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2023 Vol. 40, No. 2

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2023-2 Contents
2023, 40(2): 1-1.
News & Views
Earth Summit Mission 2022: Scientific Expedition and Research on Mt. Qomolangma Helps Reveal the Synergy between Westerly Winds and Monsoon and the Resulting Climatic and Environmental Effects
Yaoming MA, Weiqiang MA, Huaguang DAI, Lei ZHANG, Fanglin SUN, Jinqiang ZHANG, Nan YAO, Jianan HE, Zhixuan BAI, Yuejian XUAN, Yunshuai ZHANG, Yuan YUAN, Chenyi YANG, Weijun SUN, Ping ZHAO, Minghu DING, Kongju ZHU, Jie HU, Bian Bazhuga, Bai Juepingcuo, Zhuo Ma, Ren Qingnima, Suo Langwangdui, Yang Zong, Haikun WEN
2023, 40(2): 187-193. doi: 10.1007/s00376-022-2166-3
“Earth summit mission 2022” is one of the landmark scientific research activities of the Second Tibetan Plateau Scientific Expedition and Research (STEP). This scientific expedition firstly used advanced technology and methods to detect vertical meteorological elements and produce forecasts for mountain climbing. The “Earth summit mission 2022” Qomolangma scientific expedition exceeded an altitude of over 8000 meters for the first time and carried out a comprehensive scientific investigation mission on the summit of Mt. Qomolangma. Among the participants, the westerly–monsoon synergy and influence team stationed in the Mt. Qomolangma region had two tasks: 1) detecting the vertical structure of the atmosphere for parameters such as wind, temperature, humidity, and pressure with advanced instruments for high-altitude detection at the Mt. Qomolangma base camp; and 2) observing extreme weather processes to ensure that members of the mountaineering team could successfully reach the top. Through this scientific expedition, a better understanding of the vertical structure and weather characteristics of the complex area of Mt. Qomolangma is gained.
Ground–Space–Sky Observing System Experiment during Tropical Cyclone Mulan in August 2022
Pak-wai CHAN, Wei HAN, Betty MAK, Xiaohao QIN, Yongzhu LIU, Ruoying YIN, Jincheng WANG
2023, 40(2): 194-200. doi: 10.1007/s00376-022-2267-z
Forecasting tropical cyclone track and intensity is a great challenge for the meteorological community, and safeguarding the life and property of people living near the coast is an important issue. One major reason for challenging forecasts is the lack of observations over the vast oceans. During tropical cyclone Mulan between 8 and 10 August 2022 over the northern part of the South China Sea, the meteorological authority and research institutes of Chinese mainland collaborated with the meteorological service in Hong Kong on conducting the first-ever ground–space–sky observing system experiment on tropical cyclone Mulan. The enhanced targeted observations collected during the experiment include Geostationary Interferometric Infrared Sounder, round-trip radiosondes, and aircraft-launched dropsondes. This paper describes the campaign, technical details of the meteorological models used, and impact of the additional targeted observation data on the tropical cyclone forecast. Ideally, similar enhanced observation campaigns could be conducted in the future, not only in the northern part of the South China Sea, but also in other ocean basins.
