Convective storms transmit momentum through turbulence,so it is important to understand the echo characteristics of turbulence structure in severe convective storms.Focusing on the velocity spectrum width above 5 m·s -1 ,the turbulent intensity of two strong hailstorm supercells with different intensity of mesocyclones are analyzed,and the relationship between airflow structure and turbulence enhancement are revealed.The re‐sults show that:（1） The strong hail supercell has moderate or above intensity turbulence in the strong updraft re‐gion,and the supercell triggered by the gust front also shows moderate intensity spectrum width in the inflow path,indicating the possibility of moderate intensity turbulence.（2） In general,the strongest turbulence occurs in the region with the largest velocity shear intensity.The maximum spectrum width of the supercell with moder‐ate intensity mesocyclone is about 10 ms -1 ,with differential reflectivity factor (Z DR ) within 1dB,echo intensity exceeding 35 dBZ,and larger differential phase shift rate (K DP ).The strong turbulence region of the supercell with strong mesocyclone is mainly located at the intersection of positive and negative velocities at the top of Z DR column,and the spectral width near the mesocyclone can reach 16.5 m·s -1 ,and the side near the strong echo core contains more supercooled water,with about 0.96 of correlation coefficient （CC） and large K DP .While,the echo intensity on the other side is slightly lower,with CC low to 0.85,where graupel particles and large rain‐drops brought by updraft exist.These regions of strong turbulence indicate the path of momentum transmission.（3） The upper part of the supercell storm has the strongest turbulence,both updrafts and downdrafts are strong,but the turbulence is stronger near the downdrafts that probably related to horizontal shear of the wind,where the highest spectrum width for strong mesocyclone is 17.5 m·s -1 ,and Z DR is higher than that in the updraft and K DP is negative,but K DP is about 0（°）·km -1 and Z DR is about 0 dB in the updrafts,however,spectrum width of the storm with moderate mesocyclone increases slightly.Strong mesocyclone supercell has stronger turbulence en‐hancement,and these discussions provide a reference for understanding the turbulence structure and momentum transmission of severe storms by dual-polarization radar observation.

In this study, we utilized dual-polarization weather radar and disdrometer data to investigate the kinematic and microphysical characteristics of an extreme heavy rainfall event that occurred on 20 July 2021, in Zhengzhou. The results are as follows: FY-2G satellite images showed that extremely heavy rainfall mainly occurred during the merging period of medium- and small-scale convective cloud clusters. The merging of these cloud clusters enhanced the rainfall intensity. The refined three-dimensional wind field, as retrieved by the multi-Doppler radar, revealed a prominent mesoscale vortex and convergence structure at the extreme rainfall stage. This led to echo stagnation, resulting in localized extreme heavy rainfall. We explored the formation mechanism of the notable ZDR arc feature of dual-polarization variables during this phase. It was revealed that during the record-breaking hourly rainfall event in Zhengzhou (20 July 2021, 16:00–17:00 Beijing Time), the warm rain process dominated. Effective collision–coalescence processes, producing a high concentration of medium- to large-sized raindrops, significantly contributed to heavy rainfall at the surface. From an observational perspective, it was revealed that raindrops exhibited significant collision interactions during their descent. Moreover, a conceptual model for the kinematic and microphysical characteristics of this extreme rainfall event was established, aiming to provide technical support for monitoring and early warning of similar extreme rainfall events.

为了深入认识冰雹云中闪电的演变特征及云物理机制,利用VLF/LF三维闪电监测资料,结合S波段双偏振雷达、地面观测等资料,采用统计、对比方法,对福建2017—2020年31个冰雹单体闪电特征进行了分析.结果表明:降雹前闪电频数峰值约有2/3在50次·(6 min)-1以上,80％冰雹云地面降雹出现在闪电峰值后的3～25 min;降雹前总闪电频数出现跃增,70％雹暴单体频数平均递增率达4次·min-1以上,闪电快速跃增提前于降雹前6～40 min;云闪频数在成熟阶段最多,发展阶段最少;冰雹单体三个阶段云闪集中分布在2～6 km高度层;差分反射率因子(Zdr)、相关系数(CC)等参数及粒子相态识别分析表明雹云降雹前融化层以上由冰雹和霰组成,融化层下由干、湿冰雹和雨粒子组成,低层则主要由湿冰雹和中大雨粒子组成;闪电频数、正地闪或正云闪占比率与回波强度、最强回波高度、强回波伸展高度呈正相关.结合了闪电资料与双偏振雷达参量,为识别冰雹云体演变及雷电预警提供参考.

