A daily estimate of phase speed to explore the link between Arctic Amplification and Rossby waves

2020 ◽  
Author(s):  
Jacopo Riboldi ◽  
François Lott ◽  
Fabio D'Andrea ◽  
Gwendal RIvière
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Extreme Temperature ◽  
Phase Speed ◽  
Weighted Average ◽  
Boreal Summer ◽  
High Temporal Resolution ◽  
Arctic Amplification ◽  
Extreme Temperature Events

<p>Rossby wave activity is intimately related to the day-to-day weather evolution over midlatitudes and to the occurrence of extreme events. Global warming trends may also affect their characteristics: for example, it has been hypothesized that Arctic warming with respect to midlatitudes, known as Arctic Amplification, may lead to a reduction in the speed of Rossby waves, to more frequent atmospheric blocking and to extreme temperature events over midlatitudes. Testing this hypothesis requires an estimate of the evolution and of the variability of phase speed in recent decades and in climate model simulations. However, measuring the phase speed of the global Rossby wave pattern is a complex task, as the midlatitude flow consists of a superposition of waves of different nature (e.g., planetary vs synoptic) across a broad range of wavenumbers and frequencies.</p><p>We propose here a framework, based on spectral analysis, to understand the variability of Rossby wave characteristics in reanalysis and their possible future changes. A novel, daily climatology of wave spectra based on gridded upper-level wind data is employed to study the evolution of Rossby wave phase speed over the Northern Hemisphere between March 1979 and November 2018. A global estimate of phase speed is obtained by doing a weighted average of the phase speed of each wave, with the associated spectral coefficients as weights.</p><p>Several insights about the drivers of phase speed variability at different time scales and their link with extreme temperature events can be gained from this diagnostic. 1) The occurrence of low phase speeds over Northern Hemisphere midlatitudes is related to a poleward displacement of blocking frequency maxima; conversely, the occurrence of high phase speed is related to blocking occurring at lower latitudes than usual. 2) Periods of low phase speed are associated with the occurrence of anomalous temperatures over Northern Hemisphere midlatitudes in winter, while this linkage is weaker during boreal summer. 3) No significant trend in phase speed has been observed during recent decades, despite the presence of Arctic Amplification. The absence of trend in phase speed is consistent with the evolution of the meridional geopotential gradient during recent decades. On the other hand, the high temporal resolution of the phase speed metric highlights the intraseasonal and interannual variability of Rossby wave propagation and points to 2009/10 as an extreme winter characterized by particularly low phase speed.</p>

scholarly journals Warm Season Subseasonal Variability and Climate Extremes in the Northern Hemisphere: The Role of Stationary Rossby Waves

2011 ◽  
Vol 24 (18) ◽  
pp. 4773-4792 ◽  
Author(s):  
Siegfried Schubert ◽  
Hailan Wang ◽  
Max Suarez
Keyword(s):  
Surface Temperature ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Heat Waves ◽  
Empirical Orthogonal Functions ◽  
Boreal Summer ◽  
Northern Great Plains ◽  
Northern Eurasia ◽  
The U.S

Abstract This study examines the nature of boreal summer subseasonal atmospheric variability based on the new NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) for the period 1979–2010. An analysis of the June, July, and August subseasonal 250-hPa meridional υ-wind anomalies shows distinct Rossby wave–like structures that appear to be guided by the mean jets. On monthly subseasonal time scales, the leading waves [the first 10 rotated empirical orthogonal functions (REOFs) of the 250-hPa υ wind] explain about 50% of the Northern Hemisphere υ-wind variability and account for more than 30% (60%) of the precipitation (surface temperature) variability over a number of regions of the northern middle and high latitudes, including the U.S. northern Great Plains, parts of Canada, Europe, and Russia. The first REOF in particular consists of a Rossby wave that extends across northern Eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability and played an important role in the 2003 European and 2010 Russian heat waves. While primarily subseasonal in nature, the Rossby waves can at times have a substantial seasonal mean component. This is exemplified by REOF 4, which played a major role in the development of the most intense anomalies of the U.S. 1988 drought (during June) and the 1993 flooding (during July), though differed in the latter event by also making an important contribution to the seasonal mean anomalies. A stationary wave model (SWM) is used to reproduce some of the basic features of the observed waves and provide insight into the nature of the forcing. In particular, the responses to a set of idealized forcing functions are used to map the optimal forcing patterns of the leading waves. Also, experiments to reproduce the observed waves with the SWM using MERRA-based estimates of the forcing indicate that the wave forcing is dominated by submonthly vorticity transients.

