scholarly journals Representation of the Equatorial Stratopause Semiannual Oscillation in Global Atmospheric Reanalyses

2020 ◽  
Author(s):  
Yoshio Kawatani ◽  
Toshihiko Hirooka ◽  
Kevin Hamilton ◽  
Anne K. Smith ◽  
Masatomo Fujiwara
Keyword(s):  
Zonal Wind ◽  
Good Representation ◽  
Polar Regions ◽  
Quasi Biennial Oscillation ◽  
Amplitude Maximum ◽  
Systematic Improvement ◽  
Stratospheric Circulation ◽  
Biennial Oscillation ◽  
Semiannual Oscillation

Abstract. This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere among six major global atmospheric reanalysis datasets and with recent satellite SABER and MLS observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD is minimum near the equator and largest in the polar regions. Along the equator the zonal wind SD is smallest around the longitude of Singapore where consistently high-quality near-equatorial radiosonde observations are available. Interestingly the near-Singapore minimum in SD is evident to at least ~ 3 hPa, i.e. considerably higher than the usual ~ 10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as its detailed time variation and the displacement off the equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa. One of the reanalyses in our study also has a version produced without assimilating satellite observations and a comparison of the SAO in these two versions demonstrates the very great importance of satellite derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.

scholarly journals Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses

2020 ◽  
Vol 20 (14) ◽  
pp. 9115-9133
Author(s):  
Yoshio Kawatani ◽  
Toshihiko Hirooka ◽  
Kevin Hamilton ◽  
Anne K. Smith ◽  
Masatomo Fujiwara
Keyword(s):  
Zonal Wind ◽  
Good Representation ◽  
Polar Regions ◽  
Quasi Biennial Oscillation ◽  
Amplitude Maximum ◽  
Broadband Emission ◽  
Systematic Improvement ◽  
Stratospheric Circulation ◽  
Semiannual Oscillation

Abstract. This paper reports on a project to compare the representation of the semiannual oscillation (SAO) in the equatorial stratosphere and lower mesosphere within six major global atmospheric reanalysis datasets and with recent satellite Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS) observations. All reanalyses have a good representation of the quasi-biennial oscillation (QBO) in the equatorial lower and middle stratosphere and each displays a clear SAO centered near the stratopause. However, the differences among reanalyses are much more substantial in the SAO region than in the QBO-dominated region. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly mean zonal wind and temperature; this depends on latitude, longitude, height, and time. The zonal wind SD displays a prominent equatorial maximum that increases with height, while the temperature SD reaches a minimum near the Equator and is largest in the polar regions. Along the Equator, the zonal wind SD is smallest around the longitude of Singapore, where consistently high-quality near-equatorial radiosonde observations are available. Interestingly, the near-Singapore minimum in SD is evident to at least ∼3 hPa, i.e., considerably higher than the usual ∼10 hPa ceiling for in situ radiosonde observations. Our measurement of the agreement among the reanalyses shows systematic improvement over the period considered (1980–2016), up to near the stratopause. Characteristics of the SAO at 1 hPa, such as its detailed time variation and the displacement off the Equator of the zonal wind SAO amplitude maximum, differ significantly among the reanalyses. Disagreement among the reanalyses becomes still greater above 1 hPa. One of the reanalyses in our study also has a version produced without assimilating satellite observations, and a comparison of the SAO in these two versions demonstrates the very great importance of satellite-derived temperatures in the realistic analysis of the tropical upper stratospheric circulation.

scholarly journals The Semiannual Oscillation of the Tropical Zonal Wind in the Middle Atmosphere Derived from Satellite Geopotential Height Retrievals

2017 ◽  
Vol 74 (8) ◽  
pp. 2413-2425 ◽  
Author(s):  
Anne K. Smith ◽  
Rolando R. Garcia ◽  
Andrew C. Moss ◽  
Nicholas J. Mitchell
Keyword(s):  
Zonal Wind ◽  
Geopotential Height ◽  
Middle Atmosphere ◽  
Dominant Mode ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
Broadband Emission ◽  
The Tropics ◽  
Biennial Oscillation ◽  
Semiannual Oscillation

