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In the tropical stratosphere, deep layers of eastward and westward winds encircle the globe and descend regularly from the upper stratosphere to the tropical tropopause. With a complete cycle typically lasting almost 2.5 years, this quasi-biennial oscillation (QBO) is arguably the most predictable mode of atmospheric variability that is not linked to the changing seasons. The QBO affects climate phenomena outside the tropical stratosphere, including ozone transport, the North Atlantic Oscillation and the Madden–Julian Oscillation, and its high predictability could enable better forecasts of these phenomena if models can accurately represent the coupling processes. Climate and forecasting models are increasingly able to simulate stratospheric oscillations resembling the QBO, but exhibit common systematic errors such as weak amplitude in the lowermost tropical stratosphere. Uncertainties about the waves that force the oscillation, particularly the momentum fluxes from small-scale gravity waves excited by deep convection, make its simulation challenging. Improved representation of the processes governing the QBO is expected to lead to better forecasts of the oscillation and its impacts, increased understanding of unusual events such as the two QBO disruptions observed since 2016, and more reliable future projections of QBO behaviour under climate change.

Over recent years there have been concomitant advances in the development of stratosphere-resolving numerical models, our understanding of stratosphere–troposphere interaction, and the extension of long-range forecasts to explicitly include the stratosphere. These advances are now allowing for new and improved capability in long-range prediction. We present an overview of this development and show how the inclusion of the stratosphere in forecast systems aids monthly, seasonal, and annual-to-decadal climate predictions and multidecadal projections. We end with an outlook towards the future and identify areas of improvement that could further benefit these rapidly evolving predictions., Atmospheric Chemistry and Physics, 22 (4), ISSN:1680-7375, ISSN:1680-7367

Over recent years there have been parallel advances in the development of stratosphere resolving numerical models, our understanding of stratosphere-troposphere interaction and the extension of long-range forecasts to explicitly include the stratosphere. These advances are now allowing new and improved capability in long range prediction. We present an overview of this development and show how the inclusion of the stratosphere in forecast systems aids monthly, seasonal and decadal climate predictions. We end with an outlook towards the future of climate forecasts and identify areas for improvement that could further benefit these rapidly evolving predictions.

Major disruptions to the stratospheric circulation have far-reaching effects, including increased likelihood of snowstorms, growth of the ozone hole, and interference in global telecommunications.

Angular momentum is fundamental to the structure and variability of the atmosphere and hence regional weather and climate. Total atmospheric angular momentum (AAM) is also directly related to the rotation rate of the Earth and hence the length of day. However, the long-range predictability of fluctuations in the length of day, atmospheric angular momentum and the implications for climate prediction are unknown. Here we show that fluctuations in AAM and the length of day are predictable out to more than a year ahead and that this provides an atmospheric source of long-range predictability of surface climate. Using ensemble forecasts from a dynamical climate model we demonstrate predictable signals in the atmospheric angular momentum field that propagate slowly and coherently polewards into the northern and southern hemisphere due to wave-mean flow interaction within the atmosphere. These predictable signals are also shown to precede changes in extratropical surface climate via the North Atlantic Oscillation. These results provide a novel source of long-range predictability of climate from within the atmosphere, greatly extend the lead time for length of day predictions and link geodesy with climate variability.

The stratosphere can have a significant impact on winter surface weather on subseasonal to seasonal (S2S) timescales. This study evaluates the ability of current operational S2S prediction systems to capture two important links between the stratosphere and troposphere: (1) changes in probabilistic prediction skill in the extratropical stratosphere by precursors in the tropics and the extratropical troposphere and (2) changes in surface predictability in the extratropics after stratospheric weak and strong vortex events. Probabilistic skill exists for stratospheric events when including extratropical tropospheric precursors over the North Pacific and Eurasia, though only a limited set of models captures the Eurasian precursors. Tropical teleconnections such as the Madden‐Julian Oscillation, the Quasi‐Biennial Oscillation, and El Niño–Southern Oscillation increase the probabilistic skill of the polar vortex strength, though these are only captured by a limited set of models. At the surface, predictability is increased over the United States, Russia, and the Middle East for weak vortex events, but not for Europe, and the change in predictability is smaller for strong vortex events for all prediction systems. Prediction systems with poorly resolved stratospheric processes represent this skill to a lesser degree. Altogether, the analyses indicate that correctly simulating stratospheric variability and stratosphere‐troposphere dynamical coupling are critical elements for skillful S2S wintertime predictions. ISSN:0148-0227 ISSN:2169-897X

The ‘climate crisis’ describes human-caused global warming and climate change and its consequences. It conveys the sense of urgency surrounding humanity's failure to take sufficient action to slow down, stop and reverse global warming. The leading direct cause of the climate crisis is carbon dioxide (CO2) released as a by-product of burning fossil fuels,i which supply ~87% of the world's energy. The second most important cause of the climate crisis is deforestation to create more land for crops and livestock. The solutions have been stated as simply ‘leave the fossil carbon in the ground’ and ‘end deforestation’. Rather than address fossil fuel supplies, climate policies focus almost exclusively on the demand side, blaming fossil fuel users for greenhouse gas emissions. The fundamental reason that we are not solving the climate crisis is not a lack of green energy solutions. It is that governments continue with energy strategies that prioritize fossil fuels. These entrenched energy policies subsidize the discovery, extraction, transport and sale of fossil fuels, with the aim of ensuring a cheap, plentiful, steady supply of fossil energy into the future. This paper compares the climate crisis to two other environmental crises: ozone depletion and the COVID-19 pandemic. Halting and reversing damage to the ozone layer is one of humanity's greatest environmental success stories. The world's response to COVID-19 demonstrates that it is possible for governments to take decisive action to avert an imminent crisis. The approach to solving both of these crises was the same: (1) identify the precise cause of the problem through expert scientific advice; (2) with support by the public, pass legislation focused on the cause of the problem; and (3) employ a robust feedback mechanism to assess progress and adjust the approach. This is not yet being done to solve the climate crisis, but working within the 2015 Paris Climate Agreement framework, it could be. Every nation can contribute to solving the climate crisis by: (1) changing their energy strategy to green energy sources instead of fossil fuels; and (2) critically reviewing every law, policy and trade agreement (including transport, food production, food sources and land use) that affects the climate crisis.

