Stationary Wave Pattern Research Articles

Zonal-Eddy Dynamics of the North Atlantic Oscillation

Abstract This research is an attempt to understand the dynamical mechanisms that drive the wintertime North Atlantic oscillation (NAO) on monthly and longer timescales. In an earlier work by DeWeaver and Nigam, the authors showed that momentum fluxes from stationary waves play a large role in maintaining the zonal-mean zonal wind (u) perturbations associated with the NAO. In this paper, a linear stationary wave model is used to show that zonal-mean flow anomalies in turn play a large role in maintaining the NAO stationary waves. A strong two-way coupling thus exists between u and the stationary waves, in which each is both a source of and a response to the other. When forced by zonal-eddy coupling terms—terms that represent the interaction between NAO-covariant zonal-mean zonal wind anomalies and the climatological eddy flow—together with heating and transient fluxes, the model produces a realistic simulation of the observed stationary wave pattern. Zonal-eddy coupling terms make the largest contribution ...

Global water balance and atmospheric water vapour transport at last glacial maximum: climate simulations with the Canadian Climate Centre for Modelling and Analysis atmospheric general circulation model

A series of new simulations of the climate state at last glacial maximum has been performed using the Canadian second-generation atmospheric general circulation model and are described herein. The primary goal has been to assess the dynamic changes in the global water balance and water vapour transport that were characteristic of the climate state during this epoch of Earth's history. We pay special attention to comparisons of the atmospheric model simulations of last glacial maximum climate with those produced with a much simpler coupled energy balance-ice-sheet model, which has been designed to simulate the late Pleistocene cycle of glacial-interglacial ice volume variations. Our analyses, using the atmospheric model, demonstrate that the vigour of the hydrological cycle was markedly decreased under last glacial maximum conditions, as would be expected on the simplest thermodynamic grounds. The primary components of the hydrological cycle in the atmospheric model, namely precipitation and evaporation, constitute essential mechanisms that control ice-sheet mass balance. We also investigate changes in the Northern Hemisphere stationary wave patterns, as well as changes in the total and eddy moisture transport by the global circulation at last glacial maximum to illustrate the role played by the dynamics of the atmosphere in the maintenance of the Northern Hemisphere ice sheets. In particular, we find that the enhancement of the stationary wave pattern along with the convergence in atmospheric water vapour transport produces increased cooling and snow accumulation at last glacial maximum over the southeastern lobes of the Laurentide Ice Sheet. This suggests an explanation for the previously unexplained extension of these lobes deep into the New England states.

Volcanic eruptions and climate

Volcanic eruptions are an important natural cause of climate change on many timescales. A new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society. In addition, to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone‐depleting chemicals, it is crucial to quantify the natural fluctuations so as to separate them from anthropogenic fluctuations in the climate record. Studying the responses of climate to volcanic eruptions also helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. Furthermore, modeling the effects of volcanic eruptions helps us to improve climate models that are needed to study anthropogenic effects. Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e‐folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole‐to‐equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere continents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades. For a few days after an eruption the amplitude of the diurnal cycle of surface air temperature is reduced under the cloud. On a much longer timescale, volcanic effects played a large role in interdecadal climate change of the Little Ice Age. There is no perfect index of past volcanism, but more ice cores from Greenland and Antarctica will improve the record. There is no evidence that volcanic eruptions produce El Niño events, but the climatic effects of El Niño and volcanic eruptions must be separated to understand the climatic response to each.

Effects of an Imposed Quasi-Biennial Oscillation in a Comprehensive Troposphere–Stratosphere–Mesosphere General Circulation Model

