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19 pages, 6210 KiB

Open AccessArticle

Temporal and Spatial Surface Heat Source Variation in the Gurbantunggut Desert from 1950 to 2021

by Ailiyaer Aihaiti, Yu Wang, Ali Mamtimin, Junjian Liu, Jiacheng Gao, Meiqi Song, Cong Wen, Chenxiang Ju, Fan Yang and Wen Huo

Remote Sens. 2023, 15(24), 5731; https://doi.org/10.3390/rs15245731 - 14 Dec 2023

Viewed by 583

Abstract

Based on data from the Gurbantunggut Desert, the largest fixed/semi-fixed desert in China, and ERA5-Land reanalysis data, the long-term variations and spatial surface heat source (SHS) differences in the Gurbantunggut Desert are discussed herein. The results show the following: (1) The hourly SHS [...] Read more.

Based on data from the Gurbantunggut Desert, the largest fixed/semi-fixed desert in China, and ERA5-Land reanalysis data, the long-term variations and spatial surface heat source (SHS) differences in the Gurbantunggut Desert are discussed herein. The results show the following: (1) The hourly SHS at the Kelameili station during the 2013–2021 period was a weak heat source at night; contrastingly, it was a strong heat source during the day. The duration of the hourly SHS increased gradually from January to July, but it decreased gradually from July to December. The daily SHS showed obvious seasonal variation, reaching the maximum in summer and the minimum in winter. The ERA5-Land reanalysis can reproduce all the variation characteristics of the SHS well. (2) The climatology (i.e., multi-year mean) of the monthly SHS intensity was lower than 50 W/m² during the January–March and September–December periods in the Gurbantunggut Desert, indicating a weak heat source. On the other hand, the climatology recorded in April–August was higher than 50 W/m², with a strong heat source. From the perspective of spatial distribution, the eastern and western regions of the Gurbantunggut Desert show strong heat sources, while the central region shows weak heat sources. The spatial distribution of the first and second modes of the empirical orthogonal function (EOF) decomposition reflected the consistent spatial variability and a north–south (or east–west) polarity variation of the monthly SHS in the Gurbantunggut Desert, respectively. (3) The yearly SHS showed negative anomalies during the 1950–1954, 1964–1982 and 2004–2015 periods, and positive anomalies during the 1955–1963, 1983–2003 and 2016–2021 periods in the Gurbantunggut Desert. Additionally, the time series of the SHS anomalies was positively correlated with the Interdecadal Pacific Oscillation (IPO) index. During the negative IPO phase, the yearly SHS showed a negative anomaly in the Gurbantunggut Desert, while the yearly SHS showed a positive anomaly during the positive IPO phase in most regions of the Gurbantunggut Desert. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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24 pages, 7947 KiB

Open AccessArticle

Diurnal Variation Characteristics of Summer Precipitation over the Northern Slope of the Tianshan Mountains, Xinjiang, Northwest China: Basic Features and Responses to the Inhomogeneous Underlying Surface

by Zulipina Kadier, Zhiyi Li, Abuduwaili Abulikemu, Kefeng Zhu, Aerzuna Abulimiti, Dawei An and Abidan Abuduaini

Remote Sens. 2023, 15(19), 4833; https://doi.org/10.3390/rs15194833 - 05 Oct 2023

Viewed by 892

Abstract

The diurnal variation characteristics of precipitation in summer (June–August) during the period of 2015–2019 over the Northern Slope of the Tianshan Mountains (NSTM) was analyzed using hourly simulated data from Nanjing University’s real-time forecasting system (WRF_NJU) with 4 km resolution, Automatic Weather Station [...] Read more.

The diurnal variation characteristics of precipitation in summer (June–August) during the period of 2015–2019 over the Northern Slope of the Tianshan Mountains (NSTM) was analyzed using hourly simulated data from Nanjing University’s real-time forecasting system (WRF_NJU) with 4 km resolution, Automatic Weather Station (AWS) data, and the ERA5-Land data through using methods such as the Rotated Empirical Orthogonal Function (REOF) and Coefficient of Variation (CV). The results show that the diurnal variation pattern of the precipitation over the NSTM simulated by WRF_NJU aligns closely with that of the observational AWS data, and it captured spatial distribution, peak values, and the times of precipitation reasonably well. The hourly precipitation amount (PA), precipitation frequency (PF), and precipitation intensity (PI) all show characteristics of being greater in the afternoon to nighttime than from early morning to noon, and the diurnal variations of precipitation in this region are significantly influenced by altitude. The PA, PF, and PI peak over the southern edge of the Junggar Basin (JB) below 1000 m occurred at around 2200 Local Solar Time (LST). In contrast, peak PA over the mountainous regions above 3000 m occurred at around 1500 LST. Further analysis with REOF and CV indicated that the difference in diurnal variations of precipitation between the mountainous regions and the JB is most pronounced likely due to the topographical influences. The peak PA over the mountainous regions mainly occurred at around 1500 LST, while that of the JB occurred at around 0100 LST. High CV regions for PI are predominantly found over the area near the central JB and the middle Tianshan mountains, whereas high CV regions for the PF are located in the central and northern parts of Urumqi and Changji. In addition, different land surface categories exhibit distinct patterns of diurnal precipitation variation, i.e., the forests, grasslands, and water bodies exhibit their peak PA in the period from early morning to noon, while the impervious surfaces, croplands, and barren lands exhibit their peak PA in the period from afternoon to nighttime. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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26 pages, 10071 KiB