The stratosphere has been identified as an important source of predictability for a range of processes on subseasonal to seasonal (S2S) time scales. Knowledge about S2S predictability within the stratosphere is however still limited. This study evaluates to what extent predictability in the extratropical stratosphere exists in hindcasts of operational prediction systems in the S2S database. The stratosphere is found to exhibit extended predictability as compared to the troposphere. Prediction systems with higher stratospheric skill tend to also exhibit higher skill in the troposphere. The analysis also includes an assessment of the predictability for stratospheric events, including early and midwinter sudden stratospheric warming events, strong vortex events, and extreme heat flux events for the Northern Hemisphere and final warming events for both hemispheres. Strong vortex events and final warming events exhibit higher levels of predictability as compared to sudden stratospheric warming events. In general, skill is limited to the deterministic range of 1 to 2 weeks. High‐top prediction systems overall exhibit higher stratospheric prediction skill as compared to their low‐top counterparts, pointing to the important role of stratospheric representation in S2S prediction models. ISSN:0148-0227 ISSN:2169-897X

The stratosphere contains ~17% of Earth’s atmospheric mass, but its existence was unknown until 1902. In the following decades our knowledge grew gradually as more observations of the stratosphere were made. In 1913 the ozone layer, which protects life from harmful ultraviolet radiation, was discovered. From ozone and water vapor observations, a first basic idea of a stratospheric general circulation was put forward. Since the 1950s our knowledge of the stratosphere and mesosphere has expanded rapidly, and the importance of this region in the climate system has become clear. With more observations, several new stratospheric phenomena have been discovered: the quasi-biennial oscillation, sudden stratospheric warmings, the Southern Hemisphere ozone hole, and surface weather impacts of stratospheric variability. None of these phenomena were anticipated by theory. Advances in theory have more often than not been prompted by unexplained phenomena seen in new stratospheric observations. From the 1960s onward, the importance of dynamical processes and the coupled stratosphere–troposphere circulation was realized. Since approximately 2000, better representations of the stratosphere—and even the mesosphere—have been included in climate and weather forecasting models. We now know that in order to produce accurate seasonal weather forecasts, and to predict long-term changes in climate and the future evolution of the ozone layer, models with a well-resolved stratosphere with realistic dynamics and chemistry are necessary.

The first multimodel study to estimate the predictability of a boreal sudden stratospheric warming (SSW) is performed using five NWP systems. During the 2012/13 boreal winter, anomalous upward propagating planetary wave activity was observed toward the end of December, which was followed by a rapid deceleration of the westerly circulation around 2 January 2013, and on 7 January 2013 the zonal-mean zonal wind at 60°N and 10 hPa reversed to easterly. This stratospheric dynamical activity was followed by an equatorward shift of the tropospheric jet stream and by a high pressure anomaly over the North Atlantic, which resulted in severe cold conditions in the United Kingdom and northern Europe. In most of the five models, the SSW event was predicted 10 days in advance. However, only some ensemble members in most of the models predicted weakening of westerly wind when the models were initialized 15 days in advance of the SSW. Further dynamical analysis of the SSW shows that this event was characterized by the anomalous planetary wavenumber-1 amplification followed by the anomalous wavenumber-2 amplification in the stratosphere, which resulted in a split vortex occurring between 6 and 8 January 2013. The models have some success in reproducing wavenumber-1 activity when initialized 15 days in advance, but they generally failed to produce the wavenumber-2 activity during the final days of the event. Detailed analysis shows that models have reasonably good skill in forecasting tropospheric blocking features that stimulate wavenumber-2 amplification in the troposphere, but they have limited skill in reproducing wavenumber-2 amplification in the stratosphere.

We investigate seasonal forecasts of the winter North Atlantic Oscillation (NAO) and their relationship with the stratosphere. Climatological frequencies of sudden stratospheric warming (SSW) and strong polar vortex (SPV) events are well represented and the predicted risk of events varies between 25 and 90% from winter to winter, indicating predictability beyond the deterministic range. The risk of SSW and SPV events relates to predicted NAO as expected, with NAO shifts of −6.5 and +4.8 hPa in forecast members containing SSW and SPV events. Most striking of all is that forecast skill of the surface winter NAO vanishes from these hindcasts if members containing SSW events are excluded.

The atmospheric layer that lies above Earth's weather systems can exert a strong downward influence. A review of this influence on storm tracks and surface weather suggests that the dynamical links between the layers hold across timescales.

