scholarly journals Dynamics of the Disrupted 2015/16 Quasi-Biennial Oscillation

2017 ◽  
Vol 30 (15) ◽  
pp. 5661-5674 ◽  
Author(s):  
Lawrence Coy ◽  
Paul A. Newman ◽  
Steven Pawson ◽  
Leslie R. Lait
Keyword(s):  
Lower Stratosphere ◽  
Global Climate ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Wind Variability ◽  
Momentum Fluxes ◽  
Horizontal Momentum ◽  
The Tropics ◽  
Global Reanalysis ◽  
Biennial Oscillation

A significant disruption of the quasi-biennial oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015/16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here this disruptive event is examined using global reanalysis winds and temperatures from 1980 to 2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015/16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40-hPa level. Two additional NH winters, 1987/88 and 2010/11, were also found to have large tropical lower-stratospheric momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases.

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 Variability of the Brewer-Dobson circulation's meridional and vertical branch using Aura/MLS water vapor

2012 ◽  
Vol 12 (8) ◽  
pp. 21291-21320 ◽  
Author(s):  
T. Flury ◽  
D. L. Wu ◽  
W. G. Read
Keyword(s):  
Time Series ◽  
Water Vapor ◽  
Lower Stratosphere ◽  
Meridional Circulation ◽  
Time Lag ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Water Vapor ◽  
One Year ◽  
The Tropics ◽  
Biennial Oscillation

Abstract. We use Aura/MLS stratospheric water vapor measurements to infer interannual variations in the speed of the Brewer-Dobson circulation (BDC) from 2004 to 2011. Stratospheric water vapor (H2O) is utilized as a tracer for dynamics and we follow its path along the vertical and meridional branch of the BDC from the tropics to mid-latitudes. We correlate one year time series of H2O in the lower stratosphere at two subsequent altitude 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 the transport 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 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 and hence about 5000 times slower than the meridional branch.

scholarly journals On the forcings of the unusual Quasi-Biennial Oscillation structure in February 2016

2020 ◽  
Vol 20 (11) ◽  
pp. 6541-6561
Author(s):  
Haiyan Li ◽  
Robin Pilch Kedzierski ◽  
Katja Matthes
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Lower Stratosphere ◽  
Wave Activity ◽  
Kelvin Waves ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
The Tropics ◽  
First Time ◽  
Biennial Oscillation

Abstract. The westerly phase of the stratospheric Quasi-Biennial Oscillation (QBO) was reversed during Northern Hemisphere winter 2015/2016 for the first time since records began in 1953. Recent studies proposed that Rossby waves propagating from the extratropics played an important role during the reversal event in 2015/2016. Building upon these studies, we separated the extratropical Rossby waves into different wavenumbers and timescales by analyzing the combined ERA-40 and ERA-Interim reanalysis zonal wind, meridional wind, vertical velocity, and potential vorticity daily mean data from 1958 to 2017. We find that both synoptic and quasi-stationary Rossby waves are dominant contributors to the reversal event in 2015/2016 in the tropical lower stratosphere. By comparing the results for 2015/2016 with two additional events (1959/1960 and 2010/2011), we find that the largest differences in Rossby wave momentum fluxes are related to synoptic-scale Rossby waves of periods from 5 to 20 d. We demonstrate for the first time, that these enhanced synoptic Rossby waves at 40 hPa in the tropics in February 2016 originate from the extratropics as well as from local wave generation. The strong Rossby wave activity in 2016 in the tropics happened at a time with weak westerly zonal winds. This coincidence of anomalous factors did not happen in any of the previous events. In addition to the anomalous behavior in the tropical lower stratosphere in 2015/2016, we explored the forcing of the unusually long-lasting westerly zonal wind phase in the middle stratosphere (at 20 hPa). Our results reveal that mainly enhanced Kelvin wave activity contributed to this feature. This was in close relation with the strong El Niño event in 2015/2016, which forced more Kelvin waves in the equatorial troposphere. The easterly or very weak westerly zonal winds present around 30–70 hPa allowed these Kelvin waves to propagate vertically and deposit their momentum around 20 hPa, maintaining the westerlies there.

scholarly journals The Effects of Changes in Sea Surface Temperature and CO2 Concentration on the Quasi-Biennial Oscillation

2012 ◽  
Vol 69 (5) ◽  
pp. 1734-1749 ◽  
Author(s):  
Yoshio Kawatani ◽  
Kevin Hamilton ◽  
Akira Noda
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Equatorial Region ◽  
Sea Surface ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
The Future ◽  
Biennial Oscillation

