Teleconnections from Tropics to Northern Extratropics through a Southerly Conveyor

2005 ◽  
Vol 62 (11) ◽  
pp. 4057-4070 ◽  
Author(s):  
Zhuo Wang ◽  
C-P. Chang ◽  
Bin Wang ◽  
Fei-Fei Jin
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Propagation Theory ◽  
Wave Source ◽  
Tropical Forcing ◽  
Rossby Wave Source ◽  
Rossby Wave Response ◽  
Rossby Wave Propagation ◽  
The Tropics

Abstract Rossby wave propagation theory predicts that Rossby waves in a tropical easterly flow cannot escape from the Tropics to the extratropics. Here the authors show that a southerly flow component in the basic state (a southerly conveyor) may transfer a Rossby wave source northward; thus, a forcing embedded in the deep tropical easterlies may excite a Rossby wave response in the extratropical westerlies. It is shown that the southerly conveyor determines the location of the effective Rossby wave source and that the extratropical response is relatively insensitive to the location of the tropical forcing, provided that the tropical response can reach the southerly conveyor. A stronger southerly flow favors a stronger extratropical response, and the spatial structure of the extratropical response is determined by the extratropical westerly basic flows.

A more complete Rossby wave source

2020 ◽  
Author(s):  
Wolfgang Wicker ◽  
Richard Greatbatch
Keyword(s):  
Rossby Wave ◽  
Source Region ◽  
Absolute Vorticity ◽  
Wave Source ◽  
Upper Troposphere ◽  
Rossby Wave Source ◽  
Vorticity Advection ◽  
Order Of Magnitude ◽  
Wave Trains ◽  
The Tropics

<p>Tropical convection drives extratropical variability on subseasonal to interannual time-scales by exciting Rossby wave trains in the upper troposphere. Traditionally the relevant Rossby wave source is considered to be the sum of vortex stretching and vorticity advection by the divergent horizontal flow ( - ∇·<strong>u</strong><sub>χ</sub> (ζ+f) - <strong>u</strong><sub>χ</sub>·∇ (ζ+f)). Since absolute vorticity is very small at the equator, the equatorward flanks of the upper tropospheric jets have been regarded the source region of Rossby wave trains. In these considerations vertical momentum advection is neglected, although, it is an important source for westerly momentum at the equator. The curl of vertical momentum advection is the sum of vertical vorticity advection and vortex tilting ( -  ω ζ<sub>p</sub> - ω<sub>x</sub> v<sub>p</sub> + ω<sub>y</sub> u<sub>p</sub>). These contributions are smaller than the traditional Rossby wave source in midlatidues by about one order of magnitude but they are of similar size in the tropics.</p>

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 On the Seasonality of the El Niño Teleconnection to the Amundsen Sea Region

2019 ◽  
Vol 32 (15) ◽  
pp. 4829-4845 ◽  
Author(s):  
Yu Yeung Scott Yiu ◽  
Amanda C. Maycock
Keyword(s):  
Rossby Wave ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Austral Summer ◽  
South Pacific ◽  
Austral Winter ◽  
Amundsen Sea ◽  
Wave Source ◽  
Rossby Wave Source

Abstract The Amundsen Sea low (ASL) is a quasi-stationary low pressure system that affects climate in West Antarctica. Previous studies have shown that El Niño–Southern Oscillation (ENSO) modulates the position and strength of the ASL with the strongest teleconnection found in austral winter despite the amplitude of ENSO events generally being largest in austral autumn/summer. This study investigates the mechanisms behind the seasonality of the El Niño teleconnection to the Amundsen Sea region (ASR) using experiments with the HadGEM3 climate model forced with an idealized fixed El Niño sea surface temperature anomaly present throughout the year. The seasonality of the El Niño–ASR teleconnection is found to originate from seasonal differences in the large-scale zonal winds in the South Pacific sector. In austral winter, the region of strong absolute vorticity near ~30°S associated with the subtropical jet, in combination with the changes to upper-tropospheric divergence due to the El Niño perturbation, acts as an anomalous Rossby wave source that is largely absent in austral summer. Furthermore, in austral summer the poleward propagation of tropically sourced Rossby waves into the ASR is inhibited by the strong polar front jet in the South Pacific sector, which leads to Rossby wave reflection away from the ASR. In austral winter, Rossby waves are able to propagate into the ASR, forming part of the Pacific South America pattern. The lack of the Rossby wave source in the tropical Pacific and the absence of favorable conditions for wave propagation explains the weaker El Niño–ASR teleconnection in austral summer compared to austral winter.

scholarly journals Rossby wave propagation on potential vorticity fronts with finite width

2016 ◽  
Vol 794 ◽  
pp. 775-797 ◽  
Author(s):  
B. J. Harvey ◽  
J. Methven ◽  
M. H. P. Ambaum
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Rossby Waves ◽  
Phase Speed ◽  
Single Layer ◽  
Horizontal Gradient ◽  
Finite Width ◽  
Numerical Weather ◽  
Rossby Wave Propagation

The horizontal gradient of potential vorticity (PV) across the tropopause typically declines with lead time in global numerical weather forecasts and tends towards a steady value dependent on model resolution. This paper examines how spreading the tropopause PV contrast over a broader frontal zone affects the propagation of Rossby waves. The approach taken is to analyse Rossby waves on a PV front of finite width in a simple single-layer model. The dispersion relation for linear Rossby waves on a PV front of infinitesimal width is well known; here, an approximate correction is derived for the case of a finite-width front, valid in the limit that the front is narrow compared to the zonal wavelength. Broadening the front causes a decrease in both the jet speed and the ability of waves to propagate upstream. The contribution of these changes to Rossby wave phase speeds cancel at leading order. At second order the decrease in jet speed dominates, meaning phase speeds are slower on broader PV fronts. This asymptotic phase speed result is shown to hold for a wide class of single-layer dynamics with a varying range of PV inversion operators. The phase speed dependence on frontal width is verified by numerical simulations and also shown to be robust at finite wave amplitude, and estimates are made for the error in Rossby wave propagation speeds due to the PV gradient error present in numerical weather forecast models.

