Equatorial waves in the lower stratosphere. II: Annual and interannual variability

2006 ◽  
Vol 132 (614) ◽  
pp. 195-212 ◽  
Author(s):  
J. C. Tindall ◽  
J. Thuburn ◽  
E. J. Highwood
Keyword(s):  
Interannual Variability ◽  
Lower Stratosphere ◽  
Equatorial Waves ◽  
Annual And Interannual Variability

scholarly journals Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

2013 ◽  
Vol 13 (9) ◽  
pp. 4563-4575 ◽  
Author(s):  
T. Flury ◽  
D. L. Wu ◽  
W. G. Read
Keyword(s):  
Time Series ◽  
Interannual Variability ◽  
Lower Stratosphere ◽  
Meridional Circulation ◽  
Time Lag ◽  
Quasi Biennial Oscillation ◽  
One Year ◽  
The Tropics ◽  
Biennial Oscillation ◽  
Stratospheric Water Vapour

Abstract. We use Aura/MLS stratospheric water vapour (H2O) measurements as tracer for dynamics and infer interannual variations in the speed of the Brewer–Dobson circulation (BDC) from 2004 to 2011. We correlate one-year time series of H2O in the lower stratosphere at two subsequent pressure levels (68 hPa, ~18.8 km and 56 hPa, ~19.9 km at the Equator) and determine the time lag for best correlation. The same calculation is made on the horizontal on the 100 hPa (~16.6 km) level by correlating the H2O time series at the Equator with the ones at 40° N and 40° S. From these lag coefficients we derive the vertical and horizontal speeds of the BDC in the tropics and extra-tropics, respectively. We observe a clear interannual variability of the vertical and horizontal branch. The variability reflects signatures of the Quasi Biennial Oscillation (QBO). Our measurements confirm the QBO meridional circulation anomalies and show that the speed variations in the two branches of the BDC are out of phase and fairly well anti-correlated. Maximum ascent rates are found during the QBO easterly phase. We also find that transport of H2O towards the Northern Hemisphere (NH) is on the average two times faster than to the Southern Hemisphere (SH) with a mean speed of 1.15 m s−1 at 100 hPa. Furthermore, the speed towards the NH shows much more interannual variability with an amplitude of about 21% whilst the speed towards the SH varies by only 10%. An amplitude of 21% is also observed in the variability of the ascent rate at the Equator which is on the average 0.2 mm s−1.

scholarly journals Equatorial Waves in Opposite QBO Phases

2011 ◽  
Vol 68 (4) ◽  
pp. 839-862 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian J. Hoskins ◽  
Julia M. Slingo
Keyword(s):  
Group Velocity ◽  
Lower Stratosphere ◽  
Phase Speed ◽  
Kelvin Waves ◽  
Western Hemisphere ◽  
Equatorial Waves ◽  
Vertical Wavelength ◽  
Quasi Biennial Oscillation ◽  
Zonal Wavenumber ◽  
The Waves

Abstract A methodology for identifying equatorial waves is used to analyze the multilevel 40-yr ECMWF Re-Analysis (ERA-40) data for two different years (1992 and 1993) to investigate the behavior of the equatorial waves under opposite phases of the quasi-biennial oscillation (QBO). A comprehensive view of 3D structures and of zonal and vertical propagation of equatorial Kelvin, westward-moving mixed Rossby–gravity (WMRG), and n = 1 Rossby (R1) waves in different QBO phases is presented. Consistent with expectation based on theory, upward-propagating Kelvin waves occur more frequently during the easterly QBO phase than during the westerly QBO phase. However, the westward-moving WMRG and R1 waves show the opposite behavior. The presence of vertically propagating equatorial waves in the stratosphere also depends on the upper tropospheric winds and tropospheric forcing. Typical propagation parameters such as the zonal wavenumber, zonal phase speed, period, vertical wavelength, and vertical group velocity are found. In general, waves in the lower stratosphere have a smaller zonal wavenumber, shorter period, faster phase speed, and shorter vertical wavelength than those in the upper troposphere. All of the waves in the lower stratosphere show an upward group velocity and downward phase speed. When the phase of the QBO is not favorable for waves to propagate, their phase speed in the lower stratosphere is larger and their period is shorter than in the favorable phase, suggesting Doppler shifting by the ambient flow and a filtering of the slow waves. Tropospheric WMRG and R1 waves in the Western Hemisphere also show upward phase speed and downward group velocity, with an indication of their forcing from middle latitudes. Although the waves observed in the lower stratosphere are dominated by “free” waves, there is evidence of some connection with previous tropical convection in the favorable year for the Kelvin waves in the warm water hemisphere and WMRG and R1 waves in the Western Hemisphere, which is suggestive of the importance of convective forcing for the existence of propagating coupled Kelvin waves and midlatitude forcing for the existence of coupled WMRG and R1 waves.

Atmospheric circulation associated with the arrival of sargassum in the Caribbean Sea.