Original Paper
The Characteristics and Controlling Factors of Water and Heat Exchanges over the Alpine Wetland in the East of the Qinghai–Tibet Plateau
Jinlei CHEN, Yuan YUAN, Xianyu YANG, Zuoliang WANG, Shichang KANG, Jun WEN
2023, 40(2): 201-210. doi: 10.1007/s00376-022-1443-5
Alpine wetland is one of the typical underlying surfaces on the Qinghai–Tibet Plateau. It plays a crucial role in runoff regulation. Investigations on the mechanisms of water and heat exchanges are necessary to understand the land surface processes over the alpine wetland. This study explores the characteristics of hydro-meteorological factors with in situ observations and uses the Community Land Model 5 to identify the main factors controlling water and heat exchanges. Latent heat flux and thermal roughness length were found to be greater in the warm season (June–August) than in the cold season (December–February), with a frozen depth of 20–40 cm over the alpine wetland. The transfers of heat fluxes were mainly controlled by longwave radiation and air temperature and affected by root distribution. Air pressure and stomatal conductance were also important to latent heat flux, and soil solid water content was important to sensible heat flux. Soil temperature was dominated by longwave radiation and air temperature, with crucial surface parameters of initial soil liquid water content and total water content. The atmospheric control factors transitioned to precipitation and air temperature for soil moisture, especially at the shallow layer (5 cm). Meanwhile, the more influential surface parameters were root distribution and stomatal conductance in the warm season and initial soil liquid water content and total water content in the cold season. This work contributes to the research on the land surface processes over the alpine wetland and is helpful to wetland protection.
Response of Freezing/Thawing Indexes to the Wetting Trend under Warming Climate Conditions over the Qinghai –Tibetan Plateau during 1961–2010: A Numerical Simulation
Xuewei FANG, Zhi LI, Chen CHENG, Klaus FRAEDRICH, Anqi WANG, Yihui CHEN, Yige XU, Shihua LYU
2023, 40(2): 211-222. doi: 10.1007/s00376-022-2109-z
Since the 1990s, the Qinghai–Tibetan Plateau (QTP) has experienced a strikingly warming and wetter climate that alters the thermal and hydrological properties of frozen ground. A positive correlation between the warming and thermal degradation in permafrost or seasonally frozen ground (SFG) has long been recognized. Still, a predictive relationship between historical wetting under warming climate conditions and frozen ground has not yet been well demonstrated, despite the expectation that it will become even more important because precipitation over the QTP has been projected to increase continuously in the near future. This study investigates the response of the thermal regime to historical wetting in both permafrost and SFG areas and examines their relationships separately using the Community Land Surface Model version 4.5. Results show that wetting before the 1990s across the QTP mainly cooled the permafrost body in the arid and semiarid zones, with significant correlation coefficients of 0.60 and 0.48, respectively. Precipitation increased continually at the rate of 6.16 mm decade–1 in the arid zone after the 1990s but had a contrasting warming effect on permafrost through a significant shortening of the thawing duration within the active layer. However, diminished rainfall in the humid zone after the 1990s also significantly extended the thawing duration of SFG. The relationship between the ground thawing index and precipitation was significantly negatively correlated (−0.75). The dual effects of wetting on the thermal dynamics of the QTP are becoming critical because of the projected increases in future precipitation.
Ground-Based Atmospheric CO2, CH4, and CO Column Measurements at Golmud in the Qinghai-Tibetan Plateau and Comparisons with TROPOMI/S5P Satellite Observations
Minqiang ZHOU, Qichen NI, Zhaonan CAI, Bavo LANGEROCK, Jingyi JIANG, Ke CHE, Jiaxin WANG, Weidong NAN, Yi LIU, Pucai WANG
2023, 40(2): 223-234. doi: 10.1007/s00376-022-2116-0
Measurements of carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) are of great importance in the Qinghai-Tibetan region, as it is the highest and largest plateau in the world affecting global weather and climate systems. In this study, for the first time, we present CO2, CH4, and CO column measurements carried out by a Bruker EM27/SUN Fourier-transform infrared spectrometer (FTIR) at Golmud (36.42ºE, 94.91ºN, 2808 m) in August 2021. The mean and standard deviation of the column-average dry-air mixing ratio of CO2, CH4, and CO (XCO2, XCH4, and XCO) are 409.3 ± 0.4 ppm, 1905.5 ± 19.4 ppb, and 103.1 ± 7.7 ppb, respectively. The differences between the FTIR co-located TROPOMI/S5P satellite measurements at Golmud are 0.68 ± 0.64% (13.1 ± 12.2 ppb) for XCH4 and 9.81 ± 3.48% (–10.7 ± 3.8 ppb) for XCO, which are within their retrieval uncertainties. High correlations for both XCH4 and XCO are observed between the FTIR and S5P satellite measurements. Using the FLEXPART model and satellite measurements, we find that enhanced CH4 and CO columns in Golmud are affected by anthropogenic emissions transported from North India. This study provides an insight into the variations of the CO2, CH4, and CO columns in the Qinghai-Tibetan Plateau.