Abstract The effects of sea surface temperature (SST) and CO2 on future changes in the quasi-biennial oscillation (QBO) are investigated using a climate model that simulates the QBO without parameterized nonstationary gravity wave forcing. Idealized model experiments using the future SST with the present CO2 (FS run) and the present SST with the future CO2 (FC run) are conducted, as are experiments using the present SST with the present CO2 (present run) and the future SST with the future CO2 (future run). When compared with the present run, precipitation increases around the equatorial region in the FS run and decreases in the FC run, resulting in increased and decreased wave momentum fluxes, respectively. In the midlatitude lower stratosphere, westward (eastward) wave-forcing anomalies form in the FS (FC) run. In the middle stratosphere off the equator, westward wave-forcing anomalies form in both the FS and FC runs. Corresponding to these wave-forcing anomalies, the residual vertical velocity significantly increases in the lower stratosphere in the FS run but decreases to below 70 hPa in the FC run, whereas residual upward circulation anomalies form in both the FS and FC runs in the middle equatorial stratosphere. Consequently, the amplitude of the QBO becomes smaller in the lower stratosphere, and the period of the QBO becomes longer by about 1–3 months in the FS run. On the other hand, in the FC run, the QBO extends farther downward into the lowermost stratosphere, and the period becomes longer by 1 month.

scholarly journals The Climatology of the Middle Atmosphere in a Vertically Extended Version of the Met Office’s Climate Model. Part II: Variability

2010 ◽  
Vol 67 (11) ◽  
pp. 3637-3651 ◽  
Author(s):  
Scott M. Osprey ◽  
Lesley J. Gray ◽  
Steven C. Hardiman ◽  
Neal Butchart ◽  
Andrew C. Bushell ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Global Climate ◽  
Global Climate Model ◽  
Occurrence Rate ◽  
Extended Version ◽  
Quasi Biennial Oscillation ◽  
Annular Modes ◽  
Biennial Oscillation

Abstract Stratospheric variability is examined in a vertically extended version of the Met Office global climate model. Equatorial variability includes the simulation of an internally generated quasi-biennial oscillation (QBO) and semiannual oscillation (SAO). Polar variability includes an examination of the frequency of sudden stratospheric warmings (SSW) and annular mode variability. Results from two different horizontal resolutions are also compared. Changes in gravity wave filtering at the higher resolution result in a slightly longer QBO that extends deeper into the lower stratosphere. At the higher resolution there is also a reduction in the occurrence rate of sudden stratospheric warmings, in better agreement with observations. This is linked with reduced levels of resolved waves entering the high-latitude stratosphere. Covariability of the tropical and extratropical stratosphere is seen, linking the phase of the QBO with disturbed NH winters, although this linkage is sporadic, in agreement with observations. Finally, tropospheric persistence time scales and seasonal variability for the northern and southern annular modes are significantly improved at the higher resolution, consistent with findings from other studies.

scholarly journals Tropical troposphere to stratosphere transport of carbon monoxide and long-lived trace species in the Chemical Lagrangian Model of the Stratosphere (CLaMS)

2014 ◽  
Vol 7 (4) ◽  
pp. 5087-5139 ◽  
Author(s):  
R. Pommrich ◽  
R. Müller ◽  
J.-U. Grooß ◽  
P. Konopka ◽  
F. Ploeger ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Lagrangian Model ◽  
Quasi Biennial Oscillation ◽  
Data Set ◽  
Model Version ◽  
The Tropics ◽  
The Impact ◽  
Good Agreement

Abstract. Variations in the mixing ratio of trace gases of tropospheric origin entering the stratosphere in the tropics are of interest for assessing both troposphere to stratosphere transport fluxes in the tropics and the impact of these transport fluxes on the composition of the tropical lower stratosphere. Anomaly patterns of carbon monoxide (CO) and long-lived tracers in the lower tropical stratosphere allow conclusions about the rate and the variability of tropical upwelling to be drawn. Here, we present a simplified chemistry scheme for the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the simulation, at comparatively low numerical cost, of CO, ozone, and long-lived trace substances (CH4, N2O, CCl3F (CFC-11), CCl2F2 (CFC-12), and CO2) in the lower tropical stratosphere. For the long-lived trace substances, the boundary conditions at the surface are prescribed based on ground-based measurements in the lowest model level. The boundary condition for CO in the free troposphere is deduced from MOPITT measurements (at ≈ 700–200 hPa). Due to the lack of a specific representation of mixing and convective uplift in the troposphere in this model version, enhanced CO values, in particular those resulting from convective outflow are underestimated. However, in the tropical tropopause layer and the lower tropical stratosphere, there is relatively good agreement of simulated CO with in-situ measurements (with the exception of the TROCCINOX campaign, where CO in the simulation is biased low ≈ 10–20 ppbv). Further, the model results are of sufficient quality to describe large scale anomaly patterns of CO in the lower stratosphere. In particular, the zonally averaged tropical CO anomaly patterns (the so called "tape recorder" patterns) simulated by this model version of CLaMS are in good agreement with observations. The simulations show a too rapid upwelling compared to observations as a consequence of the overestimated vertical velocities in the ERA-interim reanalysis data set. Moreover, the simulated tropical anomaly patterns of N2O are in good agreement with observations. In the simulations, anomaly patterns for CH4 and CFC-11 were found to be consistent with those of N2O; for all long-lived tracers, positive anomalies are simulated because of the enhanced tropical upwelling in the easterly phase of the quasi-biennial oscillation.

