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2 pages, 143 KiB

Open AccessEditorial

Large-Scale Atmospheric Circulation Variability and Its Climate Impacts

by Bin Yu and Anthony R. Lupo

Atmosphere 2019, 10(6), 329; https://doi.org/10.3390/atmos10060329 - 18 Jun 2019

Cited by 7 | Viewed by 3085

Abstract

This special issue collects original and review articles on large-scale atmospheric circulation variability and its climate impacts [...] Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

Research

Jump to: Editorial, Review

17 pages, 2999 KiB

Open AccessArticle

Winter Weather Regimes in Southeastern China and its Intraseasonal Variations

by Yongdi Wang, Shuanggen Jin, Xinyu Sun and Fei Wang

Atmosphere 2019, 10(5), 271; https://doi.org/10.3390/atmos10050271 - 14 May 2019

Cited by 6 | Viewed by 3274

Abstract

Extreme precipitation has often occurred in Southeastern China, while the possible mechanism is not clear. In order to bridge the scale gap between large-scale circulation and extreme precipitation, in this paper, the k-means clustering technique—a common method of weather-type (WT) analysis—was applied [...] Read more.

Extreme precipitation has often occurred in Southeastern China, while the possible mechanism is not clear. In order to bridge the scale gap between large-scale circulation and extreme precipitation, in this paper, the k-means clustering technique—a common method of weather-type (WT) analysis—was applied to regional 850-hPa wind fields. The reasonable determination of k values can make the later WT analyses more reliable. Thus, the Davies–Bouldin (BD) criterion index is used in the clustering process, and the optimal value of the k was determined. Then, we obtain and analyze the frequency, persistence, and progression of WTs. The rule of transitions from one WT to another may help explain some of the physical processes in winter. We found a special evolutionary chain (WT3→WT1→WT2→WT5→WT3) that can be used to explain the cold wave weather process in winter. Different WTs in the evolutionary chain correspond well to different stages of the cold wave weather process (gestation (WT3), outbreak (WT1), eastward withdrawal (WT2), and extinction (WT5)). In addition, we found that there are obvious differences in precipitation between December and February. After reassembling five kinds of WTs, two modes are formed: dry WTs and wet WTs. Our research shows that the intraseasonal variation of precipitation can be attributed to the fluctuation between the wet and dry WTs, and the different phases of teleconnection can correspond well with it. For example, the relative frequencies of wet WTs are higher in February. These WTs correspond to the positive phase of the WP and ENSO, the negative phase of the EA and EU, and the strong MJO state of the second, third, and eighth phase. Our work has well established the relationship between synoptic scale and large-scale circulation, which provides a reference for climate model simulation and future climate prediction. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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26 pages, 32686 KiB

Open AccessArticle

Parameter Modulation of Madden-Julian Oscillation Behaviors in BCC_CSM1.2: The Key Role of Moisture-Shallow Convection Feedback

by Kai Huang, Hong-Li Ren, Xiangwen Liu, Pengfei Ren, Yuntao Wei and Mu Mu

Atmosphere 2019, 10(5), 241; https://doi.org/10.3390/atmos10050241 - 1 May 2019

Cited by 2 | Viewed by 4898

Abstract

To reveal key parameter-related physical mechanisms in simulating Madden-Julian Oscillation (MJO), seven physical parameters in the convection and cloud parameterization schemes of Beijing Climate Center Climate System Model (BCC_CSM1.2) are perturbed with Latin hypercube sampling method. A new strategy is proposed to select [...] Read more.