Future changes in the stratospheric circulation could have an important impact on northern winter tropospheric climate change, given that sea level pressure (SLP) responds not only to tropospheric circulation variations but also to vertically coherent variations in troposphere-stratosphere circulation. Here we assess northern winter stratospheric change and its potential to influence surface climate change in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) multimodel ensemble. In the stratosphere at high latitudes, an easterly change in zonally averaged zonal wind is found for the majority of the CMIP5 models, under the Representative Concentration Pathway 8.5 scenario. Comparable results are also found in the 1% CO2 increase per year projections, indicating that the stratospheric easterly change is common feature in future climate projections. This stratospheric wind change, however, shows a significant spread among the models. By using linear regression, we quantify the impact of tropical upper troposphere warming, polar amplification, and the stratospheric wind change on SLP. We find that the intermodel spread in stratospheric wind change contributes substantially to the intermodel spread in Arctic SLP change. The role of the stratosphere in determining part of the spread in SLP change is supported by the fact that the SLP change lags the stratospheric zonally averaged wind change. Taken together, these findings provide further support for the importance of simulating the coupling between the stratosphere and the troposphere, to narrow the uncertainty in the future projection of tropospheric circulation changes.

The predictability of the quasi-biennial oscillation (QBO) is examined in initialized climate forecasts extending out to lead times of years. We use initialized retrospective predictions made with coupled ocean-atmosphere climate models that have an internally generated QBO. We demonstrate predictability of the QBO extending more than 3 years into the future, well beyond timescales normally associated with internal atmospheric processes. Correlation scores with observational analyses exceed 0.7 at a lead time of 12 months. We also examine the variation of predictability with season and QBO phase and find that skill is lowest in winter. An assessment of perfect predictability suggests that higher skill may be achievable through improved initialization and climate modeling of the QBO, although this may depend on the realism of gravity wave source parameterizations in the models. Finally, we show that skilful prediction of the QBO itself does not guarantee predictability of the extratropical winter teleconnection that is important for surface winter climate prediction.

BACKGROUND Arginine is an indispensable amino acid in neonates; de novo synthesis of arginine occurs in the small intestine (SI) but is reduced during parenteral nutrition (PN), limiting the arginine available to the mucosa. We assessed the effects of route of intake and dietary concentration of arginine on protein synthesis, superior mesenteric artery (SMA) blood flow, and SI morphology. METHODS Piglets (n = 18, 14-17 days old) were given complete PN for 3 days to induce SI atrophy, then switched to 1 of 3 treatments: arginine-free PN plus an intragastric (IG) infusion of high arginine (1.6 g · kg(-1)· d(-1), IG-H Arg) or low arginine (0.6 g · kg(-1)· d(-1), IG-L Arg) or complete high-arginine PN (1.6 g · kg(-1)· d(-1), IV-H Arg). RESULTS Enteral arginine, irrespective of amount provided, stimulated hepatic protein synthesis compared with intravenous delivery of arginine (P = .01). SMA blood flow declined for all groups following the initiation of PN. After 48 hours on the test diets, all groups reached low constant levels, but the IV-H group was significantly higher than both IG groups (P < .05). Despite greater blood flow, the SI morphological characteristics in IV-H Arg pigs were not significantly improved over the other groups. IV-H Arg pigs had higher plasma concentrations of indispensable amino acids (tyrosine, isoleucine, and valine) compared with IG-H Arg, despite identical amino acid intakes. CONCLUSIONS Intravenous delivery of arginine sustained the best SMA blood flow, whereas even a moderate amount of enteral arginine stimulated liver protein synthesis and maintained SI growth, independent of blood flow.

We describe the main differences in simulations of stratospheric climate and variability by models within the fifth Coupled Model Intercomparison Project (CMIP5) that have a model top above the stratopause and relatively fine stratospheric vertical resolution (high-top), and those that have a model top below the stratopause (low-top). Although the simulation of mean stratospheric climate by the two model ensembles is similar, the low-top model ensemble has very weak stratospheric variability on daily and interannual time scales. The frequency of major sudden stratospheric warming events is strongly underestimated by the low-top models with less than half the frequency of events observed in the reanalysis data and high-top models. The lack of stratospheric variability in the low-top models affects their stratosphere-troposphere coupling, resulting in short-lived anomalies in the Northern Annular Mode, which do not produce long-lasting tropospheric impacts, as seen in observations. The lack of stratospheric variability, however, does not appear to have any impact on the ability of the low-top models to reproduce past stratospheric temperature trends. We find little improvement in the simulation of decadal variability for the high-top models compared to the low-top, which is likely related to the fact that neither ensemble produces a realistic dynamical response to volcanic eruptions.

The leading mode of variability of the lower atmosphere circulation in the Northern Hemisphere is a largely zonally symmetric mode known as the Arctic Oscillation. We calculate Arctic Oscillation (AO) indices on a range of levels from 1000 to 10 hPa by means of a principal component analysis of National Centers for Environmental Prediction daily geopotential height anomalies. We find the apparent downward propagation of anomalies noted by other authors to be statistically significant compared to a red noise model. By examining histograms of these indices for each month, we note that the distribution of the index is generally close to Gaussian in the troposphere. In the stratosphere, however, the index is negatively skewed in the winter and positively skewed in the spring. We conclude that the positive skewness in April results from the coexistence of distinct summer and winter circulation states, and by examining polar stratospheric temperatures, we conclude that the negative skewness in January may be due to the radiatively determined limit on the vortex strength. This radiative limit responds relatively slowly to anthropogenic forcing, whereas changes in planetary wave forcing could have a much faster impact on the number of warm events. This suggests a hypothesis that the vortex strength may respond nonlinearly to anthropogenic forcing, which is supported by an observed change in the shape of the histograms of 20-200 hPa AO indices in January over the past 40 years. Copyright 2001 by the American Geophysical Union.