Abstract The dominant mode of seasonal variability in the global tropical upper-stratosphere and mesosphere zonal wind is the semiannual oscillation (SAO). However, it is notoriously difficult to measure winds at these heights from satellite or ground-based remote sensing. Here, the balance wind relationship is used to derive monthly and zonally averaged zonal winds in the tropics from satellite retrievals of geopotential height. Data from the Aura Microwave Limb Sounder (MLS) cover about 12.5 yr, and those from the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) cover almost 15 yr. The derived winds agree with direct wind observations below 10 hPa and above 80 km; there are no direct wind observations for validation in the intervening layers of the middle atmosphere. The derived winds show the following prominent peaks associated with the SAO: easterly maxima near the solstices at 1.0 hPa, westerly maxima near the equinoxes at 0.1 hPa, and easterly maxima near the equinoxes at 0.01 hPa. The magnitudes of these three wind maxima are stronger during the first cycle (January at 1.0 hPa and March at 0.1 and 0.01 hPa). The month and pressure level of the wind maxima shift depending on the phase of the quasi-biennial oscillation (QBO) at 10 hPa. During easterly QBO, the westerly maxima are shifted upward, are about 10 m s−1 stronger, and occur approximately 1 month later than those during the westerly QBO phase.

scholarly journals Representation of the Tropical Stratospheric Zonal Wind in Global Atmospheric Reanalyses

2016 ◽  
Author(s):  
Y. Kawatani ◽  
K. Hamilton ◽  
K. Miyazaki ◽  
M. Fujiwara ◽  
J. Anstey
Keyword(s):  
Phase Transitions ◽  
Zonal Wind ◽  
Phase Changes ◽  
Stationary Waves ◽  
Strong Constraint ◽  
Quasi Biennial Oscillation ◽  
Systematic Improvement ◽  
Zonal Wavenumber ◽  
In Situ Observations

Abstract. This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis datasets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50–70 hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the eastern Pacific, where few in situ observations are available. At 10–20 hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed at Singapore. In addition, the timing of the easterly-to-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly mean zonal wind near the equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from mid-latitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered (1979–2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

scholarly journals Future Changes in the Ozone Quasi-Biennial Oscillation with Increasing GHGs and Ozone Recovery in CCMI Simulations

2017 ◽  
Vol 30 (17) ◽  
pp. 6977-6997 ◽  
Author(s):  
Hiroaki Naoe ◽  
Makoto Deushi ◽  
Kohei Yoshida ◽  
Kiyotaka Shibata
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Vertical Shear ◽  
Quasi Biennial Oscillation ◽  
The Past ◽  
Meteorological Research Institute ◽  
Climate Simulations ◽  
The Future ◽  
Ozone Depleting Substances ◽  
Biennial Oscillation

The future quasi-biennial oscillation (QBO) in ozone in the equatorial stratosphere is examined by analyzing transient climate simulations due to increasing greenhouse gases (GHGs) and decreasing ozone-depleting substances under the auspices of the Chemistry–Climate Model Initiative. The future (1960–2100) and historical (1979–2010) simulations are conducted with the Meteorological Research Institute Earth System Model. Three climate periods, 1960–85 (past), 1990–2020 (present), and 2040–70 (future) are selected, corresponding to the periods before, during, and after ozone depletion. The future ozone QBO is characterized by increases in amplitude by 15%–30% at 5–10 hPa and decreases by 20%–30% at 40 hPa, compared with the past and present climates; the future and present ozone QBOs increase in amplitude by up to 60% at 70 hPa, compared with the past climate. The increased amplitude at 5–10 hPa suggests that the temperature-dependent photochemistry plays an important role in the enhanced future ozone QBO. The weakening of vertical shear in the zonal wind QBO is responsible for the decreased amplitude at 40 hPa in the future ozone QBO. An interesting finding is that the weakened zonal wind QBO in the lowermost tropical stratosphere is accompanied by amplified QBOs in ozone, vertical velocity, and temperature. Further study is needed to elucidate the causality of amplification about the ozone and temperature QBOs under climate change in conditions of zonal wind QBO weakening.

scholarly journals Quasi-Biennial Oscillation in Stratospheric Zonal Wind and Indian Summer Monsoon

1985 ◽  
Vol 113 (8) ◽  
pp. 1421-1424 ◽  
Author(s):  
B. K. Mukherjee ◽  
K. Indira ◽  
R. S. Reddy ◽  
Bh V. Ramana Murty
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Zonal Wind ◽  
Quasi Biennial Oscillation ◽  
Biennial Oscillation

