A Major Stratospheric Sudden Warming Event in January 2009

Abstract The major stratospheric sudden warming (SSW) event of January 2009 is analyzed using the Japan Meteorological Agency (JMA) Climate Data Assimilation System (JCDAS). This SSW event is characterized by the extraordinary predominance of the planetary-scale wave of zonal wavenumber 2 (wave 2). The total amount of the upward Eliassen–Palm (EP) flux for wave 2 was the strongest since the winter of 1978/79. It is found that the remarkable development of the upper troposphere ridge over Alaska played important roles in the SSW in January 2009. During the first development stage, the ridge excited wave packets upward as well as eastward over around Alaska. The eastward-propagating packets intensified a trough over eastern Siberia, which led to the development of the planetary wave over eastern Siberia during the second development stage. The results of this study indicate that the pronounced wave-2 pattern observed in the stratosphere was brought about by accumulative effects of rather localized propagation of wave packets from the troposphere during the course of this SSW event rather than by the ubiquitous propagation of planetary-scale disturbances in the troposphere. The features of the SSW in January 2009 are quite similar to those during the major stratospheric warming event in February 1989: both SSWs are characterized by the predominance of wave 2, the remarkable development of the upper troposphere ridge over around Alaska, and positive SSTs in the eastern part of the North Pacific corresponding to a La Niña condition.

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Large differences in reanalyses of diabatic heating in the tropical upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-9565-2013 ◽

2013 ◽

Vol 13 (18) ◽

pp. 9565-9576 ◽

Cited By ~ 63

Author(s):

J. S. Wright ◽

S. Fueglistaler

Keyword(s):

Turbulent Mixing ◽

Lower Stratosphere ◽

Heat Budget ◽

Radiative Heating ◽

Japan Meteorological Agency ◽

Latent Heating ◽

Moist Convection ◽

Climate Data ◽

Upper Troposphere ◽

Tropical Upper Troposphere

Abstract. We present the time mean heat budgets of the tropical upper troposphere (UT) and lower stratosphere (LS) as simulated by five reanalysis models: the Modern-Era Retrospective Analysis for Research and Applications (MERRA), European Reanalysis (ERA-Interim), Climate Forecast System Reanalysis (CFSR), Japanese 25-yr Reanalysis and Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS), and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis 1. The simulated diabatic heat budget in the tropical UTLS differs significantly from model to model, with substantial implications for representations of transport and mixing. Large differences are apparent both in the net heat budget and in all comparable individual components, including latent heating, heating due to radiative transfer, and heating due to parameterised vertical mixing. We describe and discuss the most pronounced differences. Discrepancies in latent heating reflect continuing difficulties in representing moist convection in models. Although these discrepancies may be expected, their magnitude is still disturbing. We pay particular attention to discrepancies in radiative heating (which may be surprising given the strength of observational constraints on temperature and tropospheric water vapour) and discrepancies in heating due to turbulent mixing (which have received comparatively little attention). The largest differences in radiative heating in the tropical UTLS are attributable to differences in cloud radiative heating, but important systematic differences are present even in the absence of clouds. Local maxima in heating and cooling due to parameterised turbulent mixing occur in the vicinity of the tropical tropopause.

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Spectrum of Wave Forcing Associated with the Annual Cycle of Upwelling at the Tropical Tropopause

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0096.1 ◽

2016 ◽

Vol 73 (2) ◽

pp. 855-868 ◽

Cited By ~ 6

Author(s):

Joowan Kim ◽

William J. Randel ◽

Thomas Birner ◽

Marta Abalos

Keyword(s):

Annual Cycle ◽

Lower Stratosphere ◽

Mass Conservation ◽

Upper Troposphere ◽

Wave Forcing ◽

Planetary Scale ◽

Tropical Tropopause ◽

Zonal Wavenumber ◽

Wavenumber Spectrum ◽

Transformed Eulerian Mean

Abstract The zonal wavenumber spectrum of atmospheric wave forcing in the lower stratosphere is examined to understand the annual cycle of upwelling at the tropical tropopause. Tropopause upwelling is derived based on the wave forcing computed from ERA-Interim using the momentum and mass conservation equations in the transformed Eulerian-mean framework. The calculated upwelling agrees well with other upwelling estimates and successfully captures the annual cycle, with a maximum during Northern Hemisphere (NH) winter. The spectrum of wave forcing reveals that the zonal wavenumber-3 component drives a large portion of the annual cycle in upwelling. The wave activity flux (Eliassen–Palm flux) shows that the associated waves originate from the NH extratropics and the Southern Hemisphere tropics during December–February, with both regions contributing significant wavenumber-3 fluxes. These wave fluxes are nearly absent during June–August. Wavenumbers 1 and 2 and synoptic-scale waves have a notable contribution to tropopause upwelling but have little influence on the annual cycle, except the wavenumber-4 component. The quasigeostrophic refractive index suggests that the NH extratropical wavenumber-3 component can enhance tropopause upwelling because these planetary-scale waves are largely trapped in the vertical, while being refracted toward the subtropical upper troposphere and lower stratosphere. Regression analysis based on interannual variability suggests that the wavenumber-3 waves are related to tropical convection and wave breaking along the subtropical jet in the NH extratropics.

