Atmosphere

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15 pages, 7955 KiB

Open AccessArticle

Relation of Mid-High-Latitude Eurasian ISO to Ural Blocking Frequency and Their Co-Effect on Extreme Hot Events during Boreal Summer

by Shuangyan Yang, Xinsheng Wen and Mingxiang Gao

Atmosphere 2022, 13(12), 2041; https://doi.org/10.3390/atmos13122041 - 05 Dec 2022

Cited by 3 | Viewed by 1144

Abstract

Based on NCEP reanalysis daily data during 1979–2018, the spatiotemporal evolution of the 10–30-day atmospheric intraseasonal oscillations (ISO) at mid-high-latitude Eurasia and its effect on the Ural blocking frequency are investigated. The co-effect of the blocking and ISO on extreme hot event frequency [...] Read more.

Based on NCEP reanalysis daily data during 1979–2018, the spatiotemporal evolution of the 10–30-day atmospheric intraseasonal oscillations (ISO) at mid-high-latitude Eurasia and its effect on the Ural blocking frequency are investigated. The co-effect of the blocking and ISO on extreme hot event frequency is also investigated. The ISO exhibits two modes of eastward and westward propagation. During the eastward (westward) propagating mode, the northwest–southeast tilted quadrupole (east–west dipole) quasi-barotropic geopotential height anomaly coupled with the air temperature anomaly at the troposphere propagates southeastward (westward). The phase composite shows that, during both modes, the mid-high-latitude low-frequency Rossby wave trains significantly affect the frequency of the European blocking during the propagating journey. The most frequent European blocking appears in phase 2 during both the eastward- and westward- propagating mode. Compared with the situation without the Ural blocking, the blocking activity results in the positive geopotential height anomalies throughout Europe and north of 60° N in the Ural Mountains and the negative geopotential height anomalies in the south of 60° N in the Ural Mountains and north of the Japan Sea. The occurrence of Ural blocking is conducive to the occurrence of extreme high-temperature events in Europe and the high latitudes of the Ural Mountains, and a reduced frequency of extreme high-temperature events in the mid-latitudes of the Ural Mountains and north of the Japan Sea. Therefore, the Ural blocking activities significantly regulate the effect of the two propagating ISO modes on the extreme hot events over the middle and high latitudes of Eurasia. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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14 pages, 5226 KiB

Open AccessArticle

On the Successiveness of the Two Extreme Cold Events in China during the 2020/21 Winter According to Cold Air Trajectories

by Leying Zhang, Shuxiu Hou and Zuowei Xie

Atmosphere 2022, 13(11), 1915; https://doi.org/10.3390/atmos13111915 - 17 Nov 2022

Cited by 1 | Viewed by 1313

Abstract

Two extreme cold air events successively hit China during 28–31 December 2020 (the late 2020 event) and during 6–8 January 2021 (the early 2021 event), which caused great losses. These two events have received extensive attention in relation to synoptic weather systems and [...] Read more.

Two extreme cold air events successively hit China during 28–31 December 2020 (the late 2020 event) and during 6–8 January 2021 (the early 2021 event), which caused great losses. These two events have received extensive attention in relation to synoptic weather systems and remote forcing. Although it has been noted that a near-surface cool condition can greatly impact tropospheric circulation, its role in the successiveness of two such extreme cold waves remains unclear. This study focused on cold air pathways from the Lagrangian perspective, and explored the potential influence of cold air over the key region in terms of connecting the two cold events using a piecewise potential vorticity inversion. With the obtained results, three cold air sources with three corresponding air routes were identified in the two cold events. The northern pathway dominated the late 2020 event, in which the cold air intruded from the eastern Laptev Sea and moved southward to China. In contrast, the early 2021 event was mainly associated with the northwestern pathway in which the cold air came from the Ural Mountains and moved clockwise. Notably, cold air traveling along the western route from western Lake Balkhash arrived at the north of the Tianshan Mountains earlier and amplified the positive height anomaly in situ. Moreover, such an enhanced positive height anomaly moved the direction of the cold air from the northern and northwestern routes southward and thus played a key role in the successiveness of the two extreme cold events. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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16 pages, 8939 KiB

Open AccessArticle

Analysis of Intraseasonal Oscillation Features of Winter Cold Precipitation Events in Southern China

by Qingjiu Gao, Ziqi Zhang, Yesheng Zhu and Shuyi Chen

Atmosphere 2022, 13(10), 1603; https://doi.org/10.3390/atmos13101603 - 30 Sep 2022

Cited by 3 | Viewed by 1191

Abstract

Based on the daily minimum air temperature (T_min) data and the daily precipitation data from the NCC/CMA combined with the NCEP/DOE reanalysis data, the intraseasonal features and circulations of the winter cold precipitation events (CPEs) in southern China under the influence [...] Read more.

