Influences of Tropical Indian and Pacific Oceans on the Interannual Variations of Precipitation in the Early and Late Rainy Seasons in South China

Abstract Because of the seasonal northward migration of the East Asian summer monsoon, the mean-state atmospheric circulation in South China (SC) is remarkably different between the early (May–June) and late (July–August) rainy seasons. This study presents distinct teleconnections between the SC precipitation in the two periods and the sea surface temperatures (SSTs) in the tropical oceans. In the early rainy season when the major monsoon rain belt is located in SC, the increased local precipitation is related to the tropical Indian Ocean Basin warming. The basin warming induces an anomalous anticyclone in the South China Sea–western North Pacific (SCS-WNP). The related southwesterly anomalies transport more moisture to SC and lead to more moisture convergence and precipitation there. In the late rainy season when the major monsoon rain belt migrates northward to the Yangtze River valley, the precipitation increase in SC can be caused by the dipole SST anomalies in the tropical Pacific with the cold anomalies near the Maritime Continent and warm ones near the date line. The dipole SST anomalies generate an anomalous cyclone in the WNP with its center more northward than that of the anomalous anticyclone in the early rainy season. The related northeasterly anomalies along its northwestern flank reduce the climatological northward transport of moisture flux out of SC, and increase the moisture convergence and precipitation there. The distinct teleconnections between the SC precipitation and the tropical SSTs in the early and late rainy seasons can be well reproduced in the sensitivity experiments by an atmospheric general circulation model.

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Onset and End of the Rainy Season in South America in Observations and the ECHAM 4.5 Atmospheric General Circulation Model

Journal of Climate ◽

10.1175/jcli4122.1 ◽

2007 ◽

Vol 20 (10) ◽

pp. 2037-2050 ◽

Cited By ~ 70

Author(s):

Brant Liebmann ◽

Suzana J. Camargo ◽

Anji Seth ◽

José A. Marengo ◽

Leila M. V. Carvalho ◽

...

Keyword(s):

Rainy Season ◽

General Circulation ◽

Rain Rate ◽

Atmospheric General Circulation Model ◽

Circulation Model ◽

Season Length ◽

Wet Season ◽

Atmospheric General Circulation ◽

Annual Total ◽

Sst Anomalies

Abstract Rainfall in South America as simulated by a 24-ensemble member of the ECHAM 4.5 atmospheric general circulation model is compared and contrasted with observations (in areas in which data are available) for the period 1976–2001. Emphasis is placed on determining the onset and end of the rainy season, from which its length and rain rate are determined. It is shown that over large parts of the domain the onset and ending dates are well simulated by the model, with biases of less than 10 days. There is a tendency for model onset to occur early and ending to occur late, resulting in a simulated rainy season that is on average too long in many areas. The model wet season rain rate also tends to be larger than observed. To estimate the relative importance of errors in wet season length and rain rate in determining biases in the annual total, adjusted totals are computed by substituting both the observed climatological wet season length and rate for those of the model. Problems in the rain rate generally are more important than problems in the length. The wet season length and rain rate also contribute substantially to interannual variations in the annual total. These quantities are almost independent, and it is argued that they are each associated with different mechanisms. The observed onset dates almost always lie within the range of onset of the ensemble members, even in the areas with a large model onset bias. In some areas, though, the model does not perform well. In southern Brazil the model ensemble average onset always occurs in summer, whereas the observations show that winter is often the wettest period. Individual members, however, do occasionally show a winter rainfall peak. In southern Northeast Brazil the model has a more distinct rainy season than is observed. In the northwest Amazon the model annual cycle is shifted relative to that observed, resulting in a model bias. No interannual relationship between model and observed onset dates is expected unless onset in the model and observations has a mutual relationship with SST anomalies. In part of the near-equatorial Amazon, there does exist an interannual relationship between onset dates. Previous studies have shown that in this area there is a relationship between SST anomalies and variations in seasonal total rainfall.