An extreme flash rain event that occurred in Xiamen under the background of subtropical high on 11 August 2021 is analyzed based on X-band dual-polarization phased array radar observations. Dynamic and microphysical characteristics of the precipitation system are analyzed using the Doppler radar wind field retrieval technique combined with high-precision topographic data. The study yields the following results. (1) The event took place under the control of the subtropical high with the characteristics of weak synoptic-scale forcing. The surface wind convergence line promoted the formation of a quasi-linear convective system (QLCS), and the back-building process of the QLCS led to local extreme precipitation event. (2) The updraft lifted the raindrops to the mid-level, forming a large particle accumulation layer. When it descended, the rain intensified. The configuration of inclined updraft and downdraft ensured that the falling of large particles would not suppress updraft, which is favorable for the development and maintenance of convective system. The downdraft triggered the development of the upstream convective system, forming a back-building process. (3) The impact of local terrain on the precipitation system was highlighted under the weak synoptic scalebackground. The low-level convergence induced by local terrain caused the polarization parameters such as differential reflectivity (ZDR) and specific differential phase (KDP) to increase significantly on the windward slope, and the large value area was maintained there. The larger denser precipitation particles produced extremely high precipitation efficiency. (4) The warm rain process and the ice phase process coexisted in this extreme precipitation event. The warm rain process played a major role in the formation of rain, and the melting of ice particles accelerated this process. (5) At high rain rate, the breakage and collision of raindrops tend to balance, and the increase of rain rate depends on the increase of raindrop concentration. Therefore, ZDR can be used to determine whether the rain rate is increasing. (6) The evolution of the ZDR and KDP column is an appropriate index that can reflect the development of the surface rain rate. During a continuous precipitation process, the re-development of the ZDR (KDP) column height occurs earlier than that of the precipitation system.

To gain a deeper understanding of the formation and evolutionary mechanisms of a bow-shaped squall line (BSL) that occurred in East China on 10 May 2021, observations from S-band dual-polarization radars, a disdrometer and other instruments are used to investigate the characteristics and evolution of the kinematic, microphysical and radar echo structure within the squall line during its formative and mature stages. The results are as follows. The updraft induced by upper-level divergence and vertical thermal instability induced by the cold source at the middle and top of the troposphere provided environmental conditions suitable for the formation and strengthening of a squall line. The characteristics of the vertical vorticity at the leading edge of the squall line provided a good indication of its echo structure and evolutionary trend. The mechanism behind a new echo phenomenon—double high-differential reflectivity (ZDR) bands—observed in plan position indicator scans produced by the dual-polarization radar is investigated from the kinematic and microphysical structural perspectives. The evolutionary characteristics of the microphysical structure of the bulk of the squall line and its trailing stratiform cloud region are analyzed based on the quasi-vertical profiles retrieved from the S-band dual-polarization radar in Quzhou. Moreover, a conceptual model describing this type of BSL with a trailing region of stratiform rain in the warm sector is developed to provide technical support for the monitoring and early warning of BSLs.