Based on the daily minimum air temperature (T_min) data and the daily precipitation data from the NCC/CMA combined with the NCEP/DOE reanalysis data, the intraseasonal features and circulations of the winter cold precipitation events (CPEs) in southern China under the influence of strong Madden–Julian oscillation (MJO) were explored. The results show that: (1) Winter temperatures in southern China are characterized by intraseasonal oscillations (ISOs) of 10–30-d and 30–60-d, with six CPEs under strong MJO all occurring during these two intraseasonal scales in cooling phases. The invasion of cold air coupled with the availability of appropriate moisture conditions in southern China is more conducive to the CPEs. (2) A cyclone and anticyclone lying to the east of the Ural Mountains and the northwest of Lake Baikal at 925-hPa gradually move southeastward. The merging of the low-frequency (LF) blocking highs over the Ural Mountains and the North Pacific Ocean at 500-hPa leads to the contraction and southward movement of the LF cold vortex. The following anomalous northerly winds steer the cold air towards southern China. The cold advection is the dominant term in the cooling process, while the adiabatic cooling accompanied with ascending motion is also beneficial to the cooling process. (3) MJO has some effect on the LF blocking highs and the cold vortex in the mid-high latitudes and induces the CPEs over southern China. The joint effect of mid-high and low latitudes on the 30–60-d intraseasonal oscillation scale can have a significant impact on the cooling and precipitation processes of CPEs. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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14 pages, 2656 KiB

Open AccessArticle

Retrieval of Road Surface (Bridge Deck) Temperature near 0 °C Based on Random Forest Model

by Chuanhui Wang, Beixi Jia, Jianping Zhou, Lei Feng and Jian Chen

Atmosphere 2022, 13(9), 1491; https://doi.org/10.3390/atmos13091491 - 13 Sep 2022

Cited by 1 | Viewed by 1217

Abstract

Based on the road surface (bridge deck) temperature, relative humidity, air temperature, wind speed and precipitation observed at two road surface meteorological stations and two bridge deck meteorological stations, as well as subsurface temperature at different depths observed at Hefei meteorological station, the [...] Read more.

Based on the road surface (bridge deck) temperature, relative humidity, air temperature, wind speed and precipitation observed at two road surface meteorological stations and two bridge deck meteorological stations, as well as subsurface temperature at different depths observed at Hefei meteorological station, the independent variables are selected to establish the relationship between these factors and road surface temperature, using random forest and stepwise regression. The performance of these two methods was compared, and the importance of each factor was analyzed. Results show that the road surface (bridge deck) temperature linearly correlates with air temperature. In the case of low air temperature conditions (air temperature ≤ 8 °C), the road surface temperature is mainly higher than air temperature observed at the same station, and the bridge deck temperature is mainly lower than air temperature. In the retrieving of road surface temperature and bridge deck temperature, the random forest algorithm has lower mean absolute error (MAE) and root mean square error (RMSE) than the stepwise regression algorithm, especially in the retrieving of road surface temperature. MAE of road surface temperature retrieved by random forest on two bridge deck stations is reduced by 0.19 °C and 0.26 °C compared with the stepwise regression, and RMSE is reduced by 0.33 °C and 0.49 °C, respectively. The bias in the retrievals can be originated from the model itself and the error in the observations. Among the factors in the random forest model, air temperature is the most important. Meanwhile, there are differences in the importance of each factor in the retrieval of road surface temperature and bridge deck temperature. The subsurface temperature is more important in retrieving road surface temperature, while humidity and wind speed are generally more important to bridge deck temperature. It should be noted that due to the limitation of the observations, this study did not consider the net radiative flux, and the influence of net radiative flux on bridge deck and road surface temperature may be different. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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15 pages, 4625 KiB

Open AccessArticle

Intra-Seasonal Features of Winter Extreme Cold Events in Northeast–North China and Synergistic Effects of Circulation Systems in Mid-High Latitude

by Qingjiu Gao, Li Wang, Yan Li and Yafei Wang

Atmosphere 2022, 13(9), 1425; https://doi.org/10.3390/atmos13091425 - 02 Sep 2022

Cited by 1 | Viewed by 1506

Abstract

Based on the daily minimum air temperature (T_min) data from the China Meteorological Data Network and the NCEP/DOE reanalysis data, the intra-seasonal circulation characteristics and evolution of extreme cold events (ECEs) in Northeast–North China (NE-N) during the winter of 1979–2018 are [...] Read more.