Elucidating Dominant Factors Affecting Land Surface Hydrological Simulations of the Community Land Model over China
Jianguo LIU, Zong-Liang YANG, Binghao JIA, Longhuan WANG, Ping WANG, Zhenghui XIE, Chunxiang SHI
2023, 40(2): 235-250. doi: 10.1007/s00376-022-2091-5
In order to compare the impacts of the choice of land surface model (LSM) parameterization schemes, meteorological forcing, and land surface parameters on land surface hydrological simulations, and explore to what extent the quality can be improved, a series of experiments with different LSMs, forcing datasets, and parameter datasets concerning soil texture and land cover were conducted. Six simulations are run for the Chinese mainland on 0.1° × 0.1° grids from 1979 to 2008, and the simulated monthly soil moisture (SM), evapotranspiration (ET), and snow depth (SD) are then compared and assessed against observations. The results show that the meteorological forcing is the most important factor governing output. Beyond that, SM seems to be also very sensitive to soil texture information; SD is also very sensitive to snow parameterization scheme in the LSM. The Community Land Model version 4.5 (CLM4.5), driven by newly developed observation-based regional meteorological forcing and land surface parameters (referred to as CMFD_CLM4.5_NEW), significantly improved the simulations in most cases over the Chinese mainland and its eight basins. It increased the correlation coefficient values from 0.46 to 0.54 for the SM modeling and from 0.54 to 0.67 for the SD simulations, and it decreased the root-mean-square error (RMSE) from 0.093 to 0.085 for the SM simulation and reduced the normalized RMSE from 1.277 to 0.201 for the SD simulations. This study indicates that the offline LSM simulation using a refined LSM driven by newly developed observation-based regional meteorological forcing and land surface parameters can better model reginal land surface hydrological processes.
A Quantitative Method of Detecting Transient Rossby Wave Phase Speed: No Evidence of Slowing Down with Global Warming
Yashu WU, Jianhua LU
2023, 40(2): 251-261. doi: 10.1007/s00376-022-2164-5
Based on the Complex Empirical Orthogonal Functions (CEOFs) of bandpass-filtered daily streamfunction fields, a quantitative method of detecting transient (synoptic) Rossby wave phase speed (RWPhS) is presented. The transient RWPhS can be objectively calculated by the distance between a high (or low) center in the real part of a CEOF mode and its counterpart in the imaginary part of the same CEOF mode divided by the time span between two adjacent peaks (or bottoms) of two principal component curves for the real and imaginary parts of that CEOF mode. The new detection method may partly reveal the spatiotemporal heterogeneity of Rossby wave prorogation. Although the mean westerly jet at 200 hPa doubles the speed of its counterpart at 500 hPa, the estimated RWPhS at both levels are around 1000 km d–1 and quantitatively consistent with the quasigeostrophic-theory-based RWPhS, confirming that the meridional potential vorticity gradient induced by the barotropic and baroclinic shears of mean flow, together with the β effect, play an essential role in Rossby wave propagation. Both observations over the past four decades and a 150-year historical simulation suggest no evidence for slowing wintertime transient Rossby waves in the Northern Hemisphere, but possible regional changes are not excluded. We emphasize that not only the mean flow speed, but also the barotropic and baroclinic shears of the mean flow, and their associated contributions to the meridional potential vorticity (PV) gradient, should be considered in investigating the possible change of Rossby waves with global warming.
