Advances in Atmospheric Sciences最新文献

Recent observational and numerical studies have revealed the dependence of the intensification rate on the inner-core size of tropical cyclones (TCs). In this study, with the initial inner-core size (i.e., the radius of maximum wind—RMW) varied from 20–180 km in idealized simulations using two different numerical models, we found a nonmonotonic dependence of the lifetime maximum intensification rate (LMIR) on the inner-core size. Namely, there is an optimal inner-core size for the LMIR of a TC. Tangential wind budget analysis shows that, compared to large TCs, small TCs have large inward flux of absolute vorticity due to large absolute vorticity inside the RMW. However, small TCs also suffer from strong lateral diffusion across the eyewall, which partly offsets the positive contribution from large inward flux of absolute vorticity. These two competing processes ultimately lead to the TC with an intermediate initial inner-core size having the largest LMIR. Results from sensitivity experiments show that the optimal size varies in the range of 40–120 km and increases with higher sea surface temperature, lower latitude, larger horizontal mixing length, and weaker initial TC intensity. The 40–120 km RMW corresponds to the inner-core size most commonly found for intensifying TCs in observations, suggesting the natural selection of initial TC size for intensification. This study highlights the importance of accurate representation of TC inner-core size to TC intensity forecasts by numerical weather prediction models.

The diurnal temperature range (DTR) serves as a vital indicator reflecting both natural climate variability and anthropogenic climate change. This study investigates the historical and projected multitemporal DTR variations over the Tibetan Plateau. It assesses 23 climate models from phase 6 of the Coupled Model Intercomparison Project (CMIP6) using CN05.1 observational data as validation, evaluating their ability to simulate DTR over the Tibetan Plateau. Then, the evolution of DTR over the Tibetan Plateau under different shared socioeconomic pathway (SSP) scenarios for the near, middle, and long term of future projection are analyzed using 11 selected robustly performing models. Key findings reveal: (1) Among the models examined, BCC-CSM2-MR, EC-Earth3, EC-Earth3-CC, EC-Earth3-Veg, EC-Earth3-Veg-LR, FGOALS-g3, FIO-ESM-2-0, GFDL-ESM4, MPI-ESM1-2-HR, MPI- ESM1-2-LR, and INM-CM5-0 exhibit superior integrated simulation capability for capturing the spatiotemporal variability of DTR over the Tibetan Plateau. (2) Projection indicates a slightly increasing trend in DTR on the Tibetan Plateau in the SSP1-2.6 scenario, and decreasing trends in the SSP2-4.5, SSP3-7.0, and SPP5-8.5 scenarios. In certain areas, such as the southeastern edge of the Tibetan Plateau, western hinterland of the Tibetan Plateau, southern Kunlun, and the Qaidam basins, the changes in DTR are relatively large. (3) Notably, the warming rate of maximum temperature under SSP2-4.5, SSP3-7.0, and SPP5-8.5 is slower compared to that of minimum temperature, and it emerges as the primary contributor to the projected decrease in DTR over the Tibetan Plateau in the future.

Increasing the urban tree cover percentage (TCP) is widely recognized as an efficient way to mitigate the urban heat island effect. The cooling efficiency of urban trees can be either enhanced or attenuated on hotter days, depending on the physiological response of urban trees to rising ambient temperature. However, the response of urban trees’ cooling efficiency to rising urban temperature remains poorly quantified for China’s cities. In this study, we quantify the response of urban trees’ cooling efficiency to rising urban temperature at noontime [∼1330 LT (local time), LT=UTC+8] in 17 summers (June, July, and August) from 2003–19 in 70 economically developed cities of China based on satellite observations. The results show that urban trees have stronger cooling efficiency with increasing temperature, suggesting additional cooling benefits provided by urban trees on hotter days. The enhanced cooling efficiency values of urban trees range from 0.002 to 0.055°C %⁻¹ per 1°C increase in temperature across the selected cities, with larger values for the low-TCP-level cities. The response is also regulated by background temperature and precipitation, as the additional cooling benefit tends to be larger in warmer and wetter cities at the same TCP level. The positive response of urban trees’ cooling efficiency to rising urban temperature is explained mainly by the stronger evapotranspiration of urban trees on hotter days. These results have important implications for alleviating urban heat risk by utilizing urban trees, particularly considering that extreme hot days are becoming more frequent in cities under global warming.