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The South China Sea Throughflow Retrieved from Climatological Data*

Journal of Physical Oceanography ◽

10.1175/2008jpo3955.1 ◽

2009 ◽

Vol 39 (3) ◽

pp. 753-767 ◽

Cited By ~ 40

Author(s):

Max Yaremchuk ◽

Julian McCreary ◽

Zuojun Yu ◽

Ryo Furue

Keyword(s):

South China Sea ◽

General Circulation Model ◽

South China ◽

General Circulation ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Luzon Strait ◽

The South China Sea ◽

China Sea ◽

Ocean General Circulation

Abstract The salinity distribution in the South China Sea (SCS) has a pronounced subsurface maximum from 150–220 m throughout the year. This feature can only be maintained by the existence of a mean flow through the SCS, consisting of a net inflow of salty North Pacific tropical water through the Luzon Strait and outflow through the Mindoro, Karimata, and Taiwan Straits. Using an inverse modeling approach, the authors show that the magnitude and space–time variations of the SCS thermohaline structure, particularly for the salinity maximum, allow a quantitative estimate of the SCS throughflow and its distribution among the three outflow straits. Results from the inversion are compared with available observations and output from a 50-yr simulation of a highly resolved ocean general circulation model. The annual-mean Luzon Strait transport is found to be 2.4 ± 0.6 Sv (Sv ≡ 106 m3 s−1). This inflow is balanced by the outflows from the Karimata (0.3 ± 0.5 Sv), Mindoro (1.5 ± 0.4), and Taiwan (0.6 ± 0.5 Sv) Straits. Results of the inversion suggest that the Karimata transport tends to be overestimated in numerical models. The Mindoro Strait provides the only passage from the SCS deeper than 100 m, and half of the SCS throughflow (1.2 ± 0.3 Sv) exits the basin below 100 m in the Mindoro Strait, a result that is consistent with a climatological run of a 0.1° global ocean general circulation model.

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The impact of the planetary β-effect on the tilting vertical structure of a mesoscale eddy

10.5194/os-2018-39 ◽

2018 ◽

Author(s):

Shengmu Yang ◽

Jiuxing Xing ◽

Shengli Chen ◽

Jiwei Tian ◽

Daoyi Chen

Keyword(s):

South China Sea ◽

South China ◽

General Circulation ◽

Vertical Structure ◽

Mesoscale Eddy ◽

Maximum Velocity ◽

Circulation Model ◽

Mesoscale Eddies ◽

China Sea ◽

The Impact

Abstract. Tilting mesoscale eddies in the South China Sea have been reported recently from observed field data. The mechanism of the dynamic process of the tilt, however, is not well understood. In this study, the influence of planetary β on the vertical structure of mesoscale eddies and its mechanism is investigated using theoretical analysis and numerical model experiments based on the MIT General Circulation Model (MITgcm). The results of the both approaches show that vertical motion due to the planetary β effect and nonlinear dynamics causes a pressure anomaly in the horizontal domain which triggers the tilt of the eddy axis. The tilting distance extends to be the radius of the eddy maximum velocity. In addition, the vertical stratification is another key factor in controlling the tilt of a mesoscale eddy. External forcings such as wind and inflow current are not considered in this study, and topography is included only in a realistic South China Sea model. Therefore, mesoscale eddies with large vertical depth should have the similar axis tilt character in open oceans under the β-effect.

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

Journal of Climate ◽

10.1175/jcli-d-19-0143.1 ◽

2020 ◽

Vol 33 (16) ◽

pp. 6989-7010 ◽

Cited By ~ 2

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.

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Dominant Interannual Covariations of the East Asian–Australian Land Precipitation during Boreal Winter

Journal of Climate ◽

10.1175/jcli-d-18-0477.1 ◽

2019 ◽

Vol 32 (11) ◽

pp. 3279-3296 ◽

Cited By ~ 3

Author(s):

Lin Liu ◽

Jianping Guo ◽

Wen Chen ◽

Renguang Wu ◽

Lin Wang ◽

...