Based on the daily minimum air temperature (T_min) data from the China Meteorological Data Network and the NCEP/DOE reanalysis data, the intra-seasonal circulation characteristics and evolution of extreme cold events (ECEs) in Northeast–North China (NE-N) during the winter of 1979–2018 are explored, and the synergistic effects of key circulation systems in the mid-high latitude on ECEs are discussed. The results show that: (1) the winter daily T_min in the NE-N region presents a significant low-frequency period of 10–30 d; during the cooling phases, a pair of cyclone–anticyclone in the lower troposphere moves southeastward, accompanying the intensifying Siberian High, and leads to the abnormal northerly; the developing wave trains in the middle troposphere result in enhancing and maintaining cold air; furthermore, the situation of the upper tropospheric jet weakening in the north and strengthening in the south is favorable for cold air to move southward and accumulate in the NE-N region. (2) There are two wave trains in the Eurasian at 200 hPa level. The north one moves southeastward through the Ural Mountains to the coast of East Asia, with the upstream wave activity flux dispersing to NE-N region, causing the northeast cold vortex to develop. The south one with relatively weak intensity disperses the wave flux northward, and enhances the cold vortex. (3) The key circulation systems of ECEs are the Siberian High, the Ural Mountain Blocking High, the Northeast Cold Vortex, and the East Asian Subtropical Jet. The Ural Mountains Blocking High leads four phases earlier than low temperature, and the rest of the systems are basically in phase with low temperature. The synergistic effect of circulation systems will lead to extended-range cold in the NE-N region. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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18 pages, 6264 KiB

Open AccessArticle

Influence of Atmospheric 10–20 Day Low Frequency Oscillation on Regional Strong Cooling Events in the Winter of Northern China over the Past 40 Years

by Wei Zhang, Liping Li and Jinghua Ren

Atmosphere 2022, 13(9), 1406; https://doi.org/10.3390/atmos13091406 - 31 Aug 2022

Viewed by 1259

Abstract

Using daily minimum temperature data at 2481 stations provided by the National Meteorological Information Center (China) and the daily reanalysis data from NCEP/NCAR during the period from 1980 to 2019, the effects of atmospheric low frequency oscillations (LFOs) on the regional strong cooling [...] Read more.

Using daily minimum temperature data at 2481 stations provided by the National Meteorological Information Center (China) and the daily reanalysis data from NCEP/NCAR during the period from 1980 to 2019, the effects of atmospheric low frequency oscillations (LFOs) on the regional strong cooling events (RSCEs) in the winter of northern China are investigated, and the extended range forecast signals of the RSCEs are extracted. The results show that: (1) The frequency of RSCEs is higher before the year 2000 and then decreases, but its interannual variability increases. There are 10–20, 20–30 and 30–60 d significant low frequency periods in the regional average minimum temperature in northern China, and the low frequency oscillation with a period of 10–20 d is the most significant. (2) The low frequency key systems affecting RSCEs in the west, middle, and east of northern China are the Ural blocking high and the trough of Lake Balkhash-Baikal (Lake Ba-Bei), the blocking high in the northwest and the low trough in the southeast of Lake Ba-Bei, the Lake Ba-Bei blocking high and the East Asian trough, respectively, and the Siberian High (SH) that expands and moves with the blocking high all the time. The low frequency jets at the upper level are weaker in the north and stronger in the south. (3) The low frequency high potential vorticity (PV) center in the lower stratosphere moves eastward and southward along the 315 K isentropic surface via the north of Lake Ba-Bei, southern Lake Baikal and Northeast China to the Sea of Japan, causing the 2 PVU line to move southward and then the above-mentioned high PV center in the mid-high troposphere to extend vertically. Meanwhile, under the influence of gradually increasing upper level jets and vertical meridional circulation, the high PV column continues to propagate downward to the mid-low troposphere at lower latitudes along the 300–315 K isentropic surfaces, which enhances the low frequency positive vorticity and deepens the key trough. In addition, the convergence in the upper troposphere, the divergence in the lower layer, and the development of descending motion behind the trough lead to the development and southward movement of the SH. (4) At −10 d, the positive and negative low frequency anomalies at 500 hPa geopotential height appearing in the East European Plain and Western Siberian Plain are the extended range forecast signals for RSCEs in the winter of northern China, respectively. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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16 pages, 8884 KiB

