A potential vorticity‐based index for the East Asian winter monsoon

Huang, Wenyu; Wang, Bin; Wright, Jonathon S.

doi:10.1002/2016jd025053

Cited by 22 publications

(44 citation statements)

References 39 publications

(50 reference statements)

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“…While isentropic surfaces below 300 K (i.e., 280 K and 290 K) may have even tighter coupling to the surface temperature over East Asia, these lower isentropic surfaces intersect the geoid within the East Asian region. Additionally, our use of 300 K isentropic surface allows us to refer directly to the PV‐based EAWMI [ Huang et al , ].…”

Section: Methodsmentioning

confidence: 99%

“…Isentropic PV can be calculated as

PV = - g (ζ_{θ} + f) \frac{∂θ}{∂p},

where g is the gravitational acceleration, ζ θ is the relative vorticity on the isentropic surface, f is the planetary vorticity (Coriolis parameter), and

\frac{∂θ}{∂p}

is the quasi‐vertical gradient of potential temperature θ with respect to pressure p . Noting that cold surges over East Asia are reflected in the intensity of the area‐averaged PV over East Asia with respect to the zonal mean, Huang et al [] defined a PV‐based East Asian winter monsoon index (EAWMI) by

EAWMI = \overset{{PV}_{normal300K (90 - 150 ° normalE, 20 - 50 ° normalN)}}{false} - \overset{{PV}_{normal300K (0 - 360 ° normalE, 20 - 50 ° normalN)}}{false} .

The first term on the right‐hand side of equation is the area‐averaged PV over East Asia (90–150°E, 20–50°N) on the 300 K isentropic surface, while the second term is the area‐averaged PV over the entire 20–50°N latitudinal band on the 300 K isentropic surface. Basing this definition on the isentropic PV permits the application of the invertibility principle of isentropic PV [ Hoskins et al , ].…”

Section: Introductionmentioning

confidence: 99%

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Potential vorticity regimes over East Asia during winter

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Nine potential vorticity (PV) regimes over East Asia are identified by applying a Self‐Organizing Map and Hierarchical Ascendant Classification regime analysis to the daily PV reanalysis fields on the 300 K isentropic surface for December–March 1948–2014. According to the surface temperature anomalies over East Asia, these nine regimes are further classified into three classes, i.e., cold class (three regimes), warm class (four regimes), and neutral class (two regimes). The PV‐based East Asian winter monsoon index (EAWMI) is used to study the relationship between PV distributions and the temperature anomalies. The magnitude of cold (warm) anomalies over the land areas of East Asia increases (decreases) quasi‐linearly with the EAWMI. Regression analysis reveals that cold temperature anomalies preferentially occur when the EAWMI exceeds a threshold at ∼0.2 PVU (where 1 PVU ≡ 10−6 m2 K kg−1 s−1). PV inversion uncovers the mechanisms behind the relationships between the PV regimes and surface temperature anomalies and reveals that cold (warm) PV regimes are associated with significant warming (cooling) in the upper troposphere and lower stratosphere. On average, cold regimes have longer durations than warm regimes. Interclass transition probabilities are much higher for paths from warm/neutral regimes to cold regimes than for paths from cold regimes to warm/neutral regimes. Besides, intraclass transitions are rare within the warm or neutral regimes. The PV regime analysis provides insight into the causes of severe cold spells over East Asia, with blocking circulation patterns identified as the primary factor in initiating and maintaining these cold spells.

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Section: Methodsmentioning

confidence: 99%

“…Isentropic PV can be calculated as

PV = - g (ζ_{θ} + f) \frac{∂θ}{∂p},

where g is the gravitational acceleration, ζ θ is the relative vorticity on the isentropic surface, f is the planetary vorticity (Coriolis parameter), and

\frac{∂θ}{∂p}

EAWMI = \overset{{PV}_{normal300K (90 - 150 ° normalE, 20 - 50 ° normalN)}}{false} - \overset{{PV}_{normal300K (0 - 360 ° normalE, 20 - 50 ° normalN)}}{false} .