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Southern Oscillation ◽

East Asian ◽

Circulation Model ◽

Boreal Winter ◽

Dipole Structure ◽

Second Mode ◽

Precipitation Anomalies ◽

Sst Anomalies

AbstractThe present study applies the empirical orthogonal function (EOF) method to investigate the interannual covariations of East Asian–Australian land precipitation (EAALP) during boreal winter based on observational and reanalysis datasets. The first mode of EAALP variations is characterized by opposite-sign anomalies between East Asia (EA) and Australia (AUS). The second mode features an anomaly pattern over EA similar to the first mode, but with a southwest–northeast dipole structure over AUS. El Niño–Southern Oscillation (ENSO) is found to be a primary factor in modulating the interannual variations of land precipitation over EA and western AUS. By comparison, the Indian Ocean subtropical dipole mode (IOSD) plays an important role in the formation of precipitation anomalies over northeastern AUS, mainly through a zonal vertical circulation spanning from the southern Indian Ocean (SIO) to northern AUS. In addition, the ENSO-independent cold sea surface temperature (SST) anomalies in the western North Pacific (WNP) impact the formation of the second mode. Using the atmospheric general circulation model ECHAM5, three 40-yr numerical simulation experiments differing in specified SST forcings verify the impacts of the IOSD and WNP SST anomalies. Further composite analyses indicate that the dominant patterns of EAALP variability are largely determined by the out-of-phase and in-phase combinations of ENSO and IOSD. These results suggest that in addition to ENSO, IOSD should be considered as another crucial factor influencing the EAALP variability during the boreal winter, which has large implications for improved prediction of EAALP land precipitation on the interannual time scale.

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Near-Annual SST Variability in the Equatorial Pacific in a Coupled General Circulation Model

Journal of Climate ◽

10.1175/jcli3536.1 ◽

2005 ◽

Vol 18 (21) ◽

pp. 4454-4473 ◽

Cited By ~ 6

Author(s):

Renguang Wu ◽

Ben P. Kirtman

Keyword(s):

General Circulation ◽

Circulation Model ◽

Equatorial Pacific ◽

Near Surface ◽

Boreal Spring ◽

Eastern Equatorial Pacific ◽

Zonal Advection ◽

The Mean ◽

Annual Mode ◽

Sst Anomalies

Abstract Equatorial Pacific sea surface temperature (SST) anomalies in the Center for Ocean–Land–Atmosphere Studies (COLA) interactive ensemble coupled general circulation model show near-annual variability as well as biennial El Niño–Southern Oscillation (ENSO) variability. There are two types of near-annual modes: a westward propagating mode and a stationary mode. For the westward propagating near-annual mode, warm SST anomalies are generated in the eastern equatorial Pacific in boreal spring and propagate westward in boreal summer. Consistent westward propagation is seen in precipitation, surface wind, and ocean current. For the stationary near-annual mode, warm SST anomalies develop near the date line in boreal winter and decay locally in boreal spring. Westward propagation of warm SST anomalies also appears in the developing year of the biennial ENSO mode. However, warm SST anomalies for the westward propagating near-annual mode occur about two months earlier than those for the biennial ENSO mode and are quickly replaced by cold SST anomalies, whereas warm SST anomalies for the biennial ENSO mode only experience moderate weakening. Anomalous zonal advection contributes to the generation and westward propagation of warm SST anomalies for both the westward propagating near-annual mode and the biennial ENSO mode. However, the role of mean upwelling is markedly different. The mean upwelling term contributes to the generation of warm SST anomalies for the biennial ENSO mode, but is mainly a damping term for the westward propagating near-annual mode. The development of warm SST anomalies for the stationary near-annual mode is partially due to anomalous zonal advection and upwelling, similar to the amplification of warm SST anomalies in the equatorial central Pacific for the biennial ENSO mode. The mean upwelling term is negative in the eastern equatorial Pacific for the stationary near-annual mode, which is opposite to the ENSO mode. The development of cold SST anomalies in the aftermath of warm SST anomalies for the westward propagating near-annual mode is coupled to large easterly wind anomalies, which occur between the warm and cold SST anomalies. The easterly anomalies contribute to the cold SST anomalies through anomalous zonal, meridional, and vertical advection and surface evaporation. The cold SST anomalies, in turn, enhance the easterly anomalies through a Rossby-wave-type response. The above processes are most effective during boreal spring when the mean near-surface-layer ocean temperature gradient is the largest. It is suggested that the westward propagating near-annual mode is related to air–sea interaction processes that are limited to the near-surface layers.