This study was the first to conduct high-resolution consecutive detection of clouds over the hinterland of the Taklimakan Desert (TD) from April to June 2018 based on a ground-based Ka-band millimeter-wave cloud radar (MMCR), with focus on the structure and evolution of the desert clouds. We calculated reflectivity factor ( Z ), cloud boundary, and liquid water content (LWC) by use of the MMCR power spectrum data, which were verified against the observations from cloud profile radar (CPR) on board CloudSat . The results show that the TD clouds were mostly medium and high clouds, with thickness generally less than 2 km; moreover, the mean LWCs of these clouds were less than 0.01 g m −3 , implying that cirrus and stratiform clouds were predominant. For the observed low clouds, however, the average thickness was 3166 m and accompanying drizzles were concentrated within 2.5–4.5 km, indicating that precipitation was more likely to occur in the low clouds. The mean LWC in the TD clouds was 0.0196 g m −3 , less than that of clean clouds. Compared to other periods, the average durations and LWCs in the TD clouds increased significantly around noon owing to obvious surface sensible heating. The average time for evolution of high clouds into low clouds was approximately 2 h, and the average maximum LWC increased from 0.008 to 0.139 g m −3 . The results obtained herein provide a key reference for further studies of the structure and evolution characteristics of the desert clouds.

To gain a deeper understanding of the structural and evolutionary characteristics of supercell tornadoes that occurred in eastern China on 14 May 2021, observations from the S-band dual-polarization radars, soundings and other instruments are used to investigate the evolutionary process of the tornado formation by the mergering and strengthening of supercell storms. The results are described as follows. The updraft by upper divergence and vertical thermal instability induced by the cold source at the tropopause provided the environmental conditions suitable for tornado formation. The tornado event involved three storm merger processes, each of which was associated with an increase in the echo intensity, vertical rising speed, and vertical vorticity of the supercell. Furthermore, during the last merger, the merging of the two vortices resulted in the reduction of the rotation radius of the new vortex, which also provided a favorable condition for tornadogenesis. A schematic was proposed to describe storm mergers. The characteristics of the velocity spectrum width were indicative of the occurrence and evolution of the tornado in this case. During the tornado stage, distinct polarimetric variable signatures (e.g., a tornado debris signature and a differential reflectivity arc) and radial velocity signatures (i.e., a tornadic vortex signature) were observed.

The merging of a fast-moving bow echo with a convective cell of a hook-echo signature was studied by using polarimetric radar detections. Gusts with wind speeds near 35 m s−1 were recorded by the surface station, which caused significant damage. A convective cell with a mesovortex signature, which is hereafter referred to as a mini-supercell, was observed over the northeast of the bow echo before the convective merging. It was found that the mesovortex possessed cyclonic circulation and resembled a supercell-like feature. The merging of the bow echo and the mini-supercell strengthened the updraft near the apex of the bow echo. The enhanced updraft was also demonstrated by the appearance of a differential reflectivity (ZDR) column with a topmost height of 4 km above the melting layer (~4 km). The bow was separated into northern and southern sectors after merging with the mini-supercell, leading to the gusty wind over the surface of the south sector.

Radar data are essential to convection nowcasting and nudging-based radar data assimilation through diabatic initialization is one of the most effective approaches for forecasting convective systems with numerical weather prediction (NWP) models, used at several advanced global weather centers. It is desired to assess the uncertainty and physical consistency of this assimilation process. This paper investigated impacts of relaxation coefficient, radar data update intervals and continuous assimilation time duration and addressed the key issues and possible solutions of the radar data assimilation based on the WRF hydrometeor and latent heat nudging (HLHN) developed at the National Center for Atmospheric Research (NCAR). It is revealed that excessively large relaxation coefficient forced the model to observations with a tendency greater than the physical terms of the convection, causing the dynamic imbalances and serious convection “ramp-down” right after the free forecast starts. Assimilating high update frequency radar data can make the tendency terms moderate and sustained thereby maintaining the assimilation effect and reducing fortuitous convection. HLHN requires a minimum continuous assimilation duration to contain the initial forced disturbance of the model. For a summer Meiyu precipitation case studied, the minimum duration is ~1 h. Appropriate selection of the HLHN parameters is able to effectively improve the temperature, humidity, and dynamic fields of the model. In addition, several issues still remain to be solved to further enhance HLHN.

