scholarly journals Interdecadal Variability of Summer Rainfall in Taiwan Associated with Tropical Cyclones and Monsoon

2011 ◽  
Vol 24 (22) ◽  
pp. 5786-5798 ◽  
Author(s):  
Jau-Ming Chen ◽  
Hui-Shan Chen
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
Summer Rainfall ◽  
Cyclonic Circulation ◽  
Interdecadal Variability ◽  
Philippine Sea ◽  
Increasing Trend ◽  
Anomalous Cyclonic Circulation ◽  
Sst Anomalies

Abstract This study investigates interdecadal variability of summer (June–August) rainfall in Taiwan for the 1950–2008 period. Summer rainfall in Taiwan is partitioned into two components: tropical cyclone (TC) rainfall caused by TC passage and seasonal monsoon rainfall associated with monsoon southwesterly flows. The joint interdecadal mode of TC rainfall and seasonal monsoon rainfall is extracted by empirical orthogonal function (EOF) analysis. The first interdecadal mode features an increasing trend plus a near-20-yr oscillation. The spatial patterns of this mode are uniform in sign over the entirety of Taiwan with positive anomalies for TC rainfall and negative anomalies for seasonal monsoon rainfall. These results reveal that TC rainfall and seasonal monsoon rainfall tend to vary inversely in interdecadal variability, with a positive trend in TC rainfall and a negative trend in seasonal monsoon rainfall. Large-scale regulating processes associated with this interdecadal rainfall mode are interpreted from the correlation patterns. Significant warm sea surface temperature (SST) anomalies exist in the tropical central and eastern Pacific and the Indian Ocean. At the low levels, an anomalous large-scale divergent center occurs in the Australian regions, which in turn evokes an anomalous cyclonic circulation in the subtropical North Pacific. Taiwan is on its western edge and affected by anomalous northeasterly flows, in company with weakening in the prevailing southwesterly flows and moisture transport from the South China Sea into Taiwan. As such, negative seasonal monsoon rainfall anomalies occur in Taiwan with a decreasing trend. The subtropical anomalous cyclonic circulation also weakens vertical wind shear over the major TC genesis region, that is, the Philippine Sea. Warm SST anomalies in this region and accompanying anomalous ascending motion provide additional favorable conditions for TC genesis. More TCs are thus formed in the Philippine Sea. The appearance of an anomalous cyclonic circulation in the subtropical North Pacific reflects a weakening of the Pacific subtopical high, which tends to retreat eastward and provides southeasterly or southerly flows on its western boundary to guide TCs formed in the Philippine Sea northwestward toward Taiwan. TC frequency and TC rainfall thus increase in Taiwan with an increasing trend.

scholarly journals PDO-Related Wintertime Atmospheric Anomalies over the Midlatitude North Pacific: Local versus Remote SST Forcing

2020 ◽  
Vol 33 (16) ◽  
pp. 6989-7010 ◽  
Author(s):  
Lingfeng Tao ◽  
Xiu-Qun Yang ◽  
Jiabei Fang ◽  
Xuguang Sun
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Transient Eddy ◽  
Atmospheric Variability ◽  
Ridge Structure ◽  
Sst Gradient ◽  
Meridional Sst Gradient ◽  
Sst Anomalies

AbstractObserved wintertime atmospheric anomalies over the central North Pacific associated with the Pacific decadal oscillation (PDO) are characterized by a cold/trough (warm/ridge) structure, that is, an anomalous equivalent barotropic low (high) over a negative (positive) sea surface temperature (SST) anomaly. While the midlatitude atmosphere has its own strong internal variabilities, to what degree local SST anomalies can affect the midlatitude atmospheric variability remains unclear. To identify such an impact, three atmospheric general circulation model experiments each having a 63-yr-long simulation are conducted. The control run forced by observed global SST reproduces well the observed PDO-related cold/trough (warm/ridge) structure. However, the removal of the midlatitude North Pacific SST variabilities in the first sensitivity run reduces the atmospheric response by roughly one-third. In the second sensitivity run in which large-scale North Pacific SST variabilities are mostly kept, but their frontal-scale meridional gradients are sharply smoothed, simulated PDO-related cold/trough (warm/ridge) anomalies are also reduced by nearly one-third. Dynamical diagnoses exhibit that such a reduction is primarily due to the weakened transient eddy activities that are induced by weakened meridional SST gradient anomalies, in which the transient eddy vorticity forcing plays a crucial role. Therefore, it is suggested that midlatitude North Pacific SST anomalies make a considerable (approximately one-third) contribution to the observed PDO-related cold/trough (warm/ridge) anomalies in which the frontal-scale meridional SST gradient (oceanic front) is a key player, although most of those atmospheric anomalies are determined by the SST variabilities outside of the midlatitude North Pacific.