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Mechanisms of Forced Tropical Meridional Energy Flux Change

Journal of Climate ◽

10.1175/jcli-d-14-00165.1 ◽

2015 ◽

Vol 28 (5) ◽

pp. 1725-1742 ◽

Cited By ~ 53

Author(s):

Spencer A. Hill ◽

Yi Ming ◽

Isaac M. Held

Keyword(s):

Spatial Pattern ◽

Greenhouse Gas ◽

Energy Flux ◽

General Circulation ◽

Energy Transport ◽

Circulation Model ◽

Hadley Cell ◽

Energy Fluxes ◽

Hadley Cells ◽

Sst Anomalies

Abstract Anthropogenically forced changes to the mean and spatial pattern of sea surface temperatures (SSTs) alter tropical atmospheric meridional energy transport throughout the seasonal cycle—in total, its partitioning between the Hadley cells and eddies and, for the Hadley cells, the relative roles of the mass flux and the gross moist stability (GMS). The authors investigate this behavior using an atmospheric general circulation model forced with SST anomalies caused by either historical greenhouse gas or aerosol forcing, dividing the SST anomalies into two components: the tropical mean SST anomaly applied uniformly and the full SST anomalies minus the tropical mean. For greenhouse gases, the polar-amplified SST spatial pattern partially negates enhanced eddy poleward energy transport driven by mean warming. Both SST components weaken winter Hadley cell circulation and alter GMS. The Northern Hemisphere–focused aerosol cooling induces northward energy flux anomalies in the deep tropics, which manifest partially via strengthened northern and weakened southern Hadley cell overturning. Aerosol-induced GMS changes also contribute to the northward energy fluxes. A simple thermodynamic scaling qualitatively captures these changes, although it performs less well for the greenhouse gas simulations. The scaling provides an explanation for the tight correlation demonstrated in previous studies between shifts in the intertropical convergence zone and cross-equatorial energy fluxes.

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Role of Nonlinear Atmospheric Response to SST on the Asymmetric Transition Process of ENSO

Journal of Climate ◽

10.1175/2008jcli2334.1 ◽

2009 ◽

Vol 22 (1) ◽

pp. 177-192 ◽

Cited By ~ 104

Author(s):

Masamichi Ohba ◽

Hiroaki Ueda

Keyword(s):

Observational Data ◽

Zonal Wind ◽

General Circulation ◽

Circulation Model ◽

La Niña ◽

Atmospheric Response ◽

Cold Event ◽

Transition Processes ◽

La Nina ◽

Sst Anomalies

Abstract Physical processes that are responsible for the asymmetric transition processes between El Niño and La Niña events are investigated by using observational data and physical models to examine the nonlinear atmospheric response to SST. The air–sea coupled system of ENSO is able to remain in a weak, cold event for up to 2 yr, while the system of a relatively warm event turns into a cold phase. Through analysis of the oceanic observational data, it is found that there is a strong difference in thermocline variations in relation to surface zonal wind anomalies in the equatorial Pacific (EP) during the mature-to-decaying phase of ENSO. The atmospheric response for the warm phase of ENSO causes a rapid reduction of the EP westerlies in boreal winter, which play a role in hastening the following ENSO transition through the generation of upwelling oceanic Kelvin waves. However, the anomalous EP easterlies in the cold phase persist to the subsequent spring, which tends to counteract the turnabout from the cold to warm phase of ENSO. A suite of idealized atmospheric general circulation model (AGCM) experiments are performed by imposing two different ENSO-related SST anomalies, which have equal amplitudes but opposite signs. The nonlinear climate response in the AGCM is found at the mature-to-decaying phase of ENSO that closely resembles the observations, including a zonal and meridional shift in the equatorial positions of the atmospheric wind. By using a simple ocean model, it is determined that the asymmetric responses of the equatorial zonal wind result in different recovery times of the thermocline in the eastern Pacific. Thus, the differences in transition processes between the warm and cold ENSO event are fundamentally due to the nonlinear atmospheric response to SST, which originates from the distribution of climatological SST and its seasonal changes. By including the asymmetric wind responses the intermediate air–sea coupled model herein demonstrates that the essential elements of the redevelopment of La Niña arise from the nonlinear atmospheric response to SST anomalies.

