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Rossby waves (RW) propagation due to a local forcing is one of the mechanisms responsible for wave trains configurations known as teleconnections. The term teleconnection refers to anomalies patterns that are correlated in several...
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Rossby waves (RW) propagation due to a local forcing is one of the mechanisms responsible for wave trains configurations known as teleconnections. The term teleconnection refers to anomalies patterns that are correlated in several regions of the world, causing large-scale changes in atmospheric waves patterns and temperature and precipitation regimes. The aim of teleconnections studies is to provide a better understanding of atmospheric variability and their mechanisms of action in order to identify patterns that can be tracked and predicted. The purpose of this study was to characterize seasonal and spatial variability of atmospheric RW sources. The RW source at 200 hPa was calculated for the four seasons with reanalysis data of zonal and meridional wind. In the Northern Hemisphere (NH), the RW sources were located on East Asia, North America, North Atlantic and Pacific. The main RW sources in the Southern Hemisphere (SH) were located over Intertropical, South Pacific, South Atlantic and South Indian Convergence Zones. Extratropical regions were also identified, mainly to the south of Australia. The vortex stretching term (51) and the advec-tion of absolute vorticity by the divergent wind (52) were analyzed to discuss the physical mechanisms for RW generation. In the NH, the source at East Asia in DJF changed to a sink in JJA, related to the dominance of 51 term in DJF and 52 term in JJA. In the SH, the vortex stretching term had the dominant contribution for RW source located to the south of Australia. The main forcing for RW sources at east of Australia was the advection of absolute vorticity by divergent flow. Over South America, both terms contributed to the source in DJF. The main modes of RW source variability were discussed by using empirical orthogonal functions analysis. RW variability was characterized by wave trains configurations in both hemispheres over regions of jet streams and storm tracks, associated with favorable and unfavorable areas for RW generation.
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Argo float trajectory data has been used to estimate the velocities of mid-depth (1000 db) currents in the North Indian Ocean (NIO). The structure of the upper ocean absolute geostmphic currents can be derived more accurately from...
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Argo float trajectory data has been used to estimate the velocities of mid-depth (1000 db) currents in the North Indian Ocean (NIO). The structure of the upper ocean absolute geostmphic currents can be derived more accurately from the Argo temperature and salinity profiles by referring to the estimated velocities rather than by assuming a level of "no motion". The derived flow field reveals that the eastward zonal velocities generate striation-like structures in the Arabian Sea, which is most prominent above the layer of 500 db layer, with a meridional scale of similar to 300 km; however, such structures are barely observed in the Bay of Bengal. This meridional scale as well as the distribution of the mid-depth striations are unique to the NIO, as compared with the other ocean basins. The nonlinear 1 1/2-layer reduced-gravity model combined with the triad baroclinic Rossby wave interaction theory have been used to determine the essential factors controlling the characteristics of the quasizonal striation structure. Compared with the North Pacific Ocean, the meridional scale in the NIO is narrower, and is caused by the smaller basin size in the equatorial zone, rather than by the semiannual wind stress forcing period or the eastern boundary angle. Furthermore, the coastal trapped Kelvin waves significantly contribute to the generation of the zonal striations in the Arabian Sea.
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Several previous studies have reported significant El Nino Southern Oscillation (ENSO) signals in precipitation fields over the Mediterranean region during boreal summer and autumn. However, responsible physical mechanisms are unc...
