meridional and downward propagation of atmospheric circulation anomalies part ii southern hemisphere cold season variability abstract as in the northern hemisphere there exists a simultaneous poleward propagation of temperature anomalies in the stratosphere and equatorward propagation in the troposphere in the southern hemisphere s cold season it takes about 110 days for anomalies of one polarity to propagate from the equator to the pole or half the period of the complete cycle nearly twice as long as in the northern hemisphere the earlier poleward propagation of temperature anomalies in upper levels compared with those in lower levels results in an apparent downward propagation in the stratosphere accompanying the poleward and downward propagating warm cold anomalies is a successive leveling steepening of isentropic surfaces reflecting a simultaneous reduction strengthening of the meridional temperature gradient and increase decrease of the vertical static stability following changes in the thermal fields are poleward and downward propagating zonal wind anomalies of the opposite sign the arrival of the pole

downward coupling between the stratosphere and troposphere the relative roles of wave and zonal mean processes abstract wave and zonal mean features of the downward dynamic coupling between the stratosphere and troposphere are compared by applying a time lagged singular value decomposition analysis to northern hemisphere height fields decomposed into zonal mean and its deviations it is found that both zonal and wave components contribute to the downward interaction with zonal wave 1 due to reflection dominating on the short time scale up to 12 days and the zonal mean due to wave mean flow interaction dominating on the longer time scale it is further shown that the two processes dominate during different years depending on the state of the stratosphere winters characterized by a basic state that is reflective for wave 1 show a strong relationship between stratospheric and tropospheric wave 1 fields when the stratosphere is leading and show no significant correlations in the zonal mean fields on the other hand winters characterized by a stratospheric state that does not reflect waves show a strong relat

changes in occurrence of cold surges over east asia in association with arctic oscillation 1 it has been newly found that the occurrence of cold surges in east asia is significantly influenced by the arctic oscillation ao in the present study the events of cold surge are objectively determined based on several synoptic criteria and the phase dependency of its occurrences in association with the ao has been revealed during the negative ao phase the frequency of cold surge occurrence is relatively increased than that of neutral and positive ao phases the variation of upper level trough and jet stream over east asia and the siberian high in association of ao are suggested to explain the change of cold surge occurrences

biennial quasi biennial and decadal oscillations of potential vorticity in the northern 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

precursory signals of east asian winter cold anomalies in stratospheric planetary wave pattern the impacts of the stratospheric polar vortex changes on the tropospheric climate variability have been emphasized in previous studies the present study presents evidence for precursory signals of cold anomalies over east asia in the stratospheric wave pattern during november through march the leading two empirical orthogonal function eof modes of daily 50 hpa geopotential height anomalies along 65 n correspond to changes in the amplitude and phase of the stratospheric planetary wavenumber 1 respectively composite analysis is performed to unravel the temporal evolution of anomalies during 8 phases of 34 events identified based on the second eof mode with a complete life cycle for the period 1979 2016 the surface cold anomalies over eastern china emerge in phase 3 corresponding to negative and positive 50 hpa height anomalies on the north atlantic and russian far east sector respectively and peak in phase 5 corresponding to positive 50 hpa height anomalies over eurasia when the siberian high extends southeastward and the east asian trough deepens with anomalous surface northerly winds downward propagation of stratospheric signal is detected over western europe and western siberia the former is a source region of the tropospheric rossby wave trains propagating along the polar front jet and subtropical jet the downward propagation of stratospheric signal is related to the reflection of stratospheric planetary wavenumber 1 pattern and contributes to the development of the tropospheric rossby wave train that in turn leads to the strengthening of the siberian high and the deepening of the east asian trough

relationship between stationary planetary wave activity and the east asian winter monsoon 1 the variability of both the stationary planetary wave activity and the east asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses in this study we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of eliassenpalm flux between 50 n at 500 hpa and 40 n at 300 hpa it is found that compared to the winters of low wave activity the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters during these high activity winters the upward wave propagation from the troposphere into the stratosphere becomes weaker this is accompanied by a smaller perturbation in the polar vortex which tends to be colder and stronger in the meantime the east asian westerly jet stream the east asian trough the siberian high and the aleutian low all become weaker apparently in particular the weakening of the siberian high and the aleutian low decreases the northeasterly wind over east asia leading to a warming condition in the region especially in northeastern asia a further analysis reveals that the zonal wavenumber 2 pattern of planetary waves contributes dominantly to the variability of the east asian winter monsoon