To reveal key parameter-related physical mechanisms in simulating Madden-Julian Oscillation (MJO), seven physical parameters in the convection and cloud parameterization schemes of Beijing Climate Center Climate System Model (BCC_CSM1.2) are perturbed with Latin hypercube sampling method. A new strategy is proposed to select runs with good and poor MJO simulations among 85 generated ones. Outputs and parameter values from good and poor simulations are composited separately for comparison. Among the seven chosen parameters, a decreased value of precipitation efficiency for shallow convection, higher values of relative humidity threshold for low stable clouds and evaporation efficiency for deep convective precipitation are crucial to simulate a better MJO. Changes of the three parameters act together to suppress heavy precipitation and increase the frequency of light rainfall over the Indo-Pacific region, supplying more moisture in low and middle troposphere. As a result of a wetter lower troposphere ahead of the MJO main convection, the low-level moisture preconditioning along with the leading shallow convection tends to be enhanced, favorable for MJO’s further development and eastward propagation. The MJO’s further propagation across the Maritime Continent (MC) in good simulations is accompanied with more land precipitation dominated by shallow convection. Therefore, the above-mentioned three parameters are found to be crucial parameters out of the seven ones for MJO simulation, providing an inspiration for better MJO simulation and prediction with this model. This work is valuable as it highlights the key role of moisture-shallow convection feedback in the MJO dynamics. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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16 pages, 4027 KiB

Open AccessArticle

Role of the South Asian High in the Onset Process of the Asian Summer Monsoon during Spring-to-Summer Transition

by Wei Wei, Yuting Wu, Song Yang and Wen Zhou

Atmosphere 2019, 10(5), 239; https://doi.org/10.3390/atmos10050239 - 1 May 2019

Cited by 24 | Viewed by 4478

Abstract

The evolution of the South Asian high (SAH) and its role in the onset process of the Asian summer monsoon (ASM) during the spring-to-summer transition are investigated by using the NCEP-DOE reanalysis II dataset, with a focus on climatology and interannual time scales. [...] Read more.

The evolution of the South Asian high (SAH) and its role in the onset process of the Asian summer monsoon (ASM) during the spring-to-summer transition are investigated by using the NCEP-DOE reanalysis II dataset, with a focus on climatology and interannual time scales. Our results show four sudden changes of the SAH in its Northwestward evolution from the Western Pacific to the South China Sea (SCS), the Indochina Peninsula and the South Asian plateaus, coincide with the ASM onset over the Bay of Bengal, the SCS, and the Indian summer monsoon region. The physical process for the mutual promotion between the SAH and ASM rainfall is revealed. Accompanying the SAH evolution, the upper-level Easterly wind along the Southern flank and the upper-level divergence associated with the SAH shift Northwestward accordingly. The upper-level Easterly wind coordinates with the lower-level Southwesterly wind, and forms the summer circulation structure in the ASM regions gradually. Besides, the upper-level divergence associated with the SAH enhances ascending motion in ASM regions and increases the monsoon rainfall accordingly. Subsequently, the latent heat associated with the monsoon rainfall in the monsoon onset region excites an anticyclone to its Northwest in the upper level, which keeps strengthening the SAH and moving it Northwestward. This mutual promotion between the SAH and ASM rainfall can be affected by the sea surface temperatures (SSTs) in the Western Pacific and tropical Indian Ocean in the previous month. Colder (warmer) SSTs over the Western Pacific and inactive (active) convection over the Southern Philippines suppress (favor) the Northwestward development of the SAH in late April. In addition, the warmer (colder) SSTs in the tropical Indian Ocean excites anomalous anticyclone (cyclone) in the upper level near the equator, which keeps the SAH in the lower latitudes (promotes the SAH to the North), and delays (advances) the mutual promotion between the SAH and ASM rainfall. As a result, the entire ASM onset process is later (earlier) than normal. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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18 pages, 3502 KiB

Open AccessArticle

A Comparison of North American Surface Temperature and Temperature Extreme Anomalies in Association with Various Atmospheric Teleconnection Patterns

by Bin Yu, Hai Lin and Nicholas Soulard

Atmosphere 2019, 10(4), 172; https://doi.org/10.3390/atmos10040172 - 1 Apr 2019

Cited by 25 | Viewed by 4540

Abstract

The atmospheric teleconnection pattern reflects large-scale variations in the atmospheric wave and jet stream, and has pronounced impacts on climate mean and extremes over various regions. This study compares those patterns that have significant circulation anomalies over the North Pacific–North American–North Atlantic sector, [...] Read more.