Open AccessArticle

A Case Study on the Convection Initiation Mechanisms over the Northern Edge of Tarim Basin, Xinjiang, Northwest China

by Aerzuna Abulimiti, Qi Sun, Lin Yuan, Yongqiang Liu, Junqiang Yao, Lianmei Yang, Jie Ming and Abuduwaili Abulikemu

Remote Sens. 2023, 15(19), 4812; https://doi.org/10.3390/rs15194812 - 03 Oct 2023

Viewed by 834

Abstract

The convection initiation (CI) mechanisms of severe storms have received increasing attention because severe storms have been occurring more frequently around the globe in recent years. In this work, the CI mechanisms of severe convective weather associated with a gust front (GF) which [...] Read more.

The convection initiation (CI) mechanisms of severe storms have received increasing attention because severe storms have been occurring more frequently around the globe in recent years. In this work, the CI mechanisms of severe convective weather associated with a gust front (GF) which occurred on 9 July 2016, near the Korla at the northern edge of the Tarim Basin, Xinjiang, is investigated using observational data including Doppler weather radar data and automatic weather stations data, and high-resolution numerical simulation data. The results showed that, during the eastward movement of the GF, a number of convective cells were successively triggered in the vicinity of the GF, which developed rapidly and continuously merged with the convective system from behind, resulting in the further development and maintenance of this convective system. According to the diagnostic analysis of vertical acceleration which can be decomposed into dynamic acceleration (

a_{d}

) and buoyant acceleration (

a_{b}

), it was found that both

a_{d}

(up to ~4 × 10⁻³ m s⁻²) and

a_{b}

(up to ~7 × 10⁻³ m s⁻²) made positive contributions to the CI. Further analyses based on the decompositions of the

a_{d}

and

a_{b}

revealed that the extension term was the main contributor for the

a_{d}

, while the warming of the dry air due to the release of latent heat from the precipitation condensate made the major contribution to the

a_{b}

. The extension term indicates the elevated convergence jointly induced by the airflow of mid-level horizontal convective rolls (MHCRs) and updraft flow near the leading edge of the GF. The jointly induced elevated convergent updraft can be considered to be an important contributor for the CI mechanisms. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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19 pages, 5354 KiB

Open AccessArticle

Double Inversion Layers Affect Fog–Haze Events over Eastern China—Based on Unmanned Aerial Vehicles Observation

by Ruolan Liu, Duanyang Liu, Shujie Yuan, Hong Wu, Fan Zu and Ruixiang Liu

Remote Sens. 2023, 15(18), 4541; https://doi.org/10.3390/rs15184541 - 15 Sep 2023

Viewed by 728

Abstract

The goal of this work is to analyze how double inversion layers affect fog–haze events and boundary layers over Eastern China based on unmanned aerial vehicle observations. During 10–12 December 2020, two successive fog–haze events occurred in Eastern China. Based on the unmanned [...] Read more.

The goal of this work is to analyze how double inversion layers affect fog–haze events and boundary layers over Eastern China based on unmanned aerial vehicle observations. During 10–12 December 2020, two successive fog–haze events occurred in Eastern China. Based on the unmanned aerial vehicle (UAV), wind, temperature, relative humidity (RH), and aerosol mass concentration were monitored simultaneously in Lianyungang, China. Several observations were found after analyzing the physical fields of these data. The results show that the concentrations of air pollutants during fog events were negatively correlated with horizontal visibilities. The mass concentrations of particulate matter increased rapidly (After 08:00 BJT 11) in the fog dissipation stages (PM_2.5 and PM₁₀ increased from 97 and 150 μg/m³ to 213 and 300 μg/m³, respectively). Double temperature inversion significantly affected fog events, where the enhancement of the lower-level temperature inversion (where the inversion layer top height was between 150 and 300 m) corresponded to the explosive growth of fog and the dissipation of the upper-level inversion layer. (The bottom height of the inversion layer was between 350 m and 600 m) This indicates the end of fog events. Fog layer thicknesses are negatively correlated with the concentrations of air pollutants in the near-surface layer. The thickening of the inversion layer near the surface corresponds to an increase (after 05:00 BJT 11 and 03:00 BJT 12) in fog layer height. The fog event is maintained when water vapor conditions are favorable enough or when there is a deep near-surface temperature inversion but the maintenance of the near-surface temperature inversion at an intensity of above 2 °C (100 m)⁻¹ mainly contributes to the durations of these two fog events. Calculations through the trajectory model reveal that the air pollutant source varied during these two events, which was the main reason for the difference in air pollutant concentrations between the two events. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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24 pages, 27020 KiB