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Several previous studies have reported significant El Nino Southern Oscillation (ENSO) signals in precipitation fields over the Mediterranean region during boreal summer and autumn. However, responsible physical mechanisms are unclear. In this study,we report significant simultaneous ENSO signals in ship-observed visible-sky conditions over the north-eastern Atlantic and western Mediterranean Sea (WM) during late summer and autumn in 1956-95, consistent with previous studies of precipitation. This remote correlation was stronger in 1956-75 than in 1976-95 and 30-year moving average correlations were stronger throughout the 1956-95 epoch than at any other time over the last 120 years. Previous epochs of relatively weak positive and negative correlation occurred between 1890 and 1920 and between 1920 and 1950, respectively. Analysis of atmospheric flows during 1956-95 indicates that the strong ENSO-WM correlation in the August-October season arises from a previously unreported quasi-stationary Rossby wave propagating eastwards from the western equatorial Pacific. This component weakens between 1956-75 and 1976-95, consistent with the reduced correlation of the ENSO-WM sky conditions between the same periods. In order to fully understand the observed long-term variations of remote ENSO correlation over the WM, further studies are required, including the potential roles of the Pacific Decadal Oscillation, Sahelian rainfall and Atlantic sea surface temperature.
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Shelf break canyons on the west coast of Canada and the United States have been observed to be regions of enhanced upwelling during southward currents compared to the surrounding shelf break. Most shelf break canyons from Oregon n...
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Shelf break canyons on the west coast of Canada and the United States have been observed to be regions of enhanced upwelling during southward currents compared to the surrounding shelf break. Most shelf break canyons from Oregon north cross only part of the continental shelf cutting from the shelf break toward the coast but end on the continental shelf well below the mixed layer. Juan de Fuca canyon, on the other hand, cuts the continental shelf from the slope to, and actually continues into, the Strait of Juan de Fuca. This difference in geometry has a very strong effect on the subinertial flow around the canyon. Model canyon shapes, which include convergent bathymetric contours, are constructed and motivated for Juan de Fuca canyon and a typical shelf break canyon. Geostrophic analytic solutions show that the in-canyon flow in Juan de Fuca canyon is generated by first-order geostrophic dynamics, whereas in the majority of canyons, of which Astoria is an example, in-canyon flow is generated by higher-order effects. This difference is postulated to lead to the observed, very deep upwelling over Juan de Fuca canyon compared to more moderate, episodic upwelling over Astoria canyon. [References: 13]
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According to the freely linear Rossby wave theory, global 1° x 1° climatology of Rossby deformation radius and phase speed are studied under the flat bottom fluid approximation. Geographical variations in the contours of the pha...
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According to the freely linear Rossby wave theory, global 1° x 1° climatology of Rossby deformation radius and phase speed are studied under the flat bottom fluid approximation. Geographical variations in the contours of the phase speed are very similar to those of the Rossby radius of formation, which are mainly affected by stratification, rotation, water depth, topography, etc. The basin-crossing time of the first baroclinic Rossby wave is obtained and analyzed in the global ocean basins. The results are useful to learn the importance of Rossby wave and the adiabatic adjustment of large-scale ocean circulation.
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The link between Rossby wave breaking (RWB) and the four wintertime weather regimes over the North Atlantic domain is studied in this paper. Using the 40-yr ECMWF Re-Analysis (ERA-40) data, frequencies of occurrence of anticycloni...
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The link between Rossby wave breaking (RWB) and the four wintertime weather regimes over the North Atlantic domain is studied in this paper. Using the 40-yr ECMWF Re-Analysis (ERA-40) data, frequencies of occurrence of anticyclonic and cyclonic wave-breaking (AWB and CWB, respectively) events are computed. Each weather regime has its own characteristic pattern of RWB frequencies. CWB events are found to be most frequent for the Greenland anticyclone weather regime whereas AWB events occur more for the Atlantic ridge and the zonal regimes. Time-lagged composites show that the RWB events characterizing each weather regime occur more often during the formation of the regime rather than during its decay. This suggests a reinforcement of the weather regime by RWB. An exception is the blocking weather regime, which is destroyed by an increase of CWB events south of Greenland. Weather regime transitions are then studied using the low-frequency streamfunction tendency budget. Two types of precursors for the transitions have been identified. One is related to linear propagation of low-frequency transient eddies and the other to nonlinear interactions among the low-and high-frequency transient eddies. The latter has been related to the anomalous frequencies of occurrence of RWB. Two transitions are more precisely analyzed. The transition from blocking to Greenland anticyclone is triggered by a decrease of AWB events over Europe as well as a strong CWB event south of Greenland. The zonal to blocking transition presents evidence of two distinct precursors: one is a low-frequency wave train coming from the subtropical western Atlantic and the other, which occurs later, is characterized by a decrease of AWB and CWB events over western Europe that cannot continue to maintain the westerlies in that region.