The atmospheric teleconnection pattern reflects large-scale variations in the atmospheric wave and jet stream, and has pronounced impacts on climate mean and extremes over various regions. This study compares those patterns that have significant circulation anomalies over the North Pacific–North American–North Atlantic sector, which directly influence surface temperature and temperature extremes over North America. We analyze the pattern associated anomalies of surface temperature and warm and cold extremes over North America, during the northern winter and summer seasons. In particular, we assess the robustness of the regional temperature and temperature extreme anomaly patterns by evaluating the field significance of these anomalies over North America, and quantify the percentages of North American temperature and temperature extreme variances explained by these patterns. The surface temperature anomalies in association with the Pacific–North American pattern (PNA), Tropical–Northern Hemisphere pattern (TNH), North Pacific pattern (NP), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Western Pacific pattern (WP), circumglobal teleconnection (CGT), and Asian–Bering–North American (ABNA) patterns are similar to those reported in previous studies based on various datasets, indicating the robustness of the results. During winter, the temperature anomaly patterns considered are field significant at the 5% level over North America, except the WP-related one. These pattern associated anomalies explained about 5–15% of the total interannual temperature variance over North America, with relatively high percentages for the ABNA and PNA patterns, and low for the WP pattern. The pattern associated warm and cold extreme anomalies resemble the corresponding surface mean temperature anomaly patterns, with differences mainly in magnitude of the anomalies. Most of the anomalous extreme patterns are field significant at the 5% level, except the WP-related patterns. These extreme anomalies explain about 5–20% of the total interannual variance over North America. During summer, the pattern-related circulation and surface temperature anomalies are weaker than those in winter. Nevertheless, all of the pattern associated temperature anomalies are of field significance at the 5% level over North America, except the PNA-related one, and explain about 5–10% of the interannual variance. In addition, the temperature extreme anomalies, in association with the circulation patterns, are comparable in summer and winter. Over North America, the NP-, WP-, ABNA-, and CGT-associated anomalies of warm extremes are field significant at the 5% level and explain about 5–15% of the interannual variance. Most of the pattern associated cold extreme anomalies are field significant at the 5% level, except the PNA and NAO related anomalies, and also explain about 5–15% of the interannual variance over North America. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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14 pages, 3916 KiB

Open AccessArticle

Recent Strengthened Impact of the Winter Arctic Oscillation on the Southeast Asian Surface Air Temperature Variation

by Shangfeng Chen and Linye Song

Atmosphere 2019, 10(4), 164; https://doi.org/10.3390/atmos10040164 - 27 Mar 2019

Cited by 19 | Viewed by 3315

Abstract

A previous study indicated that the Arctic Oscillation (AO) and Siberian High (SH) are two important drivers for the interannual variation of winter surface air temperature (SAT) over southeast Asia. This study reveals that the impact of the winter SH on the southeast [...] Read more.

A previous study indicated that the Arctic Oscillation (AO) and Siberian High (SH) are two important drivers for the interannual variation of winter surface air temperature (SAT) over southeast Asia. This study reveals that the impact of the winter SH on the southeast Asian SAT was stable. By contrast, the connection between the winter AO and southeast Asian SAT displays a pronounced interdecadal change around the late-1990s. Significant impact of the winter AO on the southeast Asian SAT can only be detected after the late-1990s. The result shows that change in the impact of the winter AO on southeast Asian SAT was mainly attributed to change in the spatial structure of the AO. Before the late-1990s, significant atmospheric signals related to the winter AO were confined to the North Atlantic region and the atmospheric anomalies over Eurasia were weak. As such, impact of the winter AO on the southeast Asian SAT was weak. By contrast, after the late-1990s, winter AO displays a more zonally symmetric structure, with significant negative sea level pressure (SLP) anomalies over the Arctic, and positive anomalies over mid-latitudes. Specifically, the positive SLP anomalies over East China induce clear northerly wind anomalies over southeast Asia, which lead to negative SAT anomalies there via wind-induced temperature advection. Hence, the winter AO has a significant impact on the southeast Asian SAT after the late-1990s. Further analysis shows that after the late-1990s, hindcast skill of the winter southeast Asian SAT anomalies was enhanced when taking both the winter AO and SH into account. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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13 pages, 4384 KiB

