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 Role of Tropical Mean-State Biases in Modeled Winter Northern Hemisphere El Niño Teleconnections

2020 ◽  
Vol 33 (11) ◽  
pp. 4751-4768 ◽  
Author(s):  
Samantha Ferrett ◽  
Matthew Collins ◽  
Hong-Li Ren ◽  
Bo Wu ◽  
Tianjun Zhou
Keyword(s):  
Northern Hemisphere ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Teleconnection Pattern ◽  
The North ◽  
Precipitation Response ◽  
The North Pacific ◽  
Mean State

AbstractThe role of tropical mean-state biases in El Niño–Southern Oscillation teleconnections in the winter Northern Hemisphere is examined in coupled general circulation models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The main North Pacific teleconnection pattern, defined here by the strengths of the anomalous Kuroshio anticyclone and North Pacific cyclone, is linked to two anomalous Rossby wave sources that occur during El Niño: a negative source over East Asia and a positive source to the west of the North Pacific. Errors in the teleconnection pattern in models are associated with spatial biases in mean atmospheric ascent and descent and the strength of the corresponding forcing of Rossby waves via suppressed or enhanced El Niño precipitation responses in the tropical western North Pacific (WNP) and the equatorial central Pacific (CP). The WNP El Niño precipitation response is most strongly linked to the strength of the Kuroshio anticyclone and the CP El Niño precipitation response is most strongly linked to the strength of the North Pacific cyclone. The mean state and corresponding El Niño precipitation response can have seemingly distinct biases. A bias in the WNP does not necessarily correspond to a bias in the CP, suggesting that improvement of biases in both tropical WNP and equatorial CP regions should be considered for an accurate teleconnection pattern.

scholarly journals Tropospheric Rossby Wave Breaking and the NAO/NAM

2008 ◽  
Vol 65 (9) ◽  
pp. 2861-2876 ◽  
Author(s):  
Courtenay Strong ◽  
Gudrun Magnusdottir
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Time Lag ◽  
Zonal Flow ◽  
Sea Level Pressure ◽  
Rossby Wave Breaking ◽  
The North ◽  
Nao Index ◽  
The North Atlantic Oscillation

Abstract Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective wave-breaking analysis method are provided in the appendix.

scholarly journals North Atlantic Extratropical Rossby Wave Breaking during the Warm Season: Wave Life Cycle and Role of Diabatic Heating

2018 ◽  
Vol 146 (3) ◽  
pp. 695-712 ◽  
Author(s):  
Gan Zhang ◽  
Zhuo Wang
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Trajectory Analysis ◽  
Diabatic Heating ◽  
Warm Season ◽  
Rossby Wave Breaking ◽  
The North ◽  
Budget Analysis

This study investigates the life cycle of anticyclonic Rossby wave breaking during the extended warm season (July–October) over the North Atlantic basin. It was found that upper-tropospheric breaking waves are coupled with lower-level perturbations and can be traced back to a wave train that extends from the North Pacific. The overturning of potential vorticity (PV) contours during wave breaking is associated with the rapid development of an upper-level ridge, which occurs along the east coast of North America and over a warm and moist airstream. The ridge development is investigated using the PV budget analysis and trajectory analysis. The PV budget analysis suggests that the horizontal advection of PV by the perturbed flow dictates the movement and the later decay of the ridge. The ridge amplification, opposed by the horizontal advection of PV, is driven by the vertical advection and the diabatic production of PV, both of which are connected to diabatic heating. The vital role of diabatic heating in the ridge amplification is corroborated by the trajectory analysis. The analysis suggests that diabatic heating reduces the static stability near the tropopause and contributes to the ridge-related negative PV anomalies. The role of diabatic heating in anticyclonic and cyclonic wave breaking in other regions is also discussed. The findings suggest that moist diabatic processes, which were often excluded from the earlier studies of wave breaking, are crucial for Rossby wave breaking during the warm season. The updated understanding of wave breaking may benefit weather forecasting and climate predictions.

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 Source-receptor relationships between East Asian sulfur dioxide emissions and Northern Hemisphere sulfate concentrations

2008 ◽  
Vol 8 (2) ◽  
pp. 5537-5561 ◽  
Author(s):  
J. Liu ◽  
D. L. Mauzerall ◽  
L. W. Horowitz
Keyword(s):  
Northern Hemisphere ◽  
North Pacific ◽  
East Asian ◽  
Source Region ◽  
The United States ◽  
So2 Emissions ◽  
Aerosol Model ◽  
The North ◽  
The North Pacific ◽  
Sulfur Emissions

Abstract. We analyze the effect of varying East Asian (EA) sulfur emissions on sulfate concentrations in the Northern Hemisphere, using a global coupled oxidant-aerosol model (MOZART-2). We conduct a base and five sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R) relationship between EA sulfur emissions and sulfate concentrations over source and downwind regions. We find that from west to east across the North Pacific, EA sulfate contributes approximately 80%–20% of sulfate at the surface, but at least 50% at 500 hPa. In addition, EA SO2 emissions account for approximately 30%–50% and 10%–20% of North American background sulfate over the western and eastern US, respectively. The contribution of EA sulfate to the western US at the surface is highest in MAM and JJA, but is lowest in DJF. Reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence over the North Pacific both at the surface and at 500 mb in all seasons, but the extent of influence is insensitive to emission increases, particularly in DJF and JJA. We find that EA sulfate concentrations over most downwind regions respond nearly linearly to changes in EA SO2 emissions, but sulfate concentrations over the EA source region increase more slowly than SO2 emissions, particularly at the surface and in winter, due to limited availability of oxidants (mostly H2O2). We find that similar estimates of the S-R relationship for trans-Pacific transport of EA sulfate would be obtained using either sensitivity or tagging techniques. Our findings suggest that future changes in EA sulfur emissions may cause little change in the sulfate induced health impact over downwind continents but SO2 emission reductions may significantly reduce the sulfate related climate cooling over the North Pacific and the United States.

3D Structure of Striations in the North Pacific

2021 ◽  
Author(s):  
YU ZHANG ◽  
YU PING GUAN ◽  
RUI XIN HUANG
Keyword(s):  
North Pacific ◽  
3D Structure ◽  
Three Dimensional ◽  
Vertical Plane ◽  
Dimensional Structure ◽  
The North ◽  
Layer Analysis ◽  
Fluid Potential ◽  
The North Pacific

AbstractOcean striations are composed of alternating quasi-zonal band-like flows; this kind of organized structure of currents be found in all world’s oceans and seas. Previous studies have mainly been focused on the mechanisms of their generation and propagation. This study uses the spatial high-pass filtering to obtain the three-dimensional structure of ocean striations in the North Pacific in both the z-coordinate and σ-coordinate based on 10-yr averaged SODA3 data. First, we identify an ideal-fluid potential density domain where the striations are undisturbed by the surface forcing and boundary effects. Second, using the isopycnal layer analysis, we show that on isopycnal surfaces the orientations of striations nearly follow the potential vorticity (PV) contours, while in the meridional-vertical plane the central positions of striations are generally aligned with the latitude of zero gradient of the relative PV. Our analysis provides a simple dynamical interpretation and better understanding for the role of ocean striations.

The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

2019 ◽  
Vol 32 (22) ◽  
pp. 7643-7661 ◽  
Author(s):  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Wenyu Zhou ◽  
Yu Zhang ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Deep Convection ◽  
Boreal Summer ◽  
Enso Events ◽  
The North ◽  
The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

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