Open AccessArticle

Three-Dimensional Structural Anomalies of the Western Pacific Subtropical High Ridge and Its Relationship with Precipitation in China during August–September 2021

by Fei Zhang, Xianyu Yang, Qingfei Sun, Suxiang Yao and Qu Guo

Atmosphere 2022, 13(7), 1089; https://doi.org/10.3390/atmos13071089 - 10 Jul 2022

Cited by 3 | Viewed by 1600

Abstract

In August-September 2021, the western Pacific subtropical high (WPSH) showed significant anomalies, with some areas between the Yangtze and Yellow River basins in China suffering from heavy rainfall and flooding, while extreme heat occurred in Southern China. Using the 6 h reanalysis data [...] Read more.

In August-September 2021, the western Pacific subtropical high (WPSH) showed significant anomalies, with some areas between the Yangtze and Yellow River basins in China suffering from heavy rainfall and flooding, while extreme heat occurred in Southern China. Using the 6 h reanalysis data of NCEP/NCAR and the daily precipitation observation data, this paper studied the abnormal characteristics and the thermal mechanism of the three-dimensional ridge of the WPSH during the seasonal transition from late summer to early autumn in August-September 2021, and explored its connection with the precipitation in the areas between the Yangtze and Yellow River basins in China during the same period. The results showed that, in August-September 2021, the three-dimensional ridge of the WPSH appeared to be southward at the lower troposphere and tilted northward with height. According to the diagnosis of the atmospheric heat source, it was found that the center of atmospheric cold source in the low latitudes at 850 hPa enhanced the surface high pressure, corresponding to the WPSH ridge shifting southward at the lower troposphere, which led to more water vapor convergence and more precipitation between the Yangtze and Yellow River basins. The latent heat of condensation released by the increased precipitation between the Yangtze and Yellow River basins in China heated the middle and upper troposphere, increasing the intensity of the high pressure in the upper troposphere, corresponding to the WPSH ridge northward at the upper troposphere. This anomalous tilt of the WPSH ridge in August-September 2021 and the intense precipitation processes between the Yangtze and Yellow River basins in China during the same period established a reciprocal feedback mechanism through diabatic heating. Further studies also showed that the anomalous tilt of the WPSH ridge is one of the important modes of its three-dimensional structural anomalies, and that, in years when the ridge tilts from south to north with height anomalously in August-September, the areas between the Yangtze and Yellow River basins are characterized by high precipitation. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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13 pages, 2971 KiB

Open AccessArticle

Effects of Atmospheric Heat Source on the Tibetan Plateau Vortex in Different Stages: A Case Study in June 2016

by Shu Zhou, Fang Sun, Meirong Wang, Shunwu Zhou and Yiyu Qing

Atmosphere 2022, 13(5), 689; https://doi.org/10.3390/atmos13050689 - 26 Apr 2022

Cited by 2 | Viewed by 1549

Abstract

The Tibetan Plateau (TP) vortex (TPV), one of the crucial weather systems triggering rainfall, plays a key role in modulating precipitation over TP and downstream regions. The role of atmospheric heat source in TPV development is explored by a case study in June [...] Read more.

The Tibetan Plateau (TP) vortex (TPV), one of the crucial weather systems triggering rainfall, plays a key role in modulating precipitation over TP and downstream regions. The role of atmospheric heat source in TPV development is explored by a case study in June 2016, using high-resolution ERA5 reanalysis, black-body temperature (TBB) obtained from the Fengyun-2E (FY-2E) satellite, and precipitation amount from the Tropical Rainfall Measurement Mission (TRMM). The evolutions of TPV can be split into three stages, i.e., generation, development, and pre-moving-off stage. The intensity of TPV increases with fluctuations, with weaker and shallower TPV in the generation stage, strongest in the development stage and deepest in the pre-moving-off stage. Importantly, the genesis of TPV is related to the surface warming center driven by surface sensible heating while its development is primarily dependent on the latent heat of condensation. The main contributor of the latent heat of condensation is further analyzed as a vertical transport of the water vapor that promotes TPV development. Full article

(This article belongs to the Special Issue Characteristics and Attribution of Air Temperature Variability)

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