Open AccessArticle

Impacts of Onset Time of El Niño Events on Summer Rainfall over Southeastern Australia during 1980–2017

by Lingli Fan, Jianjun Xu and Liguo Han

Atmosphere 2019, 10(3), 139; https://doi.org/10.3390/atmos10030139 - 14 Mar 2019

Cited by 3 | Viewed by 4048

Abstract

El Niño–Southern Oscillation (ENSO) has large impacts on Australia’s rainfall. A composite analysis technique was utilized to distinguish the impact of onset time of El Niño on summer rainfall over southeastern Australia. Summer rainfall tended to be lower than normal in austral autumn [...] Read more.

El Niño–Southern Oscillation (ENSO) has large impacts on Australia’s rainfall. A composite analysis technique was utilized to distinguish the impact of onset time of El Niño on summer rainfall over southeastern Australia. Summer rainfall tended to be lower than normal in austral autumn El Niño events during December–January–February (DJF) and higher than normal in austral winter El Niño events, in 1980–2017. During autumn El Niño events, the Walker circulation and meridional cells served as a bridge, linking the warmer sea surface temperature (SST) in the eastern equatorial Pacific (EEP) and lower summer rainfall over southeastern Australia. This physical process can be described as follows: During DJF, a positive SST anomaly in the EEP was concurrent with anomalous downdraft over southeastern Australia via zonal anomalous Walker circulation, meridional anomalous cells along 170° E–170° W, and a Pacific South American (PSA) teleconnection wave train at 500 hPa. In addition, an anomalous convergence at 200 hPa depressed the convection. Meanwhile, an 850 hPa abnormal westerly was not conducive to transport marine water vapor into this area. These factors resulted in below-normal rainfall. During winter El Niño events, a positive SST anomaly in the central equatorial Pacific (CEP) and the changes in Walker circulation and meridional cells were weaker. The PSA teleconnection wave train shifted westward and northward, and there was a low-level anomalous ascent over southeastern Australia. At the western flank of the anomalous anticyclone, northerly transported water vapor from the ocean to southeastern Australia resulted in a sink of water vapor over this area. The development of low-level convective activity and the plentiful water vapor supply favored more rainfall over southeastern Australia. Onset time of El Niño may be a useful metric for improving the low predictive skill of southeastern Australian summer rainfall. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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20 pages, 12136 KiB

Open AccessArticle

The Linkage of the Large-Scale Circulation Pattern to a Long-Lived Heatwave over Mideastern China in 2018

by Muyuan Li, Yao Yao, Dehai Luo and Linhao Zhong

Atmosphere 2019, 10(2), 89; https://doi.org/10.3390/atmos10020089 - 20 Feb 2019

Cited by 30 | Viewed by 5122

Abstract

In this study, the large-scale circulation patterns (a blocking high, wave trains and the western Pacific subtropical high (WPSH)) associated with a wide ranging and highly intense long-lived heatwave in China during the summer of 2018 are examined using both observational data and [...] Read more.