On the Linkage Between Rossby Wave Phase Speed, Atmospheric Blocking, and Arctic Amplification

2020 ◽  
Vol 47 (19) ◽  
Author(s):  
Jacopo Riboldi ◽  
François Lott ◽  
Fabio D'Andrea ◽  
Gwendal Rivière
Keyword(s):  
Rossby Wave ◽  
Phase Speed ◽  
Arctic Amplification ◽  
Atmospheric Blocking ◽  
Wave Phase

scholarly journals Complex Wavenumber Rossby Wave Ray Tracing

2012 ◽  
Vol 69 (7) ◽  
pp. 2112-2133 ◽  
Author(s):  
Jeffrey Shaman ◽  
R. M. Samelson ◽  
Eli Tziperman
Keyword(s):  
Ray Tracing ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Boreal Summer ◽  
Equatorial Pacific Ocean ◽  
Eastern Equatorial Pacific ◽  
Wave Ray ◽  
Wave Effects ◽  
First Ray ◽  
Barotropic Vorticity

Abstract This paper presents a methodology for performing complex wavenumber ray tracing in which both wave trajectory and amplitude are calculated. This ray-tracing framework is first derived using a scaling in which the imaginary wavenumber component is assumed to be much smaller than the real wavenumber component. The approach, based on perturbation methods, is strictly valid when this scaling condition is met. The framework is then used to trace stationary barotropic Rossby waves in a number of settings. First, ray-traced Rossby wave amplitude is validated in a simple, idealized system for which exact solutions can be calculated. Complex wavenumber ray tracing is then applied to both solid-body rotation on a sphere and observed climatological upper-tropospheric fields. These ray-tracing solutions are compared with similarly forced solutions of the linearized barotropic vorticity equation (LBVE). Both real and complex wavenumber ray tracings follow trajectories matched by LBVE solutions. Complex wavenumber ray tracings on observed two-dimensional zonally asymmetric atmospheric fields are found to follow trajectories distinct from real wavenumber Rossby waves. For example, complex wavenumber ray tracings initiated over the eastern equatorial Pacific Ocean during boreal summer propagate northward and northeastward into the subtropics over the Atlantic Ocean, as well as southeastward into the Southern Hemisphere. Similarly initiated real wavenumber ray tracings remain within the deep tropics and propagate westward. These complex wavenumber Rossby wave trajectories and ray amplitudes are generally consistent with LBVE solutions, which indicates this methodology can identify Rossby wave effects distinct from traditional real wavenumber tracings.

scholarly journals Rossby Wave Propagation into the Northern Hemisphere Stratosphere: The Role of Zonal Phase Speed

2018 ◽  
Vol 45 (4) ◽  
pp. 2064-2071 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Olivia Martius ◽  
Bernat Jiménez-Esteve
Keyword(s):  
Wave Propagation ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
Phase Speed ◽  
Rossby Wave Propagation

scholarly journals Exploring the influence of the North Pacific Ocean Rossby wave sources on interannual variability of summer precipitation and surface temperature over the Northern Hemisphere.

2021 ◽  
Author(s):  
Ramon Fuentes-Franco ◽  
Torben Koenigk ◽  
David Docquier ◽  
Federico Graef ◽  
Klaus Wyser
Keyword(s):  
Pacific Ocean ◽  
North America ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
North Atlantic ◽  
Rossby Waves ◽  
The North ◽  
Northeastern Pacific ◽  
The North Atlantic

