Numerical studies of barotropic stability of stratospheric states

The linear stability properties of basic states relevant to the stratosphere are studied in a barotropic nondivergent spectral model on a sphere. The stability of realistic zonally symmetric jets is examined in the first part, and the second part a deals with zonally asymmetric basic states;In the first part attention is focused on unstable modes that are associated with a region of negative basic state absolute vorticity gradient on the poleward side of the jet. These modes are approximately nondispersive. Study of realistic analytical jet profiles shows that broader jets, and jets which peak at higher latitudes produce poleward modes that are less dispersive. Jet profiles derived from observational data are studied in detail for three Southern Hemisphere winter months, and the results are compared with quasi-nondispersive features which have been observed in satellite data in the Southern hemisphere winter stratosphere. Characteristics of the barotropically unstable modes agree remarkably well with those of the observed features. The appearance of westward moving modes in the summer hemisphere during June, and in analytical profiles with realistic global structure, is noted;The second part focuses on the stability of zonally symmetric basic states which include a realistic jet profile such as previously studied, and a traveling wave resembling observed features in the winter stratosphere. This is of interest because many planetary scale traveling waves are observed in the winter stratosphere. Basic state waves are chosen to resemble observed features. Results for growth rates and energy conversion for the most unstable disturbances are presented as a function of the amplitude and frequency of the basic state wave. These results show ranges of basic state wave amplitude where the total basic state is more stable that a zonally symmetric basic state with the same jet profile, and also ranges where it is more unstable. At very small basic state wave amplitudes, the stability characteristics differ markedly from those for the zonally symmetric problem only when the phase speed of the basic state wave is near that of a free mode of the zonally symmetric problem. Suggestions are given as to how the results may apply to the winter stratosphere

Long term changes in the upper stratospheric ozone at Syowa, Antarctica

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月15日（火） 国立極地研究所 2階大会議

Jet and Tropopause Products for Analysis and Characterization (JETPAC)

This suite of IDL programs provides identification and comprehensive characterization of the dynamical features of the jet streams in the upper troposphere, the lower stratospheric polar night jet, and the tropopause. The output of this software not only provides comprehensive information on the jets and tropopause, but also gives this information in a form that facilitates studies of observations in relation to the jets and tropopauses

Statistical characterization of arctic polar-night jet oscillation events

A novel diagnostic tool is presented, based on polar-cap temperature anomalies, for visualizing daily variability of the Arctic stratospheric polar vortex over multiple decades. This visualization illustrates the ubiquity of extended-time-scale recoveries from stratospheric sudden warmings, termed here polar-night jet oscillation (PJO) events. These are characterized by an anomalously warm polar lower stratosphere that persists for several months. Following the initial warming, a cold anomaly forms in the middle stratosphere, as does an anomalously high stratopause, both of which descend while the lower-stratospheric anomaly persists. These events are characterized in four datasets: Microwave Limb Sounder (MLS) temperature observations; the 40-yr ECMWF Re-Analysis (ERA-40) and Modern Era Retrospective Analysis for Research and Applications (MERRA) reanalyses; and an ensemble of three 150-yr simulations from the Canadian Middle Atmosphere Model. The statistics of PJO events in the model are found to agree very closely with those of the observations and reanalyses. The time scale for the recovery of the polar vortex following sudden warmings correlates strongly with the depth to which the warming initially descends. PJO events occur following roughly half of all major sudden warmings and are associated with an extended period of suppressed wave-activity fluxes entering the polar vortex. They follow vortex splits more frequently than they do vortex displacements. They are also related to weak vortex events as identified by the northern annular mode; in particular, those weak vortex events followed by a PJO event show a stronger tropospheric response. The long time scales, predominantly radiative dynamics, and tropospheric influence of PJO events suggest that they represent an important source of conditional skill in seasonal forecasting

Dynamical control of the mesosphere by orographic and non-orographic gravity wave drag during the extended northern winters of 2006 and 2009

A version of the Canadian Middle Atmosphere Model (CMAM) that is nudged toward reanalysis data up to 1 hPa is used to examine the impacts of parameterized orographic and non-orographic gravity wave drag (OGWD and NGWD) on the zonal-mean circulation of the mesosphere during the extended northern winters of 2006 and 2009 when there were two large stratospheric sudden warmings. The simulations are compared to Aura Microwave Limb Sounder (MLS) observations of mesospheric temperature, carbon monoxide (CO) and derived zonal winds. The control simulation, which uses both OGWD and NGWD, is shown to be in good agreement with MLS. The impacts of OGWD and NGWD are assessed using simulations in which those sources of wave drag are removed. In the absence of OGWD the mesospheric zonal winds in the months preceding the warmings are too strong, causing increased mesospheric NGWD, which drives excessive downwelling, resulting in overly large lower mesospheric values of CO prior to the warming. NGWD is found to be most important following the warmings when the underlying westerlies are too weak to allow much vertical propagation of the orographic gravity waves to the mesosphere. NGWD is primarily responsible for driving the circulation that results in the descent of CO from the thermosphere following the warmings. Zonal mean mesospheric winds and temperatures in all simulations are shown to be strongly constrained by (i.e. slaved to) the stratosphere. Finally, it is demonstrated that the responses to OGWD and NGWD are non-additive due to their dependence and influence on the background winds and temperatures

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada - Part 2: Future change in cryosphere, vegetation, and hydrology

