scholarly journals Northern Hemisphere Rossby Wave Initiation Events on the Extratropical Jet—A Climatological Analysis

2018 ◽  
Vol 31 (2) ◽  
pp. 743-760 ◽  
Author(s):  
Matthias Röthlisberger ◽  
Olivia Martius ◽  
Heini Wernli
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
North Pacific ◽  
Large Scale ◽  
Tropical Convection ◽  
The Arctic ◽  
Subtropical Anticyclone ◽  
The North ◽  
Surface Cyclone ◽  
Wave Forms

A climatology of Rossby wave initiation (RWI) events on the Northern Hemisphere midlatitude jet is compiled by applying an objective RWI identification algorithm to the ERA-Interim dataset. In winter, RWI events occur most frequently over the northwestern Pacific and less often over the North Atlantic. In summer, the total number of RWI events is lower than in winter and the North Pacific RWI region shifts toward the Tibetan Plateau. Composite analysis of the large-scale flow prior to, during, and after winter North Pacific RWI events shows an upstream wave train propagating across Asia on the Arctic waveguide prior to RWI. The composite wave forms on a relatively weak zonal jet streak, exhibits a baroclinic structure, and is strongly amplified by latent heat release in the warm conveyor belt of a deepening surface cyclone. Moreover, the wave forms in a region of large-scale upper-level deformation, upstream of a preexisting ridge. Further, active tropical convection affects the longitude where RWI occurs and thus acts as a geographical anchor for RWI. Individual RWI events are characterized by preferred combinations of these composite features: a strong surface cyclone tends to occur in concert with strong latent heating and a pronounced positive PV anomaly aloft. A second group of co-occurring features contains active tropical convection, a strengthened subtropical anticyclone, and the downstream ridge. These feature groups might be regarded as idealized archetypal RWI scenarios, although numerous intermediate events exist where features from both groups occur together.

scholarly journals An Investigation of the Presence of Atmospheric Rivers over the North Pacific during Planetary-Scale Wave Life Cycles and Their Role in Arctic Warming

2016 ◽  
Vol 73 (11) ◽  
pp. 4329-4347 ◽  
Author(s):  
Cory Baggett ◽  
Sukyoung Lee ◽  
Steven Feldstein
Keyword(s):  
Life Cycle ◽  
Latent Heat ◽  
Rossby Wave ◽  
North Pacific ◽  
Tropical Convection ◽  
The Arctic ◽  
Synoptic Scale ◽  
Atmospheric Rivers ◽  
Planetary Scale ◽  
The North

Abstract Heretofore, the tropically excited Arctic warming (TEAM) mechanism put forward that localized tropical convection amplifies planetary-scale waves, which transport sensible and latent heat into the Arctic, leading to an enhancement of downward infrared radiation and Arctic surface warming. In this study, an investigation is made into the previously unexplored contribution of the synoptic-scale waves and their attendant atmospheric rivers to the TEAM mechanism. Reanalysis data are used to conduct a suite of observational analyses, trajectory calculations, and idealized model simulations. It is shown that localized tropical convection over the Maritime Continent precedes the peak of the planetary-scale wave life cycle by ~10–14 days. The Rossby wave source induced by the tropical convection excites a Rossby wave train over the North Pacific that amplifies the climatological December–March stationary waves. These amplified planetary-scale waves are baroclinic and transport sensible and latent heat poleward. During the planetary-scale wave life cycle, synoptic-scale waves are diverted northward over the central North Pacific. The warm conveyor belts associated with the synoptic-scale waves channel moisture from the subtropics into atmospheric rivers that ascend as they move poleward and penetrate into the Arctic near the Bering Strait. At this time, the synoptic-scale waves undergo cyclonic Rossby wave breaking, which further amplifies the planetary-scale waves. The planetary-scale wave life cycle ceases as ridging over Alaska retrogrades westward. The ridging blocks additional moisture transport into the Arctic. However, sensible and latent heat amounts remain elevated over the Arctic, which enhances downward infrared radiation and maintains warm surface temperatures.

scholarly journals Heat transport pathways into the Arctic and their connections to surface air temperatures