The Influence of the Quasi-Biennial Oscillation on the Troposphere in Winter in a Hierarchy of Models. Part I: Simplified Dry GCMs

2011 ◽  
Vol 68 (6) ◽  
pp. 1273-1289 ◽  
Author(s):  
Chaim I. Garfinkel ◽  
Dennis L. Hartmann
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Polar Vortex ◽  
Equation Model ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
Subtropical Jet ◽  
Long Time ◽  
Biennial Oscillation

Abstract A dry primitive equation model is used to explain how the quasi-biennial oscillation (QBO) of the tropical stratosphere can influence the troposphere, even in the absence of tropical convection anomalies and a variable stratospheric polar vortex. QBO momentum anomalies induce a meridional circulation to maintain thermal wind balance. This circulation includes zonal wind anomalies that extend from the equatorial stratosphere into the subtropical troposphere. In the presence of extratropical eddies, the zonal wind anomalies are intensified and extend downward to the surface. The tropospheric response differs qualitatively between integrations in which the subtropical jet is strong and integrations in which the subtropical jet is weak. While fluctuation–dissipation theory provides a guide to predicting the response in some cases, significant nonlinearity in others, particularly those designed to model the midwinter subtropical jet of the North Pacific, prevents its universal application. When the extratropical circulation is made zonally asymmetric, the response to the QBO is greatest in the exit region of the subtropical jet. The dry model is able to simulate much of the Northern Hemisphere wintertime tropospheric response to the QBO observed in reanalysis datasets and in long time integrations of the Whole Atmosphere Community Climate Model (WACCM).

scholarly journals Observational evidences of the influences of tropospheric subtropical and midlatitude stratospheric westerly jets on the equatorial stratospheric intraseasonal oscillations

2016 ◽  
Author(s):  
G. Karthick Kumar Reddy ◽  
T. K. Ramkumar ◽  
S. Venkatramana Reddy
Keyword(s):  
Zonal Wind ◽  
Lower Atmosphere ◽  
Theoretical Modelling ◽  
Quasi Biennial Oscillation ◽  
Medium Range Weather Forecast ◽  
Westerly Jet ◽  
Longitudinal Sector ◽  
Vertical Propagation ◽  
Biennial Oscillation ◽  
Subtropical Westerly Jet

Abstract. Using six Global Positioning System (GPS) Radio Occultation (RO) satellites (SAC-C, METOP-A and COSMIC/FORMOSAT-3, CNOFS, GRACE and TerraSAR-X) determined height profiles (1–40 km) of atmospheric temperature over the Indian tropical station of Gadanki and the European Center for Medium Range Weather Forecast (ECMWF) Interim Reanalyses (ERA-Interim) zonal wind and temperature data for four years (2009–2012), the present work reports that the tropospheric Subtropical Westerly Jet (SWJ) and the Midlatitude Stratospheric Westerly Jet (MStWJ) play important roles in controlling differently the vertical propagation of tropical Intra Seasonal Oscillations (ISO) with different period bands from the troposphere up to the stratosphere during Northern winters. In the months of December–May (Northern winter to summer, NWTS) of all these years, there is significant 10–20 day and 20–40 day oscillations in the troposphere up to the height of 13 km and above this it reappears at all heights above 21 km. The 40–80 day oscillation also shows similar characteristics except that it almost disappeared during NWTS months of the year 2010–2011 in the stratosphere. The absence of these signals in the intervening heights of ~ 17–20 km is explained on the basis that these two bands actually propagate from the tropical to subtropical region near the tropopause and then reappears in the tropical stratosphere after refracted by the subtropical westerly jet. The poleward and equatorward propagation of these bands in the troposphere and stratosphere respectively are found using the ERA-interim data. Further the two longer period bands of ISO show strong quasi-biennial oscillation in the lower atmosphere with opposite phases (when one band shows maximum the other one shows minimum in a particular year) between these two bands. It is also observed that the phase of the tropical stratospheric Quasi Biennial Oscillation (QBO) has significant control on the strength of the Mid latitude stratospheric westerly jet (MStWJ) that in turn controls the refraction of the tropical tropospheric longer (40–80 days, Longer period ISO; LISO) but not the smaller periods of ISO (SISO) back to the tropical stratosphere. In accordance with earlier theoretical modelling studies, the westerly phase of the lower stratospheric QBO occurred during NWTS months of 2010–2011 over the Indian longitudinal sector causes severe disruption of the MStWJ at 30 km height. This disruption caused the prevention of refraction back again to the tropical stratosphere of significant tropospheric LISO that arrived from the tropics through the tropopause. Further, in these four years, it is observed no direct vertical propagation of tropical tropospheric ISO to the stratosphere. The interannual variations in the tropical stratospheric LISO are related strongly to the phase of the equatorial lower stratospheric QBO in zonal wind and the strength of the MStWJ.