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Spurious Grid-Scale Precipitation in the North American Regional Reanalysis

Monthly Weather Review ◽

10.1175/mwr3375.1 ◽

2007 ◽

Vol 135 (6) ◽

pp. 2168-2184 ◽

Cited By ~ 33

Author(s):

Gregory L. West ◽

W. James Steenburgh ◽

William Y. Y. Cheng

Keyword(s):

North American ◽

Prediction Models ◽

Weather Prediction ◽

Regional Climate ◽

Potential Temperature ◽

Climate Data ◽

The North ◽

North American Regional Reanalysis ◽

Upper Level ◽

Regional Reanalysis

Abstract Spurious grid-scale precipitation (SGSP) occurs in many mesoscale numerical weather prediction models when the simulated atmosphere becomes convectively unstable and the convective parameterization fails to relieve the instability. Case studies presented in this paper illustrate that SGSP events are also found in the North American Regional Reanalysis (NARR) and are accompanied by excessive maxima in grid-scale precipitation, vertical velocity, moisture variables (e.g., relative humidity and precipitable water), mid- and upper-level equivalent potential temperature, and mid- and upper-level absolute vorticity. SGSP events in environments favorable for high-based convection can also feature low-level cold pools and sea level pressure maxima. Prior to 2003, retrospectively generated NARR analyses feature an average of approximately 370 SGSP events annually. Beginning in 2003, however, NARR analyses are generated in near–real time by the Regional Climate Data Assimilation System (R-CDAS), which is identical to the retrospective NARR analysis system except for the input precipitation and ice cover datasets. Analyses produced by the R-CDAS feature a substantially larger number of SGSP events with more than 4000 occurring in the original 2003 analyses. An oceanic precipitation data processing error, which resulted in a reprocessing of NARR analyses from 2003 to 2005, only partially explains this increase since the reprocessed analyses still produce approximately 2000 SGSP events annually. These results suggest that many NARR SGSP events are not produced by shortcomings in the underlying Eta Model, but by the specification of anomalous latent heating when there is a strong mismatch between modeled and assimilated precipitation. NARR users should ensure that they are using the reprocessed NARR analyses from 2003 to 2005 and consider the possible influence of SGSP on their findings, particularly after the transition to the R-CDAS.

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Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2784.1 ◽

2009 ◽

Vol 66 (2) ◽

pp. 495-507 ◽

Cited By ~ 53

Author(s):

Lawrence Coy ◽

Stephen Eckermann ◽

Karl Hoppel

Keyword(s):

North Atlantic ◽

Wave Breaking ◽

Potential Temperature ◽

Polar Vortex ◽

Stratospheric Polar Vortex ◽

Stratospheric Sudden Warming ◽

Advanced Level ◽

Earth Observing System ◽

The North ◽

Temperature Surface

Abstract The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.

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Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks

Journal of Climate ◽

10.1175/jcli-d-12-00495.1 ◽

2013 ◽

Vol 26 (14) ◽

pp. 5220-5241 ◽

Cited By ~ 27

Author(s):

Isla R. Simpson ◽

Theodore G. Shepherd ◽

Peter Hitchcock ◽

John F. Scinocca

Keyword(s):