Squall line is a kind of common mesoscale disaster weather. At present, there are few studies on the elaborate detection of squall line by dual polarization radar. With the dual polarization upgrade of weather radar network, we need to study the relationship between squall line echoes of base data and polarization data to reveal new echo phenomena and formation mechanisms. The relationship between radar parameters and atmospheric physical processes also need to be examined. Based on the NUIST CDP radar, a squall line in the Yangtze and Huaihe River basin that occurred from July 30 to 31, 2014 is analyzed. The results show that polarization parameters have obvious advantages in the characteristics analysis of size, phase state, shape and orientation of the water condensate particles. The phase states of water condensate particles in convection cell can be distinguished through comparative discussion. Several phase states exist in the squall line, including small, medium and large raindrops, melting hails, dry hails and ice crystal particles and the Z DR column can be used to identify the location of the main updraft. In addition, the polarization parameters are more sensitive to the melting layer. The gust front is presented as a narrow linear echo in Z affected by strong turbulence. It is an obvious velocity convergence line in V and approximately 0.70 in ρ HV . The Z DR can be used as a criterion to distinguish the horizontal and vertical scale of turbulence. The deforming turbulence, which is affected by environmental airflow, will cause an abnormally high Z DR in the gust front and a negative Z DR before and after the gust front. The variation of Z DR depends on the turbulence arrangement, orientation and relative position between turbulence and radar. These dual polarization parameter characteristics offer insights into understanding the structure and evolution of the squall line.

苏北平原易发龙卷,为深入认识其形成机理和回波演变特征,针对2020年6月12日江苏高邮的一次EF2级的龙卷,利用NCEP/NCEP再分析资料、探空资料、V-3θ资料、葵花8号静止卫星资料和双偏振雷达资料对本次龙卷天气过程进行详细分析.(1)苏北的天气形势处于强的热力不稳定状态,尤其是925-850 hPa呈现罕见的变干变冷结构,有利于龙卷的爆发.(2)龙卷形成前经历了两个阶段的风暴单体合并,回波合并加强了不稳定能量.(3)中气旋和TVS对龙卷有预警作用,龙卷发生前的23 min和17 min,雷达分别探测到了中气旋和TVS;龙卷及地时,雷达同时探测到了气旋性TVS和反气旋TVS,据此提出了一种龙卷涡管的三维结构模型.(4)速度谱宽大值区的出现是预警龙卷的有效信息.(5)龙卷发生时,出现了龙卷碎屑特征、ZDR柱和KDP柱等显著特征.研究结果为深入认识苏北平原龙卷的演变特征并改进预警提供了参考依据.

To assess the quality of the retrieved products from ground-based microwave radiometers, the "clear-sky" Level-2 data (LV2) products (profiles of atmospheric temperature and humidity) filtered through a radiometer in Beijing during the 24 months from January 2010 to December 2011 were compared with radiosonde data. Evident differences were revealed. Therefore, this paper investigated an approach to calibrate the observed brightness temperatures by using the model-simulated brightness temperatures as a reference under clear-sky conditions. The simulation was completed with a radiative transfer model and National Centers for Environmental Prediction final analysis (NCEP FNL) data that are independent of the radiometer system. Then, the least-squares method was used to invert the calibrated brightness temperatures to the atmospheric temperature and humidity profiles. A comparison between the retrievals and radiosonde data showed that the calibration of the brightness temperature observations is necessary, and can improve the inversion of temperature and humidity profiles compared with the original LV2 products. Specifically, the consistency with radiosonde was clearly improved: the correlation coefficients are increased, especially, the correlation coefficient for water vapor density increased from 0.2 to 0.9 around the 3 km height; the bias decreased to nearly zero at each height; the RMSE (root of mean squared error) for temperature profile was decreased by more than 1 degree at most heights; the RMSE for water vapor density was decreased from greater than 4 g/m(3) to less than 1.5 g/m(3) at 1 km height; and the decrease at all other heights were also noticeable. In this paper, the evolution of a temperature inversion process is given as an example, using the high-temporal-resolution brightness temperature after quality control to obtain a temperature and humidity profile every two minutes. Therefore, the characteristics of temperature inversion that cannot be seen by conventional radiosonde data (twice daily) were obtained by radiometer. This greatly compensates for the limited temporal coverage of radiosonde data. The approach presented by this paper is a valuable reference for the reprocessing of the historical observations, which have been accumulated for years by less-calibrated radiometers.

