scholarly journals Interdecadal Variations in Extreme High–Temperature Events over Southern China in the Early 2000s and the Influence of the Pacific Decadal Oscillation

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 829
Author(s):  
Baoyan Zhu ◽  
Bo Sun ◽  
Hua Li ◽  
Huijun Wang
Keyword(s):  
Water Vapor ◽  
High Temperature ◽  
Pacific Decadal Oscillation ◽  
Southern China ◽  
Walker Circulation ◽  
Interdecadal Variation ◽  
Water Vapor Content ◽  
Negative Phase ◽  
The Pacific ◽  
Extreme High Temperature

This study documents a sudden interdecadal variation in the frequency of extreme high–temperature events (FEHE) over southern China during summer in the early 2000s, which is characterized by a relatively small (large) FEHE during 1991–2000 (2003–2018). The composite analysis on the extreme high–temperature events (EHEs) over southern China indicates that the occurrence of EHEs is mainly influenced by increased downward surface net shortwave radiation, which is induced by the cloud–forced radiation anomalies associated with reduced cloud; the reduced cloud is attributed to anomalous descent motion and decreased water vapor content in the troposphere. Compared to the situation during 1991–2000, anomalous descent motion and decreased atmospheric water vapor content occurred over southern China in summer during 2003–2018, providing a more favorable climatic condition for EHEs. This interdecadal variation is associated with the strengthened Pacific Walker circulation after 2003. The Pacific decadal oscillation (PDO) is suggested to be an important driver for the above interdecadal variation, which shifted from a positive phase towards a negative phase after 2003. Numerical experiments demonstrate that a negative phase of PDO may induce a strengthened Walker circulation and anomalous atmospheric descent motion as well as water vapor divergence over Southern China.

Manifestation of the Pacific Decadal Oscillation in the stationary planetary waves activity

2021 ◽  
Author(s):  
Daria Sobaeva ◽  
Yulia Zyulyaeva ◽  
Sergey Gulev
Keyword(s):  
Pacific Decadal Oscillation ◽  
North American ◽  
Lower Stratosphere ◽  
El Nino ◽  
Planetary Waves ◽  
Positive Phase ◽  
Negative Phase ◽  
Middle Troposphere ◽  
The Pacific ◽  
The Tropics

<p>Strong quasi-decadal oscillations of the stratospheric polar vortex (SPV) intensity are in phase with the Pacific decadal oscillation (PDO). A stronger SPV is observed during the positive phase of the PDO, and during the negative phase, the intensity of the SPV is below the mean climate values. The SPV intensity anomalies, formed by the planetary waves and zonal mean flow interaction, lead to the weakening/intensification of the vortex.</p><p>This research aimed to obtain the differences in the characteristics and the spatial propagation pattern of the planetary waves in the middle troposphere and lower stratosphere during different PDO phases. We analyzed composite periods of years when the PDO index has extremely high and low values. Two periods were constructed for both positive and negative phases, the first consisting of years with El-Nino/La-Nina events and the second without prominent sea surface temperature anomalies in the tropics. </p><p>During the wintertime in the Northern Hemisphere (December-February), wave 2 with two ridges (Siberian and North American Highs) and two troughs (Icelandic and Aleutian Lows) dominates in the middle troposphere, along with wave 1 dominating in the lower stratosphere. In the middle troposphere, at the positive phase ​​of the PDO, the amplitude of wave 2 is higher than in years with negative values of the PDO index. The differences in the Aleutian Low and the North American High intensity between the two phases are significant at the 97.5% level. In the lower stratosphere, the wave amplitude is lower at the negative phase ​​of the PDO, but we can also talk about a slight shift of the wave phase to the east. The regions of the heavy rains in the tropics during El-Nino events are the planetary waves source. They propagate from low to high latitudes, which results in modifying the characteristics and locations of the intensification of the stationary planetary waves in mid-latitudes.</p>

Increasing Influence of Central Pacific El Niño on the Interdecadal Variation of Spring Rainfall in Northern Taiwan and Southern China Since 1980

2020 ◽  
Author(s):  
Pei-ken Kao ◽  
Chi-Cherng Hong ◽  
Chih-wen Hung
Keyword(s):  
North Pacific ◽  
Transition Period ◽  
Southern China ◽  
Interdecadal Variation ◽  
Decadal Variation ◽  
Central Pacific ◽  
Circulation Anomaly ◽  
The Pacific ◽  
Sst Anomaly ◽  
Northern Taiwan

<p>Decadal variation of spring (February–April) rainfall in Northern Taiwan and Southern China was significantly related to the Pacific Decadal Oscillation (PDO) during the twentieth century. However, this interdecadal relationship subsequently weakened, and the sea surface temperature (SST) associated with the central Pacific El Niño (CPEN) has determined the interdecadal variation of spring rainfall in Northern Taiwan and Southern China since the 1980s. In this study, the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China was investigated. We found that a CPEN-associated positive SST anomaly in the eastern North Pacific forced an east–west overturning circulation anomaly in the subtropical North Pacific, the descending motion of which may have generated an anticyclonic circulation anomaly in the Philippine Sea. Simultaneously, the anticyclone associated southerly winds anomaly may enhance the southwesterly in northwest of the anticyclone, which in term enhance the trough extending from Japan to Northern Taiwan. The anticyclone and trough associated with the respective southwesterly and northeasterly anomalies created a convergence environment in Northern Taiwan. In turn, this convergence environment contributed substantially to an interdecadal rainfall enhancement in Northern Taiwan and Southern China. Our results suggest that the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China has increased since 1980, especially during the transition period from the termination of a warm PDO phase to a cold phase in the late 1990s</p>

scholarly journals Summer High Temperature Extremes over China Linked to the Pacific Meridional Mode