scholarly journals Influence of the Quasi-Biennial Oscillation on the Extratropical Winter Stratosphere in an Atmospheric General Circulation Model and in Reanalysis Data

2010 ◽  
Vol 67 (5) ◽  
pp. 1402-1419 ◽  
Author(s):  
James A. Anstey ◽  
Theodore G. Shepherd ◽  
John F. Scinocca
Keyword(s):  
Zonal Wind ◽  
General Circulation ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Empirical Orthogonal Functions ◽  
Vertical Profiles ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Atmospheric General Circulation ◽  
Biennial Oscillation

Abstract The interannual variability of the stratospheric polar vortex during winter in both hemispheres is observed to correlate strongly with the phase of the quasi-biennial oscillation (QBO) in tropical stratospheric winds. It follows that the lack of a spontaneously generated QBO in most atmospheric general circulation models (AGCMs) adversely affects the nature of polar variability in such models. This study examines QBO–vortex coupling in an AGCM in which a QBO is spontaneously induced by resolved and parameterized waves. The QBO–vortex coupling in the AGCM compares favorably to that seen in reanalysis data [from the 40-yr ECMWF Re-Analysis (ERA-40)], provided that careful attention is given to the definition of QBO phase. A phase angle representation of the QBO is employed that is based on the two leading empirical orthogonal functions of equatorial zonal wind vertical profiles. This yields a QBO phase that serves as a proxy for the vertical structure of equatorial winds over the whole depth of the stratosphere and thus provides a means of subsampling the data to select QBO phases with similar vertical profiles of equatorial zonal wind. Using this subsampling, it is found that the QBO phase that induces the strongest polar vortex response in early winter differs from that which induces the strongest late-winter vortex response. This is true in both hemispheres and for both the AGCM and ERA-40. It follows that the strength and timing of QBO influence on the vortex may be affected by the partial seasonal synchronization of QBO phase transitions that occurs both in observations and in the model. This provides a mechanism by which changes in the strength of QBO–vortex correlations may exhibit variability on decadal time scales. In the model, such behavior occurs in the absence of external forcings or interannual variations in sea surface temperatures.

scholarly journals Influence of the Equatorial QBO on the Extratropical Stratosphere

2006 ◽  
Vol 63 (3) ◽  
pp. 936-951 ◽  
Author(s):  
John Hampson ◽  
Peter Haynes
Keyword(s):  
Correlation Coefficient ◽  
Zonal Wind ◽  
Potential Temperature ◽  
Lower Boundary ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Least Squares Fit ◽  
Phase Alignment ◽  
Biennial Oscillation ◽  
Extratropical Circulation

Abstract The work described here examines the influence of the equatorial quasi-biennial oscillation (QBO) on the extratropics in a zonally truncated 3D mechanistic stratospheric model. Model results show that the extratropical response to the QBO depends critically on the phase alignment of the QBO with the annual cycle: the signal of extratropical response varies by a factor of 8 between the phase alignment that gives minimum response and that which gives maximum response. Model simulations in which the time and height structure of the QBO are varied suggest that, in this zonally truncated model, the equatorial height of 21–23 km is most influential for the extratropical response and that late autumn/early winter is the time at which the QBO has the most influence over the extratropical circulation. The correlation coefficient between the QBO (measured by zonal wind) and the extratropics (measured by zonal wind or potential temperature) is as high as 0.95. The correlation coefficient is largest for simulations with lower boundary wave forcing weaker than that which gives largest extratropical interannual variability. For stronger extratropical wave forcing, the correlation coefficient is slightly smaller, but the regression coefficient of the linear term in a least squares fit is significantly larger.

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