We used observed concentrations of air pollutants, reanalyzed meteorological parameters, and results from the Goddard Earth Observing System Chemical Transport Model to examine the relationships between concentrations of maximum daily 8-h average ozone (MDA8 O₃), PM_2.5 (particulate matter with diameter of 2.5 µm or less), and PM_2.5 components and 2-m temperature (T2) or relative humidity (RH), as well as the effectiveness of precursor emission reductions on the control of O₃ and PM_2.5 in Beijing–Tianjin–Hebei (BTH) under different summertime temperature and humidity conditions. Both observed (simulated) MDA8 O₃ and PM_2.5 concentrations increased as T2 went up, with linear trends of 4.8 (3.2) ppb °C⁻¹ and 1.9 (1.5) µg m⁻³ °C⁻¹, respectively. Model results showed that the decreases in MDA8 O₃ from precursor emission reductions were more sensitive to T2 than to RH. Reducing a larger proportion of volatile organic compound (VOC) emissions at higher T2 was more effective for the control of summertime O₃ in BTH. For the control of summertime PM_2.5 in BTH, reducing nitrogen oxides (NO_x) combined with a small proportion of VOCs was the best measure. The magnitude of reduction in PM_2.5 from reducing precursor emissions was more sensitive to RH than to T2, with the best efficiency at high RH. Results from this study are helpful for formulating effective policies to tackle O₃ and PM_2.5 pollution in BTH.

Recently, extreme meteorological droughts have affected China, causing terrible socioeconomic impacts. Despite previous research on the spatiotemporal characteristics and mechanisms of drought, two crucial issues remain seldom explored. First, an event-oriented drought chronology with detailed spatiotemporal evolutions is urgently required. Second, the complex migration patterns and diversity of synchronous temperature extremes need to be quantitatively investigated. Accordingly, the main achievements of our investigation are as follows. We produced an event-oriented set of extreme meteorological droughts over China through the application of a newly developed 3D DBSCAN-based detection method (deposited on https://doi.org/10.25452/figshare.plus.25512334), which was verified with a historical atlas and monographs on a case-by-case basis. In addition, distinctive migration patterns (i.e., stationary/propagation types) are identified and ranked, considering the differences in latitudinal zones and coastal/inland locations. We also analyze the diversity of synchronous temperature extremes (e.g., hotness and coldness). Notably, an increasing trend in hot droughts occurred over China since the late 1990s, predominantly appearing to the south of 30°N and north of 40°N. All drought events and synchronous temperature extremes are ranked using a comprehensive magnitude index, with the 2022 summer-autumn Yangtze River hot drought being the hottest. Furthermore, Liang-Kleeman information flow-based causality analysis emphasizes key areas where the PDO and AMO influenced decadal variations in coverages of droughts and temperature extremes. We believe that the achievements in this study may offer new insights into sequential mechanism exploration and prediction-related issues.

Cloud base height (CBH) is a crucial parameter for cloud radiative effect estimates, climate change simulations, and aviation guidance. However, due to the limited information on cloud vertical structures included in passive satellite radiometer observations, few operational satellite CBH products are currently available. This study presents a new method for retrieving CBH from satellite radiometers. The method first uses the combined measurements of satellite radiometers and ground-based cloud radars to develop a lookup table (LUT) of effective cloud water content (ECWC), representing the vertically varying cloud water content. This LUT allows for the conversion of cloud water path to cloud geometric thickness (CGT), enabling the estimation of CBH as the difference between cloud top height and CGT. Detailed comparative analysis of CBH estimates from the state-of-the-art ECWC LUT are conducted against four ground-based millimeter-wave cloud radar (MMCR) measurements, and results show that the mean bias (correlation coefficient) is 0.18±1.79 km (0.73), which is lower (higher) than 0.23±2.11 km (0.67) as derived from the combined measurements of satellite radiometers and satellite radar-lidar (i.e., CloudSat and CALIPSO). Furthermore, the percentages of the CBH biases within 250 m increase by 5% to 10%, which varies by location. This indicates that the CBH estimates from our algorithm are more consistent with ground-based MMCR measurements. Therefore, this algorithm shows great potential for further improvement of the CBH retrievals as ground-based MMCR are being increasingly included in global surface meteorological observing networks, and the improved CBH retrievals will contribute to better cloud radiative effect estimates.