Open AccessArticle

A Case Study on the Convection Initiation Mechanisms of an Extreme Rainstorm over the Northern Slope of Kunlun Mountains, Xinjiang, Northwest China

by Qi Sun, Abuduwaili Abulikemu, Junqiang Yao, Ali Mamtimin, Lianmei Yang, Yong Zeng, Ruqi Li, Dawei An and Zhiyi Li

Remote Sens. 2023, 15(18), 4505; https://doi.org/10.3390/rs15184505 - 13 Sep 2023

Cited by 2 | Viewed by 947

Abstract

Extreme precipitation events have been occurring frequently worldwide, and their causative factors and convection initiation (CI) mechanisms have been attracting more and more attention in recent years. As a comprehensive study on the CI mechanisms of extreme rainstorms over the northern slope of [...] Read more.

Extreme precipitation events have been occurring frequently worldwide, and their causative factors and convection initiation (CI) mechanisms have been attracting more and more attention in recent years. As a comprehensive study on the CI mechanisms of extreme rainstorms over the northern slope of the Kunlun Mountains (KLM), Xinjiang, based on both observational and high tempo-spatial numerical simulation, the major findings of this work are as follows: A cold pool (CP) was formed in the northwestern Tarim Basin under the influence of early precipitation evaporation, and it moved towards the northern slope of the KLM several hours before the CI. With the movement of the CP, a significant vertical temperature gradient was formed close to the leading edge of the CP, thereby enhancing local convective instability (up to ~10 PVU). In addition, the vertical shear of the horizontal winds at the leading edge of the CP led to a notable increase in the baroclinic component of moist potential vorticity, thus reinforcing the local conditional symmetric instability (up to ~8 PVU), providing another important unstable energy for the CI. In addition, the combined effect of the convergent lifting of a boundary layer jet (BLJ, the maximum wind speed below 1 km exceeding 10 m s⁻¹) and the significant frontogenetical forcing (up to ~100 × 10⁻⁸ K m⁻¹ s⁻¹) at the leading edge of the CP were the causes of the release of the unstable energies. Further analysis of the frontogenetical forcing associated with the CP indicates that the convergence (up to ~2 × 10⁻³ s⁻¹), diabatic heating and slantwise terms (indicates the baroclinicity and inhomogeneity of the vertical momentum in horizontal direction) were the major contributors, whereas the deformation term at the leading edge of the CP provided a relatively weaker contribution. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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21 pages, 27098 KiB

Open AccessArticle

Temporal and Spatial Variations in Carbon Flux and Their Influencing Mechanisms on the Middle Tien Shan Region Grassland Ecosystem, China

by Kun Zhang, Yu Wang, Ali Mamtimin, Yongqiang Liu, Jiacheng Gao, Ailiyaer Aihaiti, Cong Wen, Meiqi Song, Fan Yang, Chenglong Zhou and Wen Huo

Remote Sens. 2023, 15(16), 4091; https://doi.org/10.3390/rs15164091 - 20 Aug 2023

Viewed by 1710

Abstract

Grassland ecosystems are an important component of global terrestrial ecosystems and play a crucial role in the global carbon cycle. Therefore, it is important to study the carbon dioxide (CO₂) process in the Middle Tien Shan grassland ecosystem, which can be [...] Read more.

Grassland ecosystems are an important component of global terrestrial ecosystems and play a crucial role in the global carbon cycle. Therefore, it is important to study the carbon dioxide (CO₂) process in the Middle Tien Shan grassland ecosystem, which can be regarded as a typical representative of the mountain grasslands in Xinjiang. Eddy covariance (EC) and the global carbon fluxes dataset (GCFD) were utilized to continuously monitor the Middle Tien Shan grassland ecosystem in Xinjiang throughout the 2018 growing season. The findings revealed notable daily and monthly fluctuations in net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco). On a daily basis, there was net absorption of CO₂ during the day and net emission during the night. The grassland acted as a carbon sink from 6:00 to 18:00 and as a carbon source for the remaining hours of the day. On a monthly scale, June and July served as carbon sinks, whereas the other months acted as carbon sources. The accumulated NEE, GPP, and Reco during the growing season were −329.49 g C m⁻², 779.04 g C m⁻², and 449.55 g C m⁻², respectively. On the half-hourly and daily scales, soil temperature (Ts) was the main contributor to CO₂ fluxes and had the greatest influence on the variations in CO₂ fluxes. Additionally, air temperature (Ta) showed a strong correlation with CO₂ fluxes. The grassland ecosystems exhibited the strongest CO₂ uptake, reaching its peak at soil temperatures of 25 °C. Moreover, as the air temperatures rose above 15 °C, there was a gradual decrease in NEE, while CO₂ uptake increased. The applicability of GCFD data is good in the grassland ecosystem of the Middle Tien Shan Mountains, with correlations of 0.59, 0.81, and 0.73 for NEE, GPP, and Reco, respectively, compared to field observations. In terms of remote sensing spatial distribution, the Middle Tien Shan grassland ecosystem exhibits a carbon sink phenomenon. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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23 pages, 16300 KiB