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Stratospheric aerosol radiative forcing simulated by the chemistry climate model EMAC using aerosol CCI satellite data

10.5194/acp-2018-330 ◽

2018 ◽

Author(s):

Christoph Brühl ◽

Jennifer Schallock ◽

Klaus Klingmüller ◽

Charles Robert ◽

Christine Bingen ◽

...

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

General Circulation ◽

Asian Summer Monsoon ◽

Michelson Interferometer ◽

Circulation Model ◽

Volcanic Eruptions ◽

Radiative Heating ◽

Tropospheric Aerosol ◽

Atmospheric Sounding

Abstract. This paper presents decadal simulations of stratospheric and tropospheric aerosol by the chemistry general circulation model EMAC constrained with satellite observations in the framework of the ESA-Aerosol-CCI project like GOMOS (Global Ozone Monitoring by Occultation of Stars) and (A)ATSR ((Advanced) Along Track Scanning Radiometer) on ENVISAT (European Environmental Satellite), and IASI (Infrared Atmospheric Sounding Interferometer) on Metop (Meteorological Operational Satellite). The EMAC simulations with modal interactive aerosol and observations by GOMOS show that sulfate particles from about 230 volcanic eruptions identified mostly from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) SO2 limb measurements dominate the interannual variability of aerosol extinction in the lower stratosphere, and of radiative forcing at the tropopause. To explain the observations, desert dust and organic and black carbon, transported to the lowermost stratosphere by the Asian summer monsoon and tropical convection, are also important. This holds also for radiative heating by aerosol in the lowermost stratosphere. Comparison with (A)ATSR total aerosol optical depth at different wavelengths and IASI dust optical depth shows that the model is able to represent stratospheric and tropospheric aerosol in a consistent way.

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Interannual Variations in Summer Precipitation in Southwest China: Anomalies in Moisture Transport and the Role of the Tropical Atlantic

Journal of Climate ◽

10.1175/jcli-d-19-0809.1 ◽

2020 ◽

Vol 33 (14) ◽

pp. 5993-6007 ◽

Cited By ~ 1

Author(s):

Chaoxia Yuan ◽

Mengzhou Yang

Keyword(s):

Pacific Ocean ◽

North Pacific ◽

Moisture Transport ◽

General Circulation ◽

Western North Pacific ◽

North Pacific Ocean ◽

Circulation Model ◽

Summer Precipitation ◽

Tropical Atlantic ◽

Anomalous Anticyclone

AbstractUsing a Lagrangian trajectory model, contributions of moisture from the Indian Ocean (IO), the South China Sea (SCS), the adjacent land region (LD), and the Pacific Ocean (PO) to interannual summer precipitation variations in southwestern China (SWC) are investigated. Results show that, on average, the IO, SCS, LD, and PO contribute 48.8%, 21.1%, 23.6%, and 3.7% of the total moisture release in SWC, respectively. In summers with the above-normal precipitation, moisture release from the IO and SCS increases significantly by 41.4% and 15.1%, respectively. In summers with below-normal precipitation, moisture release from the IO and SCS decreases significantly by 44.2% and 24.6%, respectively. In addition, the moisture anomalies from the four source regions together explain 86.5% of the total interannual variances of SWC summer precipitation, and the IO and SCS only can explain 75.7%. Variations in moisture transport from the IO, SCS, and LD to SWC are not independent of one another and are commonly influenced by the anomalous anticyclone in the western North Pacific Ocean, which enhances the moisture transport from the IO and SCS by the anomalous southwesterlies over its northwestern quadrant but reduces that from the LD east of SWC by the anomalous westerlies along its northern edge. Anomalous warming in the tropical Atlantic Ocean can modify the Walker circulation, induce anomalous descending motion over the central tropical Pacific, and excite the anomalous anticyclone in the western North Pacific as the classic Matsuno–Gill response. The observed impacts of the tropical Atlantic warming on the anomalous anticyclone and summer precipitation in SWC can be well reproduced in an atmospheric general circulation model.

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