2019 ◽  
Vol 19 (6) ◽  
pp. 3927-3937 ◽  
Author(s):  
Daniel Mewes ◽  
Christoph Jacobi
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Large Scale ◽  
The Arctic ◽  
Positive Temperature ◽  
Transport Pathways ◽  
Temperature Anomalies ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract. Arctic amplification causes the meridional temperature gradient between middle and high latitudes to decrease. Through this decrease the large-scale circulation in the midlatitudes may change and therefore the meridional transport of heat and moisture increases. This in turn may increase Arctic warming even further. To investigate patterns of Arctic temperature, horizontal transports and their changes in time, we analysed ERA-Interim daily winter data of vertically integrated horizontal moist static energy transport using self-organizing maps (SOMs). Three general transport pathways have been identified: the North Atlantic pathway with transport mainly over the northern Atlantic, the North Pacific pathway with transport from the Pacific region, and the Siberian pathway with transport towards the Arctic over the eastern Siberian region. Transports that originate from the North Pacific are connected to negative temperature anomalies over the central Arctic. These North Pacific pathways have been becoming less frequent during the last decades. Patterns with origin of transport in Siberia are found to have no trend and show cold temperature anomalies north of Svalbard. It was found that transport patterns that favour transport through the North Atlantic into the central Arctic are connected to positive temperature anomalies over large regions of the Arctic. These temperature anomalies resemble the warm Arctic–cold continents pattern. Further, it could be shown that transport through the North Atlantic has been becoming more frequent during the last decades.

scholarly journals A New Variable-Threshold Persistent Anomaly Index: Northern Hemisphere Anomalies in the ERA-Interim Reanalysis

2019 ◽  
Vol 148 (1) ◽  
pp. 43-62 ◽  
Author(s):  
Rebecca L. Miller ◽  
Gary M. Lackmann ◽  
Walter A. Robinson
Keyword(s):  
Northern Hemisphere ◽  
North Pacific ◽  
Geopotential Height ◽  
The Arctic ◽  
Reanalysis Dataset ◽  
Variable Threshold ◽  
The North ◽  
Persistent Anomalies ◽  
The North Pacific ◽  
Height Data

Abstract Persistent weather regimes characterized by anomalous temperature or precipitation are often associated with persistent anomalies (PAs) in the tropospheric geopotential height field. To identify PAs throughout the annual cycle, an earlier definition is modified to apply a seasonally varying magnitude threshold, based on a smoothed, daily varying climatological average of daily 500-hPa geopotential height variability. The modified index can be applied to a wide variety of analysis, reanalysis, or model-forecast gridded data. Here, the modified PA index is used to identify positive and negative Northern Hemisphere PAs in all seasons and to compute trends in PA frequency, strength, location, and duration, in the ECMWF ERA-Interim reanalysis dataset (1979–2016). Height data are detrended and anomalies are weighted with an inverse sine-of-latitude function. In addition to maxima in PA frequency identified previously (North Pacific, North Atlantic, and Russia), an additional summertime maximum appears in the Arctic; this feature has not been analyzed extensively. A composite of summertime positive Arctic PA events reveals an equivalent barotropic structure, similar to that documented for midlatitude PAs. Arctic PA frequency is greatest in summer; it exhibits no trend in frequency over the 38-yr ERA-Interim analysis period. In fact, no discernable trends in PA frequency, strength, or duration are evident in the analysis period for the primary PA regions, although there is a suggestion of a northward shift in positive PA activity in the North Pacific.

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 The Climatology and Characteristics of Rossby Wave Packets Using a Feature-Based Tracking Technique

2014 ◽  
Vol 142 (10) ◽  
pp. 3528-3548 ◽  
Author(s):  
Matthew B. Souders ◽  
Brian A. Colle ◽  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Wave Packets ◽  
The Arctic ◽  
Average Intensity ◽  
Feature Based ◽  
The Arctic Oscillation

Abstract This paper describes an objective, track-based climatology of Rossby wave packets (RWPs). NCEP–NCAR reanalysis wind and geopotential height data at 300 hPa every 6 h were spectrally filtered using a Hilbert transform technique under the assumption that RWPs propagate along a waveguide defined by the 14-day running average of the 300-hPa wind. Track data and feature-based descriptive statistics, including area, average intensity, intensity volume (intensity multiplied by area), intensity-weighted centroid position, and velocity, were gathered to describe the interannual, annual, seasonal, and regime-based climatology of RWPs. RWPs have a more pronounced seasonal cycle in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). RWPs are nearly nonexistent in the summer months (June–August; JJA) in the NH, while there is nearly continuous RWP activity downstream of South Africa during austral summer (December–February; DJF). Interannual variability in RWP frequency and intensity in the Northern Hemisphere is found to be strongly connected with the large-scale flow regimes such as El Niño–Southern Oscillation and the Arctic Oscillation. Enhanced RWP activity is also found to coherently propagate from the Pacific into the Atlantic on average when the Arctic Oscillation switches from a positive to a negative phase. No significant long-term (~30 yr) trend in RWP frequency, activity, or amplitude is found.