International audience; Extratropical cyclones are storm systems that are observed to travel preferentially within confined regions known as storm tracks. They contribute to precipitation, wind and temperature extremes in mid-latitudes. Cyclones tend to form where surface temperature gradients are large, and the jet stream influences their speed and direction of travel. Storm tracks shape the global climate through transport of energy and momentum. The intensity and location of storm tracks varies seasonally, and in response to other natural variations, such as changes in tropical sea surface temperature. A hierarchy of numerical models of the atmosphere-ocean system -- from highly idealized to comprehensive -- has been used to study and predict responses of storm tracks to anthropogenic climate change. The future position and intensity of storm tracks depend on processes that alter temperature gradients. However, different processes can have opposing influences on temperature gradients, which leads to a tug of war on storm track responses and makes future projections more difficult. For example, as climate warms, surface shortwave cloud radiative changes increase the Equator-to-pole temperature gradient, but at the same time, longwave cloud radiative changes reduce this gradient. Future progress depends on understanding and accurately quantifying the relative influence of such processes on the storm tracks.

We have studied the characterization of the 11-year solar cycle (SC) signals in the Southern Hemisphere (SH) during the winter and spring using European Centre for Medium-Range Weather Forecasts (ECMWF) daily and monthly data from 1979 to 2009. By separating the response into high ( 36 months) frequency domains, we have found that spatially different 11-year SC signals exist for high- and low-frequency domains. In the stratosphere, the high- and low-frequency responses tend to enhance each other near the Equator and Subtropics, while they oppose one another at high latitudes. The high-frequency response is marked by a strengthened stratospheric jet during winter and the response is not static but tracks with the centre of the polar vortex. In the lower stratosphere, the positive response of temperature to the 11-year SC is dominated by its low-frequency component, which extends from the North Pole to the South Pole. The low-frequency tropospheric response is latitudinally symmetrical about the Equator and consistent with the modelled responses to temperature perturbation in the lower stratosphere. The signals are found to be sensitive to contamination from the 2002 sudden stratospheric warming event and major volcanic eruptions but the general spatial pattern of the responses remains similar. A significant projection of the 11-year SC onto the Southern Annular Mode (SAM) can only be detected in the stratosphere and in the high-frequency component. The signature is marked by a strengthening of the stratospheric SAM during winter and a weakening of the SAM in the uppermost stratosphere during spring. Copyright © 2011 Royal Meteorological Society

Assessing stratosphere-troposphere coupling in observational data or model output requires a multi-level index with high time resolution. Ideally, such an index would (1) represent spatial patterns in the troposphere that are most strongly coupled with stratospheric variability and (2) be robust and computationally feasible in both observations and standard model output. Several of the indices used to diagnose extratropical stratosphere-troposphere coupling are based on the Northern and Southern Hemisphere annular modes. The annular mode indices are commonly defined as the leading empirical orthogonal functions (EOFs) of monthly-mean, hemispheric geopotential height. In the lowermost troposphere, the structure of the annular modes is defined as the leading EOF of the near-surface geopotential height field, and these patterns correspond well to the patterns of variability induced by stratospheric circulation changes. At pressure levels above the surface, the structure of the annular modes is typically found by either calculating the local EOF or regressing geopotential height data onto the leading principal component time series of near-surface geopotential height. Here we make a critical comparison of the existing methodologies used to diagnose stratosphere-troposphere coupling, including EOF-based indices as well as measures based on zonal-mean wind at a fixed latitude and geopotential height over the polar cap. We argue in favour of an alternative methodology based on EOFs of daily zonally-averaged geopotential. We find that (1) the daily evolution of stratosphere-troposphere coupling events is seen most clearly with this methodology, and (2) the methodology is robust and requires few subjective choices, making it readily applicable to climate model output available only in zonal-mean form. Copyright c ! 2009 Royal Meteorological Society

This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958-2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of similar to 30-50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of similar to 10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (similar to 3-4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Copyright (C) 2009 Royal Meteorological Society

Often there is a need to consider spatial weighting in methods for finding spatial patterns in climate data. The focus of this paper is on techniques that maximize variance, such as empirical orthogonal functions (EOFs). A weighting matrix is introduced into a generalized framework for dealing with spatial weighting. One basic principal in the design of the weighting matrix is that the resulting spatial patterns are independent of the grid used to represent the data. A weighting matrix can also be used for other purposes, such as to compensate for the neglect of unrepresented subgrid-scale variance or, in the form of a prewhitening filter, to maximize the signal-to-noise ratio of EOFs. The new methodology is applicable to other types of climate pattern analysis, such as extended EOF analysis and maximum covariance analysis. The increasing availability of large datasets of three-dimensional gridded variables (e.g., reanalysis products and model output) raises special issues for data-reduction methods such as EOFs. Fast, memory-efficient methods are required in order to extract leading EOFs from such large datasets. This study proposes one such approach based on a simple iteration of successive projections of the data onto time series and spatial maps. It is also demonstrated that spatial weighting can be combined with the iterative methods. Throughout the paper, multivariate statistics notation is used, simplifying implementation as matrix commands in high-level computing languages.

This study examines the temporal evolution of the tropospheric circulation following large-amplitude variations in the strength of the Southern Hemisphere (SH) stratospheric polar vortex in data from 1979 to 2001 and following the SH sudden stratospheric warming of 2002. In both cases, anomalies in the strength of the SH stratospheric polar vortex precede similarly signed anomalies in the tropospheric circulation that persist for more than 2 months. The SH tropospheric circulation anomalies reflect a bias in the polarity of the SH annular mode (SAM), a large-scale pattern of climate variability characterized by fluctuations in the strength of the SH circumpolar flow. Consistent with the climate impacts of the SAM, variations in the stratospheric polar vortex are also followed by coherent changes in surface temperatures throughout much of Antarctica. The results add to a growing body of evidence that suggests that stratospheric variability plays an important role in driving climate variability at Earth’s surface on a range of time scales.