Influences of MJO-induced Tropical Cyclones on the Circulation-Convection Inconsistency for the 2021 South China Sea Summer Monsoon Onset
Yanying CHEN, Ning JIANG, Yang AI, Kang XU, Longjiang MAO
2023, 40(2): 262-272. doi: 10.1007/s00376-022-2103-5
The South China Sea Summer Monsoon (SCSSM) onset is characterized by an apparent seasonal conversion of circulation and convection. Accordingly, various indices have been introduced to identify the SCSSM onset date. However, the onset dates as determined by various indices can be very inconsistent. It not only limits the determination of onset dates but also misleads the assessment of prediction skills. In 2021, the onset time as identified by the circulation criteria was 20 May, which is 12 days earlier than that deduced by also considering the convection criteria. The present study mainly ascribes such circulation-convection inconsistency to the activities of tropical cyclones (TCs) modulated by the Madden-Julian Oscillation (MJO). The convection of TC “Yaas” (2021) acted as an upper-level diabatic heat source to the north of the SCS, facilitating the circulation transition. Afterward, TC “Choi-wan” (2021) over the western Pacific aided the westerlies to persist at lower levels while simultaneously suppressing moist convection over the SCS. Accurate predictions using the ECMWF S2S forecast system were obtained only after the MJO formation. The skillful prediction of the MJO during late spring may provide an opportunity to accurately predict the establishment of the SCSSM several weeks in advance.
A Time Neighborhood Method for the Verification of Landfalling Typhoon Track Forecast
Daosheng XU, Jeremy Cheuk-Hin LEUNG, Banglin ZHANG
2023, 40(2): 273-284. doi: 10.1007/s00376-022-1398-6
Landfalling typhoons can cause disasters over large regions. The government and emergency responders need to take measures to mitigate disasters according to the forecast of landfall position, while slight timing error can be ignored. The reliability of operational model forecasts of typhoon landfall position needs to be evaluated beforehand, according to the forecasts and observation of historical cases. In the evaluation of landfalling typhoon track, the traditional method based on point-to-point matching methods could be influenced by the predicted typhoon translation speed. Consequently, the traditional track evaluation method may result in a large track error even if the predicted landfall position is close to observation. The purpose of this paper is to address the above issue using a simple evaluation method of landfalling typhoon track forecast based on the time neighborhood approach. In this new method, the timing error was lessened to highlight the importance of the position error during the landfall of typhoon. The properties of the time neighborhood method are compared with the traditional method based on numerical forecast results of 12 landfalling typhoon cases. Results demonstrated that the new method is not sensitive to the sampling frequency, and that the difference between the time neighborhood and traditional method will be more obvious when the moving speed of typhoon is moderate (between 15−30 km h−1). The time neighborhood concept can be easily extended to a broader context when one attempts to examine the position error more than the timing error.
A New Sensitivity Analysis Approach Using Conditional Nonlinear Optimal Perturbations and Its Preliminary Application
Qiujie REN, Mu MU, Guodong SUN, Qiang WANG
2023, 40(2): 285-304. doi: 10.1007/s00376-022-1445-3
Simulations and predictions using numerical models show considerable uncertainties, and parameter uncertainty is one of the most important sources. It is impractical to improve the simulation and prediction abilities by reducing the uncertainties of all parameters. Therefore, identifying the sensitive parameters or parameter combinations is crucial. This study proposes a novel approach: conditional nonlinear optimal perturbations sensitivity analysis (CNOPSA) method. The CNOPSA method fully considers the nonlinear synergistic effects of parameters in the whole parameter space and quantitatively estimates the maximum effects of parameter uncertainties, prone to extreme events. Results of the analytical g-function test indicate that the CNOPSA method can effectively identify the sensitivity of variables. Numerical results of the theoretical five-variable grassland ecosystem model show that the maximum influence of the simulated wilted biomass caused by parameter uncertainty can be estimated and computed by employing the CNOPSA method. The identified sensitive parameters can easily change the simulation or prediction of the wilted biomass, which affects the transformation of the grassland state in the grassland ecosystem. The variance-based approach may underestimate the parameter sensitivity because it only considers the influence of limited parameter samples from a statistical view. This study verifies that the CNOPSA method is effective and feasible for exploring the important and sensitive physical parameters or parameter combinations in numerical models.
