scholarly journals Understanding of Interdecadal Changes in Variability and Predictability of the Northern Hemisphere Summer Tropical–Extratropical Teleconnection

2015 ◽  
Vol 28 (21) ◽  
pp. 8634-8647 ◽  
Author(s):  
June-Yi Lee ◽  
Kyung-Ja Ha
Keyword(s):  
Correlation Coefficient ◽  
Northern Hemisphere ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Interannual Variation ◽  
Monsoon Rainfall ◽  
Summer Monsoon Rainfall ◽  
Boreal Summer ◽  
Interdecadal Changes

Abstract Two dominant global-scale teleconnections—namely, western North Pacific–North American (WPNA) and circumglobal teleconnection (CGT)—in the Northern Hemisphere (NH) extratropics during boreal summer (June–August) have been identified as important sources for NH summer climate variability and predictability. An interdecadal shift in interannual variability and predictability of the WPNA and CGT that occurred around the late 1970s was investigated using reanalysis data and six coupled models’ retrospective forecast with a 1 May initial condition for the period 1960–79 (P1) and 1980–2005 (P2). The WPNA had a tight relationship with the decaying phase of El Niño–Southern Oscillation (ENSO) in P1, whereas it had a remarkably enhanced linkage with western North Pacific (WNP) summer monsoon rainfall in P2. The correlation coefficient between the WPNA and preceding ENSO (WNP monsoon rainfall) was reduced (increased) from −0.69 (0.1) in P1 to −0.60 (0.5) in P2. The CGT had a considerable connection with Indian summer monsoon rainfall (ISMR) in P1, whereas it had a strengthened relationship with the developing ENSO in P2. The correlation coefficient between the CGT and simultaneous ENSO (ISMR) was increased (decreased) from −0.41 (0.47) in P1 to −0.59 (0.24) in P2. Although dynamical models have difficulties in capturing the observed interdecadal changes, they are able to predict the interannual variation of the WPNA and CGT one month ahead, to some extent. The prediction skill of six models’ multimodel ensemble (MME) decreased (increased) from 0.78 (0.23) to 0.67 (0.67) for the WPNA (CGT) interannual variation. It is also noted that the spatial distribution of predictability and MME skill for 200-hPa geopotential height has been changed in relation to the changes in the WPNA and CGT.

Future Change of Northern Hemisphere Summer Tropical–Extratropical Teleconnection in CMIP5 Models*

2014 ◽  
Vol 27 (10) ◽  
pp. 3643-3664 ◽  
Author(s):  
June-Yi Lee ◽  
Bin Wang ◽  
Kyong-Hwan Seo ◽  
Jong-Seong Kug ◽  
Yong-Sang Choi ◽  
...  
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Cmip5 Models ◽  
Boreal Summer ◽  
Moderate Increase ◽  
Coupled Models ◽  
Teleconnection Patterns

Abstract Two dominant global-scale teleconnections in the Northern Hemisphere (NH) extratropics during boreal summer season (June–August) have been identified: the western North Pacific–North America (WPNA) and circumglobal teleconnection (CGT) patterns. These teleconnection patterns are of critical importance for the NH summer seasonal climate prediction. Here, how these teleconnections will change under anthropogenic global warming is investigated using representative concentration pathway 4.5 (RCP4.5) experiments by 20 coupled models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The six best models are selected based on their performance in simulation of the two teleconnection patterns and climatological means and variances of atmospheric circulation, precipitation, and sea surface temperature. The selected models capture the CGT and its relationship with the Indian summer monsoon (ISM) reasonably well. The models can also capture the WPNA circulation pattern but with striking deficiencies in reproducing its associated rainfall anomalies due to poor simulation of the western North Pacific summer monsoon rainfall. The following changes are anticipated in the latter half of twenty-first century under the RCP4.5 scenario: 1) significant weakening of year-to-year variability of the upper-level circulation due to increased atmospheric stability, although the moderate increase in convective heating over the tropics may act to strengthen the variability; 2) intensification of the WPNA pattern and major spectral peaks, particularly over the eastern Pacific–North America and North Atlantic–Europe sectors, which is attributed to the strengthening of its relationship with the preceding mature phase of El Niño–Southern Oscillation (ENSO); and 3) weakening of the CGT due to atmospheric stabilization and decreasing relationship with ISM as well as weakening of the ISM–ENSO relationship.