Open AccessArticle

Effect of Water Vapor Transport on a Typical Rainstorm Process in the Arid Region of Southern Xinjiang: Observations and Numerical Simulations

by Chen Jin, Qing He and Qian Huang

Remote Sens. 2023, 15(16), 4082; https://doi.org/10.3390/rs15164082 - 19 Aug 2023

Cited by 1 | Viewed by 755

Abstract

There are frequent and intensive periods of heavy rain in the arid areas of southern Xinjiang. This study uses a typical rainstorm process in the South Xinjiang Basin to investigate the weather, physical mechanisms, mesoscale characteristics, and income and expenditure characteristics of water [...] Read more.

There are frequent and intensive periods of heavy rain in the arid areas of southern Xinjiang. This study uses a typical rainstorm process in the South Xinjiang Basin to investigate the weather, physical mechanisms, mesoscale characteristics, and income and expenditure characteristics of water vapor sources, analyzing them using the observation data from southern Xinjiang regional automatic stations, ERA5 reanalysis data, multi-source satellite data, and WRF numerical simulation results. The study results show that torrential rain processes occur in the double-body distribution of the South Asian High in the upper troposphere, which is “high in the east and low in the west,” with “two ridges and one trough” in the middle layer. The development and movement of the low vortex, the configuration of low-level convergence and high-level divergence, and vertical upward movement provide favorable dynamic conditions for heavy rain. Additionally, the Black Sea, the Caspian Sea, the Aral Sea, the Arabian Sea, and the Bay of Bengal are important water vapor sources for this rainstorm. The water vapor reaches the South Xinjiang Basin along westward, southwest, and eastward paths. It is mainly imported into the South Xinjiang Basin from 500 to 300 hPa on the southern border and 700–500 hPa on the west, north, and east borders, and exported from 500 to 300 hPa on the eastern border. The simulation results show that the change in water vapor content significantly influences the precipitation intensity and range. The water vapor transport at the southern boundary contributes the most precipitation during the rainstorm. As the water vapor in the rainstorm area increases (decreases), the ascending motion is strengthened (weakened), the low-level convergence and high-level divergence are strengthened (weakened), the water vapor transport to the middle and high levels increases (decreases), and the precipitation increases (decreases). Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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20 pages, 8478 KiB

Open AccessArticle

Pavement Temperature Forecasts Based on Model Output Statistics: Experiments for Highways in Jiangsu, China

by Shoupeng Zhu, Yang Lyu, Hongbin Wang, Linyi Zhou, Chengying Zhu, Fu Dong, Yi Fan, Hong Wu, Ling Zhang, Duanyang Liu, Ting Yang and Dexuan Kong

Remote Sens. 2023, 15(16), 3956; https://doi.org/10.3390/rs15163956 - 10 Aug 2023

Cited by 1 | Viewed by 768

Abstract

Forecasts on transportation meteorology, such as pavement temperature, are becoming increasingly important in the face of global warming and frequent disruptions from extreme weather and climate events. In this study, we propose a pavement temperature forecast model based on stepwise regression—model output statistics [...] Read more.

Forecasts on transportation meteorology, such as pavement temperature, are becoming increasingly important in the face of global warming and frequent disruptions from extreme weather and climate events. In this study, we propose a pavement temperature forecast model based on stepwise regression—model output statistics (SRMOS) at the short-term timescale, using highways in Jiangsu, China, as examples. Experiments demonstrate that the SRMOS model effectively calibrates against the benchmark of the linear regression model based on surface air temperature (LRT). The SRMOS model shows a reduction in mean absolute errors by 0.7–1.6 °C, with larger magnitudes observed for larger biases in the LRT forecasts. Both forecasts exhibit higher accuracy in predicting minimum nighttime temperatures compared to maximum daytime temperatures. Additionally, it overall shows increasing biases from the north to the south, and the SRMOS superiority is greater over the south with larger initial LRT biases. Predictor importance analysis indicates that temperature, moisture, and larger-scale background are basically the key predictors in the SRMOS model for pavement temperature forecasts, of which the air temperature is the most crucial factor in the model’s construction. Although larger-scale circulation backgrounds are generally characterized by relatively low importance, their significance increases with longer lead times. The presented results demonstrate the considerable skill of the SRMOS model in predicting pavement temperatures, highlighting its potential in disaster prevention for extreme transportation meteorology events. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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29 pages, 29706 KiB