2020 ◽  
Vol 33 (14) ◽  
pp. 5905-5917
Author(s):  
Ming Luo ◽  
Ngar-Cheung Lau ◽  
Wei Zhang ◽  
Qiang Zhang ◽  
Zhen Liu
Keyword(s):  
High Temperature ◽  
Land Surface ◽  
Southern China ◽  
Eastern China ◽  
Northern China ◽  
Temperature Extremes ◽  
The Pacific ◽  
Meridional Mode ◽  
High Temperature Extremes ◽  
Pacific Meridional Mode

AbstractThis study investigates the association between summer high temperature extremes (HTEs) over China and the Pacific meridional mode (PMM) that is characterized by an anomalous north–south sea surface temperature gradient and an anomalous surface circulation over the northeastern subtropical Pacific. It is found that the HTE activities over most parts of southern China (particularly eastern China) are prominently intensified during the positive PMM phase and weakened during the negative phase. Further examinations suggest that the PMM is linked with HTEs in China through processes that entail both eastward and westward development of signals emanating from the PMM site. The westward development is associated with the formation of an anomalous low-level cyclone over the western North Pacific (WNP), which may be viewed as a Matsuno–Gill-type response to the off-equatorial heating in the eastern Pacific. This circulation change is accompanied by anomalous ascent over WNP and northern China, and subsidence over eastern China. On the other hand, the eastward development process is linked to the PMM-induced displacement of the East Asian jet stream and the generation of a midlatitude Rossby wave train. In the positive PMM phase, the above circulation changes are accompanied by anomalous air subsidence and enhanced adiabatic heating, reduced precipitation, anomalous lower-level anticyclone, and rising surface pressure over the eastern part of China. Moreover, the land surface of that region receives more solar radiation. Opposite changes are discernible over northern China. These changes are favorable for the occurrence and persistence of HTEs over eastern China and tend to suppress HTEs over northern China.

scholarly journals Interdecadal Variation in the Synoptic Features of Mei-Yu in the Yangtze River Valley Region and Relationship with the Pacific Decadal Oscillation

2019 ◽  
Vol 32 (19) ◽  
pp. 6251-6270 ◽  
Author(s):  
Bo Sun ◽  
Huijun Wang ◽  
Botao Zhou ◽  
Hua Li
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Yangtze River ◽  
Vertical Motion ◽  
Yangtze River Valley ◽  
Interdecadal Variation ◽  
Boreal Summer ◽  
The Yangtze River ◽  
The Pacific ◽  
Synoptic Features

Abstract This study introduces a multivariable covariance index (MVCI) to illustrate the synoptic features of mei-yu in the Yangtze River valley (YRV) region, which contains information of three indicators of mei-yu including precipitation, surface relative humidity, and tropospheric vertical motion. The interdecadal variation in the synoptic features of mei-yu during 1961–2016 is investigated using the MVCI. The date of mei-yu peak and the intensity of mei-yu underwent noticeable interdecadal variations over past decades, which are characterized by a delayed (relatively early) mei-yu peak and a relatively large (small) mei-yu intensity during 1985–97 (1961–80 and 2006–16). The mechanisms of these interdecadal variations are further discussed. The interdecadal variation in the date of mei-yu peak is mainly modulated by the meridional water vapor transport over eastern China during June, which may be partially attributed to an influence of the Pacific decadal oscillation (PDO) on the clockwise gyre over the North Pacific during boreal summer. The interdecadal variation in mei-yu intensity is associated with the interdecadal variation of tropospheric vertical motion over the YRV region during boreal summer, which may be partially attributed to an interaction between the PDO and the large-scale tropical east–west circulation during boreal summer. In addition, the interdecadal variation in the water vapor flux budget and relative humidity over the YRV region also exerted an impact on the interdecadal variation of mei-yu intensity in the YRV region.

Inter-basin interactions between the Pacific and Atlantic Oceans depending on the phase of Pacific decadal Oscillation and Atlantic multi-decadal oscillation

2021 ◽  
pp. 1-38
Keyword(s):  
Pacific Ocean ◽  
Atlantic Ocean ◽  
Pacific Decadal Oscillation ◽  
Walker Circulation ◽  
Equatorial Pacific ◽  
Equatorial Pacific Ocean ◽  
Equatorial Atlantic ◽  
The Pacific ◽  
Equatorial Atlantic Ocean ◽  
Relationship Of

Abstract The authors investigated the inter-basin interactions between the Pacific and Atlantic Oceans depending on the phase relationship of Pacific decadal oscillation (PDO)/Atlantic multi-decadal oscillation (AMO) based on observations and idealized model experiments. When the AMO and the PDO are in-phase (i.e., +PDO/+AMO or −PDO/-AMO), the Pacific Ocean regulates the SST anomalies in the equatorial Atlantic Ocean with altering a Walker circulation. During this period, there is a negative SST-precipitation relationship in the equatorial Atlantic Ocean where the atmosphere forces the ocean. In contrast, when they are out-of-phase (i.e., either +PDO/-AMO or −PDO/+AMO), the Atlantic Ocean influences the equatorial Pacific Ocean by modifying Walker circulation, resulting in a westward shift of a center of convective forcing in the equatorial Pacific Ocean compared to that during an inphase relationship of PDO/AMO. During this period, a positive SST-precipitation relationship is dominant in the equatorial Atlantic Ocean where the ocean forces the atmosphere. To verify this result, we conducted pacemaker experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM3). Model results supported our findings obtained from the observations. We infer that the characteristics of the Pacific-Atlantic inter-basin interactions depend on whether the PDO and AMO phases are either in-phase or out of phase.

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