scholarly journals A Meteorological Analysis of the 2013 Alberta Flood: Antecedent Large-Scale Flow Pattern and Synoptic–Dynamic Characteristics

2015 ◽  
Vol 143 (7) ◽  
pp. 2817-2841 ◽  
Author(s):  
Shawn M. Milrad ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
Rossby Wave ◽  
North Pacific ◽  
Extreme Rainfall ◽  
Flash Floods ◽  
Rainfall Event ◽  
Extreme Rainfall Event ◽  
Front Range ◽  
The North ◽  
The North Pacific ◽  
Meteorological Analysis

Abstract The 19–21 June 2013 Alberta flood was the costliest (CAD $6 billion) natural disaster in Canadian history. The flood was caused by a combination of above-normal spring snowmelt in the Canadian Rockies, large antecedent precipitation, and an extreme rainfall event on 19–21 June that produced rainfall totals of 76 mm in Calgary and 91 mm in the foothills. As is typical of flash floods along the Front Range of the Rocky Mountains, rapidly rising streamflow proceeded to move downhill (eastward) into Calgary. A meteorological analysis traces an antecedent Rossby wave train across the North Pacific Ocean, starting with intense baroclinic development over East Asia on 11 June. Subsequently, downstream Rossby wave development occurred across the North Pacific; a 1032-hPa subtropical anticyclone located northeast of Hawaii initiated a southerly atmospheric river into Alaska, which contributed to the development of a cutoff anticyclone over Alaska and a Rex block (ridge to the north, cyclone to the south) in the northeastern North Pacific. Upon breakdown of the Rex block, lee cyclogenesis occurred in Montana and strong easterly upslope flow was initiated in southern Alberta. The extreme rainfall event was produced in association with a combination of quasigeostrophically and orographically forced ascent, which acted to release conditional and convective instability. As in past Front Range flash floods, moisture flux convergence and positive θe advection were collocated with the heavy rainfall. Backward trajectories show that air parcels originated in the northern U.S. plains, suggesting that evapotranspiration from the local land surface may have acted as a moisture source.

Impact of Sea Ice Reduction in the Barents and Kara Seas on the Variation of the East Asian Trough in Late Winter

2021 ◽  
Vol 34 (3) ◽  
pp. 1081-1097
Author(s):  
Mian Xu ◽  
Wenshou Tian ◽  
Jiankai Zhang ◽  
Tao Wang ◽  
Kai Qie
Keyword(s):  
Sea Ice ◽  
Rossby Wave ◽  
North Pacific ◽  
East Asian ◽  
Late Winter ◽  
East Asian Trough ◽  
The North ◽  
Wave Ray ◽  
The North Pacific ◽  
Sea Ice Reduction

AbstractUsing the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) dataset and the Specified Chemistry Whole Atmosphere Community Climate Model (WACCM-SC), the impacts of sea ice reduction in the Barents–Kara Seas (BKS) on the East Asian trough (EAT) in late winter are investigated. Results from both reanalysis data and simulations show that the BKS sea ice reduction leads to a deepened EAT in late winter, especially in February, while the EAT axis tilt is not sensitive to the BKS sea ice reduction. Further analysis shows that the BKS sea ice reduction influences the EAT through the tropospheric and stratospheric pathways. For the tropospheric pathway, the results from a linearized barotropic model and Rossby wave ray tracing model reveal that long Rossby wave trains stimulated by the BKS sea ice loss propagate downstream to the North Pacific, strengthening the EAT. For the stratospheric pathway, the upward planetary waves enhanced by the BKS sea ice reduction shift the subpolar westerlies near the tropopause southward. With the critical lines displaced equatorward, the poleward transient eddies break at lower latitudes, shifting the eddy momentum deposit throughout the troposphere equatorward. Tropospheric westerlies maintained by eddy momentum deposit are also shifted southward, inducing the cyclonic anomalies over the North Pacific and deepening the EAT in late winter. Nudging experiments show that the tropospheric pathway only contributes to around 29.7% of the deepening of the EAT in February induced by the BKS sea ice loss, while the remaining 70.3% is caused by stratosphere–troposphere coupling.

scholarly journals Multiscale Upstream and In Situ Precursors to the Elevated Mixed Layer and High-Impact Weather over the Midwest United States

2017 ◽  
Vol 32 (3) ◽  
pp. 905-923 ◽  
Author(s):  
Jason M. Cordeira ◽  
Nicholas D. Metz ◽  
Macy E. Howarth ◽  
Thomas J. Galarneau
Keyword(s):  
United States ◽  
Rossby Wave ◽  
North Pacific ◽  
Wave Train ◽  
Severe Weather ◽  
Upper Midwest ◽  
Midwest United States ◽  
The North ◽  
Rossby Wave Train ◽  
The North Pacific