Open AccessArticle

Diurnal Variation Characteristics of Summer Precipitation and Related Statistical Analysis in the Ili Region, Xinjiang, Northwest China

by Zhiyi Li, Abuduwaili Abulikemu, Kefeng Zhu, Ali Mamtimin, Yong Zeng, Jiangang Li, Aerzuna Abulimiti, Zulipina Kadier, Abidan Abuduaini, Chunyang Li and Qi Sun

Remote Sens. 2023, 15(16), 3954; https://doi.org/10.3390/rs15163954 - 10 Aug 2023

Cited by 3 | Viewed by 1225

Abstract

The diurnal variation characteristics and basic statistical features of summer precipitation (from June to August) in the Ili region from 2015 to 2019 were investigated based on 4 km resolution Weather Research and Forecasting model simulation data from Nanjing University (WRF_NJU). The results [...] Read more.

The diurnal variation characteristics and basic statistical features of summer precipitation (from June to August) in the Ili region from 2015 to 2019 were investigated based on 4 km resolution Weather Research and Forecasting model simulation data from Nanjing University (WRF_NJU). The results show that the overall diurnal variation characteristics of precipitation (DVCP) reflected by the WRF_NJU data were consistent with respect to the observations and reanalysis data. The total precipitation pattern exhibited high (low) values on the east (west), with higher (lower) values over the mountainous (valley) area. Hourly precipitation amount (PA), precipitation frequency (PF), and precipitation intensity (PI) show similar diurnal variation characteristics, with peaks occurring at around 1700 LST in the mountainous area and around 2000 LST in valleys. Furthermore, moderate to intense precipitation contributes up to 87.88% of the total precipitation. The peaks in the mountainous area occur earlier than the valleys, while the peaks in western part of the valleys occur earlier than the eastern part. The PA peaks over the valleys and slopes occurred from the evening to early morning and from the afternoon to evening, respectively. In addition, the rotated empirical orthogonal function (REOF) analysis implied that the DVCP exhibits distinct differences between mountainous and valleys, and peak precipitation occurs during the evening in basin– and wedge–shaped areas, while the mountain peaks and foothill regions exhibit semi–diurnal variation characteristics. Among several basic meteorological factors, the vertical velocity (VV) and water vapor mixing ratio (WVMR) provided major contributions to the DVCP in both areas with high and low coefficients of variation, and the WVMR (VV) probably played a more significant role in mountainous (valleys) areas. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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18 pages, 9067 KiB

Open AccessArticle

Validation of FY-4A Temperature Profiles by Radiosonde Observations in Taklimakan Desert in China

by Yufen Ma, Juanjuan Liu, Ali Mamtimin, Ailiyaer Aihaiti and Lan Xu

Remote Sens. 2023, 15(11), 2925; https://doi.org/10.3390/rs15112925 - 03 Jun 2023

Cited by 3 | Viewed by 1201

Abstract

The atmospheric temperature profiles (ATPs) retrieved through the geostationary Interferometric Infrared Sounder (GIIRS) onboard the FY-4A satellite (GIIRS/FY-4A) can effectively fill the gap of the scarce conventional sounding data in the Taklimakan Desert (TD), the second largest desert in the world, with an [...] Read more.