Large internal variability dominates over global warming signal in observed lower stratospheric QBO amplitude

2021 ◽  
pp. 1-43
Author(s):  
Aaron Match ◽  
Stephan Fueglistaler
Keyword(s):  
Global Warming ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Internal Variability ◽  
Dynamical Process ◽  
Quasi Biennial Oscillation ◽  
Amplitude Profile ◽  
Biennial Oscillation ◽  
Middle Stratosphere

AbstractGlobal warming projections of dynamics are less robust than projections of thermodynamics. However, robust aspects of the thermodynamics can be used to constrain some dynamical aspects. This paper argues that tropospheric expansion under global warming (a thermodynamical process) explains changes in the amplitude of the Quasi-Biennial Oscillation (QBO) in the lower and middle stratosphere (a dynamical process). A theoretical scaling for tropospheric expansion of approximately 6 hPa K−1 is derived, which agrees well with global climate model (GCM) experiments. Using this theoretical scaling, the response of QBO amplitude to global warming is predicted by shifting the climatological QBO amplitude profile upwards by 6 hPa per Kelvin of global warming. In global warming simulations, QBO amplitude in the lower- to mid-stratosphere shifts upwards as predicted by tropospheric expansion. Applied to observations, the tropospheric expansion framework suggests a historical weakening of QBO amplitude at 70 hPa of 3% decade−1 from 1953-2020. This expected weakening trend is half of the 6% decade−1 from 1953-2012 detected and attributed to global warming in a recent study. The previously reported trend was reinforced by record low QBO amplitudes during the mid-2000s, from which the QBO has since recovered. Given the modest weakening expected on physical grounds, past decadal modulations of QBO amplitude are reinterpreted as a hitherto unrecognized source of internal variability. This large internal variability dominates over the global warming signal, such that despite 65 years of observations, there is not yet a statistically significant weakening trend.

scholarly journals Tropical Waves and the Quasi-Biennial Oscillation in a 7-km Global Climate Simulation

2016 ◽  
Vol 73 (9) ◽  
pp. 3771-3783 ◽  
Author(s):  
Laura A. Holt ◽  
M. Joan Alexander ◽  
Lawrence Coy ◽  
Andrea Molod ◽  
William Putman ◽  
...  
Keyword(s):  
General Circulation ◽  
Shear Zones ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Healthy Population ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Tropical Waves ◽  
Biennial Oscillation ◽  
Very High

Abstract This study investigates tropical waves and their role in driving a quasi-biennial oscillation (QBO)-like signal in stratospheric winds in a global 7-km-horizontal-resolution atmospheric general circulation model. The Nature Run (NR) is a 2-yr global mesoscale simulation of the Goddard Earth Observing System Model, version 5 (GEOS-5). In the tropics, there is evidence that the NR supports a broad range of convectively generated waves. The NR precipitation spectrum resembles the observed spectrum in many aspects, including the preference for westward-propagating waves. However, even with very high horizontal resolution and a healthy population of resolved waves, the zonal force provided by the resolved waves is still too low in the QBO region and parameterized gravity wave drag is the main driver of the NR QBO-like oscillation (NR-QBO). The authors suggest that causes include coarse vertical resolution and excessive dissipation. Nevertheless, the very-high-resolution NR provides an opportunity to analyze the resolved wave forcing of the NR-QBO. In agreement with previous studies, large-scale Kelvin and small-scale waves contribute to the NR-QBO driving in eastward shear zones and small-scale waves dominate the NR-QBO driving in westward shear zones. Waves with zonal wavelength < 1000 km account for up to half of the small-scale (<3300 km) resolved wave forcing in eastward shear zones and up to 70% of the small-scale resolved wave forcing in westward shear zones of the NR-QBO.

scholarly journals Momentum forcing of the quasi-biennial oscillation by equatorial waves in recent reanalyses

2015 ◽  
Vol 15 (12) ◽  
pp. 6577-6587 ◽  
Author(s):  
Y.-H. Kim ◽  
H.-Y. Chun
Keyword(s):  
Gravity Wave ◽  
Transition Phase ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Opposite Phase ◽  
Level Data ◽  
Equatorial Wave ◽  
Biennial Oscillation ◽  
Wave Modes

Abstract. The momentum forcing of the QBO (quasi-biennial oscillation) by equatorial waves is estimated using recent reanalyses. Based on the estimation using the conventional pressure-level data sets, the forcing by the Kelvin waves (3–9 m s−1 month−1) dominates the net forcing by all equatorial wave modes (3–11 m s−1 month−1) in the easterly-to-westerly transition phase at 30 hPa. In the opposite phase, the net forcing by equatorial wave modes is small (1–5 m s−1 month−1). By comparing the results with those from the native model-level data set of the ERA-Interim reanalysis, it is suggested that the use of conventional-level data causes the Kelvin wave forcing to be underestimated by 2–4 m s−1 month−1. The momentum forcing by mesoscale gravity waves, which are unresolved in the reanalyses, is deduced from the residual of the zonal wind tendency equation. In the easterly-to-westerly transition phase at 30 hPa, the mesoscale gravity wave forcing is found to be smaller than the resolved wave forcing, whereas the gravity wave forcing dominates over the resolved wave forcing in the opposite phase. Finally, we discuss the uncertainties in the wave forcing estimates using the reanalyses.

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