Objective Identification and Climatic Characteristics of Heavy-Precipitation Northeastern China Cold Vortexes
Xu CHEN, Xiaoyong ZHUGE, Xidi ZHANG, Yuan WANG, Daokai XUE
2023, 40(2): 305-316. doi: 10.1007/s00376-022-2037-y
The northeastern China cold vortex (NCCV) plays an important role in regional rainstorms over East Asia. Using the National Centers for Environmental Prediction Final reanalysis dataset and the Global Precipitation Measurement product, an objective algorithm for identifying heavy-precipitation NCCV (HPCV) events was designed, and the climatological features of 164 HPCV events from 2001 to 2019 were investigated. The number of HPCV events showed an upward linear trend, with the highest frequency of occurrence in summer. The most active region of HPCV samples was the Northeast China Plain between 40°–55°N. Most HPCV events lasted 3–5 days and had radii ranging from 250 to 1000 km. The duration of HPCV events with larger sizes was longer. About half of the HPCV events moved into (moved out of) the definition region (35°–60°N, 115°–145°E), and half initiated (dissipated) within the region. The initial position was close to the western boundary of the definition region, and the final position was mainly near the eastern boundary. The locations associated with the precipitation were mostly concentrated within 2000 km southeast of the HPCV systems, and they were farther from the center in the cold season than in the warm season.
Possibility of Solid Hydrometeor Growth Zone Identification Using Radar Spectrum Width
Sung-Ho SUH, Eun-Ho CHOI, Hong-Il KIM, Woonseon JUNG
2023, 40(2): 317-332. doi: 10.1007/s00376-022-1472-0
In this study, the correlation between simulated and measured radar velocity spectrum width (σv) is investigated. The results show that the dendrites growth zones (DGZs) and needles growth zones (NGZs) mostly contain dendrites (DN) and needles (NE), respectively. Clear σv zones (1.1 < σv (m s–1) < 1.3 and 0.3 < σv (m s–1) < 0.7 for the DGZ and NGZ, respectively) could be identified in the case studies (27 and 28 February 2016) near altitudes corresponding to temperatures of –15°C and –5°C, according to the Japan Meteorological Agency and mesoscale model reanalysis data. Oblate particles with diverse particle shapes were observed in the DGZ with σv > 1.2 m s–1, a differential reflectivity (ZDR) higher than 0 dB, and a cross-correlation coefficient (ρhv) less than 0.96. In contrast, prolate particles with relatively uniform shapes were observed in the NGZ with σv < 0.6 m s–1, a ZDR less than 0 dB, and ρhv higher than 0.97. The simulation results show that the DN exhibited a larger σv compared to the NE, and this observed σv was strongly dependent on the wind fluctuations (v’) due to turbulence or wind shear. In contrast, the NE exhibited a significantly small σv ~ 0.55 m s–1, which converges irrespective of v’. In addition, a strong correlation between the measured σv values at five radar elevation angles (θ = 6.2°, 9.1°, 13.1°, 19°, and 80°) and those simulated in this study confirmed the significance of the analysis results.
Correction to: Urbanization Impact on Regional Climate and Extreme Weather: Current Understanding, Uncertainties, and Future Research Directions
Yun QIAN, TC CHAKRABORTY, Jianfeng LI, Dan LI, Cenlin HE, Chandan SARANGI, Fei CHEN, Xuchao YANG, L. Ruby LEUNG
2023, 40(2): 333-333. doi: 10.1007/s00376-022-2007-4