scholarly journals Importance of Resolving Kuroshio Front and Eddy Influence in Simulating the North Pacific Storm Track

2017 ◽  
Vol 30 (5) ◽  
pp. 1861-1880 ◽  
Author(s):  
Xiaohui Ma ◽  
Ping Chang ◽  
R. Saravanan ◽  
Raffaele Montuoro ◽  
Hisashi Nakamura ◽  
...  
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Climate Model ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Small Scale ◽  
Low Resolution ◽  
The North ◽  
The North Pacific ◽  
Sst Anomalies

Abstract Local and remote atmospheric responses to mesoscale SST anomalies associated with the oceanic front and eddies in the Kuroshio Extension region (KER) are studied using high- (27 km) and low-resolution (162 km) regional climate model simulations in the North Pacific. In the high-resolution simulations, removal of mesoscale SST anomalies in the KER leads to not only a local reduction in cyclogenesis but also a remote large-scale equivalent barotropic response with a southward shift of the downstream storm track and jet stream in the eastern North Pacific. In the low-resolution simulations, no such significant remote response is found when mesoscale SST anomalies are removed. The difference between the high- and low-resolution model simulated atmospheric responses is attributed to the effect of mesoscale SST variability on cyclogenesis through moist baroclinic instability. It is only when the model has sufficient resolution to resolve small-scale diabatic heating that the full effect of mesoscale SST forcing on the storm track can be correctly simulated.

scholarly journals Influence of the Meridional Shifts of the Kuroshio and the Oyashio Extensions on the Atmospheric Circulation

2011 ◽  
Vol 24 (3) ◽  
pp. 762-777 ◽  
Author(s):  
Claude Frankignoul ◽  
Nathalie Sennéchael ◽  
Young-Oh Kwon ◽  
Michael A. Alexander
Keyword(s):  
Atmospheric Circulation ◽  
North Pacific ◽  
Large Scale ◽  
Kuroshio Extension ◽  
Statistical Significance ◽  
The North ◽  
Enso Teleconnections ◽  
Historical Temperature ◽  
The Kuroshio ◽  
Sst Anomalies

Abstract The meridional shifts of the Oyashio Extension (OE) and of the Kuroshio Extension (KE), as derived from high-resolution monthly sea surface temperature (SST) anomalies in 1982–2008 and historical temperature profiles in 1979–2007, respectively, are shown based on lagged regression analysis to significantly influence the large-scale atmospheric circulation. The signals are independent from the ENSO teleconnections, which were removed by seasonally varying, asymmetric regression onto the first three principal components of the tropical Pacific SST anomalies. The response to the meridional shifts of the OE front is equivalent barotropic and broadly resembles the North Pacific Oscillation/western Pacific pattern in a positive phase for a northward frontal displacement. The response may reach 35 m at 250 hPa for a typical OE shift, a strong sensitivity since the associated SST anomaly is 0.5 K. However, the amplitude, but not the pattern or statistical significance, strongly depends on the lag and an assumed 2-month atmospheric response time. The response is stronger during fall and winter and when the front is displaced southward. The response to the northward KE shifts primarily consists of a high centered in the northwestern North Pacific and hemispheric teleconnections. The response is also equivalent barotropic, except near Kamchatka, where it tilts slightly westward with height. The typical amplitude is half as large as that associated with OE shifts.

scholarly journals Assessing the Importance of Prominent Warm SST Anomalies over the Midlatitude North Pacific in Forcing Large-Scale Atmospheric Anomalies during 2011 Summer and Autumn