meridional and vertical out of phase relationships of temperature anomalies associated with the northern annular mode variability 1 using the ncar ncep reanalysis we here present evidence suggesting that the out of phase relationships of temperature anomalies both between the low and high latitudes and between the stratosphere and troposphere are intimately related to the meridional and downward propagation of anomalies of both signs the temperature anomalies propagate poleward and downward above the tropopause and propagate equatorward below the tropopause the characteristic time scale for anomalies of one polarity to propagate from the equator to the pole or the half period of the complete cycle is about 55 days the relatively slow meridional propagation helps to explain the well known seesaw oscillatory pattern between low and high latitudes found in monthly data the equatorward propagation in the troposphere is synchronized with the poleward propagation of the stratospheric temperature anomalies of the opposite sign in both low and high latitudes responsible for the out of phase relation between the stratospheric and tropospheric temperature anomalies in the polar region since it takes about 55 days for anomalies of one polarity to propagate from the tropics to the pole such an intimate linkage between the anomalies in the deep tropics and high latitudes would imply a longer lead time for intra seasonal climate prediction in the extratropics

temporal changes in the cumulative piecewise gradient of a variant of the gutenberg richter relationship and the imminence of extreme events abstract it is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution for a long term dataset the overall slope of this logarithmically transformed distribution is usually indicated by a best fit straight line and expressed as a b value this slope is stable and normally lies between 0 8 and 1 2 the actual value depending on the region examined and the threshold selected for data completeness the linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run and with appropriate reservations may even be extrapolated to magnitudes that are beyond recent experience we suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution an emergence through time of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low end piecewise gradients of this distribution a marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent larger event on two separate occasions in 1982 and 1997 such temporal variations were seen in the magnitude distributions of sequences of events near tobago west indies and used to anticipate subsequent damaging mainshocks the recognition of temporal departures from overall linearity of the magnitude frequency relation in a suitable dataset may thus provide an evidential element that can contribute to earthquake forecasting this phenomenological approach was used in the analysis of the neic global dataset of earthquakes of magnitude 6 1 and bigger for the period 1973 2003 to explore its wider applicability trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake perhaps exceeding magnitude 8 5 such an event did occur shortly afterwards in the form of the great sumatran earthquake of 2004 12 26 following that event global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins indicating that another similar event was likely the second sumatran earthquake on 2005 03 28 satisfied that projection since that time a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake or earthquakes in the magnitude range 8 6 9 0 or even greater this contribution describes the piecewise gradient approach and examines its application to global earthquake data

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

influence of the vertical and zonal propagation of stratospheric planetary waves on tropospheric blockings 1 case studies are used to elucidate the relationship between stratospheric planetary wave reflection and blocking formation in the troposphere the enhanced upward propagation of a planetary scale wave packet from the eurasian sector involving a euro atlantic blocking leads to a stratospheric sudden warming ssw following the weakening of the stratospheric westerly jet due to polar warming the stratospheric planetary wave packet then propagates downward over the american sector inducing a ridge over the north pacific as well as a trough over eastern canada in the upper troposphere the ridge promotes the formation of a pacific blocking this result explains why pacific blockings tend to form after ssw and why they are associated with suppressed upward propagation of planetary waves

partially locked low angle normal faults in cohesive upper crust it is well established that slip on a frictionally weak low angle normal fault lanf can be more favorable than breaking a steep fault in strong crust very few studies however have considered the specific effect of crust and fault cohesion on lanf viability we do so using limit analysis a methodology for predicting the optimal orientation of faults with varying strength subjected to a specific set of boundary conditions accounting for crustal cohesion in our models reduces the lowest admissible lanf dip and even allows slip on high friction lanfs if the contrast between crust and fault cohesion is large fault cohesion however increases the lowest admissible lanf dip and introduces a locking depth above which lanf slip is not mechanically feasible this is consistent with observations of steep splay faults rooting onto lanfs in a variety of settings we further demonstrate that locking depth can help constrain lanf cohesion friction and fluid pressure on the alto tiberina italy and western corinth greece lanfs specifically assuming a measured fault friction of 0 2 0 3 we find that the shallow locking depth of the alto tiberina fault requires either 1 moderate fluid overpressure 57 of lithostatic with cohesion of 8 12 mpa or 2 strong overpressure 77 of lithostatic with cohesion of 13 20 mpa along the fault by contrast the larger locking depth characterizing the western corinth lanf can reflect greater fault cohesion