Observations and modeling studies support the hypothesis that solar cycle/ozone interactions create temperature and wind anomalies in the tropical upper stratosphere near 1 hPa. During extended winter (October–April), interactions with planetary-scale Rossby waves draw low-latitude stratospheric wind anomalies poleward and downward through the stratosphere. Solar influence on surface climate would likely involve interactions with stratospheric Rossby waves and the coupling of the lower stratospheric circulation to the circulation near Earth's surface. Here we provide an overview of stratosphere–troposphere dynamical coupling. We discuss dynamical mechanisms that might communicate stratospheric circulation anomalies downward to the troposphere and surface.

Recent analysis of the Arctic Oscillation (AO) in the stratosphere and troposphere has suggested that predictability of the state of the tropospheric AO may be obtained from the state of the stratospheric AO. However, much of this research has been of a purely qualitative nature. We present a more thorough statistical analysis of a long AO amplitude dataset which seeks to establish the magnitude of such a link. A relationship between the AO in the lower stratosphere and on the 1000 hPa surface on a 10-45 day time-scale is revealed. The relationship accounts for 5% of the variance of the 1000 hPa time series at its peak value and is significant at the 5% level. Over a similar time-scale the 1000 hPa time series accounts for 1% of itself and is not significant at the 5% level. Further investigation of the relationship reveals that it is only present during the winter season and in particular during February and March. It is also demonstrated that using stratospheric AO amplitude data as a predictor in a simple statistical model results in a gain of skill of 5% over a troposphere-only statistical model. This gain in skill is not repeated if an unrelated time series is included as a predictor in the model. Copyright © 2003 Royal Meteorological Society

We use an empirical statistical model to demonstrate significant skill in making extended-range forecasts of the monthly-mean Arctic Oscillation (AO). Forecast skill derives from persistent circulation anomalies in the lowermost stratosphere and is greatest during boreal winter. A comparison to the Southern Hemisphere provides evidence that both the time scale and predictability of the AO depend on the presence of persistent circulation anomalies just above the tropopause. These circulation anomalies most likely affect the troposphere through changes to waves in the upper troposphere, which induce surface pressure changes that correspond to the AO.

The dynamical coupling between the stratospheric and tropospheric circulations yields a statistically significant level of potential predictability for extreme cold events throughout much of the Northern Hemisphere (NH) mid‐high latitudes on both month-to-month and winter-to-winter timescales. Pronounced weakenings of the NH wintertime stratospheric polar vortex tend to be followed by episodes of anomalously low surface air temperatures and increased frequency of occurrence of extreme cold events throughout densely populated regions such as eastern North America, northern Europe, and eastern Asia that persist for ;2 months. Strengthenings of the vortex tend to be followed by surface temperature anomalies in the opposite sense. During midwinter, the quasibiennial oscillation (QBO) in the equatorial stratosphere has a similar but somewhat weaker impact on NH weather, presumably through its impact on the strength and stability of the stratospheric polar vortex; that is, the easterly phase of the QBO favors an increased incidence of extreme cold events, and vice versa. The signature of the QBO in NH wintertime temperatures is roughly comparable in amplitude to that observed in relation to

Annular modes are patterns characterized by synchronous fluctuations in surface pressure of one sign over the polar caps and the opposite sign at lower latitudes. The Southern Annular Mode (SAM) and Northern Annular Mode (NAM, also called the Arctic Oscillation) patterns are the leading empirical orthogonal functions (EOFs) of slowly-varying, hemispheric, cold-season, sea-level pressure anomalies (deviations from climatology). Daily indices of the SAM and NAM are a measure of the similarity between surface pressure anomaly patterns and the annular modes. Here it is shown that the first two EOF time series of daily, global, year-round, zonally-averaged surface pressure are nearly identical to the SAM and NAM indices. Together they account for more than 57% of the daily variance of zonally-averaged surface pressure. The SAM and NAM patterns extend through the tropics, well into the opposite hemispheres. Fluctuations of the SAM and NAM indices are accompanied by interhemispheric transfer of mass.

Equatorial winds in the stratosphere are known to influence the frequency of stratospheric midwinter sudden warmings. Sudden warmings, in turn, influence the Earth's climate both through their direct influence on polar temperatures and through the temperature dependence of ozone depletion in the lower stratosphere. The conventional (Holton-Tan) explanation for the equatorial influence on sudden warmings is in terms of the equatorial winds in the lower stratosphere (∼20-30 km) acting as a waveguide for midlatitude planetary wave propagation. This study employs stratospheric-temperature analyses and equatorial rocketsonde wind data extending to 58 km to diagnose the relationship between the northern-hemisphere polar temperatures and equatorial zonal winds at all height levels in the stratosphere. In addition to the recognized Holton-Tan relationship linking the polar temperatures to the quasi-biennial oscillation in equatorial winds in the lower stratosphere, a strong correlation of polar temperatures with equatorial winds in the upper stratosphere is found. We suggest that this may be associated with the strength and vertical extent of the westerly phase of the semi-annual oscillation in the upper stratosphere, although the observations alone cannot provide a conclusive, causal relationship. The main diagnostic tools employed are correlation studies and composite analysis. The results underline the need for continued high quality, equatorial wind measurements at all stratospheric levels.