Does Topographic Form Stress Impede Prograde Ocean Currents?

2021 ◽  
Author(s):  
YUE BAI ◽  
YAN WANG ◽  
ANDREW L. STEWART
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Bottom Friction ◽  
Stress Generation ◽  
Momentum Balance ◽  
Mean Flow ◽  
Rossby Wave Propagation ◽  
Circumpolar Current ◽  
Current Systems

AbstractTopographic form stress (TFS) plays a central role in constraining the transport of the Antarctic Circumpolar Current (ACC), and thus the rate of exchange between the major ocean basins. Topographic form stress generation in the ACC has been linked to the formation of standing Rossby waves, which occur because the current is retrograde (opposing the direction of Rossby wave propagation). However, it is unclear whether TFS similarly retards current systems that are prograde (in the direction of Rossby wave propagation), which cannot arrest Rossby waves. An isopycnal model is used to investigate the momentum balance of wind-driven prograde and retrograde flows in a zonal channel, with bathymetry consisting of either a single ridge or a continental shelf and slope with a meridional excursion. Consistent with previous studies, retrograde flows are almost entirely impeded by TFS, except in the limit of flat bathymetry, whereas prograde flows are typically impeded by a combination of TFS and bottom friction. A barotropic theory for standing waves shows that bottom friction serves to shift the phase of the standing wave’s pressure field from that of the bathymetry, which is necessary to produce TFS. The mechanism is the same in prograde and retrograde flows, but is most efficient when the mean flow arrests a Rossby wave with a wavelength comparable to that of the bathymetry. The asymmetry between prograde and retrograde momentum balances implies that prograde current systems may be more sensitive to changes in wind forcing, for example associated with climate shifts.

scholarly journals Influence of the Background State on Rossby Wave Propagation into the Great Lakes Region Based on Observations and Model Simulations*

2014 ◽  
Vol 27 (24) ◽  
pp. 9302-9322 ◽  
Author(s):  
Kathleen D. Holman ◽  
David J. Lorenz ◽  
Michael Notaro
Keyword(s):  
Great Lakes ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Lake Superior ◽  
Great Lakes Region ◽  
The Pacific ◽  
Wave Trains ◽  
Rossby Wave Propagation ◽  
Upper Level ◽  
The Tropics

Abstract The authors investigate the relationship between hydrology in the Great Lakes basin—namely, overlake precipitation and transient Rossby waves—using the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data and historical output from phase 3 of the Coupled Model Intercomparison Project (CMIP3). The preferred path of observed Rossby wave trains associated with overlake precipitation on Lake Superior depends strongly on season and appears to be related to the time-mean, upper-level flow. During summer and fall, the Northern Hemisphere extratropical jet is relatively narrow and acts as a waveguide, such that Rossby wave trains traversing the Great Lakes region travel along the extratropical Pacific and Atlantic jets. During other months, the Pacific jet is relatively broad, which allows more wave activity originating in the tropics to penetrate into the midlatitudes and influence Lake Superior precipitation. Analysis is extended to CMIP3 models and is intended to 1) further understanding of how variations in the mean state influence transient Rossby waves and 2) assess models’ ability to capture observed features, such as wave origin and track. Results indicate that Rossby wave train propagation in twentieth-century simulations can significantly differ by model. Unlike observations, some models do not produce a well-defined jet across the Pacific Ocean during summer and autumn. In these models, some Rossby waves affecting the Great Lakes region originate in the tropics. Collectively, observations and model results show the importance of the time-mean upper-level flow on Rossby wave propagation and therefore on the relative influence of the tropics versus the extratropics on the hydroclimate of the Great Lakes region.

Coupled Interannual Rossby Waves in a Quasigeostrophic Ocean–Atmosphere Model

2007 ◽  
Vol 37 (5) ◽  
pp. 1192-1214 ◽  
Author(s):  
Riccardo Farneti
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Phase Relationship ◽  
Phase Speed ◽  
Middle Latitude ◽  
Mean Flow ◽  
Ocean Atmosphere ◽  
Rossby Wave Propagation ◽  
Atmosphere Model

Abstract Rossby wave propagation is investigated in the framework of an idealized middle-latitude quasigeostrophic coupled ocean–atmosphere model. The Rossby waves are observed to propagate faster than both the classical linear theory (unperturbed solution) and the phase speed estimates when the effect of the zonal mean flow is added (perturbed solution). Moreover, using statistical eigentechniques, a clear coupled Rossby wave mode is identified between a baroclinic oceanic Rossby wave and an equivalent barotropic atmospheric wave. The spatial phase relationship of the coupled wave is similar to the one predicted by Goodman and Marshall, suggesting a positive ocean–atmosphere feedback. It is argued that oceanic Rossby waves can be efficiently coupled to the overlying atmosphere and that the atmospheric coupling is capable of adding an extra speedup to the wave; in fact, when the ocean is simply forced, the Rossby wave propagation speed approaches the perturbed solution.

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