Abstract The influence of Rossby wave sources (RWS) emitted on the Northeastern Pacific Ocean in the Northern Hemisphere during summer is analysed in the ERA5 reanalysis and new large ensemble performed with the EC-Earth3 model. Using extreme years composites of precipitation, surface temperature, geopotential height, we found a causal influence of the Rossby waves generated over the Northeastern Pacific Ocean, on a global climate response. Both the reanalysis ERA5 and the EC-Earth3 model show that RWS triggers wave-like patterns arising from the upper troposphere Northeastern Pacific region. We show that an increased Rossby wave sources intensity is related with negative temperature anomalies over western North America, and positive temperature anomalies over eastern North America concurrently increased precipitation over Northern Europe during summer and sea-ice concentration decrease in the Arctic. We also show that the North Atlantic plays a very important role hindering or permitting that Rossby waves generated in the Pacific reach the Atlantic and modulate the atmospheric conditions over Europe. Such conditions were found in ERA5 and SMHI-LENS during colder and icier conditions over the North Atlantic.

Modification of Long Equatorial Rossby Wave Phase Speeds by Zonal Currents

2011 ◽  
Vol 41 (6) ◽  
pp. 1077-1101 ◽  
Author(s):  
Theodore S. Durland ◽  
Roger M. Samelson ◽  
Dudley B. Chelton ◽  
Roland A. de Szoeke
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Current System ◽  
Phase Speed ◽  
Meridional Velocity ◽  
Zonal Velocity ◽  
The Mean ◽  
Meridional Mode ◽  
Mean Current ◽  
Pv Gradient

Abstract Previously unaddressed aspects of how equatorial currents affect long Rossby wave phase speeds are investigated using solutions of the shallow-water equations linearized about quasi-realistic currents. Modification of the background potential vorticity (PV) gradient by curvature in the narrow equatorial currents is shown to play a role comparable to the Doppler shift emphasized by previous authors. The important variables are the meridional projections of mean-current features onto relevant aspects of the wave field. As previously shown, Doppler shifting of long Rossby waves is determined by the projection of the mean currents onto the wave’s squared zonal-velocity and pressure fields. PV-gradient modification matters only to the extent that it projects onto the wave field’s squared meridional velocity. Because the zeros of an equatorial wave’s meridional velocity are staggered relative to those of the zonal velocity and pressure, and because the meridional scales of the equatorial currents are similar to those of the low-mode Rossby waves, different parts of the current system dominate the advective and PV-gradient modification effects on a single mode. Since the equatorial symmetry of classical equatorial waves alternates between symmetric and antisymmetric with increasing meridional mode number, the currents produce opposite effects on adjacent modes. Meridional mode 1 is slowed primarily by a combination of eastward advection by the Equatorial Undercurrent (EUC) and the PV-gradient decrease at the peaks of the South Equatorial Current (SEC). The mode-2 phase speed, in contrast, is increased primarily by a combination of westward advection by the SEC and the PV-gradient increase at the core of the EUC. Perturbation solutions are carried to second order in ε, the Rossby number of the mean current, and it is shown that this is necessary to capture the full effect of quasi-realistic current systems, which are asymmetric about the equator. Equatorially symmetric components of the current system affect the phase speed at O(ε), but antisymmetric components of the currents and distortions of the wave structures by the currents do not influence the phase speed until O(ε2).

scholarly journals Features of Rossby Wave Propagation Associated with the Evolution of Summertime Blocking Highs with Different Configurations over Northeast Asia

2016 ◽  
Vol 144 (7) ◽  
pp. 2531-2546 ◽  
Author(s):  
Ning Shi ◽  
Xiaoqiong Wang ◽  
Leying Zhang ◽  
Haiming Xu
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Wave Train ◽  
Northeast Asia ◽  
Precipitation Anomaly ◽  
Boreal Summer ◽  
Average Life ◽  
Blocking High ◽  
Rossby Wave Propagation

Abstract This study categorized blocking high (BH) episodes during the boreal summer in northeast Asia (40°–70°N, 100°–150°E) into four types according to their wave-breaking features at the dynamic tropopause on the initial day: anticyclonic warm, cyclonic warm, anticyclonic cold, and cyclonic cold. Based on the results of a statistical analysis, it was shown that 1) the anticyclonic-warm type tended to occur in eastern Russia (55°–70°N, 127.5°–142.5°E), whereas the other three types preferentially occurred in the vicinity of Lake Baikal; 2) the two cold types generally were more common than the two warm types; and 3) the average life spans of the two anticyclonic types were longer than those of the two cyclonic types. According to a composite analysis, the four BH types were preceded by different wave train–like anomalies over the Eurasian continent over approximately one week. Correspondingly, each BH type was characterized by distinct Rossby wave propagation features. Interestingly, a northeastward propagation of the Rossby waves around the BHs was evident in the two cyclonic types. This feature differs from the quasi-meridional propagation of Rossby waves originating from suppressed convection activity over subtropical regions documented in previous studies. This study also found that every BH type was accompanied by distinct precipitation anomaly patterns over East Asia, highlighting the necessity of classifying BHs.