scholarly journals Highly variable Pliocene sea surface conditions in the Norwegian Sea

2016 ◽  
Author(s):  
Paul E. Bachem ◽  
Bjørg Risebrobakken ◽  
Stijn De Schepper ◽  
Erin L. McClymont
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Regional Climate ◽  
Sea Surface ◽  
The Arctic ◽  
Bering Strait ◽  
Nordic Seas ◽  
Norwegian Sea ◽  
Surface Conditions ◽  
The North

Abstract. The Pliocene was a time of global warmth, during which the Northern Hemisphere transitioned from small, sporadic glaciation towards the larger-scale Pleistocene glacial-interglacial variability. Here, we present high-resolution records of sea surface temperature (SST) and ice rafted debris (IRD) in the Norwegian Sea from 5.32 to 3.14 Ma, providing evidence that the Pliocene surface conditions of the Norwegian Sea underwent a series of transitions in response to orbital forcing and gateway changes. Average SSTs are 2 °C above the regional Holocene mean, with notable variability on millennial to orbital timescales. Both gradual changes and threshold effects are proposed for the progression of regional climate towards the expansion of large-scale Northern Hemisphere glaciation. Cooling from 4.5 to 4.3 Ma may be linked to the onset of poleward flow through the Bering Strait. This cooling was further intensified by a period of cool summers due to weak obliquity forcing. Warming of up to 7 °C the Norwegian Sea at 4.0 Ma suggests a major increase in northward heat transport from the North Atlantic at this time, leading to an enhanced zonal SST gradient in the Nordic Seas, and may be linked to the expansion of sea ice in the Arctic and Nordic Seas. A warm Norwegian Sea and enhanced zonal temperature gradient between 4.0 and 3.6 Ma may have been a priming factor for increased glaciation around the Nordic Seas due to enhanced evaporation and precipitation at high northern latitudes.

scholarly journals A New Perspective toward Cataloging Northern Hemisphere Rossby Wave Breaking on the Dynamic Tropopause

2019 ◽  
Vol 147 (2) ◽  
pp. 409-431 ◽  
Author(s):  
Kevin A. Bowley ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
Rossby Wave ◽  
North Pacific ◽  
Wave Breaking ◽  
Potential Temperature ◽  
Low Frequency ◽  
The Arctic ◽  
Rossby Wave Breaking ◽  
Modes Of Variability ◽  
The North ◽  
The North Atlantic Oscillation

Abstract Rossby wave breaking (RWB) events are a common feature on the dynamic tropopause and act to modulate synoptic-scale jet dynamics. These events are characterized on the dynamic tropopause by an irreversible overturning of isentropes and are coupled to troposphere-deep vertical motions and geopotential height anomalies. Prior climatologies have focused on the poleward streamer, the equatorward streamer, or the reversal in potential temperature gradient between the streamers, resulting in differences in the frequencies of RWB. Here, a new approach toward cataloging these events that captures both streamers is applied to the National Centers for Environmental Prediction Reanalysis-2 dataset for 1979–2011. Anticyclonic RWB (AWB) events are found to be nearly twice as frequent as cyclonic RWB (CWB) events. Seasonal decompositions of the annual mean find AWB to be most common in summer (40% occurrence), which is likely due to the Asian monsoon, while CWB is most frequent in winter (22.5%) and is likely due to the equatorward shift in mean baroclinicity. Trends in RWB from 1980 to 2010 illustrate a westward shift in North Pacific AWB during winter and summer (up to 0.4% yr−1), while CWB in the North Pacific increases in winter and spring (up to 0.2% yr−1). These changes are hypothesized to be associated with localized changes in the two-way interaction between the jet and RWB. The interannual variability of AWB and CWB is also explored, and a notable modality to the frequency of RWB is found that may be attributable to known low-frequency modes of variability including the Arctic Oscillation, the North Atlantic Oscillation, and the Pacific–North American pattern.

scholarly journals Spatio-temporal associations of albacore CPUEs in the Northeastern Pacific with regional SST and climate environmental variables

2014 ◽  
Vol 71 (7) ◽  
pp. 1717-1727 ◽  
Author(s):  
A. Jason Phillips ◽  
Lorenzo Ciannelli ◽  
Richard D. Brodeur ◽  
William G. Pearcy ◽  
John Childers
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Environmental Variability ◽  
Southern Oscillation ◽  
Spatial Dynamics ◽  
Catch Per Unit Effort ◽  
Variable Effect ◽  
Positive Effects ◽  
The North ◽  
Additive Mixed Models