为了研究雹暴的偏振特征及其在实际业务中的应用,使用S波段双偏振雷达所观测到的46例冰雹数据,对其中反复出现的3种偏振特征:冰雹在各高度层的偏振参数特征、差分反射率因子柱、三体散射偏振特征进行了分析,重点分析了3种偏振特征大、小冰雹事件的差异.结果表明:(1)大冰雹的水平反射率因子中位数要高于小冰雹,二者的水平反射率因子分布存在较大重合区域.(2)冰雹偏振参数的变化主要集中在融化层之下,相较于小冰雹,大冰雹具有更低的差分反射率因子和相关系数.(3)所有雹暴的差分反射率因子柱最大伸展高度均超过?10℃层,有83％的大冰雹事件其差分反射率因子柱最大伸展高度可超过?20℃层;在小冰雹事件中这一比例仅为46％.(4)差分反射率因子柱高度的演变对于雹暴的发展具有预示性,特别是在持续降雹过程中,差分反射率因子柱的再度发展预示着雹暴的再次增强.差分反射率因子柱高度的极值相对于降雹具有时间提前量,在大冰雹事件中这一提前量的中位数为24 min,而在小冰雹事件中这一数值为11 min.(5)三体散射的偏振特征有助于识别高空的冰雹,尤其是当冰雹核的后侧存在其他降水回波时.在所统计的19例大冰雹事件中均发现三体散射偏振特征.在小冰雹事件中同样可发现三体散射偏振特征,出现比例为52％.

Although satellite-based precipitation estimation has extensive application potential, validation of its reliability is challenging for areas lacking ground-based data which is particularly true for many arid and semiarid regions. The triple collocation (TC) method can be used to evaluate three independent inputs with unknown true values, and thus provides an appealing alternative for assessment of satellite precipitation products in lack of observation regions. This study is the first to utilize TC to comprehensively assess the uncertainties of various satellite precipitation products in Central Asia (CA) with a distinctive continental arid and semi-arid climate. TC requires the errors of inputs to be independent with each other, while many multi-satellite precipitation products use overlapped data sources. To address this problem, this study uses a soil moisture-based product (SM2RAIN) and a reanalysis model-based product (ERA5) as two inputs of a triplet with the last input coming from each one of the six satellite precipitation products (3B42, CHIRPS, CMORPH, GSMaP, IMERG, PERSIANN). Six independent triplets are obtained in this way. The temporal/spatial resolution is daily/0.1° and the period is 2007–2019. The results show the overall performance of GSMaP is best among eight gridded precipitation products over CA, followed by IMERG, CMORPH and PERSIANN. All precipitation products show degraded performance with increasing altitude. Moreover, the accuracy estimates are subjected to uncertainties caused by the TC method and data inputs. Overall, the study concludes the TC method can provide a new perspective for the assessment of precipitation products over data-absent arid and semiarid regions, while careful check and explanation of evaluation results are always necessary to defend the rationality of TC in specific cases.