Negative Feedback ◽

Planetary Wave ◽

Southern Annular Mode ◽

Summer Season ◽

Substantial Contribution ◽

Mean Flow ◽

Annular Mode ◽

Planetary Scale ◽

Zonal Wavenumber ◽

Climatological Circulation

Abstract Many global climate models (GCMs) have trouble simulating southern annular mode (SAM) variability correctly, particularly in the Southern Hemisphere summer season where it tends to be too persistent. In this two-part study, a suite of experiments with the Canadian Middle Atmosphere Model (CMAM) is analyzed to improve the understanding of the dynamics of SAM variability and its deficiencies in GCMs. Here, an examination of the eddy–mean flow feedbacks is presented by quantification of the feedback strength as a function of zonal scale and season using a new methodology that accounts for intraseasonal forcing of the SAM. In the observed atmosphere, in the summer season, a strong negative feedback by planetary-scale waves, in particular zonal wavenumber 3, is found in a localized region in the southwest Pacific. It cancels a large proportion of the positive feedback by synoptic- and smaller-scale eddies in the zonal mean, resulting in a very weak overall eddy feedback on the SAM. CMAM is deficient in this negative feedback by planetary-scale waves, making a substantial contribution to its bias in summertime SAM persistence. Furthermore, this bias is not alleviated by artificially improving the climatological circulation, suggesting that climatological circulation biases are not the cause of the planetary wave feedback deficiency in the model. Analysis of the summertime eddy feedbacks in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) confirms that this is indeed a common problem among GCMs, suggesting that understanding this planetary wave feedback and the reason for its deficiency in GCMs is key to improving the fidelity of simulated SAM variability in the summer season.

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A nonlinear multi-scale theory of atmospheric blocking: Structure and evolution of blocking linked to meridional and vertical structures of storm tracks

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0349.1 ◽

2021 ◽

Author(s):

Dehai Luo ◽

Wenqi Zhang

Keyword(s):

Storm Track ◽

Interaction Model ◽

Maximum Amplitude ◽

Transient Eddy ◽

Baroclinic Mode ◽

Upper Troposphere ◽

Multi Scale ◽

The North ◽

Baroclinic Modes ◽

The Impact

AbstractThis paper examines the impact of the meridional and vertical structures of a preexisting upstream storm track (PUST) organized by preexisting synoptic-scale eddies on eddy-driven blocking in a nonlinear multi-scale interaction model. In this model, the blocking is assumed, based on observations, to be comprised of barotropic and first baroclinic modes, whereas the PUST consists of barotropic, first baroclinic and second baroclinic modes. It is found that the nonlinearity (dispersion) of blocking is intensified (weakened) with increasing amplitude of the first baroclinic mode of the blocking itself. The blocking tends to be long-lived in this case. The lifetime and strength of blocking are significantly influenced by the amplitude of the first baroclinic mode of blocking for given basic westerly winds (BWWs), whereas its spatial pattern and evolution are also affected by the meridional and vertical structures of the PUST.It is shown that the blocking mainly results from the transient eddy forcing induced by the barotropic and first baroclinic modes of PUST, whereas its second baroclinic mode contributes little to the transient eddy forcing. When the PUST shifts northward, eddy-driven blocking shows an asymmetric dipole structure with a strong anticyclone/weak cyclone in a uniform BWW, which induces northward-intensified westerly jet and storm track anomalies mainly on the north side of blocking. However, when the PUST has no meridional shift and is mainly located in the upper troposphere, a north-south anti-symmetric dipole blocking and an intensified split jet with maximum amplitude in the upper troposphere form easily for vertically varying BWWs without meridional shear.

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Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

10.5194/acp-2015-988 ◽

2016 ◽

Cited By ~ 3

Author(s):

M. Venkat Ratnam ◽

S. Ravindra Babu ◽

S. S. Das ◽

Ghouse Basha ◽

B. V. Krishnamurthy ◽

...

Keyword(s):

Water Vapor ◽

Indian Ocean ◽

Tropical Cyclones ◽

Lower Stratosphere ◽

North Indian Ocean ◽

Satellite Observations ◽

Upper Troposphere ◽

North West ◽

The North ◽

The Impact

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.

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Planetary Scale Selection of the Madden–Julian Oscillation*

Journal of the Atmospheric Sciences ◽

10.1175/2009jas2968.1 ◽

2009 ◽

Vol 66 (8) ◽

pp. 2429-2443 ◽

Cited By ~ 40

Author(s):

Tim Li ◽

Chunhua Zhou

Keyword(s):