Impact of El Niño Modoki on Indian summer monsoon rainfall: Role of western north Pacific circulation in observations and CMIP5 models

2019 ◽  
Vol 40 (4) ◽  
pp. 2117-2133 ◽  
Author(s):  
Ramu A. Dandi ◽  
Jasti S. Chowdary ◽  
Prasanth A. Pillai ◽  
Sradhara Sidhan N. S. ◽  
Koteswararao K ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
El Nino ◽  
Summer Monsoon Rainfall ◽  
Cmip5 Models

Dependence of Indian summer monsoon rainfall forecast skill of CFSv2 on initial conditions and the role of bias in SST boundary forcing

2021 ◽  
Author(s):  
Stella Jes Varghese ◽  
Kavirajan Rajendran ◽  
Sajani Surendran ◽  
Arindam Chakraborty
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Lead Time ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
Initial Conditions ◽  
Summer Monsoon Rainfall ◽  
Forecast Skill ◽  
Boreal Summer ◽  
Central Pacific

<p>Indian summer monsoon seasonal reforecasts by CFSv2, initiated from January (4-month lead time, L4) through May (0-month lead time, L0) initial conditions (ICs), are analysed to investigate causes for the highest Indian summer monsoon rainfall (ISMR) forecast skill of CFSv2 with February (3-month lead time, L3) ICs. Although theory suggests forecast skill should degrade with increase in lead-time, CFSv2 shows highest skill with L3, due to its forecasting of ISMR excess of 1983 which other ICs failed to forecast. In contrast to observation, in CFSv2, ISMR extremes are largely decided by sea surface temperature (SST) variation over central Pacific (NINO3.4) associated with El Niño-Southern Oscillation (ENSO), where ISMR excess (deficit) is associated with La Niña (El Niño) or cooling (warming) over NINO3.4. In 1983, CFSv2 with L3 ICs forecasted strong La Niña during summer, which resulted in 1983 ISMR excess. In contrast, in observation, near normal SSTs prevailed over NINO3.4 and ISMR excess was due to variation of convection over equatorial Indian Ocean, which CFSv2 fails to capture with all ICs. CFSv2 reforecasts with late-April/early-May ICs are found to have highest deterministic ISMR forecast skill, if 1983 is excluded and Indian monsoon seasonal biases are also reduced. During the transitional ENSO in Boreal summer of 1983, faster and intense cooling of NINO3.4 SSTs in L3, could be due to larger dynamical drift with longer lead time of forecasting, compared to L0. Boreal summer ENSO forecast skill is also found to be lowest for L3 which gradually decreases from June to September. Rainfall occurrence with strong cold bias over NINO3.4, is because of the existence of stronger ocean-atmosphere coupling in CFSv2, but with a shift of the SST-rainfall relationship pattern to slightly colder SSTs than the observed. Our analysis suggests the need for a systematic approach to minimize bias in SST boundary forcing in CFSv2, to achieve improved ISMR forecasts.</p>

scholarly journals Interannual Variation of the Summer Rainfall Center in the South China Sea

2017 ◽  
Vol 30 (19) ◽  
pp. 7909-7931 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Jenq-Dar Tsay ◽  
Jun Matsumoto
Keyword(s):  
Summer Monsoon ◽  
Interannual Variation ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Summer Rainfall ◽  
The Philippines ◽  
Monsoon Trough ◽  
Summer Monsoon Rainfall ◽  
Tropical Depression ◽  
Easterly Wave

Abstract A northwest–southeast-oriented summer monsoon trough exists between northern Indochina and northwestern Borneo. Ahead of this the South China Sea (SCS) trough is located at a convergent center west of the Philippines, which provides an environment favorable for rain-producing synoptic systems to produce rainfall over this center and form the SCS summer rainfall center. Revealed from the x–t diagram for rainfall, this rainfall center is developed by multiple-scale processes involved with the SCS trough (TR), tropical depression (TY), interaction of the SCS trough with the easterly wave/tropical depression (EI), and easterly wave (EW). It is found that 56% of this rainfall center is produced by the SCS trough, while 41% is generated by the other three synoptic systems combined. Apparently, the formation of the SCS summer monsoon rainfall center is contributed to by these four rain-producing synoptic systems from the SCS and the Philippines Sea. The Southeast Asian summer monsoon undergoes an interannual variation and exhibits an east–west-oriented cyclonic (anticyclonic) anomalous circulation centered at the western tropical Pacific east of the Luzon Strait. This circulation change is reflected by the deepening (filling) of the SCS summer monsoon trough, when the monsoon westerlies south of 15°N intensify (weaken). This interannual variation of the monsoon westerlies leads to the interannual variation of the SCS summer monsoon rainfall center to follow the Pacific–Japan oscillation of rainfall. The rainfall amount produced over this rainfall center during the weak monsoon season is about two-thirds of that produced during the strong monsoon season. The rain-production ratio between TR and TY + EI + EW is 60:38 during the strong monsoon season and 47:49 during the weak monsoon season.