Section: Introductionmentioning

confidence: 99%

Potential vorticity regimes over East Asia during winter

et al. 2017

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“…By contrast, although the AO index did show an increasing trend during 1950–2000 [ Gong and Drange , ], it experienced a decreasing trend after the mid‐1990s [ Overland and Wang , ; Cohen and Barlow , ; Cohen et al , ]. Moreover, while the EAWM experienced continuous weakening around 1988 [ Watanabe and Nitta , ; Jhun and Lee , ; Wang et al , ; Huang et al , ], there was a recent recovery that began around 2009 [ Wang and Chen , ; Ding et al , ; Huang et al , ]. Therefore, the long‐term trends in the SLP anomalies and surface temperature anomalies are not removed.…”

Section: Methodsmentioning

confidence: 99%

Exploring the combined effects of the Arctic Oscillation and ENSO on the wintertime climate over East Asia using self‐organizing maps

et al. 2017

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To examine the combined effects of the different spatial patterns of the Arctic Oscillation (AO)‐related sea level pressure (SLP) anomalies and the El Niño–Southern Oscillation (ENSO)‐related sea surface temperature (SST) anomalies on the wintertime surface temperature anomalies over East Asia, a nonlinear method based on self‐organizing maps is employed. Investigation of identified regimes reveals that the AO can affect East Asian temperature anomalies when there are significant SLP anomalies over the Arctic Ocean and northern parts of Eurasian continent. Analogously, ENSO is found to affect East Asian temperature anomalies when significant SST anomalies are present over the tropical central Pacific. The regimes with the warmest and coldest temperature anomalies over East Asia are both associated with the negative phase of the AO. The ENSO‐activated, Pacific‐East Asian teleconnection pattern could affect the higher latitude continental regions when the impact of the AO is switched off. When the spatial patterns of the AO and ENSO have significant, but opposite, impacts on the coastal winds, no obvious temperature anomalies can be observed over south China. Further, the circulation state with nearly the same AO and Niño3 indices may drive rather different responses in surface temperature over East Asia. The well‐known continuous weakening (recovery) of the East Asian winter monsoon that occurred around 1988 (2009) can be attributed to the transitions of the spatial patterns of the SLP anomalies over the Arctic Ocean and Eurasian continent, through their modulation on the occurrences of the Ural and central Siberian blocking events.

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“…First, many previous studies have suggested that March is as important as the time period from December to February when examining the wintertime temperature anomalies over eastern North America [ Wang and Fu , ; Alexander et al , ; Mo and Schemm , ; Notaro et al , ]. Second, Huang et al [], studying the wintertime climate of eastern Asia, considered the intensity of potential vorticity (PV) intrusion from high latitudes into eastern Asia as a means for determining which months should be regarded as climatological winter. They found that the intensity of PV intrusion into eastern Asia in March is comparable in magnitude to that in December and far exceeds the levels seen in November.…”

Section: Methodsmentioning

confidence: 99%

On the cooccurrence of wintertime temperature anomalies over eastern Asia and eastern North America

et al. 2017

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The cooccurrence of wintertime temperature anomalies over eastern Asia and eastern North America is examined. The winter days during 1948–2014 are assigned to nine regimes by applying the self‐organizing map clustering method to the area‐averaged land surface temperature anomalies over these two regions. About half of the winter days are associated with concurrent temperature anomalies. The occurrence of the concurrent/nonconcurrent regimes is closely related to the large‐scale circulation conditions. The Eurasian teleconnection pattern and the Pacific‐North American teleconnection pattern are two dominant large‐scale circulation modes associated with the cooccurrence of the temperature anomalies, through their impacts on the intensities of the corresponding troughs. The precursor analysis reveals that the lead time of the early signals for the concurrent cold anomalies is about 4 days longer than that for the concurrent warm anomalies. In addition, the average lead time of the precursor signals for the wintertime temperature anomalies over eastern Asia is longer than that over eastern North America.

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A potential vorticity‐based index for the East Asian winter monsoon

Cited by 22 publications

References 39 publications

Potential vorticity regimes over East Asia during winter

Potential vorticity regimes over East Asia during winter

Exploring the combined effects of the Arctic Oscillation and ENSO on the wintertime climate over East Asia using self‐organizing maps

On the cooccurrence of wintertime temperature anomalies over eastern Asia and eastern North America

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