The Dynamics of Quasi-Stationary Atmospheric Rivers and Their Implications for Monsoon Onset

2021 ◽  
Author(s):  
Hung-I Lee ◽  
Jonathan L. Mitchell
Keyword(s):  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Monsoon Onset ◽  
Western Pacific ◽  
Eastern Pacific ◽  
The Tibetan Plateau ◽  
Atmospheric Rivers ◽  
Upper Level ◽  
The Western Pacific

AbstractA global Hovmöller diagram of column water vapor (CWV) at 30°N from daily ERA-Interim reanalysis data shows seasonally migrating North Pacific/Atlantic quasi-stationary atmospheric rivers (QSARs) located in the Eastern Pacific/Atlantic in winter and propagate to the Western Pacific/Atlantic in summer. Simplified general circulation model (GCM) experiments produce QSAR-like features if the boundary conditions include (1) the sea surface temperature contrast from the tropical warm pool-cold tongue and (2) topographic contrast similar to the Tibetan plateau. Simulated QSARs form downstream of topographic contrast during winter and coincide with it in summer. Two models of baroclinic instability demonstrate that QSARs coincide with the location where the most unstable mode phase speed equals that of the upper-level zonal winds. A consistent interpretation is that the waves become quasi-stationary at this location and break. The location of quasistationarity migrates from the Eastern Pacific/Atlantic in the winter, when upper-level winds are strong and extended over the basin, to the Western Pacific/Atlantic when winds are weak and contracted. Low-level wind convergence and moist static energy coincide with QSARs, and since the former two are essential ingredients to monsoon formation, this implies an important role for QSARs in monsoon onset. This connection opens a new window into the dynamics of subtropical monsoon extensions.

Simulation of the Southern Oscillation in an atmospheric general circulation model

1989 ◽  
Vol 329 (1604) ◽  
pp. 179-188 ◽  
Keyword(s):  
General Circulation Model ◽  
Wind Stress ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Circulation Model ◽  
Western Pacific ◽  
Atmospheric General Circulation ◽  
The Western Pacific

An atmospheric general circulation model (GCM) was forced with the observed near-global sea surface temperature (SST) pattern for the period January 1970-December 1985. Its response over the Pacific Ocean is compared with Tahiti and Darwin station sea-level pressure and wind stress analyses obtained from Florida State University. The time-dependent SST clearly induces in the model run a Southern Oscillation that is apparent in the time series of all considered variables. The phase of the GCM Southern Oscillation is as observed but its low-frequency variance is too low and the spatial pattern is confined mainly to the western Pacific. The model is successful in reproducing the warm events of 1972—73 and 1982—83 and the cold event 1970—71, but fails with the cold events 1973-74 and 1975-76 and with the warm event 1976-77. Because the GCM is used as the atmospheric component in a coupled model, the response of an equatorial oceanic primitive equation model to both the modelled and observed wind stress is examined. The ocean model responds in essentially the same way to forcing with the observed wind stress and to forcing that corresponds to the first two low-frequency empirical orthogonal functions (EOFS) of the wind variations. These first two EOFS describe a regular eastward propagation of the so signal from the western Pacific to the central Pacific within about one year. The ocean model’s response to the modelled wind stress is too weak. It is similar to the response to the first observed wind stress EOF only. That is, the observed Southern Oscillation appears as a sequence of propagating patterns but the simulated Southern Oscillation appears as one standing pattern. The nature of the deviation of simulated wind stress from observations is further analysed by means of model output statistics.

scholarly journals Improving the Northeast Asian Monsoon Simulation: Remote Impact of Tropical Heating Bias Correction

2009 ◽  
Vol 137 (2) ◽  
pp. 797-803 ◽  
Author(s):  
Kyong-Hee An ◽  
Chi-Yung Tam ◽  
Chung-Kyu Park
Keyword(s):  
General Circulation ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Western Pacific ◽  
Boreal Summer ◽  
Simple Method ◽  
Northeast Asian ◽  
The Western Pacific

Abstract This study investigates the role of model tropical diabatic heating error on the boreal summer northeast Asian monsoon (NEAM) simulation given by a general circulation model (GCM). A numerical experiment is carried out in which the GCM diabatic heating is adjusted toward more realistic values in the tropics. It is found that the seasonal mean NEAM circulation and rainfall are improved in the GCM. This can be attributed to the reduced positive heating bias in the western Pacific Ocean around 10°–15°N in the model, which in turn leads to better-simulated low-level southerly winds over eastern Asia and more moisture supply to the NEAM region. The GCM’s ability in capturing the year-to-year variation of NEAM rainfall is also markedly improved in the experiment. These results show that the diabatic heating error over the western Pacific can be one reason for poor NEAM simulations in GCMs. The authors also suggest a simple method to reduce model heating biases that can be readily applied to dynamical seasonal prediction systems.