2014 ◽  
Vol 27 (11) ◽  
pp. 3889-3903 ◽  
Author(s):  
Satoru Okajima ◽  
Hisashi Nakamura ◽  
Kazuaki Nishii ◽  
Takafumi Miyasaka ◽  
Akira Kuwano-Yoshida
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Large Scale ◽  
Storm Track ◽  
Anticyclonic Anomaly ◽  
The North ◽  
Basin Scale ◽  
Sst Anomaly ◽  
The North Pacific ◽  
Sst Anomalies

Abstract Sets of atmospheric general circulation model (AGCM) experiments are conducted to assess the importance of prominent positive anomalies in sea surface temperature (SST) observed over the midlatitude North Pacific in forcing a persistent basin-scale anticyclonic circulation anomaly and its downstream influence in 2011 summer and autumn. The anticyclonic anomaly observed in October is well reproduced as a robust response of an AGCM forced only with the warm SST anomaly associated with the poleward-shifted oceanic frontal zone in the midlatitude Pacific. The equivalent barotropic anticyclonic anomaly over the North Pacific is maintained under strong transient eddy feedback forcing associated with the poleward-deflected storm track. As the downstream influence of the anomaly, abnormal warmth and dryness observed over the northern United States and southern Canada in October are also reproduced to some extent. The corresponding AGCM response over the North Pacific to the tropical SST anomalies is similar but substantially weaker and less robust, suggesting the primary importance of the prominent midlatitude SST anomaly in forcing the large-scale atmospheric anomalies observed in October 2011. In contrast, the model reproduction of the atmospheric anomalies observed in summer was unsuccessful. This appears to arise from the fact that, unlike in October, the midlatitude SST anomalies accompanied reduction of heat and moisture release from the ocean, indicative of the atmospheric thermodynamic forcing on the SST anomalies. Furthermore, the distinct seasonality in the AGCM responses to the warm SST anomalies may also be contributed to by the seasonality of background westerlies and storm track.

scholarly journals Cluster Analysis of Tropical Cyclone Tracks over the Western North Pacific Using a Self-Organizing Map

2016 ◽  
Vol 29 (10) ◽  
pp. 3731-3751 ◽  
Author(s):  
Han-Kyoung Kim ◽  
Kyong-Hwan Seo
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
The Philippines ◽  
Self Organizing Map ◽  
Central Pacific ◽  
Philippine Sea ◽  
Genesis Frequency ◽  
Sst Anomalies ◽  
Self Organizing

Abstract Tropical cyclone (TC) tracks over the western North Pacific (WNP) in 1979–2013 are classified by a self-organizing map technique. A false detection rate method identifies five optimal TC clusters. Physical mechanisms of the intraseasonal and interannual variations in the TC genesis frequency are investigated for each cluster. The five clusters are separated by genesis location, from the westernmost area (east of the Philippines, C1) to the easternmost (~150°E, C5) onset area over the WNP. The intraseasonal Madden–Julian oscillation (MJO) significantly affects the genesis frequency for all clusters except for C5. In particular, MJO phases 5 and 6 (1 and 2) provide significantly favorable (unfavorable) large-scale conditions for TC genesis. Two types of El Niño–Southern Oscillation influence the interannual variation of the genesis frequency for only C2 (generated over the western Philippine Sea and East China Sea) and C4 (formed near the eastern Philippine Sea). Enhanced eastern Pacific sea surface temperature (SST) anomalies lead to a ~40% decrease in the C2 TC frequency through a reversed Walker circulation with downward motion over the WNP. Conversely, increased central Pacific SST anomalies generate a cyclonic Rossby wave northwest of the forcing, inducing a significant increase (~50%) in the C4 TC frequency. The interannual variability for the C5 TCs is strongly controlled by the variation of the western Pacific subtropical high (WPSH). A positive WPSH variation reduces the C5 TC genesis frequency by 66%, while negative WPSH anomalies enhance the frequency by 50%. A prediction scheme using information from the first four 6-h TC locations demonstrates a skillful determination of TC clusters.