Geopotential anomalies ranging from the Earth's surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the Arctic Oscillation (AO). The AO is represented herein by the leading mode (the first empirical orthogonal function) of low-frequency variability of wintertime geopotential between 1000 and 10 hPa. In the middle stratosphere the signature of the AO is a nearly zonally symmetric pattern representing a strong or weak polar vortex. At 1000 hPa the AO is similar to the North Atlantic Oscillation, but with more zonal symmetry, especially at high latitudes. In zonal-mean zonal wind the AO is seen as a north-south dipole centered on 40°–45°N; in zonal-mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to ∼10 hPa. The association of the AO pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere. By examining separately time series of AO signatures at tropospheric and stratospheric levels, it is shown that AO anomalies typically appear first in the stratosphere and propagate downward. The midwinter correlation between the 90-day low-pass-filtered 10-hPa anomaly and the 1000-hPa anomaly exceeds 0.65 when the surface anomaly time series is lagged by about three weeks. The tropospheric signature of the AO anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow, especially over the North Atlantic and Europe. The implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed.

Observations reveal that the wintertime southern hemisphere stratospheric polar vortex is modulated by the phase of the equatorial quasi-biennial oscillation (QBO). The high-latitude southern stratosphere is shown to be slightly colder throughout the winter, and the final warming occurs later, when the QBO is in its west phase. During May–October, the modulation of winds by the QBO is confined to midlatitudes, at the edge of the polar vortex. The difference between west and east phase composites of zonal mean wind during November, at the time of the final warming in the southern hemisphere, exceeded 14 ms−1. This difference is very similar to that in January in the northern hemisphere. While northern hemisphere QBO effects are optimized using equatorial winds near 40 hPa, southern hemisphere effects are best seen using ∼25 hPa winds.

Data from the historical rocketsonde network demonstrate that significant cooling of the upper stratosphere and lower mesosphere (∼30–60 km) occurred in northern midlatitudes of the western hemisphere and in the tropics during 1962–1991. The downward trend of temperature averaged over this layer was about −1.7 K/decade and temperatures were apparently modulated by the solar cycle with amplitude ∼1.1 K. The trend was a function of height and somewhat larger in the lower mesosphere relative to the middle and upper stratosphere.

Seasonal and interannual variations of the northern hemisphere stratosphere on the 600 K isentropic surface (20–35 hPa) are investigated by using observations for 1964–1996. An area diagnostic is defined in terms of Ertel's potential vorticity (PV), which measures the area enclosed by PV contours as a function of equivalent latitude and is not tied to the spherical coordinate system. Data from all seasons are examined for oscillations with periods of 6 months to more than a decade. Spectral analysis of PV at equivalent latitudes from 20°N to the pole reveals several possible signals: (1) In addition to the well-known annual cycle of the polar vortex there is a striking semiannual oscillation of PV in middle equivalent latitudes. At 34°–53°N the semiannual oscillation is larger than the annual cycle. This oscillation arises from the formation of a surf zone in winter, due to planetary wave breaking, superposed on the annual cycle. (2) A signal associated with the quasi-biennial oscillation (QBO) of the equatorial stratosphere, with average period slightly less than 30 months, is strongest at low equivalent latitudes and is apparent in middle equivalent latitudes up to 67°N. Through interaction with the annual cycle, oscillations with periods of 20.2 and 8.5 months are generated. These three spectral peaks at approximately 30, 20, and 8.5 months have been observed in ozone and wind data and are seen here, for the first time, in PV. (3) At middle to high equivalent latitudes, on the other hand, we observe biennial and associated 8-month oscillations related to the occurrence of stratospheric warmings and strong, undisturbed vortices in midwinter to late winter. The data record is remarkable in that, at high equivalent latitudes, strong and weak polar vortices alternated from year to year, producing the biennial signal and a significant negative lag-1-year autocorrelation. The addition of an 8-month harmonic generates a much better fit to the sharp late winter anomalies. (4) South of 60°N a spectral peak at 10.6 years is observed, with the clearest signal near 20°N. This spectral peak may be caused by the solar cycle, or it may arise through interaction of biennial and quasi-biennial oscillations.

A strong link exists between stratospheric variability and anomalous weather patterns at the earth’s surface. Specifically, during extreme variability of the Arctic polar vortex termed a “weak vortex event,” anomalies can descend from the upper stratosphere to the surface on time scales of weeks. Subsequently the outbreak of cold-air events have been noted in high northern latitudes, as well as a quadrupole pattern in surface temperature over the Atlantic and western European sectors, but it is currently not understood why certain events descend to the surface while others do not. This study compares a new classification technique of weak vortex events, based on the distribution of potential vorticity, with that of an existing technique and demonstrates that the subdivision of such events into vortex displacements and vortex splits has important implications for tropospheric weather patterns on weekly to monthly time scales. Using reanalysis data it is found that vortex splitting events are correlated with surface weather and lead to positive temperature anomalies over eastern North America of more than 1.5 K, and negative anomalies over Eurasia of up to −3 K. Associated with this is an increase in high-latitude blocking in both the Atlantic and Pacific sectors and a decrease in European blocking. The corresponding signals are weaker during displacement events, although ultimately they are shown to be related to cold-air outbreaks over North America. Because of the importance of stratosphere–troposphere coupling for seasonal climate predictability, identifying the type of stratospheric variability in order to capture the correct surface response will be necessary.