In part I, the clear air echo in front of the squall line is caused by turbulence diffraction, which makes the Z DR echo characteristics different from particle scattering. To study the turbulence deformation phenomenon that is affected by environmental wind, the turbulence-related method is used to analyze the characteristics of three-dimensional turbulence energy spectrum density, and the parametric model of turbulence integral length scale and environmental wind speed is established. The results show that the horizontal scale of turbulence is generally larger than the vertical scale. The turbulence is nearly isotropic in the horizontal direction, presenting a flat ellipsoid with the vertical orientation of the rotation axis when there is no horizontal wind or the horizontal velocity is small. When horizontal wind exists, the turbulence scale increases along the dominant wind direction. The turbulence scale is positively correlated with the wind speed. The power function is used to fit the relationships of turbulence integral length scale and horizontal wind speed, which obtains the best fitting effect, and the goodness of fit (GF) is above 0.99 in each direction. The deforming turbulence can cause 8–9 dB Z DR anomalies in the echo of dual polarization radar, which the ratio of scales in the dominant wind and the vertical direction of deforming turbulence ( L u / L w ) is around 4.3. The variation in Z DR depends on the turbulence shape, orientation and the relative position between turbulence and radar. The shape of turbulence derived from radar detection results is consistent with that of the parametric model, which can provide a parametric scheme for turbulence research. The results reveal the mechanism of abnormal Z DR echo caused by deforming turbulence.

Atmospheric temperature and humidity retrievals from ground-based microwave remote sensing are useful in a variety of meteorological and environmental applications. Though the influence of clouds is usually considered in current retrieval algorithms, the resulting temperature and humidity estimates are still biased high in overcast conditions compared to radiosonde observations. Therefore, there is a need to improve the quality of retrievals in cloudy conditions. This paper presents an approach to make brightness temperature (TB) correction for cloud influence before the data can be used in the inversion of vertical profiles of atmospheric temperature and humidity. A three-channel method is proposed to make cloud parameter estimation, i.e., of the total 22 channels of the ground-based radiometer, three are adopted to set up a relationship between cloud parameters and brightness temperatures, so that the observations from the three channels can be used to estimate cloud thickness and water content and complete the cloud correction for the rest of the channels used in the retrieval. Based on two years of data from the atmosphere in Beijing, a comparison of the retrievals with radiosonde observations (RAOB) shows: (1) the temperature retrievals from this study have a higher correlation with RAOB and are notably better than in the vendor-provided LV2. The bias of the temperature retrievals from this study is close to zero at all heights, and the RMSE is greatly reduced from >5 °C to <2 °C in the layer, from about 1.5 km up to 5 km. The temperature retrievals from this study have higher correlation with RAOB data compared to the vendor-provided LV2, especially at and above a 2 km height. (2) The bias of the water vapor density profile from this study is near to zero, while the LV2 has a positive bias as large as 4 g/m3. The RMSE of the water vapor density profile from this study is <2 g/m3, while the RMSE for LV2 is as large as 10 g/m3. That is, both the bias and RMSE from this study are evidently less than the LV2, with a greater improvement in the lower troposphere below 5 km. Correlation with RAOB is improved even more for the water vapor density. The correlation of the retrievals from this study increases to one within the boundary layer, but the correlation of LV2 with RAOB is only 0.8 at 0.5 km height, 0.7 at 1 km, and even less than 0.5 at 2 km. (3) A parameter named the Cloud Impact index, determined by cloud water concentration and cloud thickness, together with the cloud base height, has been defined to show that both BIAS and RMSE of “high-CI subsample” are larger than those of the “low-CI subsample”, indicating that high-CI cloud has a higher impact on the retrievals and the correction for cloud influence is more necessary.

通过研究大冰雹超级单体风暴的偏振特征、动力及云物理结构的演变,可了解大冰雹形成的物理过程,并获得与大冰雹形成、生长相关的相关征兆偏振特征,进而提升对大冰雹超级单体的预警能力.利用厦门S波段双偏振雷达资料,结合双雷达风场反演和粒子相态识别算法对2019年4月22日发生在闽南地区一次导致大冰雹的超级单体进行了分析.研究表明:差分反射率因子(Zdr)大值区位于三体散射(TBSS)的起始位置及反射率因子(Zh)强中心的远端.同时,TBSS中的相关系数(CC)较低,TBSS的偏振特征有助于识别高空中的大冰雹.大冰雹区表现出高Zh和低Zdr的偏振特点,随着大冰雹降落融化,其表面存在外包水膜现象使得大冰雹周围的Zdr增大,CC减小.在超级单体低层的Zh强中心内存在一个差分相位常数(Kdp)增大的区域,被称为Kdp足.Kdp对大冰雹较不敏感,是冰雹融化的较好指标.因此,Kdp足可用于指示由冰雹融化导致的下沉气流区.在水平风场上存在明显的双涡旋结构.双涡旋结构有助于超级单体的发展及大冰雹的循环增长.在中气旋的东北侧,存在一个中等强度Zh、低Zdr、高CC的区域,被称为霰带.粒子相态识别算法显示霰带中主要的水凝物为霰.由于靠近中气旋,部分霰作为雹胚被卷入上升气流中.基于上述分析给出大冰雹超级单体的偏振特征和三维风场结构示意图.