scholarly journals Interdecadal change in the genesis activity of the first tropical cyclone of each year over the western North Pacific

2021 ◽  
Author(s):  
Yumi Cha ◽  
JaeWon Choi ◽  
Joong-Bae Ahn
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Walker Circulation ◽  
The Philippines ◽  
Cyclonic Circulation ◽  
Equatorial Pacific ◽  
Trade Winds ◽  
Anticyclonic Circulation ◽  
Anomalous Cyclonic Circulation

Abstract This study analyzed time series of the genesis latitude, longitude, and date of the first tropical cyclone (TC) each year over the 38 years between 1979 and 2016. Statistical change-point analysis applied to these three variables showed that a shift in climate regime occurred around 1998. More specifically, recent TCs have shown a strong tendency to occur more northwest in the western North Pacific (WNP), and day of TC genesis tend to be delayed. Also, we compared differences between the periods 1998 to 2016 (post-1998) and 1979–1997 (pre-1998) in terms of outgoing longwave radiation (OLR), total cloud cover, precipitable water, precipitation, vertical wind shear, 850 hPa relative vorticity, and sea surface temperature (SST). Our results showed that a favorable environment for TC genesis was formed near the South China Sea (SCS) and the Philippines and an unfavorable environment for TC genesis was formed in the southeastern part of the WNP. Analysis of stream flow showed that an anomalous cyclonic circulation at 850 hPa was formed in the SCS and an anomalous large anticyclonic circulation was formed in the North Pacific. From these circulations, a ridge extended to the east sea of the Philippines, and consequently, anomalous trade winds were strengthened in the equatorial Pacific. Such anomalous atmospheric circulation seems to be associated with the cold Pacific Decadal Oscillation (PDO) phase. At 200 hPa, the anomalous anticyclonic circulation was strengthened in the SCS, and an anomalous cyclonic circulation formed in the east sea of the Philippines, which strengthened anomalous westerlies in the equatorial Pacific. Furthermore, this circulation pattern is found to be related with a strengthening of Walker circulation. Therefore, during the post-1998, when trade winds were strengthened by the development of Walker circulation, the cold PDO phase was strengthened, the location of TC genesis moved toward the northwestern WNP, and TC genesis day tended to be delayed.

scholarly journals Coherent Interdecadal Variability of Tropical Cyclone Rainfall and Seasonal Rainfall in Taiwan during October

2013 ◽  
Vol 26 (1) ◽  
pp. 308-321 ◽  
Author(s):  
Jau-Ming Chen ◽  
Hui-Shan Chen ◽  
Jin-Shuen Liu
Keyword(s):  
Tropical Cyclone ◽  
Moisture Transport ◽  
Large Scale ◽  
Western Pacific ◽  
Interdecadal Variability ◽  
Seasonal Rainfall ◽  
Windward Side ◽  
Western Boundary ◽  
Anomalous Anticyclone ◽  
Sst Anomalies

Abstract By separating total rainfall into tropical cyclone (TC) rainfall caused by TC passage and seasonal rainfall associated with moisture transport of prevailing seasonal flows, this study examines the interdecadal variability of these two rainfall components in Taiwan during fall. It is found that interdecadal variability of TC rainfall and seasonal rainfall tends to vary coherently in October. This coherent interdecadal rainfall mode features islandwide patterns in Taiwan and evident interdecadal oscillations. The associated large-scale regulating processes for the positive phase are characterized by warm sea surface temperature (SST) anomalies in the northern South China Sea and the western North Pacific, which in turn induce an anomalous anticyclonic circulation over the subtropical western Pacific to the east of Taiwan. On the western boundary of this anomalous anticyclone, anomalous southeasterly flows enhance mean moisture transport from the tropical western Pacific into Taiwan. Seasonal rainfall increases in Taiwan with stronger anomalies on the windward side over eastern Taiwan. Warm SST anomalies and accompanying large-scale convergence, ascendance, and positive relative vorticity anomalies provide favorable conditions for more TC formation in the Philippine Sea. More TCs tend to move along the western boundary of the anomalous anticyclone to cross the northern Philippines toward eastern Taiwan or toward the open oceans southwest of Taiwan. Taiwan is influenced by enhanced TC activity to have more TC rainfall with the largest anomalies being in the eastern parts.