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To better understand the potential effects of climate change on atmospheric dynamics, this paper studies Rossby wave breaking and isentropic stratosphere-troposphere exchange (STE) in the Northern Hemisphere between 320 and 380 K ...
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To better understand the potential effects of climate change on atmospheric dynamics, this paper studies Rossby wave breaking and isentropic stratosphere-troposphere exchange (STE) in the Northern Hemisphere between 320 and 380 K during 1981-2015 using the Modern-Era Retrospective Analysis for Research and Application version 2 data. The isentropic STE is estimated using Contour Advection. Our results show that anticyclonic wave breaking events have become more frequent, especially in summer at higher isentropic surfaces, and cyclonic wave breaking events have become less frequent at 320 K. The anticyclonic wave breaking has shifted poleward in summer. The isentropic STE is found to be strongest over the regions where Rossby wave breaking activities are most frequent. Both isentropic STE and Rossby wave breaking are shown to be strongest in summer and weakest in winter. Our results do not show any discernable trends during isentropic STE during 1981-2015.
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Midlatitude Rossby waves substantiated in the upper tropospheric (300-200 hPa) potential vorticity field exert significant influences on surface conditions. The physical changes associated with the propagation of Rossby waves are ...
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Midlatitude Rossby waves substantiated in the upper tropospheric (300-200 hPa) potential vorticity field exert significant influences on surface conditions. The physical changes associated with the propagation of Rossby waves are investigated from a climatological perspective, particularly over the oceans. Detailed analysis quantitatively shows that the passing of positive Rossby waves with cyclonic vortexes increases net shortwave and longwave radiation over an ocean's surface by promoting a clearer sky condition. Further, the reduced humidity and temperature above the sea surface increases latent and sensible heat fluxes. The increased latent and sensible heat fluxes, in turn, induce secondary atmospheric circulation, characterized by anticyclonic and divergent motion in the lower atmospheric layer above the sea surface. Although the increased latent and sensible heat fluxes may change sea surface temperatures, the complexity of ocean dynamics with complicated land-ocean configurations and the mismatch of the temporal and spatial scales of atmospheric and oceanic motions smears the footprint of Rossby waves.
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The first baroclinic Rossby radius of deformation (R_1) is a fundamental horizontal scale of mesoscale processes. This scale is important for planning both numerical modelling and study areas.
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Simulated current velocity and long-term reanalysis wind data are used to investigate interannual variations in the bifurcation of the Pacific North Equatorial Current (NEC) after the 1976 climate regime shift. Wind stress curl an...
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Simulated current velocity and long-term reanalysis wind data are used to investigate interannual variations in the bifurcation of the Pacific North Equatorial Current (NEC) after the 1976 climate regime shift. Wind stress curl anomaly (WSCA) in the region of 10°N–15°N and 160°E–170°E generates Rossby waves and affects the NEC bifurcation along the Philippine coast. From 1976 to 1992, following a regime shift to the positive Pacific Decadal Oscillation (PDO) phase, PDO and El Ni~no-Southern Oscillation (ENSO) match each other in strength and have a neutralized effect on the WSCA. From 1993 to 2009, WSCA matches PDO well, and its correlation with ENSO is lower. Using a linear regression model, we show that the influence of PDO has nearly 13 times weight over that of ENSO. Prior to the 1976 regime shift, WSCA is closely related to ENSO from 1961 to 1975, and it does not correlate significantly with PDO. Our analysis results show that Rossby waves are preferentially generated in either the negative PDO phase when the ENSO signal dominates, or in the positive PDO phase when the ENSO signal is overshadowed. In the phase when the positive PDO counteracts with the ENSO signal, neither ENSO nor PDO has a significant influence on Rossby wave generations through the WSCA.
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