Abstract Two severe MCSs over the upper Midwest United States resulted in >100 mm of rain in a ~24-h period and >200 severe weather reports, respectively, during 30 June–2 July 2011. This period also featured 100 (104) daily maximum high (low) temperature records across the same region. These high-impact weather events occurred in the presence of an elevated mixed layer (EML) that influenced the development of the severe MCSs and the numerous record high temperatures. The antecedent large-scale flow evolution was influenced by early season Tropical Cyclone Meari over the western North Pacific. The recurvature and subsequent interaction of Meari with the extratropical large-scale flow occurred in conjunction with Rossby wave train amplification over the North Pacific and dispersion across North America during 22 June–2 July 2011. The Rossby wave train dispersion contributed to trough (ridge) development over western (central) North America and the development of an EML and the two MCSs over the upper Midwest United States. A composite analysis of 99 warm-season days with an EML at Minneapolis, Minnesota, suggests that Rossby wave train amplification and dispersion across the North Pacific may frequently occur in the 7 days leading up to EMLs across the upper Midwest. The composite analysis also demonstrates an increased frequency of severe weather and elevated temperatures relative to climatology on days with an EML. These results suggest that EMLs over the upper Midwest may often be preceded by Rossby wave train amplification over the North Pacific and be followed by a period of severe weather and elevated temperatures.

scholarly journals The Role of Dynamic Tropopause Rossby Wave Breaking for Synoptic-Scale Buildups in Northern Hemisphere Zonal Available Potential Energy

2019 ◽  
Vol 147 (2) ◽  
pp. 433-455 ◽  
Author(s):  
Kevin A. Bowley ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
Potential Energy ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
North Pacific ◽  
Wave Breaking ◽  
Synoptic Scale ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Pacific

Abstract Zonal available potential energy AZ measures the magnitude of meridional temperature gradients and static stability of a domain. Here, the role of Northern Hemisphere dynamic tropopause (2.0-PVU surface) Rossby wave breaking (RWB) in supporting an environment facilitating buildups of AZ on synoptic time scales (3–10 days) is examined. RWB occurs when the phase speed of a Rossby wave slows to the advective speed of the atmosphere, resulting in a cyclonic or anticyclonic RWB event (CWB and AWB, respectively). These events have robust dynamic and thermodynamic feedbacks through the depth of the troposphere that can modulate AZ. Significant synoptic-scale buildups in AZ and RWB events are identified from the National Centers for Environmental Prediction Reanalysis-2 dataset from 1979 to 2011 for 20°–85°N. Anomalies in AWB and CWB are assessed seasonally for buildup periods of AZ. Positive anomalies in AWB and negative anomalies in CWB are found for most AZ buildup periods in the North Pacific and North Atlantic basins and attributed to localized poleward shifts in the jet stream. Less frequent west–east dipoles in wave breaking anomalies for each basin are attributed to elongated and contracted regional jet exit regions. Finally, an analysis of long-duration AWB events for winter AZ buildup periods to an anomalously high AZ state is performed using a quasi-Lagrangian grid-shifting technique. North Pacific AWB events are shown to diabatically intensify the North Pacific jet exit region (increasing Northern Hemisphere AZ) through latent heating equatorward of the jet exit and radiative and evaporative cooling poleward of the jet exit.

scholarly journals Effect of the North Pacific Tropospheric Waveguide on the Fidelity of Model El Niño Teleconnections

2020 ◽  
Vol 33 (12) ◽  
pp. 5223-5237 ◽  
Author(s):  
Ronald K. K. Li ◽  
Tim Woollings ◽  
Christopher O’Reilly ◽  
Adam A. Scaife
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Wave Source ◽  
The North ◽  
The Caribbean ◽  
The North Atlantic ◽  
The North Pacific

AbstractIn a free-running climate model, DJF tropical–extratropical teleconnections are assessed and compared to observed teleconnections in reanalysis data. From reanalysis, the leading mode of covariability between tropical outgoing longwave radiation (OLR) and Northern Hemisphere extratropical geopotential height (Z500) is identified using maximum covariance analysis (MCA). This mode relates closely to the El Niño pattern. The GCM captures the tropical OLR well but the associated extratropical Z500 less well. The GCM climatology has an equatorward shifted North Pacific jet bias. We examine whether the difference in the teleconnection pattern is related to the GCM’s jet bias. In both a ray-tracing analysis and a barotropic model, this jet bias is shown to affect the Rossby wave propagation from the tropical Pacific into the North Pacific. These idealized model results suggest qualitatively that the MCA difference is largely consistent with linear Rossby wave dynamics. While the basic state has a larger effect on the North Pacific MCA, a Rossby wave source (RWS) bias in the Caribbean has a larger effect on the North Atlantic MCA. The North Pacific jet bias is also proposed to affect the downstream propagation of waves from North America into the Caribbean, where it affects tropical RWS and the triggering of secondary waves into the North Atlantic. We propose that climatological biases in the tropics are one underlying cause of the jet bias. Our study may also help understand the results of other climate models with similar jet biases.