China–Nepal Highway is an important international passage connecting China and Nepal. Owing to its location in a complex mountainous area in the Qinghai– Tibet Plateau, the Shigatse section of the China–Nepal Highway is often impacted and troubled by mudflow. In order to effectively conduct road construction and maintenance and improve early disaster-warning capability, the relationship between various hazard factors and disaster points was analysed. It is found that four factors such as slope, precipitation, soil type and digital elevation have the strongest correlation with the occurrence of the disasters. From the distribution of disaster points, it is observed that the disaster point is closely related to the slope, its local correlation with precipitation is good and the its local correlation with the soil type and Digital Elevation Model (DEM) data is significant. In order to quantitatively evaluate the susceptibility of mudflow disasters in the Shigatse region, this paper uses the analytic hierarchy process (AHP) as the main analysis method supplemented by the fuzzy clustering method. The results show that the slope, when accompanied by heavy rainfall, is the most important factor among four factors. In this paper, the neural network method is used to establish the identification and early warning model of mudflow susceptibility. When the recognition rate reaches 66% or above, it can be used as an early-warning threshold for mudflow disasters. This study has conducted a useful exploration of the research, assessment and early warning of mudflow disasters along the Shigatse section of the China–Nepal Highway.

Weather conditions and flow are frequently analyzed using the multisource precipitation products, where rain gauge network is not available or dispersed. This study has been designed to evaluate the precipitation and flow using rain gauges, satellite, and reanalysis data (TRMM 3B42RT v-7 and ERA-Interim) over Gilgit (glacier fed), a river basin of northern Pakistan. Statistical matrices, such as Bias, Mean Absolute Error (MAE), Root Mean Square Error (RMSE), coefficient of determination (R2), and percentage (%) difference, were used to report the discrepancies in the precipitation and flow. Moreover, the spatial distribution, rain occurrence, and volume precipitation were used for further analysis. However, both sources showed ability to capture the pattern well. In the rain occurrence, light precipitation (< 1 mm/h) contributes more than 60% (October–March) and heavy precipitation (> 10 mm/h) shares more than 40% in total volume (April–September). Overall, the TRMM outperforms for precipitation estimation in the catchment. Moreover, the findings of the study would be helpful in controlling flood-causing disaster in this particular area and provide important information for sustainable development and to overcome food security and energy issues in the country. These findings indicate the potential of satellite and reanalysis data as alternative to rain gauge in many applications where data are not available or very limited.

An iterative local Fourier transform (ILFT)-based high-accuracy wavelength calibration for Fourier transform imaging spectrometer (FTIS) is proposed. The wavelength calibration for FTIS is to determine the relation between the wavelength and the wavenumber position. However, the wavenumber position solved by conventional method is only accurate up to integers restricted by the picket-fence effect of discrete Fourier transform. While the proposed ILFT can increase the accuracy of calculating the wavenumber position by combining the local Fourier transform and a few iterations. In this paper, the method is investigated in theory and then by simulations and experiments. The simulations show that the accuracy of the wavenumber position calculated by the ILFT is increased by 100 times than conventional method with noise, phase error, and non-uniform sampling of optical path difference. And the experimental results indicate that the ILFT decreases the absolute error of wavelength calibration from about 2.03 nm to 0.16 nm. Therefore, the method provides theoretical and technical support for FTIS and promotes the development of superior resolutions therein.