The atmospheric temperature profiles (ATPs) retrieved through the geostationary Interferometric Infrared Sounder (GIIRS) onboard the FY-4A satellite (GIIRS/FY-4A) can effectively fill the gap of the scarce conventional sounding data in the Taklimakan Desert (TD), the second largest desert in the world, with an area of 330,000 square kilometers. In this study, we take the experimental radiosonde observations (RAOB) from one RAOB station in the hinterland of TD and seven conventional radiosondes in the oasis region around the desert as the true values and analyze the bias distribution characteristics of GIIRS/FY-4A ATPs with quality control (QC) flags 0 or 1 for this region. In addition, a bias comparison is made with GIIRS/FY-4A ATPs, and the fifth generation ECMWF atmospheric reanalysis of the global climate (ERA5) ATPs. The results show that (1) Missing measurements in GIIRS/FY-4A ATPs are the most frequent in the near-surface layer, accounting for more than 80% of all the retrieved grid points. The averaged total proportion of GIIRS/FY-4A ATPs with QC marks 0 or 1 is about 33.06%. (2) The root mean square error (RMSE) of GIIRS/FY-4A ATPs is less than 3 K, smaller than that of ERA5 ATPs. The RMSE of ERA5 ATPs can exceed 10 K in the desert hinterland. The absolute mean biases of GIIRS/FY-4A ATPs and ERA5 ATPs are, respectively, smaller than 3 K and 2 K, the former being slightly larger. The correlation coefficients of GIIRS/FY-4A ATPs with ERA5 ATPs and RAOB ATPs are higher than 0.98 and 0.99, respectively, and the correlation between GIIRS/FY-4A ATPs and RAOB ATPs is inferior to the latter. (3) The overall atmospheric temperature retrieved by GIIRS/FY-4A is 0.08 K higher than the temperature of RAOB, on average, while the overall temperature from ERA5 is 0.13 K lower than that of RAOB, indicating that the temperature profile obtained by integrating GIIRS/FY-4A ATPs and ERA5 ATPs may be much closer to RAOB ATPs. (4) The probability density of the GIIRS/FY-4A ATP biases in the TD region generally follows the Gaussian distribution so that it can be effectively assimilated in the 3-D variational assimilation modules. The probability density distribution characteristics of the GIIRS/FY-4A ATP biases in the desert hinterland and oasis are not much different. However, due to the fusion analysis of the relatively rich multi-source conventional observation data from the oasis stations, the probability density of ERA5 ATPs biases at the oasis stations is nearer to Gaussian distribution than that of the GIIRS/FY-4A ATPs. In the desert hinterland, where conventional observation is not enough, the probability density distributions of the ATPs biases from ERA5 and GIIRS/FY-4A are alike. Therefore, the GIIRS FY4A can contribute to a more accurate estimation of ERA5 ATPs in the TD region. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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26 pages, 16392 KiB

Open AccessArticle

Spatiotemporal Variation of Hourly Scale Extreme Rainstorms in the Huang-Huai-Hai Plain and Its Impact on NDVI

by Huiting Zuo, Yunsheng Lou and Zhongliang Li

Remote Sens. 2023, 15(11), 2778; https://doi.org/10.3390/rs15112778 - 26 May 2023

Cited by 1 | Viewed by 1070

Abstract

This paper utilizes high-resolution ERA5 hourly data from 1980 to 2020 and long-term normalized difference vegetation index (NDVI) time series obtained from remote sensing and applies trend analysis, correlation analysis, lag analysis, and other methods to study the spatiotemporal characteristics of extreme rainfall [...] Read more.

This paper utilizes high-resolution ERA5 hourly data from 1980 to 2020 and long-term normalized difference vegetation index (NDVI) time series obtained from remote sensing and applies trend analysis, correlation analysis, lag analysis, and other methods to study the spatiotemporal characteristics of extreme rainfall at daily and hourly scales in the Huang-Huai-Hai Plain. The paper explores the NDVI’s variability and its relationship with extreme hourly precipitation and analyzes the main factors affecting it. The study made the following observations: (1) The extreme daily precipitation in the Huang-Huai-Hai Plain shows a decreasing trend, with a 13.6 mm/yr reduction rate. In contrast, the proportion of extreme rainfall to total precipitation generally exceeds 20%, and the intensity of extreme rain has gradually increased. The spatial distribution pattern of extreme rainfall follows the distribution pattern of China’s rain belts, with the terrain being an important influencing factor. The high-incidence areas for extreme rainfall are the Huaihe River region and the Shandong Peninsula. (2) The observed significant increase in hourly extreme precipitation events in the Shandong and Henan provinces of the Huang-Huai-Hai Plain has led to an increased risk of flooding, while the corresponding events in the northwest region of the Plain have exhibited a gradual weakening trend over time. (3) The extreme hourly precipitation in the Huang-Huai-Hai plain shows a frequent and scattered pattern, with decreasing intensity over time. Extreme precipitation mainly occurs in the first half of the night, especially between 19:00 and 21:00, with extreme hourly rainfall intensity fluctuating between 0.2 and 0.25 and the proportion of rainfall to total precipitation reaching as high as 10%. The spatial distribution of extreme hourly rainstorms during the peak period (19:00–21:00) exhibits a high rainfall volume, intensity, and frequency pattern in the eastern region, while the western part exhibits low rainfall volume, intensity, and frequency. (4) The incidence of extremely heavy rainfall in an hour has exhibited a more significant increase compared to extreme daily events in the Huang-Huai-Hai Plain, primarily in the form of backward-type precipitation. Hourly extreme precipitation events in the Huang-Huai-Hai Plain are affected by terrain and land use/cover change (LUCC), with the micro-topography of hilly areas leading to a concentrated distribution of precipitation and LUCC suppressing extreme precipitation events in arid climates. (5) At the ten-day scale, the spatial distribution of the NDVI shows a gradually increasing trend from northwest to southeast, with the highest NDVI value reaching up to 0.6 in the southern part of the study area. For extreme hourly precipitation, there is no significant change observed at the multi-year ten-day scale; while the NDVI in the northern and central parts of the Huang-Huai-Hai Plain shows a significant decreasing trend, in contrast, it presents a significant increasing trend in the southern region. (6) Finally, the correlation between NDVI at the ten-day scale and extreme hourly precipitation exhibits a decreasing pattern from north to south, with a correlation coefficient decreasing from 0.48 to 0.08. The lagged correlation analysis of extreme hourly rainfall and NDVI for one, two, and three ten-day periods shows that the lagged effect of extreme hourly precipitation on NDVI is negligible. Analyzing the correlation between extreme hourly rainfall and NDVI for different months, the impact of extreme hourly precipitation on NDVI is predominantly negative, except for June, which shows a positive correlation (0.35), passing the significance test. This study offers a scientific foundation for enhancing disaster warning accuracy and timeliness and strengthening the research on disaster reduction techniques. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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18 pages, 6854 KiB