In this study, the large-scale circulation patterns (a blocking high, wave trains and the western Pacific subtropical high (WPSH)) associated with a wide ranging and highly intense long-lived heatwave in China during the summer of 2018 are examined using both observational data and reanalysis data. Four hot periods are extracted from the heatwave and these are related to anticyclones (hereafter referred to as heatwave anticyclone) over the hot region. Further analysis shows a relationship between the heatwave anticyclone and a synthesis of low, mid- and high latitude circulation systems. In the mid-high latitudes, a midlatitude wave train and a high latitude wave train are associated with a relay process which maintains the heatwave anticyclone. The midlatitude wave train acts during 16–21 July, whereas the high latitude wave train takes affect during 22–28 July. The transition between the two wave trains leads to the northward movement of the hot region. With the help of a wave flux analysis, it was found that both wave trains originate from the positive North Atlantic Oscillation (NAO+) which acts as an Atlantic wave source. Serving as a circulation background, the blocking situated over the Scandinavia-Ural sector is maintained for 18 days from 14 to 15 August, which is accompanied by the persistent wave trains and the heatwave anticyclone. Additionally, the abnormal northward movement of the WPSH and its combination with the high latitude wave train lead to the occurrence of extreme hot weather in north-eastern China occurring during the summer of 2018. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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23 pages, 1998 KiB

Open AccessArticle

Changes in the Atmospheric Circulation Conditions and Regional Climatic Characteristics in Two Remote Regions Since the Mid-20th Century

by Maria G. Lebedeva, Anthony R. Lupo, Yury G. Chendev, Olga V. Krymskaya and Aleksandr B. Solovyev

Atmosphere 2019, 10(1), 11; https://doi.org/10.3390/atmos10010011 - 3 Jan 2019

Cited by 15 | Viewed by 3581

Abstract

A meridional Northern Hemisphere (NH) circulation epoch, which began in 1957, is marked by changes in the temperature and precipitation regimes over southwest Russia and central USA depending on the occurrence of NH atmospheric circulation regimes. A classification scheme proposed in 1968, and [...] Read more.

A meridional Northern Hemisphere (NH) circulation epoch, which began in 1957, is marked by changes in the temperature and precipitation regimes over southwest Russia and central USA depending on the occurrence of NH atmospheric circulation regimes. A classification scheme proposed in 1968, and studied later put forth 13 NH circulation types, fitting more broadly into four groups, two of which are more zonal type flows and two of which are more meridional flows. Using the results of a previous study that showed four distinct sub-periods during the 1957–2017 epoch, the temperature and precipitation regimes of both regions were studied across all seasons in order to characterize modern day climate variability and their suitability for vegetation growth. Then the Hydrologic Coefficient, which combined the temperature and precipitation variables, was briefly studied. The most optimal conditions for vegetation growth, positive temperature and precipitation anomalies, were noted during the period 1970–1980 for southwest Russia, which was dominated by an increasingly more zonal flow regime in the Belgorod region and NH in general. For the central USA, the HTC showed more ideal conditions for agriculture in recent years due to favorable precipitation occurrence. In southwest Russia, variable precipitation regimes were noted during the meridional flow periods, and with the increase in temperature (since 1998), these can adversely affect the hydrothermal characteristics of the growing season. Finally, a comparison of the 13 NH circulation types with several teleconnection indexes demonstrated the robustness of the NH flow regime classification scheme used here. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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26 pages, 13479 KiB

Open AccessEditor’s ChoiceArticle

Variability and Mechanisms of Megadroughts over Eastern China during the Last Millennium: A Model Study

by Liang Ning, Jian Liu, Bin Wang, Kefan Chen, Mi Yan, Chunhan Jin and Qianru Wang

Atmosphere 2019, 10(1), 7; https://doi.org/10.3390/atmos10010007 - 28 Dec 2018

Cited by 24 | Viewed by 4439

Abstract

The variability and mechanisms of multi-decadal megadroughts over eastern China during the last millennium were investigated using a control, full-forcing, and four sensitivity experiments from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive. The model simulated megadroughts have comparable magnitudes [...] Read more.