Tropical–Extratropical Teleconnections in Boreal Summer: Observed Interannual Variability*

2011 ◽  
Vol 24 (7) ◽  
pp. 1878-1896 ◽  
Author(s):  
Qinghua Ding ◽  
Bin Wang ◽  
John M. Wallace ◽  
Grant Branstator
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Monsoon Rainfall ◽  
Wave Train ◽  
Western Pacific ◽  
Boreal Summer ◽  
Enso Cycle ◽  
Height Field ◽  
Energy Propagation ◽  
Rainfall Anomalies

Abstract Maximum covariance analysis is performed on the fields of boreal summer, tropical rainfall, and Northern Hemisphere (NH) 200-hPa height for the 62-yr period of record of 1948–2009. The leading mode, which appears preferentially in summers preceding the peak phases of the El Niño–Southern Oscillation (ENSO) cycle, involves a circumglobal teleconnection (CGT) pattern in the NH extratropical 200-hPa height field observed in association with Indian monsoon rainfall anomalies. The second mode, which tends to occur in summers following ENSO peak phases, involves a western Pacific–North America (WPNA) teleconnection pattern in the height field observed in association with western North Pacific summer monsoon rainfall anomalies. The CGT pattern is primarily a zonally oriented wave train along the westerly waveguide, while the WPNA pattern is a wave train emanating from the western Pacific monsoon trough and following a great circle. The CGT is accompanied by a pronounced tropical–extratropical seesaw in the zonally symmetric geopotential height and temperature fields, and the WPNA is observed in association with hemispherically uniform anomalies. These ENSO-related features modulate surface air temperature in both the tropics and extratropics. ENSO also affects the wave structure of the CGT and WPNA indirectly, by modulating the strengths of the Indian and western North Pacific monsoons. Linear barotropic mechanisms, including energy propagation and barotropic instability of the basic-state flow, also act to shape and maintain the CGT. The implications of these findings for seasonal prediction of the NH extratropical circulation are discussed.

scholarly journals Subseasonal Predictability of Boreal Summer Monsoon Rainfall from Ensemble Forecasts

2017 ◽  
Vol 5 ◽  
Author(s):  
Nicolas Vigaud ◽  
Andrew W. Robertson ◽  
Michael K. Tippett ◽  
Nachiketa Acharya
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Summer Monsoon Rainfall ◽  
Boreal Summer ◽  
Ensemble Forecasts

scholarly journals Monitoring and Predicting the Intraseasonal Variability of the East Asian–Western North Pacific Summer Monsoon

2013 ◽  
Vol 141 (3) ◽  
pp. 1124-1138 ◽  
Author(s):  
Hai Lin
Keyword(s):  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
East Asian ◽  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Global Environmental ◽  
Northward Propagation

Abstract In this study, a new index is defined to capture the prominent northward propagation of the intraseasonal oscillation (ISO) in boreal summer in the East Asian and western North Pacific (EAWNP) region. It is based on the first two modes of empirical orthogonal function (EOF) analysis of the combined fields of daily anomalies of zonally averaged outgoing longwave radiation (OLR) and 850-hPa zonal wind (U850) in the EAWNP region. These two EOFs are well separated from the rest of the modes, and their principal components (PCs) capture the intraseasonal variability. They are nearly in quadrature in both space and time and their combination reasonably well represents the northward propagation of the ISO. As no future information beyond the current date is required as in conventional time filtering, this ISO index can be used in real-time applications. This index is applied to the output of the 24-yr historical hindcast experiment using the Global Environmental Multiscale (GEM) model of Environment Canada to evaluate the forecast skill of the ISO of the EAWNP summer monsoon.

scholarly journals Characterizing the highest tropical cyclone frequency in the Western North Pacific since 1984

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Joseph Basconcillo ◽  
Eun-Jeong Cha ◽  
Il-Ju Moon
Keyword(s):  
Tropical Cyclone ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Tropical Indian Ocean ◽  
Boreal Summer ◽  
Central Pacific ◽  
Impact Reduction ◽  
Cyclone Frequency ◽  
Sst Anomalies

AbstractThe 2018 boreal summer in the Western North Pacific (WNP) is highlighted by 17 tropical cyclones (TC)—the highest record during the reported reliable years of TC observations. We contribute to the existing knowledge pool on this extreme TC frequency record by showing that the simultaneous highest recorded intensity of the WNP summer monsoon prompted the eastward extension of the monsoon trough and enhancement of tropical convective activities, which are both favorable for TC development. Such changes in the WNP summer monsoon environment led to the extreme TC frequency record during the 2018 boreal summer. Meanwhile, the highest record in TC frequency and the intensity of the WNP summer monsoon are both attributed with the combined increase in the anomalous westerlies originating from the cold tropical Indian Ocean sea surface temperature (SST) anomalies drawn towards the convective heat source that is associated with the warm central Pacific SST anomalies. Our results provide additional insights in characterizing above normal tropical cyclone and summer monsoon activities in the WNP in understanding seasonal predictable horizons in the WNP, and in support of disaster risk and impact reduction.

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