scholarly journals Elucidating the role of vegetation in the initiation of rainfall-induced shallow landslides: Insights from an extreme rainfall event in the Colorado Front Range

2016 ◽  
Vol 43 (17) ◽  
pp. 9084-9092 ◽  
Author(s):  
Luke A. McGuire ◽  
Francis K. Rengers ◽  
Jason W. Kean ◽  
Jeffrey A. Coe ◽  
Benjamin B. Mirus ◽  
...  
Keyword(s):  
Extreme Rainfall ◽  
Shallow Landslides ◽  
Rainfall Event ◽  
Colorado Front Range ◽  
Extreme Rainfall Event ◽  
Front Range

scholarly journals Mechanisms driving MJO teleconnection changes with warming in CMIP6

2021 ◽  
Author(s):  
Andrea M. Jenney ◽  
David A. Randall ◽  
Elizabeth A. Barnes
Keyword(s):  
North America ◽  
Rossby Wave ◽  
North Pacific ◽  
Static Stability ◽  
Future Climate ◽  
Extended Time ◽  
The North ◽  
The Mean ◽  
The North Pacific ◽  
Mean State

Abstract. Teleconnections from the Madden-Julian Oscillation (MJO) are a key source of predictability of weather on the extended time scale of about 10–40 days. The MJO teleconnection is sensitive to a number of factors, including the mean state dry static stability, the mean flow, and the propagation and intensity characteristics of the MJO itself, which are traditionally difficult to separate across models. Each of these factors may evolve in response to increasing greenhouse gas emissions, which will impact MJO teleconnections and potentially impact potential predictability on extended time scales. Current state-of-the-art climate models do not agree on how MJO teleconnections will change in a future climate. Here, we use results from the Coupled Model Intercomparison Project Phase 6 (CMIP6) historical and SSP585 experiments in concert with a linear baroclinic model to separate and investigate alternate mechanisms explaining why and how MJO teleconnections over the North Pacific and North America will change in a future climate, and to identify key sources of inter-model uncertainty. We find that decreases to the MJO teleconnection due to increases in tropical dry static stability alone are robust, and that uncertainty in mean state winds are a key driver of uncertainty in future MJO teleconnections. We find no systematic relationship between changes in Rossby wave excitation and the MJO teleconnection. However, we find that models that predict increases (decreases) in the stationary Rossby wave number over the gulf of Alaska also predict stronger (weaker) teleconnections over North America. Uncertainty in future changes to the MJO's intensity, eastward propagation speed, and eastward propagation extent are other important sources of uncertainty in future MJO teleconnections, although to a lesser degree than uncertainty in the mean state. The overall outlook is a reduction of the boreal winter MJO teleconnection across the vast majority of CMIP6 models, especially over the North Pacific, but with some nuance over North America due to larger sensitivity to expansion of the MJO's eastward extent.

scholarly journals Rossby Waves and the Variability of the North Pacific Current during 2002–03

2011 ◽  
Vol 41 (9) ◽  
pp. 1708-1719
Author(s):  
Shawn M. Donohue ◽  
Michael W. Stacey
Keyword(s):  
Rossby Wave ◽  
North Pacific ◽  
Rossby Waves ◽  
North Pacific Ocean ◽  
The North ◽  
Time Period ◽  
North Pacific Current ◽  
The North Pacific ◽  
Current Drift ◽  
Local Winds

Abstract A numerical model, the Parallel Ocean Program (POP), with 0.25° horizontal spatial resolution and 28 vertical levels is used to simulate the circulation of the North Pacific Ocean for the time period 1960–2006. Spectral nudging is used so that model drift of the mean state over the 46-yr time period of the simulation is prevented while allowing for the prognostic evolution of the circulation at time scales that are not nudged. The simulation successfully reproduces a southward shift in the North Pacific Current in 2002–03 as calculated from scalar observations. It is suggested that this calculated shift may not be solely due to meridional current drift but also a consequence of the shifting intensity of two eastward-moving current bands separated by 300–500 km, a distance consistent with the Rhines scale (the scale at which the 2D turbulence cascade tends to be arrested), which implies an influence from Rossby waves that are heavily affected by nonlinearities. The simulation suggests that the North Pacific Current may indeed have been influenced by a Rossby wave–like disturbance. This disturbance could have been forced to a significant extent by the local winds, but there is also evidence in the model for a coastally generated Rossby wave–like disturbance. This coastal disturbance was generated during the 1997/98 ENSO and traveled westward from the coast at about 1 cm s−1, taking 3–5 yr to travel into the region of the North Pacific Current. The noncoastal portion of the disturbance, which was generated by the local winds away from the coast, propagated westward at about 1 cm s−1 as well.

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