scholarly journals Role of Stochastic Atmospheric Forcing from the South and North Pacific in Tropical Pacific Decadal Variability

2019 ◽  
Vol 32 (13) ◽  
pp. 4013-4038 ◽  
Author(s):  
Tianyi Sun ◽  
Yuko M. Okumura
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Decadal Variability ◽  
South Pacific ◽  
Tropical Pacific ◽  
Ocean Dynamics ◽  
The South ◽  
Pacific Decadal Variability ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract Stochastic variability of internal atmospheric modes, known as teleconnection patterns, drives large-scale patterns of low-frequency SST variability in the extratropics. To investigate how the decadal component of this stochastically driven variability in the South and North Pacific affects the tropical Pacific and contributes to the observed basinwide pattern of decadal variability, a suite of climate model experiments was conducted. In these experiments, the models are forced with constant surface heat flux anomalies associated with the decadal component of the dominant atmospheric modes, particularly the Pacific–South American (PSA) and North Pacific Oscillation (NPO) patterns. Both the PSA and NPO modes induce basinwide SST anomalies in the tropical Pacific and beyond that resemble the observed interdecadal Pacific oscillation. The subtropical SST anomalies forced by the PSA and NPO modes propagate to the equatorial Pacific mainly through the wind–evaporation–SST feedback. This atmospheric bridge is stronger from the South Pacific than the North Pacific due to the northward displacement of the intertropical convergence zone and the associated northward advection of momentum anomalies. The equatorial ocean dynamics is also more strongly influenced by atmospheric circulation changes induced by the PSA mode than the NPO mode. In the PSA experiment, persistent and zonally coherent wind stress curl anomalies over the South Pacific affect the zonal mean depth of the equatorial thermocline and weaken the equatorial SST anomalies resulting from the atmospheric bridge. This oceanic adjustment serves as a delayed negative feedback and may be important for setting the time scales of tropical Pacific decadal variability.

Impacts of ENSO and IOD on Snow Depth over the Tibetan Plateau: Roles of Convections over the Western North Pacific and Indian Ocean

2020 ◽  
Author(s):  
Tuantuan Zhang ◽  
Xingwen Jiang ◽  
Chi-Yung Tam ◽  
Junwen Chen ◽  
Ngar-Cheung Lau ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
North Pacific ◽  
Snow Depth ◽  
Western North Pacific ◽  
Cyclonic Circulation ◽  
Cold Temperature ◽  
The Tibetan Plateau ◽  
The Tropics ◽  
Anomalous Cyclonic Circulation

<p>This is a consensus that snow over the Tibetan Plateau (TP) modulates the regional climate significantly. Possible causes for the interannual variability of snow over the TP, however, are under debate, especially regarding the independent roles of El Niño-Southern (ENSO) and Indian Ocean dipole (IOD). Based on in-situ observational data analyses and model simulations, our study shows that impacts of ENSO and IOD on snow depth (SD) over the TP are different during early winter. In particular, ENSO mostly affects SD over the eastern TP, while IOD affects SD over the central-western TP. Both above-normal snowfall and cold temperature anomaly contribute to deeper-than-normal SD, with the former playing a more important role. Diabatic cooling of the suppressed convection over the western North Pacific that related to the positive phase of ENSO could excite an anomalous cyclonic circulation and strong cold temperature anomalies over the eastern TP. There is an enhanced moisture transported over the eastern TP from the tropics due to the anomalous cyclonic circulation; along with strong cold temperature anomalies, resulting in above-normal snowfall in the eastern TP. On the other hand, anomalous convection over the western Indian Ocean related to the positive IOD could generate a wave-train propagating northeastward and induce an anomalous cyclonic circulation over the central-western TP. The associated anomalous circulation transports extra moisture from the tropics to the central-western TP, providing conditions favorable for more snowfall over the central-western TP. Opposite conditions tend to occur during negative phases of ENSO and IOD.</p>

Sign in / Sign up

Export Citation Format

Share Document