scholarly journals Wave trains of 10–30-day meridional wind variations over the North Pacific during summer

2021 ◽  
pp. 1
Author(s):  
Lei Du ◽  
Riyu Lu
Keyword(s):  
North America ◽  
Energy Conversion ◽  
North Pacific ◽  
Maximum Amplitude ◽  
Meridional Wind ◽  
Reanalysis Dataset ◽  
The North ◽  
Zonal Wavenumber ◽  
Wave Trains ◽  
The North Pacific

AbstractThe present study investigates the intraseasonal oscillations over the North Pacific during summer based on the ERA-Interim reanalysis dataset. It is shown that the main component of intraseasonal variations in meridional wind is dominated by 10–30-day variability. Zonally-oriented wave trains are identified over the North Pacific at this band, with a zonal wavenumber 6. The wave trains exhibit an equivalent-barotropic structure, with the maximum amplitude in the upper troposphere, and are manifested as quasi-stationary Rossby waves with the energy dispersing eastward. The wave trains do not show a phase-locking feature, that is, they have no preferred geographical locations in the zonal direction. Furthermore, energy analyses suggest that the intraseasonal waves gain energy through baroclinic energy conversion, while the barotropic energy conversion plays a negligible role. The present results have implications for better understanding and forecasting weather and climate in North America, since the intraseasonal waves over the North Pacific may act as precursory signals for extreme events occurring over North America.

Future Changes to El Niño Teleconnections over the North Pacific and North America

2021 ◽  
pp. 1-43
Author(s):  
Jonathan D. Beverley ◽  
Matthew Collins ◽  
F. Hugo Lambert ◽  
Robin Chadwick
Keyword(s):  
North America ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Positive Temperature ◽  
Central Pacific ◽  
Wave Source ◽  
The North ◽  
Precipitation Anomalies ◽  
The North Pacific

AbstractThe El Niño-Southern Oscillation (ENSO) is the leading mode of interannual climate variability and it exerts a strong influence on many remote regions of the world, for example in northern North America. Here, we examine future changes to the positive-phase ENSO teleconnection to the North Pacific/North America sector and investigate the mechanisms involved. We find that the positive temperature anomalies over Alaska and northern North America that are associated with an El Niño event in the present day are much weaker, or of the opposite sign, in the CMIP6 abrupt 4×CO2 experiments for almost all models (22 out of 26, of which 15 are statistically significant differences). This is largely related to changes to the anomalous circulation over the North Pacific, rather than differences in the equator-to-pole temperature gradient. Using a barotropic model, run with different background circulation basic states and Rossby wave source forcing patterns from the individual CMIP6 models, we find that changes to the forcing from the equatorial central Pacific precipitation anomalies are more important than changes in the global basic state background circulation. By further decomposing this forcing change into changes associated with the longitude and magnitude of ENSO precipitation anomalies, we demonstrate that the projected overall eastward shift of ENSO precipitation is the main driver of the temperature teleconnection change, rather than the increase in magnitude of El Niño precipitation anomalies which are, nevertheless, seen in the majority of models.

scholarly journals Contrastive Influence of ENSO and PNA on Variability and Predictability of North American Winter Precipitation

2019 ◽  
Vol 32 (19) ◽  
pp. 6271-6284 ◽  
Author(s):  
Xiaofan Li ◽  
Zeng-Zhen Hu ◽  
Ping Liang ◽  
Jieshun Zhu
Keyword(s):  
North America ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North American ◽  
North Pacific ◽  
Winter Precipitation ◽  
Sea Surface ◽  
The North ◽  
Remote Forcing ◽  
The North Pacific

Abstract In this work, the roles of El Niño–Southern Oscillation (ENSO) in the variability and predictability of the Pacific–North American (PNA) pattern and precipitation in North America in winter are examined. It is noted that statistically about 29% of the variance of PNA is linearly linked to ENSO, while the remaining 71% of the variance of PNA might be explained by other processes, including atmospheric internal dynamics and sea surface temperature variations in the North Pacific. The ENSO impact is mainly meridional from the tropics to the mid–high latitudes, while a major fraction of the non-ENSO variability associated with PNA is confined in the zonal direction from the North Pacific to the North American continent. Such interferential connection on PNA as well as on North American climate variability may reflect a competition between local internal dynamical processes (unpredictable fraction) and remote forcing (predictable fraction). Model responses to observed sea surface temperature and model forecasts confirm that the remote forcing is mainly associated with ENSO and it is the major source of predictability of PNA and winter precipitation in North America.

scholarly journals Near-Global Atmospheric Responses to Observed Springtime Tibetan Plateau Snow Anomalies

2020 ◽  
Vol 33 (5) ◽  
pp. 1691-1706 ◽  
Author(s):  
Shizuo Liu ◽  
Qigang Wu ◽  
Steven R. Schroeder ◽  
Yonghong Yao ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
North America ◽  
Tibetan Plateau ◽  
North Pacific ◽  
Snow Water Equivalent ◽  
North Pacific Ocean ◽  
Surface Cooling ◽  
The North ◽  
Snow Cover Extent ◽  
The North Pacific

AbstractPrevious studies show that there are substantial influences of winter–spring Tibetan Plateau (TP) snow anomalies on the Asian summer monsoon and that autumn–winter TP heavy snow can lead to persisting hemispheric Pacific–North America-like responses. This study further investigates global atmospheric responses to realistic extensive spring TP snow anomalies using observations and ensemble transient model integrations. Model ensemble simulations are forced by satellite-derived observed March–May TP snow cover extent and snow water equivalent in years with heavy or light TP snow. Heavy spring TP snow causes simultaneous significant local surface cooling and precipitation decreases over and near the TP snow anomaly. Distant responses include weaker surface cooling over most Asian areas surrounding the TP, a weaker drying band extending east and northeast into the North Pacific Ocean, and increased precipitation in a region surrounding this drying band. Also, there is tropospheric cooling from the TP into the North Pacific and over most of North America and the North Atlantic Ocean. The TP snow anomaly induces a negative North Pacific Oscillation/western Pacific–like teleconnection response throughout the troposphere and stratosphere. Atmospheric responses also include significantly increased Pacific trade winds, a strengthened intertropical convergence zone over the equatorial Pacific Ocean, and an enhanced local Hadley circulation. This result suggests a near-global impact of the TP snow anomaly in nearly all seasons.

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