stratospheric origin of cold surge occurrence in east asia 1 in the present study we have found a precursory signal in the stratospheric circulation prior to the cold surge occurrence in east asia over northern eurasia about one week before the cold surge occurrence strong stratospheric negative potential vorticity anomalies and rising of geopotential height are observed the dynamic linkage between the stratospheric perturbations and the tropospheric adjustment along with initial disturbances for a cold surge occurrence are discussed

tropospheric wave response to decelerated stratosphere seen as downward propagation in northern annular mode 1 baldwin and dunkerton 1999 found that negative northern annular mode nam anomalies sometimes descend all the way from the stratosphere into the lower troposphere however no viable mechanism has been proposed so far to account for the magnitude of the anomalies in the denser troposphere further analysis shows that the character of the anomaly changes across the tropopause above the tropopause the nam pattern is approximately zonal and its descent represents the descent of decelerated zonal mean winds this stratospheric change is explainable using theories similar to those for the descent of the zero wind line associated with a major stratospheric sudden warming however such a reversal in the zonal mean wind rarely reaches the denser troposphere the descent of the nam anomalies into the troposphere may be implying a different relationship between the stratosphere and the troposphere we note that in the troposphere the structure of the nam has a large wave component in some cases this wave component appears to react to the decelerated wind configuration aloft here we show observations of the wave component and the zonal mean component in comparison to corresponding nam events to show that the wave response is a sizable component of the nam anomaly in the troposphere we will also present a simple model calculation to show that tropospheric waves forced by topography can react to changing stratospheric winds these tropospheric waves can project directly onto the tropospheric nam patterns and produce anomalies in the index which appear to be connected to the negative nam anomalies in the stratosphere

propagation of the arctic oscillation from the stratosphere to the troposphere 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

the association between stratospheric weak polar vortex events and cold air outbreaks in the northern hemisphere previous studies have identified an association between temperature anomalies in the northern hemisphere and the strength of stratospheric polar westerlies large regions in northern asia europe and north america have been found to cool during the mature and late stages of weak vortex events in the stratosphere a substantial part of the temperature changes are associated with changes in the northern annular mode nam and north atlantic oscillation nao pressure patterns in the troposphere the apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting but only if the temporal and spatial nature of the coupling is known using 51 winters of re analysis data we show that the development of the lower tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well defined stages including the formation of geographically distinct cold air outbreaks at the inception of weak vortex events a precursor signal in the form of a strong high pressure anomaly over northwest eurasia is associated with long lived and robust cold anomalies over asia and europe a few weeks later near the mature stage of the weak vortex events a shorter lived cold anomaly emerges off the east coast of north america the probability of cold air outbreaks increases by more than 50 in one or more of these regions during all phases of the weak vortex events this shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks as large changes in the frequency of extremes are involved this process is important for the medium range and seasonal prediction of extreme cold winter days three hundred year pre industrial control simulations by 13 coupled climate models corroborate our results copyright 2010 royal meteorological society and crown copyright

observational evidence of a stratospheric influence on the troposphere by planetary wave reflection abstract recent studies have pointed out the impact of the stratosphere on the troposphere by dynamic coupling in the present paper observational evidence for an effect of downward planetary wave reflection in the stratosphere on northern hemisphere tropospheric waves is given by combining statistical and dynamical diagnostics a time lagged singular value decomposition analysis is applied to daily tropospheric and stratospheric height fields recomposed for a single zonal wavenumber a wave geometry diagnostic for wave propagation characteristics that separates the index of refraction into vertical and meridional components is used to diagnose the occurrence of reflecting surfaces for zonal wavenumber 1 this study suggests that there is one characteristic configuration of the stratospheric jet that reflects waves back into the troposphere when the polar night jet peaks in the high latitude midstratosphere this configuration is related to the formation of a reflecting surface for vertical propagation