Twenty years of rawinsonde data (1973–1992) were examined in conjunction with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and outgoing longwave radiation (OLR) in 1980–1989 to determine the horizontal structure, propagation, and convective coupling of 3–6-day meridional wind oscillations over the tropical Pacific. Wave properties from ECMWF data, determined by lag correlation with respect to rawinsonde or ECMWF principal components, were consistent with what could be determined from the sparse rawinsonde network alone. Gridded analyses allowed a clearer distinction between equatorially trapped Rossby-gravity waves (RGW) and off-equatorial “tropical-depression” (TD) disturbances, so that the contrasting properties of these waves, including their seasonal and interannual variation, could be studied in better detail. Significant correlations with OLR were found, increasing in magnitude from eastern to western Pacific. The apparent group propagation of disturbances was equator...

Using 30 years of Northern Hemisphere geopotential data, from 1000 to 10 hPa, the link between three fundamental modes of tropospheric variability [the Pacific/North America (PNA), Western Pacific Oscillation (WPO), and Tropical/Northern Hemisphere (TNH) patterns] and the extratropical wintertime northern stratospheric circulation is explored. These modes of variability are known to be influenced by El Nino/Southern Oscillation (ENSO) and may provide a mechanism for ENSO to influence interannual variability of the strato-spheric flow. Aside from any link to ENSO, these modes may be important in providing tropospheric wave forcing to the stratosphere. These modes may be characterized by three of the leading rotated empirical orthogonal functions of the wintertime 5OO-hPa height field. An index of the amplitude of each of the modes is given by time series of principal components of that mode. By examining composites of years with high-index values minus years with low-index values it is shown that ...

Is the stratosphere, the atmospheric layer between about 10 and 50 km, important for predicting changes in weather and climate? The traditional view is that the stratosphere is a passive recipient of energy and waves from weather systems in the underlying troposphere, but recent evidence suggests otherwise. At a workshop in Whistler, British Columbia (1), scientists met to discuss how the stratosphere responds to forcing from below, initiating feedback processes that in turn alter weather patterns in the troposphere. The lowest layer of the atmosphere, the troposphere, is highly dynamic and rich in water vapor, clouds, and weather. The stratosphere above it is less dense and less turbulent (see the figure). Variability in the stratosphere is dominated by hemispheric-scale changes in airflow on time scales of a week to several months. Occasionally, however, stratospheric air flow changes dramatically within just a day or two, with large-scale jumps in temperature of 20 K or more. The troposphere influences the stratosphere mainly through atmospheric waves that propagate upward. Recent evidence shows that the stratosphere organizes this chaotic wave forcing from below to create long-lived changes in the stratospheric circulation. These stratospheric changes can feed back to affect weather and climate in the troposphere.

Proline and arginine are each indispensable during parenteral feeding due to limited interconversion by an atrophied gut. Commercial amino acid parenteral products designed for neonates contain proline concentrations that differ by almost 4-fold. To assess the adequacy of the lowest concentration of proline provided in commercial total parenteral nutrition (TPN) products, we compared rates of tissue-specific protein synthesis and nitrogen balance in neonatal piglets provided TPN at 2 different proline concentrations. Yucatan miniature piglets (9‐11 d old, n = 12) were randomized to complete isonitrogenous TPN diets with low proline (LP; L-proline as 3% of amino acids) or proline supplemented (PS; 9%). After 7 d of receiving TPN, rates of protein synthesis in liver, gastrocnemius muscle, jejunal mucosa, and skin were determined by the flooding dose technique and tissue free amino acids were measured. Nitrogen balance was assessed during the last 3 d. The LP TPN resulted in lower free proline concentrations in plasma, muscle, and skin (P , 0.05) and lower rates of protein synthesisin the jejunum (by 25%;P = 0.02), muscle (by 45%;P = 0.015), and skin (by 60%;P = 0.01); there was no difference in liver. Nitrogen retention was 20% lower in the LP group (P = 0.01). In conclusion, muscle and skin protein synthesis was profoundly sensitive to parenteral proline supply and the reduced protein synthesis in the intestine could affect intestinal integrity. Low-proline TPN solutions that are currently in wide use in neonatal care may result in impaired tissue growth. J. Nutr. 142: 1004‐1008, 2012.

Received 26 June 2012; accepted 26 August 2012; published 12 October 2012. [1] Extreme cold spells over Northern Europe during winter are examined in order to address the question to what degree and in which ways stratospheric dynamics may influence the state of the troposphere. The study is based on 500 years of a preindustrial control simulation with a comprehensive global climate model which well resolves the stratosphere, the MPI Earth System Model. Geopotential height anomalies leading to cold air outbreaks leave imprints throughout the atmosphere including the middle and lower stratosphere. A significant connection between tropospheric winter cold spells over Northern Europe and erosion of the stratospheric polar vortex is detected up to 30 hPa. In about 40 percent of the cases, the extreme cold spells are preceded by dynamical disturbances in the stratosphere. The strong warmings associated with the deceleration of the stratospheric jet cause the tropopause height to decrease over high latitudes. The compression of the tropospheric column below favors the development of high pressure anomalies and blocking signatures over polar regions. This in turn leads to the advection of cold air towards Northern Europe and the establishment of a negative annular mode pattern in the troposphere. Anomalies in the residual mean meridional circulation during the stratospheric weak vortex events contribute to the warming of the lower stratosphere, but are not key in the mechanism through which the stratosphere impacts the troposphere.

It is shown that interannual variability of the northern winter stratospheric flow in 1964-1993 was closely linked to large-scale circulation anomalies in the middle troposphere. Of the known tropospheric teleconnection patterns, the one having the strongest relation to the DJF (December-February) zonal-mean stratospheric flow was the North Atlantic Oscillation (NAO). Singular value decomposition between the 500 and 50-hPa geopotential heights produced a 500-hPa structure containing elements of the NAO pattern, but including an anomaly in eastern Siberia. During this time period, the correlation of NAO-related modes to the polar lower stratosphere exceeded that of the equatorial quasi-biennial oscillation.