2020 ◽  
Author(s):  
Jose Antonio Salinas ◽  
María Eugenia Maya ◽  
Constantina Hernández
Keyword(s):  
Interannual Variability ◽  
Extreme Values ◽  
Atlantic Coast ◽  
Surface Wind ◽  
Caribbean Sea ◽  
Atmospheric Conditions ◽  
Annual And Interannual Variability ◽  
The Caribbean ◽  
Extreme Winds ◽  
Central Atlantic

<p>The arrival of sargassum in a massive way generates adverse environmental, social and economic impacts. Little is known about its origin and trajectory, as well as the atmospheric and oceanic conditions under which it arrives at the Mexican coasts of the Caribbean. This poster presents a diagnosis of the seasonal, annual and interannual variability of atmospheric circulations in the Atlantic and Caribbean Sea, identifying the atmospheric conditions under which sargassum arrived on the Mexican coasts. 30 years of surface wind data from CFSR (Climate Forecast System Reanalysis) of NCAR on the Atlantic and Caribbean were analyzed, dividing the area into six areas, for each one its seasonal, annual and interannual variability was estimated, as well as its extreme values from 1989 to 2018, focusing the study on both the Caribbean Sea and the Atlantic coast of Brazil.</p><p>Once the mean, extreme winds (10th and 90th percentiles) and their correlation with the NAO (North Atlantic Oscillation) were diagnosed interannually, particular years of the recent period were analyzed: from 2010 to 2019 incorporating the wind convergence as a physical process associated with the accumulation of sargassum, surface pressure and sea surface temperature (SST) and also correlating it with the NAO index.</p><p>The results show that the atmospheric conditions for transporting sargassum along the Mexican coasts of the Caribbean are more favorable in summer than in winter, besides it, the higher extremes (90th percentile) in the Caribbean favor the transport of sargassum both in winter and in summer. However, "connectivity" with other regions (Central Atlantic) makes summer more favorable, but winter is potentially viable. The atmospheric conditions of recent extreme years are discussed: 2013 (without the arrival of sargassum), medium: 2015 and extreme 2018 (with abundant sargassum) for both summer and winter.</p>

scholarly journals Interannual variability of ozone in the winter lower stratosphere and the relationship to lamina and irreversible transport

2010 ◽  
Vol 115 (D15) ◽  
Author(s):  
Mark A. Olsen ◽  
Anne R. Douglass ◽  
Mark R. Schoeberl ◽  
Jose M. Rodriquez ◽  
Yasuko Yoshida
Keyword(s):  
Interannual Variability ◽  
Lower Stratosphere ◽  
The Relationship

Morphology of Tropical Upwelling in the Lower Stratosphere

2008 ◽  
Vol 65 (7) ◽  
pp. 2360-2374 ◽  
Author(s):  
Marvin A. Geller ◽  
Tiehan Zhou ◽  
Kevin Hamilton
Keyword(s):  
Interannual Variability ◽  
Climate Models ◽  
Lower Stratosphere ◽  
Surf Zone ◽  
Mechanistic Model ◽  
Wave Drag ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Stratospheric Water Vapor ◽  
Sensitivity Tests ◽  
Mean Meridional Circulation

Abstract Sensitivity tests of a mechanistic model of the mean meridional circulation driven by specified eddy forcing are conducted to investigate how the morphology of tropical upwelling in the lower stratosphere is related to the structure of the forcing expected to be associated with the stratospheric surf zone. The basic morphology of tropical upwelling is found to be similar among the mechanistic model forced with reasonable eddy fluxes, the Geophysical Fluid Dynamics Laboratory (GFDL) SKYHI GCM, U.K. Met Office (UKMO) analyses, and other climate models, indicating the robustness of the upwelling features. Atmospheric data are analyzed to characterize the interannual variability of wave drag. The influence of such variations on the interannual variability of tropical upwelling in the lower stratosphere is explored, which may help explain the observed interannual variability of stratospheric water vapor.

scholarly journals On the presence of equatorial waves in the lower stratosphere of a general circulation model

2013 ◽  
Vol 13 (8) ◽  
pp. 22607-22637 ◽  
Author(s):  
P. Maury ◽  
F. Lott
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Lower Stratosphere ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Kelvin Waves ◽  
Flux Analysis ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
The Waves

Abstract. To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby-gravity waves are also very close but significantly weaker than in observations. We demonstrate that this bias on the Rossby-gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward: during a westward phase of the QBO, the Rossby-gravity waves in ERA-Interim compare well with those in the model. These results suggest that in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering and the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions whereas in the ERA-Interim reanalysis the sources are more equatorial. We also show that non-equatorial sources are significant in reanalysis data, and we consider the case of the Rossby-gravity waves. We identify situations in the reanalysis where here are large Rossby-gravity waves in the middle stratosphere, and for dates when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a "stratospheric reloading".

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