Boundary Layer ◽

Rossby Wave ◽

Initial Perturbation ◽

Madden Julian Oscillation ◽

Kelvin Wave ◽

Scale Selection ◽

Planetary Scale ◽

Zonal Wavenumber ◽

Nonlinear Heating ◽

Selection Of

Abstract Numerical experiments with a 2.5-layer and a 2-level model are conducted to examine the mechanism for the planetary scale selection of the Madden–Julian oscillation (MJO). The strategy here is to examine the evolution of an initial perturbation that has a form of the equatorial Kelvin wave at zonal wavenumbers of 1 to 15. In the presence of a frictional boundary layer, the most unstable mode prefers a short wavelength under a linear heating; but with a nonlinear heating, the zonal wavenumber 1 grows fastest. This differs significantly from a model without the boundary layer, in which neither linear nor nonlinear heating leads to the long wave selection. Thus, the numerical simulations point out the crucial importance of the combined effect of the nonlinear heating and the frictional boundary layer in the MJO planetary scale selection. The cause of this scale selection under the nonlinear heating is attributed to the distinctive phase speeds between the dry Kelvin wave and the wet Kelvin–Rossby wave couplet. The faster dry Kelvin wave triggered by a convective branch may catch up and suppress another convective branch, which travels ahead of it at the phase speed of the wet Kelvin–Rossby wave couplet if the distance between the two neighboring convective branches is smaller than a critical distance (about 16 000 km). The interference between the dry Kelvin wave and the wet Kelvin–Rossby wave couplet eventually dissipates and “filters out” shorter wavelength perturbations, leading to a longwave selection. The boundary layer plays an important role in destabilizing the MJO through frictional moisture convergences and in retaining the in-phase zonal wind–pressure structure.

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Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part I: A Simple Model of North Atlantic Oscillations

Journal of the Atmospheric Sciences ◽

10.1175/jas3818.1 ◽

2007 ◽

Vol 64 (1) ◽

pp. 3-28 ◽

Cited By ~ 86

Author(s):

Dehai Luo ◽

Anthony R. Lupo ◽

Han Wan

Keyword(s):

Life Cycle ◽

Theoretical Model ◽

North Atlantic ◽

Low Frequency ◽

Positive Phase ◽

Negative Phase ◽

Synoptic Scale ◽

Planetary Scale ◽

The North ◽

The North Atlantic Oscillation

Abstract A simple theoretical model is proposed to clarify how synoptic-scale waves drive the life cycle of the North Atlantic Oscillation (NAO) with a period of nearly two weeks. This model is able to elucidate what determines the phase of the NAO and an analytical solution is presented to indicate a high similarity between the dynamical processes of the NAO and zonal index, which is not derived analytically in previous theoretical studies. It is suggested theoretically that the NAO is indeed a nonlinear initial-value problem, which is forced by both preexisting planetary-scale and synoptic-scale waves. The eddy forcing arising from the preexisting synoptic-scale waves is shown to be crucial for the growth and decay of the NAO, but the preexisting low-over-high (high-over-low) dipole planetary-scale wave must be required to match the preexisting positive-over-negative (negative-over-positive) dipole eddy forcing so as to excite a positive (negative) phase NAO event. The positive and negative feedbacks of the preexisting dipole eddy forcing depending upon the background westerly wind seem to dominate the life cycle of the NAO and its life period. An important finding in the theoretical model is that negative-phase NAO events could be excited repeatedly after the first event has decayed, but for the positive phase downstream isolated dipole blocks could be produced after the first event has decayed. This is supported by observed cases of the NAO events presented in this paper. In addition, a statistical study of the relationship between the phase of the NAO and blocking activity over Europe in terms of the seasonal mean NAO index shows that blocking events over Europe are more frequent and long-lived for strong positive-phase NAO years, indicating that the positive-phase NAO favors the occurrence of European blocking events.

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Sugarcane Yield Forecast in Ivory Coast (West Africa) Based on Weather and Vegetation Index Data

Atmosphere ◽

10.3390/atmos12111459 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1459

Author(s):

Edouard Pignède ◽

Philippe Roudier ◽

Arona Diedhiou ◽

Vami Hermann N’Guessan Bi ◽

Arsène T. Kobea ◽

...

Keyword(s):

West Africa ◽

Ivory Coast ◽

Vegetation Index ◽

Cultural Practices ◽

Machine Learning Algorithms ◽

Climate Data ◽

Climate Services ◽

Climate Risks ◽

The North ◽

Sugarcane Yield

One way to use climate services in the case of sugarcane is to develop models that forecast yields to help the sector to be better prepared against climate risks. In this study, several models for forecasting sugarcane yields were developed and compared in the north of Ivory Coast (West Africa). These models were based on statistical methods, ranging from linear regression to machine learning algorithms such as the random forest method, fed by climate data (rainfall, temperature); satellite products (NDVI, EVI from MODIS Vegetation Index product) and information on cropping practices. The results show that the forecasting of sugarcane yield depended on the area considered. At the plot level, the noise due to cultivation practices can hide the effects of climate on yields and leads to poor forecasting performance. However, models using satellite variables are more efficient and those with EVI alone may explain 43% of yield variations. Moreover, taking into account cultural practices in the model improves the score and enables one to forecast 3 months before harvest in 50% and 69% of cases whether yields will be high or low, respectively, with errors of only 10% and 2%, respectively. These results on the predictive potential of sugarcane yields are useful for planning and climate risk management in this sector.

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