Global reanalyses from data assimilation systems are among the most widely used datasets in weather and climate studies, and potential vorticity (PV) from reanalyses is invaluable for many studies of dynamical and transport processes. We assess how consistently modern reanalyses represent potential vorticity (PV) among each other, focusing not only on PV but also on process-oriented dynamical diagnostics including equivalent latitude calculated from PV and PV-based tropopause and stratospheric polar vortex characterization. In particular we assess the National Centers for Environmental Prediction Climate Forecast System Reanalysis/Climate Forecast System, version 2 (CFSR/CFSv2) reanalysis, the European Centre for Medium-Range Weather Forecasts Interim (ERA-Interim) reanalysis, the Japanese Meteorological Agency's 55-year (JRA-55) reanalysis, and the NASA Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2). Overall, PV from all reanalyses agrees well with the reanalysis ensemble mean, providing some confidence that all of these recent reanalyses are suitable for most studies using PV-based diagnostics. Specific diagnostics where some larger differences are seen include PV-based tropopause locations in regions that have strong tropopause gradients (such as around the subtropical jets) or are sparse in high-resolution data (such as over Antarctica), and the stratospheric polar vortices during fall vortex formation and (especially) spring vortex breakup; studies of sensitive situations or regions such as these should examine PV from multiple reanalyses. &nbsp;</p

Northern Hemisphere mid-winter vortex-displacement and vortex-split stratospheric sudden warmings: Influence of the Madden-Julian Oscillation and Quasi-Biennial Oscillation

We investigate the connection between the equatorial Madden‐Julian Oscillation (MJO) and different types of the Northern Hemisphere mid‐winter major stratospheric sudden warmings (SSWs), i.e., vortex‐displacement and vortex‐split SSWs. The MJO‐SSW relationship for vortex‐split SSWs is stronger than that for vortex‐displacement SSWs, as a result of the stronger and more coherent eastward propagating MJOs before vortex‐split SSWs than those before vortex‐displacement SSWs. Composite analysis indicates that both the intensity and propagation features of MJO may influence the MJO‐related circulation pattern at high latitudes and the type of SSWs. A pronounced Quasi‐Biennial Oscillation (QBO) dependence is found for vortex‐displacement and vortex‐split SSWs, with vortex‐displacement (‐split) SSWs occurring preferentially in easterly (westerly) QBO phases. The lagged composites suggest that the MJO‐related anomalies in the Arctic are very likely initiated when the MJO‐related convection is active over the equatorial Indian Ocean (around the MJO phase 3). Further analysis suggests that the QBO may modulate the MJO‐related wave disturbances via its influence on the upper tropospheric subtropical jet. As a result, the MJO‐related circulation pattern in the Arctic tends to be wave number‐one/wave number‐two ~25–30 days following phase 3 (i.e., approximately phases 7–8, when the MJO‐related convection is active over the western Pacific) during easterly/westerly QBO phases, which resembles the circulation pattern associated with vortex‐displacement/vortex‐split SSWs

Aura Microwave Limb Sounder Observations of Dynamics and Transport During the Record-Breaking 2009 Arctic Stratospheric Major Warming

A major stratospheric sudden warming (SSW) in January 2009 was the strongest and most prolonged on record. Aura Microwave Limb Sounder (MLS) observations are used to provide an overview of dynamics and transport during the 2009 SSW, and to compare with the intense, long-lasting SSW in January 2006. The Arctic polar vortex split during the 2009 SSW, whereas the 2006 SSW was a vortex displacement event. Winds reversed to easterly more rapidly and reverted to westerly more slowly in 2009 than in 2006. More mixing of trace gases out of the vortex during the decay of the vortex fragments, and less before the fulfillment of major SSW criteria, was seen in 2009 than in 2006; persistent well-defined fragments of vortex and anticyclone air were more prevalent in 2009. The 2009 SSW had a more profound impact on the lower stratosphere than any previously observed SSW, with no significant recovery of the vortex in that region. The stratopause breakdown and subsequent reformation at very high altitude, accompanied by enhanced descent into a rapidly strengthening upper stratospheric vortex, were similar in 2009 and 2006. Many differences between 2006 and 2009 appear to be related to the different character of the SSWs in the two years

A Multi-Parameter Dynamical Diagnostics for Upper Tropospheric and Lower Stratospheric Studies

Ozone trend estimates have shown large uncertainties in the upper troposphere/lower stratosphere (UTLS) region despite multi-decadal observations available from ground-based, balloon, aircraft, and satellite platforms. These uncertainties arise from large natural variability driven by dynamics (reflected in tropopause and jet variations) as well as the strength in constituent transport and mixing. Additionally, despite all the community efforts there is still a lack of representative high-quality global UTLS measurements to capture this variability. The Stratosphere-troposphere Processes And their Role in Climate (SPARC) Observed Composition Trends and Variability in the UTLS (OCTAV-UTLS) activity aims to reduce uncertainties in UTLS composition trend estimates by accounting for this dynamically induced variability. In this paper, we describe the production of dynamical diagnostics using meteorological information from reanalysis fields that facilitate mapping observations from several platforms into numerous geophysically-based coordinates (including tropopause and upper tropospheric jet relative coordinates). Suitable coordinates should increase the homogeneity of the air masses analyzed together, thus reducing the uncertainty caused by spatio-temporal sampling biases in the quantification of UTLS composition trends. This approach thus provides a framework for comparing measurements with diverse sampling patterns and leverages the meteorological context to derive maximum information on UTLS composition and trends and its relationships to dynamical variability. The dynamical diagnostics presented here are the first comprehensive set describing the meteorological context for multi-decadal observations by ozonesondes, lidar, aircraft, and satellite measurements in order to study the impact of dynamical processes on observed UTLS trends by different sensors on different platforms. Examples using these diagnostics to map multi-platform datasets into different geophysically-based coordinate systems are provided. The diagnostics presented can also be applied to analysis of greenhouse gases other than ozone that are relevant to surface climate and UTLS chemistry.</p