A 48-yr integration was performed using the Geophysical Fluid Dynamics Laboratory SKYHI troposphere‐ stratosphere‐mesosphere GCM with an imposed zonal momentum forcing designed to produce a quasi-biennial oscillation (QBO) in the tropical stratosphere. In response to this forcing, the model generates a QBO in the tropical circulation that includes some very realistic features, notably the asymmetry between the strength of the descending easterly and westerly shear zones, and the tendency for the initial westerly accelerations to appear quite narrowly confined to the equator. The extratropical circulation in the Northern Hemisphere (NH) winter stratosphere is affected by the tropical QBO in a manner similar to that observed. In particular, the polar vortex is generally weaker in winters in which there are easterlies in the tropical middle stratosphere. Roughly twothirds of the largest midwinter polar warmings occur when the equatorial 30-mb winds are easterly, again in rough agreement with observations. Despite this effect, however, the total interannual variance in the zonalmean extratropical circulation in the model apparently is slightly decreased by the inclusion of the tropical QBO. The observed QBO dependence of the winter-mean stratospheric extratropical stationary wave patterns is also quite well reproduced in the model. The QBO was also found to have a profound influence on stratospheric stationary waves at low latitudes. Near and above 10 mb the NH stationary waves were found to penetrate across the equator during the westerly QBO phase, but to be restricted to latitudes poleward of ;108N during the easterly phase. This means that the equatorial QBO in prevailing wind near and above 10 mb has a significant zonally asymmetric component. If this is also true in the real atmosphere, there are important implications for the adequacy of the current observational rawindsonde network near the equator. Analysis of the zonal-mean zonal momentum budget in the tropical stratosphere reveals that the resolved waves in the model are strong enough to force the realized accelerations through much of the QBO cycle. The exception appears to be the easterly acceleration phase below about 20 mb. The implications of this for the generation of a self-consistent QBO by GCMs will be considered. The effects of the imposed QBO on the troposphere were found to be very modest. There does appear to be a statistically significant weakening (by ; 1ms 21) of the high-latitude winter vortex in the middle and upper troposphere. Given the very high predictability of the stratospheric QBO itself, this effect could possibly be used to enhance the skill of seasonal weather forecasts. No significant QBO influence was found in the model precipitation field.

Exact solutions for the kinematic model of autowaves in two-dimensional excitable media

The kinematic model for autowaves propagating in two-dimensional homogeneous excitable media is shown to be integrable exactly for steady-state patterns of zero topological charge. A whole set of solutions is found and the stability of the solutions is studied. V-shaped waves observed recently in experiments with Belousov-Zhabotinsky reaction correspond to one of the solutions found. Other solutions turn out to be self-crossing: revealing one or an infinite number of loops. It is shown that regular parts of self-crossing solutions describe different parts of steady-state autowave patterns in piecewise excitable media. Recent experiments with autowaves in excitable media with a stripe of enhanced excitability are analyzed and a new stationary wave pattern is predicted to exist in the case of a stripe of reduced excitability.

A Case Study of the Adequacy of GCM Simulations for Input to Regional Climate Change Assessments

Abstract The Sacramento Basin is used as the focus for a case study testing whether general circulation models (GCMS) are capable of simulating the large-scale and synoptic-scale processes important in studies of regional water resources. Output from a variety of GCMs developed at GISS and NCAR were examined, but only results from Community Climate Model (CCM) simulations are presented since they are typical. The stationary waves, jet streams, and storm tracks in the North Pacific-North America region in the CCM simulators show major differences from the observations, both in the mean and in their interannual variations. In addition, although the stationary wave and jet stream patterns associated with individual storms in the basin exhibit robust differences from mean fields in the observations, these differences are not captured in the models. Consequently, the larger-scale fields necessary for driving nested models and impact models for the basin, or for western North America in general, are problematic...

Stationary waves on cylindrical fluid jets

An obstacle in the path of a water jet emerging from a tap gives rise to a stationary wave pattern upstream of the obstacle. In this paper, the wavelengths and the damping coefficients of these waves are calculated for various jet radii and velocities. The calculations indicate that the wavelength decreases and the damping coefficient increases with increasing jet velocity, in qualitative agreement with observations.

A Diagnostic Comparison of the 1980 and 1988 U.S. Summer Heat Wave-Droughts

Abstract Observational analyses are performed to examine the roles of remote and local forcing in the evolutions of the extreme U.S. summer heat wave-drought cases of 1980 and 1988. At early stages, both events are associated with anomalous stationary wave patterns. Wave activity flux analyses suggest that in the 1980 case anomalous wave activity propagates southeastward from an apparent source region to the south of the Aleutians. The flux pattern is more complex in the 1988 case but suggests two possible source regions, one over the central North Pacific to the north of the Hawaiian Islands and a second located over the far western Pacific. The 1988 analyses show no anomalous wave propagation out of the eastern tropical Pacific, although this result does not necessarily preclude a role for tropical forcing in generating the anomalous wave train. In both cases the anomalous wave trains and associated wave activity fluxes become very weak by early July, indicating that remotely forced anomalous stationary...