scholarly journals Circumglobal Rossby wave patterns during boreal winter highlighted by wavenumber/phase speed spectral analysis

2021 ◽  
Author(s):  
Jacopo Riboldi ◽  
Efi Rousi ◽  
Fabio D'Andrea ◽  
Gwendal Rivière ◽  
François Lott
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Spectral Power ◽  
Storm Track ◽  
Phase Speed ◽  
Principal Component ◽  
Boreal Winter ◽  
The Pacific ◽  
Wave Patterns ◽  
The Indian Ocean

Abstract. The classic partitioning between slow-moving, low-wavenumber planetary waves and fast-moving, high-wavenumber synoptic waves is systematically extended by means of a wavenumber/phase speed spectral decomposition to characterize the day-to-day evolution of Rossby wave activity in the upper troposphere. This technique is employed to study the origin and the propagation of circumglobal Rossby wave patterns (CRWPs), amplified Rossby waves stretching across the Northern Hemisphere in the zonal direction and characterized by few, dominant wavenumbers. Principal component analysis of daily anomalies in spectral power allows for two CRWPs to emerge as dominant variability modes in the spectral domain during boreal winter. These modes correspond to the baroclinic propagation of amplified Rossby waves from the Pacific to the Atlantic storm track in a hemispheric flow configuration displaying enhanced meridional gradients of geopotential height over midlatitudes. The first CRWP is forced by tropical convection anomalies over the Indian Ocean and features the propagation of amplified Rossby wave packets over northern midlatitudes, while the second one propagates rapidly over latitudes between 35° N and 55° N and appears to have extratropical origin. Propagation of Rossby waves from the Atlantic eddy-driven jet to the African subtropical jet occurs for both CRWPs following anticyclonic wave breaking.

scholarly journals Rossby Wave Initiation by Recurving Tropical Cyclones in the Western North Pacific

2018 ◽  
Vol 146 (5) ◽  
pp. 1283-1301 ◽  
Author(s):  
Jacopo Riboldi ◽  
Matthias Röthlisberger ◽  
Christian M. Grams
Keyword(s):  
Ab Initio ◽  
Tropical Cyclones ◽  
Rossby Wave ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Rossby Waves ◽  
Boreal Summer ◽  
Large Scale Flow ◽  
Upper Level Jet

Abstract The interaction of recurving tropical cyclones (TCs) with midlatitude Rossby waves during extratropical transition (ET) can significantly alter the midlatitude flow configuration. This study provides a climatological investigation of Rossby wave initiation (RWI) by transitioning TCs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during ET. Recurving TCs interacting with a zonally oriented waveguide in the western North Pacific (WNP) basin from 1979 to 2013 are categorized into cases initiating Rossby waves (TC-RWI) or not (TC-noRWI). Interactions with a zonally oriented waveguide occurred for 22.7% of the recurving TCs, and one-third of these resulted in TC-RWI. In the presence of a TC, the probability of RWI on a zonally oriented waveguide is 3 times larger than in situations without a TC. The occurrence of TC-RWI exhibits a seasonality and is relatively more common during boreal summer than in autumn. We further reveal that a strong preexisting upper-level jet stream, embedded in a deformative large-scale flow pattern, hinders TC-RWI as air from the diabatic outflow of the TC is rapidly advected downstream and does not lead to strong ridge building. In contrast, an enhanced monsoon trough favors TC-RWI as the poleward moisture transport strengthens diabatic outflow and leads to strong ridge building during ET. Thus, we conclude that TC-related ab initio flow amplification over the WNP is governed by characteristics of the large-scale flow more so than by characteristics of the recurving TC.

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