Open AccessArticle

Parameterization and Remote Sensing Retrieval of Land Surface Processes in the Gurbantunggut Desert, China

by Wei Li, Jiacheng Gao, Ali Mamtimin, Yongqiang Liu, Yu Wang, Meiqi Song, Cong Wen, Ailiyaer Aihaiti, Fan Yang, Wen Huo, Chenglong Zhou, Wenbiao Wang and Zhengnan Cui

Remote Sens. 2023, 15(10), 2646; https://doi.org/10.3390/rs15102646 - 19 May 2023

Viewed by 1666

Abstract

The exchange of energy between the land surface and atmosphere is dependent upon crucial parameters, including surface roughness, emissivity, bulk transfer coefficients for momentum (C_D) and heat (C_H). These parameters are calculated through site observation data and remote sensing [...] Read more.

The exchange of energy between the land surface and atmosphere is dependent upon crucial parameters, including surface roughness, emissivity, bulk transfer coefficients for momentum (C_D) and heat (C_H). These parameters are calculated through site observation data and remote sensing data. The following conclusions are drawn: (1) the aerodynamic roughness of the Gurbantunggut Desert measures 1.1 × 10⁻² m, which is influenced by the varying conditions of the underlying surface. The roughness decreases as wind speed increases and is seen to be directly proportional to the growth of vegetation. From April to June, the aerodynamic roughness increases with increasing vegetation cover, but begins to gradually decrease after July. Spatially, the middle regions show higher roughness values than the eastern and western areas. In the central part of the desert, the roughness is between 2.37 × 10⁻² m and 2.46 × 10⁻² m from April to November. The northwest and northeast regions measure 1.41 × 10⁻² m–2.04 × 10⁻² m and 1.53 × 10⁻² m–2.39 × 10⁻² m, respectively. (2) The surface emissivity is 0.93, and it varies depending on the snow and vegetation present in the underlying area. (3) C_D and C_H exhibit an inverse relationship with wind speed. When wind speed falls below 6 m/s, the C_D declines rapidly as wind speed increases. In contrast, once wind speed surpasses 6 m/s, the propensity for the C_D to decrease with increasing wind speed slows down and approaches stability. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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20 pages, 3616 KiB

Open AccessArticle

Evapotranspiration of Winter Wheat in the Semi-Arid Southeastern Loess Plateau Based on Multi-Source Satellite Data

by Peng He, Rutian Bi, Lishuai Xu, Zhengchun Liu, Fan Yang, Wenbiao Wang, Zhengnan Cui and Jingshu Wang

Remote Sens. 2023, 15(8), 2095; https://doi.org/10.3390/rs15082095 - 16 Apr 2023

Cited by 1 | Viewed by 1025

Abstract

Continuous monitoring of evapotranspiration (ET) at high spatio-temporal resolutions is vital for managing agricultural water resources in arid and semi-arid regions. This study used the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) to calculate the ET of winter wheat between the [...] Read more.

Continuous monitoring of evapotranspiration (ET) at high spatio-temporal resolutions is vital for managing agricultural water resources in arid and semi-arid regions. This study used the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) to calculate the ET of winter wheat between the green-up and milk stages in Linfen Basin, a typical, semi-arid area of the Loess Plateau, at temporal and spatial resolutions of 30 m and 8 d, respectively. We then analyzed the impact of meteorological factors on ET and its variation during the main growth period of winter wheat. The fused ET data displayed the spatial details of the OLI ET data better and could accurately reflect ET variation and local sudden variations during the main growth period of winter wheat. Moreover, winter wheat ET in rain-fed areas is more heavily influenced by meteorological factors, and the effect is more direct. Affected by the synergistic effect of wind velocity, precipitation, and temperature, the ET of winter wheat in rain-fed area was lower in the green-up stage. Then, ET gradually increased, reaching its maximum in the heading–grain filling stage. At the jointing stage, temperature had a significant effect on ET. A combination of precipitation and temperature had the greatest impact on the ET of winter wheat in the heading–filling stage. In the milk stage, meteorological factors had a minor impact on ET. This study serves as a reference for ET in winter wheat in semi-arid areas and its influencing meteorological factors, which can assist in drought mitigation and regional food security strategies. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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19 pages, 14275 KiB