Mongolian Mountains Matter Most: Impacts of the Latitude and Height of Asian Orography on Pacific Wintertime Atmospheric Circulation

2017 ◽  
Vol 30 (11) ◽  
pp. 4065-4082 ◽  
Author(s):  
R. H. White ◽  
D. S. Battisti ◽  
G. H. Roe
Keyword(s):  
Tibetan Plateau ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
The Tibetan Plateau ◽  
Contributing Factors ◽  
The Pacific ◽  
Upper Level ◽  
Hemisphere Winter

Abstract The impacts of Asian orography on the wintertime atmospheric circulation over the Pacific are explored using altered-orography, semi-idealized, general circulation model experiments. The latitude of orography is found to be far more important than height. The Mongolian Plateau and nearby mountain ranges, centered at ~48°N, have an impact on the upper-level wintertime jet stream that is approximately 4 times greater than that of the larger and taller Tibetan Plateau and Himalayas to the south. Key contributing factors to the importance of the Mongolian mountains are latitudinal variations in the meridional potential vorticity gradient and the strength of the impinging wind—both of which determine the amplitude of the atmospheric response—and the structure of the atmosphere, which influences the spatial pattern of the downstream response. Interestingly, while the Mongolian mountains produce a larger response than the Tibetan Plateau in Northern Hemisphere winter, in April–June the response from the Tibetan Plateau predominates. This result holds in two different general circulation models. In experiments with idealized orography, varying the plateau latitude by 20°, from 43° to 63°N, changes the response amplitude by a factor of 2, with a maximum response for orography between 48° and 53°N, comparable to the Mongolian mountains. In these idealized experiments, the latitude of the maximum wintertime jet increase changes by only ~6°. It is proposed that this nearly invariant spatial response pattern is due to variations in the stationary wavenumber with latitude leading to differences in the zonal versus meridional wave propagation.

Molecular taxonomy of vestimentiferans of the western Pacific and their phylogenetic relationship to species of the eastern Pacific

2002 ◽  
Vol 141 (1) ◽  
pp. 57-64 ◽  
Author(s):  
Kojima S. ◽  
Ohta S. ◽  
Yamamoto T. ◽  
Miura T. ◽  
Fujiwara Y. ◽  
...  
Keyword(s):  
Phylogenetic Relationship ◽  
Molecular Taxonomy ◽  
Western Pacific ◽  
Eastern Pacific ◽  
The Western Pacific

First Record of the Ceratioid Anglerfish Species Gigantactis microdontis (Teleostei: Lophiiformes: Gigantactinidae) in the Western Pacific Ocean

Zootaxa ◽  
2019 ◽  
Vol 4664 (3) ◽  
pp. 441-444 ◽  
Author(s):  
ARTEM M. PROKOFIEV ◽  
THEODORE W. PIETSCH
Keyword(s):  
Pacific Ocean ◽  
Hawaiian Islands ◽  
First Record ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Eastern Pacific ◽  
Western Pacific Ocean ◽  
Western Tropical Pacific ◽  
Caroline Islands ◽  
The Western Pacific

The rare ceratioid anglerfish Gigantactis microdontis was formerly known from 12 specimens collected in the Eastern Pacific from 158° W eastward: off Hawaiian Islands, Oregon, California and Peru. Thirteenth specimen reported herein extends the known distribution of this species some 7630 km westward into the western tropical Pacific (off Caroline Islands). The newly reported specimen shows no principal differences in morphology from the previously known individuals. 

scholarly journals Reexamination of the Late Pliocene Climate over China Using a 25-km Resolution General Circulation Model

2019 ◽  
Vol 32 (3) ◽  
pp. 897-916 ◽  
Author(s):  
Qing Yan ◽  
Ting Wei ◽  
Zhongshi Zhang
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
East Asian ◽  
Circulation Model ◽  
Northwest China ◽  
Precipitation Change ◽  
The Tibetan Plateau ◽  
Model Resolution ◽  
Geological Evidence ◽  
Late Pliocene

Simulations of past warm climate provide an opportunity to better understand how the climate system may respond to increased greenhouse gas emissions. Using the ~25-km-resolution Community Atmosphere Model, version 4 (CAM4), we examine climate change over China in the Late Pliocene warm period (3.264–3.025 Ma) and further explore the influences of different sea surface temperature (SST) forcings and model horizontal resolutions. Initial evaluation shows that the high-resolution CAM4 performs well in capturing the climatological distribution of present-day temperature, precipitation, and low-level monsoon circulations over China. Based on the standard Pliocene Research, Interpretation and Synoptic Mapping (version 4; PRISM4) boundary conditions, CAM4 predicts an increase of annual mean temperature by ~0.5°C over China in the Late Pliocene relative to the preindustrial era, with the greatest warming in northwest China but cooling in southwest China. Enhanced annual mean precipitation is observed in the Late Pliocene over most of China except for northwest China where precipitation is decreased. The East Asian summer (winter) monsoon is intensified (weakened) in the Late Pliocene as suggested by geological evidence, which is attributed to the enhanced (reduced) land–sea thermal contrast. The East Asian monsoon domain exhibits a northwestward expansion in the Late Pliocene, especially over the Tibetan Plateau. Additionally, our results indicate that the modeled climate change is sensitive to the Late Pliocene SST forcings and model resolution. Particularly, different SST forcings [PRISM4-based vs Pliocene Model Intercomparison Project (PlioMIP)-based SSTs] affect the modeled phase change of summer monsoon and the associated precipitation change, while model resolution (~25 vs 400 km) mainly impacts precipitation change.

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