The variability and mechanisms of multi-decadal megadroughts over eastern China during the last millennium were investigated using a control, full-forcing, and four sensitivity experiments from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive. The model simulated megadroughts have comparable magnitudes and durations with those derived from reconstructed proxy data, although the megadroughts are not temporally synchronous. In all experiments, the megadroughts exhibit similar spatial structures, corresponding to a weakening of the East Asia summer monsoon (EASM) and a strengthening of the East Asia winter monsoon (EAWM). The results show that internal climate variability within the coupled climate system plays an essential role in triggering megadroughts, while different external forcings may contribute to persistence and modify the anomaly patterns of megadroughts. A pattern of meridional tripolar (warm-cold-warm) sea surface temperature (SST) anomalies in the western Pacific stretching from the equator to high latitude is responsible for the EASM weakening and EAWM strengthening. The weakening of the EASM and strengthening of the EAWM are essentially caused by negative SST anomalies over the northwestern Pacific and positive SST anomalies over the equatorial western Pacific, which are associated with a La Niña-like SST gradient across the tropical Pacific. The external forcings prolong the megadroughts through maintenance of the meridional tripolar SST anomalies and enlarge the megadrought spatial extent by magnifying the meridional tripolar SST anomalies. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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15 pages, 4879 KiB

Open AccessEditor’s ChoiceArticle

Contrasting Impacts of ENSO on the Interannual Variations of Summer Runoff between the Upper and Mid-Lower Reaches of the Yangtze River

by Xiaochen Ye and Zhiwei Wu

Atmosphere 2018, 9(12), 478; https://doi.org/10.3390/atmos9120478 - 5 Dec 2018

Cited by 16 | Viewed by 4579

Abstract

The Yangtze River Basin is an El Niño–Southern Oscillation (ENSO)-sensitive region, prone to floods and droughts. Hydrological records were collected to examine the temporal and spatial distribution of runoff in this drainage basin. An apparent difference in runoff variations between the upper and [...] Read more.

The Yangtze River Basin is an El Niño–Southern Oscillation (ENSO)-sensitive region, prone to floods and droughts. Hydrological records were collected to examine the temporal and spatial distribution of runoff in this drainage basin. An apparent difference in runoff variations between the upper and mid-lower Yangtze reaches was detected in response to ENSO. The upper basin usually experiences floods or droughts during the summer of ENSO developing years, while the mid-lower runoff variations tend to coincide with ENSO decaying phases. Composite analysis is employed to investigate the underlying mechanism for the teleconnection between the specific phases of the ENSO cycle and Yangtze runoff variation. Results show that the Western Pacific Subtropical High (WPSH) exhibits large variability on its western side in summer with different ENSO phases, thus resulting in a contrasting influence between the upper and mid-lower Yangtze floods and droughts. During the central Pacific-La Niña developing summers, the WPSH is significantly enhanced with its westward extension over the Yangtze upper basin. Anomalous water vapor converges in its northwest edge thus favoring upper-basin flooding. Meanwhile, the mid-lower reaches are controlled by the WPSH, and the local rainfall is not obvious. In addition, when the El Niño decaying phases occur, the WPSH denotes a westward extending trend and the position of its ridge line shifts to the mid-lower Yangtze reaches. The southwest moisture cannot extend to the upper basin but converges in the mid-lower basin. Accompanied by the anomalous 100 hPa South Asia High and lower-tropospheric Philippines anticyclone movements, this upper–middle–lower configuration acts as a key bridge linking ENSO and Yangtze floods and droughts. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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17 pages, 11295 KiB

Open AccessArticle

Interdecadal Variations in the Walker Circulation and Its Connection to Inhomogeneous Air Temperature Changes from 1961–2012

by Xiaoya Hou, Jianbo Cheng, Shujuan Hu and Guolin Feng

Atmosphere 2018, 9(12), 469; https://doi.org/10.3390/atmos9120469 - 29 Nov 2018

Cited by 7 | Viewed by 4765

Abstract

The tropical Pacific Walker circulation (PWC) is fundamentally important to global atmospheric circulation, and changes in it have a vital influence on the weather and climate systems. A novel three-pattern decomposition of a global atmospheric circulation (3P-DGAC) method, which can be used to [...] Read more.

