found within 18 minutes. The boxplot features show that with the increase of the echo intensity, the extension height of the echo is lowered correspondingly, but the echo thickness is added slightly. Thus, the radar echo characteristics of the 10 km radius range around the CG lightning occurrence grid point, where the radar echo intensities are different, are obtained.

Abstract:Using the precipitable water vapor (PWV) data from Global Navigation Satellite System (GNSS) meteorological network and the time series of hourly precipitation, temperature, pressure and relative humidity from the adjacent meteorological stations in Hubei Province from June to July in 2019 and 2020, we build a new threshold prediction model of short-time severe precipitation on the basis of PWV, 6 h PWV tendency (PWV*) and pseudo-equivalent temperature anomaly (θse*) in this study. The critical success index (CSI) and probability of detection (POD) are used to determine and validate the thresholds for the three predictors. This new model is tested by the precipitation data in June and July, 2021. The results show that CSI and POD scores are 0.167 and 0.593, respectively, which are higher than the objective forecast scores for short-time severe precipitation by conventional operational methods. About 48% of the short-time severe precipitation events are successfully predicted with a lead time of 24 h, and 78% occur within 48 h. The analysis results show that 78.6% of the severe precipitation occur under the condition of the 15 h cumulative value of PWV* (∑PWV*) ≥75 mm and the 24 h cumulative value of θse* (∑θse*) ≥ 30 K. This finding could be positively indicative of severe rainfall in Meiyu season and torrential rains with the PWV high-value zone superimposed to the high-value zones of ∑PWV* and ∑θse*.

Abstract:Based on the data of automatic weather stations in Beijing region, complementary rain gauge stations of Beijing Municipal Commission of Planning and Natural Resources, dualpolarization radar and windprofiling radar as well as the GPS data and ERA5 reanalysis data, we analyze the spatiotemporal characteristics, and causes of this July 2023 extremely torrential rain in Beijing. The results indicate that the accumulated precipitation and intensity of this event were significant, with an average accumulated precipitation of 331 mm and maximum precipitation 1025 mm at a single station, both of which broke historical records. The maximum hourly rainfall of 126.6 mm·h-1 ranked the second in history. This rainfall process can be divided into five stages, of which stage Ⅱ and stage Ⅳ of the rainfall accounted for 37.1% and 39.7% of the total process, being the primary phases. During stage Ⅳ, the corresponding jet stream intensity got much stronger, and the characteristics of high temperature and high humidity were more obvious. Terrain had a significant impact on the increase in rainfall. The rainfall increased most rapidly in the region between 100-300 m above sea level， and the maximum value appeared near the areas approximately at the altitude of 400 m. The average accumulated rainfall and maximum hourly rainfall in mountainous areas were 2.1 (3.0) times and 2.0 (2.7) times that of the plains during stage Ⅱ (stage Ⅳ), respectively. Stage Ⅱ was primarily influenced by the direct terrain lifting of lowlevel jet, while stage Ⅳ was characterized by the combined effect of terrain lifting and blocking convergence. On the morning of the 31 (stage Ⅳ), the coupling of the boundary layer convergence at the terminus and the lowlevel divergence at its entrance led strong ascending motions, promoting the massive βMCS to develop into a linear shape accompanied by a mesoγ scale vortex. This βMCS propagated northward along the western mountainous regions, forming a short train effect and triggering the shorttime extremely severe rainfall over 100 mm·h-1 at eight stations.

Abstract:Operational positioning and intensity estimation errors, as well as track and intensity forecast errors of typhoons over the Western North Pacific and the South China Sea in 2022 are evaluated according to the “Regulations on Typhoon Operations and Services”. The results show that in 2022, the positioning errors made by the official typhoon forecasting agencies displayed a negative correlation with the typhoon intensity grades. The mean error of position estimation made by the National Meteorological Centre (NMC), China Meteorological Administration （CMA）, were the smallest at each typhoon intensity grade. In 2022, the mean error of position estimation (15.4 km) made by NMC was 21.8% lower than 19.7 km in 2021, and the mean absolute error of intensity estimation (1.3 m·s-1) made by NMC was slightly smaller than the value (1.4 m·s-1) in 2021. Relative to 2021, the mean errors of track forecast by subjective and objective forecasts in 2022 were generally reduced, but the mean absolute errors of intensity forecasts were generally increased. Track forecast skill scores by SSTC, CMA-TRAMS, and ECMWF-IFS were relatively high. Intensity forecast systematic biases by NCEP-GFS, JMA-GSM, CMA-TRAMS, and CMA-TYM were insignificant, while forecast skill scores by NCEP-GFS, HWRF, and CMA-TRAMS were relatively high.

Abstract:The main characteristics of the atmospheric circulation in February 2024 are as follows. There were two polar vortex centers in the Northern Hemisphere. The eastern polar vortex, which was stronger than normal, was centered over the Sea of Okhotsk to the Kamchatka Peninsula, making the trajectory of cold air more eastward. In midlatitude the circulation was distributed in a threewave pattern, with the average trough in Siberia stronger than usual, causing the frequent occurrence of shortwave trough in the westerlies. The southern trough was more eastward than before and the Western 〖JP2〗Pacific subtropical high was significantly stronger. The monthly mean temperature was -1.8℃, 0.5℃ lower than normal (-1.3℃),〖JP〗 and the monthly mean precipitation was 22.5 mm, 38% more than normal (16.3 mm). There were three major cold air processes during the month, of which the strong cold wave during 17-22 February led to severe cooling and significant low temperatures. Due to the combined influence of southward cold air and the southwest warmhumid airflow, two extreme persistent lowtemperature rainy and snowy weather processes occurred in the central and eastern regions of China. During the processes of lowtemperature and freezing weather, the intensity and range of freezing rain were large, and the precipitation amount was somewhat extreme. Such a weather condition created many difficulties for the Spring Festival traffic. In addition, sandstorm and severe convective weather were monitored for the first time in this year.