Comparison of NCAR community climate model (CCM) climates

The simulated mean January and July climates of four versions of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) are compared. The models include standard configurations of CCM1 and CCM2, as well as two widely-cited research versions, the Global Environmental and Ecological Simulation of Interactive Systems (GENESIS) model and the Climate Sensitivity and Carbon Dioxide (CSC02) model. Each CCM version was integrated for 10 years with a horizontal spectral resolution of rhomboidal 15 (R15). Additionally, the standard T42 version of CCM2 was integrated for 20 years. Monthly mean, annually repeating climatological sea surface temperatures provided a lower boundary condition for each of the model simulations. The CCM troposphere is generally too cold, especially in the polar upper troposphere in the summer hemisphere. This is least severe in CCM2 and most pronounced in CCM1. CSC02 is an exception with a substantial warm bias, especially in the tropical upper troposphere. Corresponding biases are evident in atmospheric moisture. The overall superior CCM2 thermodynamic behavior is principally compromised by a large warm and moist bias over the Northern Hemisphere middle and high latitudes during summer. Differences between the simulated and observed stationary wave patterns reveal sizeable amplitude errors and phase shifts in all CCM versions. A common problem evident in the upper troposphere is an erroneous cyclone pair that straddles the equatorial central Pacific in January. The overall January stationary wave error pattern in CCM2 and CSCO2 is suggestive of a reverse Pacific-North American teleconnection pattern originating from the tropical central Pacific. During July, common regional biases include simulated North Pacific troughs that are stronger and shifted to the west of observations, and each model overestimates the strength of the anticyclone pair associated with the summer monsoon circulation over India. The simulated major convergence and divergence centers tend to be very localized in all CCM versions, with a tendency in each model for the maximum divergent centers to be unrelistically concentrated in monsoon regions and tied to regions of steep orography. Maxima in CCM-simulated precipitation correspond to the simulated outflow maxima and are generally larger than observational estimates, and the associated atmospheric latent heating appears to contribute to the stationary wave errors. Comparisons of simulated radiative quantities to satellite measurements reveal that the overall CCM2 radiative balance is better than in the other CCM versions. An error common to all models is that too much solar radiation is absorbed in the middle latitudes during summer.

Sensitivity of Dynamical Quantities to Horizontal Resolution for a Climate Simulation Using the ECMWF (Cycle 33) Model

Abstract The European Centre for Medium-Range Weather Forecasts (ECMWF) model (cycle 33) was integrated for a full seasonal cycle at four horizontal resolutions, T21, T42, T63, and T106. Within the limits imposed by the varying horizontal resolution all other aspects of the model were identical for each integration. In this paper a comparison is made of the dynamical aspects of the simulations. Fields of zonally averaged zonal wind, eddy heat and momentum fluxes, global divergent wind and vorticity, and stationary wave patterns are presented and compared for each resolution. The conclusions reached by this study are (i) T21 is qualitatively different from the higher resolutions; (ii) the highest resolution does not provide a simulation that is egregiously superior to T42. There are aspects of the T21 simulation, especially in tropical convection, that are clearly better than the higher resolutions; (iii) aside from differences in smaller-scale boundary forcing at the higher resolutions, the T42. T63, T106...

Stationary Turing patterns versus time-dependent structures in the chlorite-iodide-malonic acid reaction

The standing concentration patterns recently discovered in open gel-filled reactors, with the chlorite-iodide-malonic acid (CIMA) oscillating reaction in the presence of starch, were ascribed to a Turing-type reaction-diffusion symmetry breaking instability. Here we extend the investigations to other regions of parameters, with a particular emphasis to the role played by the chemical nature of the gel matrix and by the starch concentration on the onset of stationary patterns. Stationary Turing patterns are shown to develop in gel-free systems. Transitions between stationary Turing structures and wave patterns are presented. The first evidence of an anti-symmetric “homogeneous” wave source is presented.