The tropical Pacific Walker circulation (PWC) is fundamentally important to global atmospheric circulation, and changes in it have a vital influence on the weather and climate systems. A novel three-pattern decomposition of a global atmospheric circulation (3P-DGAC) method, which can be used to investigate atmospheric circulations including the PWC, was proposed in our previous study. Therefore, the present study aims to examine the capability of this 3P-DGAC method to acquire interdecadal variations in the PWC and its connection to inhomogeneous air temperature changes in the period from 1961–2012. Our findings reveal that interdecadal variations in the PWC, i.e., weakening (strengthening) between the periods 1961–1974 and 1979–1997 (1979–1997 and 1999–2012), can be observed using the zonal stream function (ZSF) derived from the 3P-DGAC method. Enhancement of the PWC is also associated with the strengthening and weakening of zonal circulations in the tropical Indian Ocean (IOC) and Atlantic (AOC), respectively, and vice versa, implying a connection between these zonal overturning circulations in the tropics. The interdecadal variations in the zonal circulations correspond well to inhomogeneous air temperature changes, i.e., an enhancement of the PWC is associated with a warming (cooling) of the air temperature from 1000 to 300 hPa in the western (mid–eastern) Pacific Ocean and a cooling (warming) of the air temperature in the tropopause in the western (mid–eastern) Pacific Ocean. Furthermore, a novel index for the PWC intensity based on air temperature is defined, and the capability of the novel index in representing the PWC intensity is evaluated. This novel index is potentially important for the prediction of the PWC by using dynamic equations derived from the 3P-DGAC method. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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16 pages, 7193 KiB

Open AccessArticle

Impacts of Pacific SSTs on Atmospheric Circulations Leading to California Winter Precipitation Variability: A Diagnostic Modeling

by Boksoon Myoung, Sang-Wook Yeh, Jinwon Kim and Menas C. Kafatos

Atmosphere 2018, 9(11), 455; https://doi.org/10.3390/atmos9110455 - 19 Nov 2018

Cited by 5 | Viewed by 3651

Abstract

One of the primary meteorological causes of the winter precipitation deficits and droughts in California (CA) is anomalous developments and maintenance of upper-tropospheric ridges over the northeastern Pacific. In order to understand and find the key factors controlling the winter precipitation variability in [...] Read more.

One of the primary meteorological causes of the winter precipitation deficits and droughts in California (CA) is anomalous developments and maintenance of upper-tropospheric ridges over the northeastern Pacific. In order to understand and find the key factors controlling the winter precipitation variability in CA, the present study examines two dominant atmospheric modes of the 500 hPa geopotential height in the Northern Hemisphere using an Empirical Orthogonal Function (EOF) and their associated large-scale circulation patterns for the last 41 winters (1974/75–2014/15). Explaining 17.5% of variability, the second mode (EOF2) shows strong anti-cyclonic circulations in the North Pacific and cyclonic circulations in the eastern USA and mid-latitude North Atlantic, similar to the atmospheric circulation observed in the 2013/14 drought of CA. EOF2 is tightly and significantly correlated with CA winter precipitation. EOF2 is associated with warm western‒cool eastern tropical Pacific, resembling a mirror image of canonical El Niño events. In particular, it is found that, since the mid-1990s, sea surface temperatures (SSTs) in the western tropical Pacific have been more tightly correlated with EOF2 and with the variability of CA precipitation. A diagnostic regression model based on the west‒east SST difference in the tropical Pacific developed for two recent decades (1994/95–2014/15) has been found to capture the slow-moving interannual variability of the CA winter precipitation (about 50%). The regression model performs well, especially for the central and northern CA precipitation, where the impacts of El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on precipitation are indecisive. Our results emphasize the significant role of the western tropical Pacific SST forcing in the recent past, and in turn on CA droughts and potentially other precipitation extremes. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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Review