The purpose of this chapter is to give an overview about effects of climate change on the temporal evolution of the stratospheric ozone layer. Climate change is affecting the ozone layer through changes in air mass transport, chemical composition, and temperature. In turn, changes to the ozone layer are influencing climate through radiative processes; consequential changes in temperature gradients are modifying atmospheric dynamics. Therefore, climate change and the evolution of the ozone layer are coupled. Understanding all of the processes involved is made more complex by the fact that many of the feedbacks between physical, dynamical and chemical processes in Earth's atmosphere are nonlinear. Investigations of the relationships and feedbacks between ozone depletion and climate change processes have demonstrated that it is not possible to achieve a complete understanding of long-term changes of stratospheric ozone content without the consideration of climate change.

International audience; The internal variability and coupling between the stratosphere and troposphere in CCMVal-2 chemistry-climate models are evaluated through analysis of the annular mode patterns of variability. Computation of the annular modes in long data sets with secular trends requires refinement of the standard definition of the annular mode, and a more robust procedure that allows for slowly varying trends is established and verified. The spatial and temporal structure of the models' annular modes is then compared with that of reanalyses. As a whole, the models capture the key features of observed intraseasonal variability, including the sharp vertical gradients in structure between stratosphere and troposphere, the asymmetries in the seasonal cycle between the Northern and Southern hemispheres, and the coupling between the polar stratospheric vortices and tropospheric midlatitude jets. It is also found that the annular mode variability changes little in time throughout simulations of the 21st century. There are, however, both common biases and significant differences in performance in the models. In the troposphere, the annular mode in models is generally too persistent, particularly in the Southern Hemisphere summer, a bias similar to that found in CMIP3 coupled climate models. In the stratosphere, the periods of peak variance and coupling with the troposphere are delayed by about a month in both hemispheres. The relationship between increased variability of the stratosphere and increased persistence in the troposphere suggests that some tropospheric biases may be related to stratospheric biases and that a well-simulated stratosphere can improve simulation of tropospheric intraseasonal variability.

During 1964-91, stratospheric temperature and circulation in Northern Hemisphere winter varied interannually on time scales from 2 to about 12 years. A substantial percentage of December-February interannual variance was correlated with the quasi-biennial oscillation (QBO). Additional monthly variance could be accounted for by quasi-decadal oscillation and QBO/low-frequency modulation. The QBO was the largest and most consistent of these signals, and its decadal modulation explains an apparent correlation with the solar cycle depending on the sign of the QBO - an interpretation supported by principal component analysis.

It is shown that the quasi-biennial oscillation of the equatorial lower stratosphere was correlated with mean zonal wind in the upper stratosphere, 1979-1990. Correlations were positive near 60 deg N and 30 deg S during Northern Hemisphere (NH) winter and negative in the equatorial upper stratosphere during all seasons. Spatial autocorrelation of mean zonal wind during NH winter was actually largest in the upper stratosphere, between 10 deg S and 62 deg N, due to strong coupling between tropical and extratropical flow at upper levels.

Using 25 years of National Meteorological Center (NMC) data for 1964-88 the relation between tropical and extratropical quasi-biennial oscillations (QBOs) was examined for zonally averaged quantities and planetary-wave Eliassen-Palm fluxes in the Northern Hemisphere winter. The extratropical QBO discussed by Holton and Tan (1980) existed in both temporal halves of the dataset. Autocorrelation analysis demonstrated that it was an important mode of interannual variability in the extratropical winter stratosphere. Correlation with the tropics was strongest when 40-mb equatorial winds were used to define the tropical QBO. Easterly phase at 40 mb implied a weaker than normal polar night jet and warmer than normal polar temperature and vice versa. An opposite relationship was obtained using 10-mb equatorial winds. The association between tropical and extratropical QBOs was observed in about 90 percent of the winters and was statistically significant. It is shown that planetary-wave Eliassen-Palm fluxes were generally consistent with the extratropical QBO. These fluxes were more (less) convergent in the midlatitude (subtropical) upper stratosphere in the 40-mb east (= easterly) phase category relative to the west category.

This study documents decadal-scale changes in the Holton and Tan (HT) relationship, i.e., the influence of the lower stratospheric equatorial quasi-biennial oscillation (QBO) on the northern hemisphere (NH) extratropical. circulation. Using a combination of ECMWF ERA-40 Reanalysis and Operational data from 1958-2006, we find that the Arctic stratosphere is indeed warmer under easterly QBO and colder under westerly QBO. During November to January, composite easterly minus westerly QBO signals in zonal wind extend from the lower stratosphere to the upper stratosphere and are centered at ∼5 hPa, 55-65°N with a magnitude of ∼10 m s-1. In temperature, the maximum signal is near ∼20-30 hPa at the pole with a magnitude of ∼4 K. During winter, the dominant feature is a poleward and downward transfer of wind and temperature anomalies from the midlatitude upper stratosphere to the high latitude lower stratosphere. For the first time, a statistically significant decadal scale change of the HT relationship during 1977-1997 is diagnosed. The main feature of the change is that the extratropical QBO signals reverse sign in late winter, resulting in fewer and delayed major stratospheric sudden warmings (SSWs), which occurred more often under westerly QBO. Consistent with earlier studies, it is found that the HT relationship is significantly stronger under solar minima overall, but the solar cycle does not appear to be the primary cause for the detected decadal-scale change. Possible mechanisms related to changes in planetary wave forcing are discussed. Copyright 2008 by the American Geophysical Union.