Abstract This study investigated the spatial distribution of juvenile North Pacific albacore (Thunnus alalunga) in relation to local environmental variability [i.e. sea surface temperature (SST)], and two large-scale indices of climate variability, [the Pacific Decadal Oscillation (PDO) and the Multivariate El Niño/Southern Oscillation Index (MEI)]. Changes in local and climate variables were correlated with 48 years of albacore troll catch per unit effort (CPUE) in 1° latitude/longitude cells, using threshold Generalized Additive Mixed Models (tGAMMs). Model terms were included to account for non-stationary and spatially variable effects of the intervening covariates on albacore CPUE. Results indicate that SST had a positive and spatially variable effect on albacore CPUE, with increasingly positive effects to the North, while PDO had an overall negative effect. Although albacore CPUE increased with SST both before and after a threshold year of 1986, such effect geographically shifted north after 1986. This is the first study to demonstrate the non-stationary spatial dynamics of albacore tuna, linked with a major shift of the North Pacific. Results imply that if ocean temperatures continue to increase, US west coast fisher communities reliant on commercial albacore fisheries are likely to be negatively affected in the southern areas but positively affected in the northern areas, where current albacore landings are highest.

scholarly journals Tropical Cyclogenesis in the Western North Pacific as Revealed by the 2008–09 YOTC Data*

2013 ◽  
Vol 28 (4) ◽  
pp. 1038-1056 ◽  
Author(s):  
Yamei Xu ◽  
Tim Li ◽  
Melinda Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Energy Dispersion ◽  
Reanalysis Dataset ◽  
Initial Development ◽  
Wave Trains

Abstract The Year of Tropical Convection (YOTC) high-resolution global reanalysis dataset was analyzed to reveal precursor synoptic-scale disturbances related to tropical cyclone (TC) genesis in the western North Pacific (WNP) during the 2008–09 typhoon seasons. A time filtering is applied to the data to isolate synoptic (3–10 day), quasi-biweekly (10–20 day), and intraseasonal (20–90 day) time-scale components. The results show that four types of precursor synoptic disturbances associated with TC genesis can be identified in the YOTC data. They are 1) Rossby wave trains associated with preexisting TC energy dispersion (TCED) (24%), 2) synoptic wave trains (SWTs) unrelated to TCED (32%), 3) easterly waves (EWs) (16%), and 4) a combination of either TCED-EW or SWT-EW (24%). The percentage of identifiable genesis events is higher than has been found in previous analyses. Most of the genesis events occurred when atmospheric quasi-biweekly and intraseasonal oscillations are in an active phase, suggesting a large-scale control of low-frequency oscillations on TC formation in the WNP. For genesis events associated with SWT and EW, maximum vorticity was confined in the lower troposphere. During the formation of Jangmi (2008), maximum Rossby wave energy dispersion appeared in the middle troposphere. This differs from other TCED cases in which energy dispersion is strongest at low level. As a result, the midlevel vortex from Rossby wave energy dispersion grew faster during the initial development stage of Jangmi.

scholarly journals Atmospheric Circulation Effects on Wind Speed Variability at Turbine Height

2007 ◽  
Vol 46 (4) ◽  
pp. 445-456 ◽  
Author(s):  
Katherine Klink
Keyword(s):  
Wind Speed ◽  
Pressure Gradient ◽  
Large Scale ◽  
Ground Level ◽  
The Arctic ◽  
Circulation Index ◽  
Regression Equations ◽  
Change Models ◽  
Wind Speeds ◽  
The North

Abstract Mean monthly wind speed at 70 m above ground level is investigated for 11 sites in Minnesota for the period 1995–2003. Wind speeds at these sites show significant spatial and temporal coherence, with prolonged periods of above- and below-normal values that can persist for as long as 12 months. Monthly variation in wind speed primarily is determined by the north–south pressure gradient, which captures between 22% and 47% of the variability (depending on the site). Regression on wind speed residuals (pressure gradient effects removed) shows that an additional 6%–15% of the variation can be related to the Arctic Oscillation (AO) and Niño-3.4 sea surface temperature (SST) anomalies. Wind speeds showed little correspondence with variation in the Pacific–North American (PNA) circulation index. The effect of the strong El Niño of 1997/98 on the wind speed time series was investigated by recomputing the regression equations with this period excluded. The north–south pressure gradient remains the primary determinant of mean monthly 70-m wind speeds, but with 1997/98 removed the influence of the AO increases at nearly all stations while the importance of the Niño-3.4 SSTs generally decreases. Relationships with the PNA remain small. These results suggest that long-term patterns of low-frequency wind speed (and thus wind power) variability can be estimated using large-scale circulation features as represented by large-scale climatic datasets and by climate-change models.

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