Jump to: Editorial, Research

15 pages, 901 KiB

Open AccessReview

A Review on the Methods for Observing the Substance and Energy Exchange between Atmosphere Boundary Layer and Free Troposphere

by Haozhe Zhang, Xuehua Zhou, Jun Zou, Wuke Wang, Likun Xue, Qiuji Ding, Xinfeng Wang, Ning Zhang, Aijun Ding, Jianning Sun and Wenxing Wang

Atmosphere 2018, 9(12), 460; https://doi.org/10.3390/atmos9120460 - 22 Nov 2018

Cited by 4 | Viewed by 4359

Abstract

Atmosphere boundary layer (ABL or BL) acts as a pivotal part in the climate by regulating the vertical exchange of moisture, aerosol, trace gases and energy between the earth surface and free troposphere (FT). However, compared with research on the exchange between earth [...] Read more.

Atmosphere boundary layer (ABL or BL) acts as a pivotal part in the climate by regulating the vertical exchange of moisture, aerosol, trace gases and energy between the earth surface and free troposphere (FT). However, compared with research on the exchange between earth surface and ABL, there are fewer researches on the exchange between ABL and FT, especially when it comes to the quantitative measurement of vertical exchange flux between them. In this paper, a number of various methodologies for investigating the exchange of the substance and energy between ABL and FT are reviewed as follows: (1) methods to obtain entrainment rate, which include method by investigating the height of inversion layer, method of flux-jump, estimating with dataset from the ASTEX Lagrangian Experiments and method of using satellite observations and Microwave Imager; (2) mass budget method, which can yield quantitative measurements of exchange flux between ABL and FT; (3) qualitative measurements: method based on Rayleigh distillation and mixing processes, methods of ground-based remote sensing and airborne tracer-tracer relationship/ratio method. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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24 pages, 9498 KiB

Open AccessEditor’s ChoiceReview

A Review of Atmosphere–Ocean Forcings Outside the Tropical Pacific on the El Niño–Southern Oscillation Occurrence

by Shangfeng Chen, Bin Yu, Wen Chen and Renguang Wu

Atmosphere 2018, 9(11), 439; https://doi.org/10.3390/atmos9110439 - 12 Nov 2018

Cited by 21 | Viewed by 6900

Abstract

The El Niño–Southern Oscillation (ENSO) is the strongest interannual air–sea coupled variability mode in the tropics, and substantially impacts the global weather and climate. Hence, it is important to improve our understanding of the ENSO variability. Besides the well-known air–sea interaction process over [...] Read more.

The El Niño–Southern Oscillation (ENSO) is the strongest interannual air–sea coupled variability mode in the tropics, and substantially impacts the global weather and climate. Hence, it is important to improve our understanding of the ENSO variability. Besides the well-known air–sea interaction process over the tropical Pacific, recent studies indicated that atmospheric and oceanic forcings outside the tropical Pacific also play important roles in impacting and modulating the ENSO occurrence. This paper reviews the impacts of the atmosphere–ocean variability outside the tropical Pacific on the ENSO variability, as well as their associated physical processes. The review begins with the contribution of the atmosphere–ocean forcings over the extratropical North Pacific, Atlantic, and Indian Ocean on the ENSO occurrence. Then, an overview of the extratropical atmospheric forcings over the Northern Hemisphere (including the Arctic Oscillation and the Asian monsoon systems) and the Southern Hemisphere (including the Antarctic Oscillation and the Pacific–South American teleconnection), on the ENSO occurrence, is presented. It is shown that the westerly (easterly) wind anomaly over the tropical western Pacific is essential for the occurrence of an El Niño (a La Niña) event. The wind anomalies over the tropical western Pacific also play a key role in relaying the impacts of the atmosphere–ocean forcings outside the tropical Pacific on the ENSO variability. Finally, some relevant questions, that remain to be explored, are discussed. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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