Open AccessArticle

Numerical Study on the Effects of Intraseasonal Oscillations for a Persistent Drought and Hot Event in South China Summer 2022

by Yi Qin, Yujing Qin, Yichen Shen, Yonghua Li and Bo Xiang

Remote Sens. 2023, 15(4), 892; https://doi.org/10.3390/rs15040892 - 06 Feb 2023

Cited by 3 | Viewed by 3534

Abstract

From 19 July 2022 to 31 August 2022, a rare persistent drought and heat event occurred in the middle of the Yangtze River basin (MYRB). Normalized difference vegetation Index (NDVI) over 25% of the area decreased more than 0.05 compared with the climatology, [...] Read more.

From 19 July 2022 to 31 August 2022, a rare persistent drought and heat event occurred in the middle of the Yangtze River basin (MYRB). Normalized difference vegetation Index (NDVI) over 25% of the area decreased more than 0.05 compared with the climatology, causing extremely agricultural drought disaster and economic losses to China. Previous studies have shown that the occurrence of compound drought and heat events (CDHEs) in the MYRB was associated with intra-seasonal oscillations (ISOs) from different latitudes. Nevertheless, what was the role of ISOs at different latitudes in the formation of the CDHE? To address this question, this paper designed a numerical simulation experiment of partial lateral forcing to investigate the changes in meteorological elements by removing the signals of ISOs on different lateral boundaries. We found that the wave series formed in the upper troposphere at 200 hPa played a significant role in the occurrence of the CDHE in the northern part of the MYRB in this progress. It was found that the ISO component of the northern boundary caused the mean temperature to rise by 2.4 °C and aggravated the drought in 53.7% of the region. On the other hand, the anticyclone anomaly in the lower troposphere at 800 hPa had a continuous impact on the southern and eastern boundaries. It was found that the ISO component of these two boundaries can increase the average temperature by 1.93 °C in the MYRB and intensify the drought in 49.7% of the area. In the developing period of the CDHE, the South Asian high and the Western North Pacific subtropical high were coupled with each other and jointly controlled the MYRB, so that the significant positive geopotential height anomaly stayed above the MYRB for a long time, which was conducive to the development of local subsidence. The results of this paper will help to better understand the formation mechanism of CDHEs in the MYRB and assist meteorologists to prevent and forecast the occurrence of CDHEs in advance. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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13 pages, 2905 KiB

Open AccessTechnical Note

Snowpack Dynamics Influence Tree Growth and Signals in Tree Rings of Tianshan Mountain, Central Asia

by Yuting Fan, Qian Li, Huaming Shang, Shengxia Jiang, Tongwen Zhang, Ruibo Zhang, Li Qin, Shulong Yu and Heli Zhang

Remote Sens. 2023, 15(11), 2849; https://doi.org/10.3390/rs15112849 - 30 May 2023

Viewed by 1323

Abstract

Snow is an important source of freshwater in the Tianshan Mountains of Central Asia. This study established 18 tree ring width chronologies and compound chronologies and analyzed the effects of snow depth, measured both by remote sensing and at meteorological stations, on the [...] Read more.

Snow is an important source of freshwater in the Tianshan Mountains of Central Asia. This study established 18 tree ring width chronologies and compound chronologies and analyzed the effects of snow depth, measured both by remote sensing and at meteorological stations, on the radial growth of spruce trees. The results showed that the established standard chronology of tree ring width is suitable for the analysis of tree ring climatology. The correlation coefficient of the ring width index (RWI) and the remote sensing snow depth was greater than that of the meteorological station snow depth. For the remote sensing snow depth, the correlation coefficients were greater in the winter and spring months compare to other periods, while the correlation coefficients of the meteorological stations were greater only in the winter. The nonlinear method (BRNN) showed good fitting in the reconstruction of the historical snow depth. The reconstructed snow depth exhibited a decreasing trend in the Bharakonu Mountains (BM), Narathi Mountains (NM), and Halke mountains (KM) sub-regions in the overall reconstructed period; however, the trends were inconsistent in both the historical and the observed periods, indicating the importance of reconstructing snow depth in the Tianshan Mountains. Full article

(This article belongs to the Special Issue Understanding the Meteorological Environment in Arid Regions through the Integrative Analyses of Remote Sensing, Ground Observational Stations and Numerical Models)

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