A mesoscale convective system (MCS) occurred over the East China coastal provinces and the East China Sea on 30 April 2021, producing damaging surface winds near the coastal city Nantong with observed speeds reaching 45 m s⁻¹. A simulation using the Weather Research and Forecasting model with a 1.5-km grid spacing generally reproduces the development and subsequent organization of this convective system into an MCS, with an eastward protruding bow segment over the sea. In the simulation, an east-west-oriented high wind swath is generated behind the gust front of the MCS. Descending dry rear-to-front inflows behind the bow and trailing gust front are found to feed the downdrafts in the main precipitation regions. The inflows help to establish spreading cold outflows and enhance the downdrafts through evaporative cooling. Meanwhile, front-to-rear inflows from the south are present, associated with severely rearward-tilted updrafts initially forming over the gust front. Such inflows descend behind (north of) the gust front, significantly enhancing downdrafts and near-surface winds within the cold pool. Consistently, calculated trajectories show that these parcels that contribute to the derecho originate primarily from the region ahead (south) of the east-west-oriented gust front, and dry southwesterly flows in the low-to-middle levels contribute to strong downdrafts within the MCS. Moreover, momentum budget analyses reveal that a large westward-directed horizontal pressure gradient force within the simulated cold pool produced rapid flow acceleration towards Nantong. The analyses enrich the understanding of damaging wind characteristics over coastal East China and will prove helpful to operational forecasters.

This study investigates the impact of the salinity barrier layer (BL) on the upper ocean response to Super Typhoon Mangkhut (2018) in the western North Pacific. After the passage of Mangkhut, a noticeable increase (∼0.6 psu) in sea surface salinity and a weak decrease (< 1°C) in sea surface temperature (SST) were observed on the right side of the typhoon track. Mangkhut-induced SST change can be divided into the three stages, corresponding to the variations in BL thickness and SST before, during, and after the passage of Mangkhut. During the pre-typhoon stage, SST slightly warmed due to the entrainment of BL warm water, which suppressed the cooling induced by surface heat fluxes and horizontal advection. During the forced stage, SST cooling was controlled by entrainment, and the preexisting BL reduced the total cooling by 0.89°C d⁻¹, thus significantly weakening the overall SST cooling induced by Mangkhut. During the relaxation stage, the SST cooling was primarily caused by the entrainment. Our results indicate that a preexisting BL can limit typhoon-induced SST cooling by suppressing the entrainment of cold thermocline water, which contributed to Mangkhut becoming the strongest typhoon in 2018.

In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar (DPR) suitable over the Tibetan Plateau (TP) was proposed by analyzing Global Precipitation Measurement (GPM) DPR Level-2 data in summer from 2014 to 2020. It was found that the DPR rain type classification algorithm (simply called DPR algorithm) has mis-identification problems in two aspects in summer TP. In the new algorithm of rain type classification in summer TP, four rain types are classified by using new thresholds, such as the maximum reflectivity factor, the difference between the maximum reflectivity factor and the background maximum reflectivity factor, and the echo top height. In the threshold of the maximum reflectivity factors, 30 dBZ and 18 dBZ are both thresholds to separate strong convective precipitation, weak convective precipitation and weak precipitation. The results illustrate obvious differences of radar reflectivity factor and vertical velocity among the three rain types in summer TP, such as the reflectivity factor of most strong convective precipitation distributes from 15 dBZ to near 35 dBZ from 4 km to 13 km, and increases almost linearly with the decrease in height. For most weak convective precipitation, the reflectivity factor distributes from 15dBZ to 28 dBZ with the height from 4 km to 9 km. For weak precipitation, the reflectivity factor mainly distributes in range of 15–25 dBZ with height within 4–10 km. It is also shows that weak precipitation is the dominant rain type in summer TP, accounting for 40%–80%, followed by weak convective precipitation (25%–40%), and strong convective precipitation has the least proportion (less than 30%).

As a new type of wind field detection equipment, coherent Doppler wind lidar (CDWL) still needs more relevant observation experiments to compare and verify whether it can achieve the accuracy and precision of traditional observation equipment in urban areas. In this experiment, a self-developed CDWL provided four months of observations in the southern Beijing area. After the data acquisition time and height match, the wind profile data obtained based on a Doppler beam swinging (DBS) five-beam inversion algorithm were compared with radiosonde data released from the same location. The standard deviation (SD) of wind speed is 0.8 m s⁻¹, and the coefficient of determination R² is 0.95. The SD of the wind direction is 17.7° with an R² of 0.96. Below the height of the roughness sublayer (about 400 m), the error in wind speed and wind direction is significantly greater than the error above the height of the boundary layer (about 1500 m). For the case of wind speeds less than 4 m s⁻¹, the error of wind direction is more significant and is affected by the distribution of surrounding buildings. Averaging at different height levels using suitable time windows can effectively reduce the effects of turbulence and thus reduce the error caused by the different measurement methods of the two devices.