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

response of the stratosphere to interannual variability of tropospheric planetary waves a primitive equation global model of the middle atmosphere is used to investigate the response of the extratropical stratosphere to different levels of wave forcing from steady perturbations of the geopotential height near the tropopause the response of the stratosphere is compared to that in quasi geostrophic beta plane models used in previous studies the primitive equation model exhibits three flow regimes under perpetual january conditions strong westerly steady flow for small wave amplitude forcing strong westerly but unsteady flow for moderate wave amplitude forcing and oscillations between easterly and westerly flow for large wave amplitude forcing the regimes for low and high forcing are analogous to solutions of the simpler holton mass hm quasi geostrophic model the moderate forcing regime does not occur in the hm model and it is attributed to instability of the strongly sheared flow generated by planetary waves in the upper stratosphere we also show how the observed patterns of interannual variability in the winter stratosphere can be explained in terms of these three flow regimes in the northern hemisphere the flow often enters the high forcing regime where variations in conditions in the early winter flow or quasi steady upper tropospheric planetary wave amplitudes make similar contributions to the interannual variability in the stratospheric circulation for the southern hemisphere we suggest that the flow alternates between the low and moderate forcing regimes through year to year changes in the amplitude of quasi steady waves near the tropopause this mechanism produces large enough changes to explain the interannual variability in the southern stratosphere

the influence of stratospheric vortex displacements and splits on surface climate abstracta 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 correl

interdecadal variations of the east asian winter monsoon and their association with quasi stationary planetary wave activity abstract interdecadal variations of the east asian winter monsoon eawm and their association with the quasi stationary planetary wave activity are analyzed by using the 40 yr european centre for medium range weather forecasts re analysis dataset and the national centers for environmental prediction national center for atmospheric research reanalysis dataset it is found that the eawm experienced a significant weakening around the late 1980s that is the eawm was strong during 1976 87 and became weak after 1988 this leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold waves over east asia the dynamical process through which the eawm is weakened is investigated from the perspective of quasi stationary planetary waves it is found that both the propagation and amplitude of quasi stationary planetary waves have experienced obvious interdecadal variations which are well related to those of the eawm compared to the period 1976

interannual variability of the east asian winter monsoon and related modulations of the planetary waves abstractinterannual variability of the east asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years although the monsoon activity itself is confined into the lower troposphere its midwinter variability tends to accompany upper tropospheric geopotential height anomalies similar to the eurasian eu and western pacific wp teleconnection patterns the eu like pattern is characterized by a wavy signature over the eurasian continent and the north atlantic with surface temperature anomalies over the far east and north america in the wp like pattern a meridional dipole of upper level height anomalies is evident over the far east these anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper tropospheric planetary waves from late autumn to midwinter enhanced monsoon activity in january associated with the wp like pattern involves anomalous seasonal

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

tropospheric impact of reflected planetary waves from the stratosphere 1 a reflection of stratospheric planetary waves and its impact on the troposphere during a stratospheric sudden warming of march 2007 are investigated zonal propagation and reflection of the planetary waves is clearly seen in the longitude height sections of the eddy geopotential height and the vertical and zonal component of the three dimensional wave activity flux a wave packet propagating upward and eastward from eurasian continent was reflected by a negative wind shear in the upper stratospheric westerly jet caused by stratospheric warming waves then propagated downward to the american atlantic sector of the troposphere which led to the formation of a deep trough over the atlantic and brought cold weather to the northeastern part of the american continent

the effect of reflecting surfaces on the vertical structure and variability of stratospheric planetary waves the effects of an upper stratospheric reflecting surface on the vertical structure of stratospheric planetary waves are considered a diagnostic of the basic state wave propagation characteristics which is particularly useful for determining the existence and location of turning surfaces for meridional and vertical propagation is developed the diagnostic used is a more accurate indicator of wave propagation regions than the index of refraction because it diagnoses meridional and vertical propagation separately the diagnostic is tested on a series of simple models both steady state and time dependent it is found that the stratospheric waveguide sets the meridional wavenumber of the waves regardless of the characteristics of their tropospheric forcing making it easier to understand the effects of damping and turning surfaces on the vertical structure of the waves the diagnostic is then applied to observations of the southern hemisphere winter of 1996 it is shown that the differences in vertical wave structure between middle and late winter can be explained as a linear response to the seasonal evolution of the basic state which involves a formation of a reflecting surface in late winter it is also shown that on daily timescales wave mean flow interactions cause significant changes in the basic state propagation characteristics for periods of a few days these changes along with the time variations in the forcing of the waves are responsible for the observed daily timescale variations in wave structure the fact that the observed evolution of the waves and the basic state are consistent with linear or quasi linear wave theory depending on the timescale looked at supports the applicability of the theory as well as the validity of the observations