Blocking distributions in the atmosphere

The zonal momentum generation in forced stationary waves may exceed the requirement for momentum balance after long, if the waves do not change their patterns. This suggests that the changes in stationary wave patterns would be required by maintenance of momentum balance over the external forcings. It will be found that the low frequency anomalies like blocking regimes may produce reversed zonal momentum variations, if they happen in the observed centre areas. The zonal momentum balance in the stationary waves may be maintained effectively by alternation between the normal and blocking circulation regimes. Thus, from the point of long-term zonal momentum balance, we may explain the geographical distributions of the blocking centres and the seasonal variations in blocking areas and frequencies.

Stationary MHD waves generated by a source in a moving plasma

The inductive interaction between a conducting body and a magnetized plasma in relative motion is formulated in terms of a source driving stationary magnetohydrodynamic waves in the frame of the body. Of particular interest is the existence of analytic solutions which describe the stationary wave pattern associated with a point source current. Such solutions are significant because not only do they, in principle, facilitate the construction of more general solutions by serving as Green's functions but also they provide an asymptotic description of the far field of the stationary wave pattern generated from each point of a source of finite size. The total pressure perturbation exhibits a Laplacian type behavior in the case of “subsonic” flow and a Mach cone like disturbance for “supersonic” flow. On the other hand, the associated electric potential response is mixed in nature in that it consists of compressive magnetoacoustic perturbations as well as the well‐known Alfvén wings corresponding to the shear Alfvén mode. In the subsonic case it is shown that although there is a strong disturbance in the potential on the Alfvén wings it is not narrowly confined to these wings by virtue of the two‐dimensional dipolelike contributions from the fast magnetoacoustic mode. In supersonic flow the potential disturbance is swept downstream and confined to the fast Mach cone, on which it is singular and within which lies the other singularity on the Alfvén wings.

Three-dimensional wave patterns generated by moving disturbances at transcritical speeds

Disturbances in the form of pressure fields, source distributions and time-dependent bottom topographies are discussed and found to produce similar wave patterns. Results obtained for wide channels are discussed in the light of the features of soliton reflection at a wall. Comparison with experiments shows excellent agreement. The introduction of radiation conditions enables long-time simulation of the development of wave patterns in infinite and semi-infinite fluids. A stationary wave pattern is also found to emerge for slightly supercritical Froude numbers, but contrary to linear results the leading divergent waves may originate ahead of the disturbance. This behaviour is due to nonlinear interactions similar to those governing collisions between solitons. This study on wave generation by a moving disturbance is based on numerical solutions of Boussinesq-type equations. The equations in their most general form are integrated by an implicit difference method. Strongly supercritical cases are described by a simplified set of equations which is solved by a semi-implicit difference scheme.

Differences between the Spring and Autumn Circulation of the Northern Hemisphere

The phase of the annual cycle in the mean temperature of the Northern Hemisphere troposphere lags the conventional meteorological seasons (centered on April and October) by about two weeds. Hence, the conventional spring season is colder and generally more winter-like than the autumn season. When the transition seasons are redefined so as to bring them more closely into line with the annual cycle in tropospheric mean temperature, a distinctive pattern of differences emerges, which is dominated by a zonally symmetric component. These differences are investigated, making use of three different climatological datasets. Spring is characterized by higher pressure over the polar regions, and lower pressures in the vicinity of 40°N at all levels in the troposphere and lower stratosphere. The amplitude of this difference pattern increases with height. Consistent with the pressure pattern, the belt of strongest zonally averaged westerlies is located farther equatorward, by 5–10° latitude, during spring than during autumn. These differences are observed during virtually every year. It is hypothesized that the difference in the position of the jet stream is responsible for some of the marked climatic contrasts between the two seasons observed over parts of the hemisphere. Differences between the climatological mean stationary wave patterns in the two seasons are documented and discussed. Differences in the phase tilts of the waves in the horizontal plane are consistent with the hypothesis that the, orographic forcing shifts equatorward during spring and poleward during autumn with the strongest zonally averaged zonal winds. The subtropical jetstreams are almost twice as strong during spring as during autumn, and outgoing longwave radiation data indicate that the tropical rain belt shifts northward from spring to autumn.

Influence of in vitro experimental design

<h2>Abstract</h2> In the design of experiments the methods for project initiation may involve a hypothesis formulation. Once identified, the hypothesis should be testable, internally consistent, repeatable, verifiable, and show dose dependency. Alternatively a project may begin after a screening study has been undertaken. In this case the hypothesis is formulated at end of the study and any observed positive "effect" can serve as a working postulate. <i>In vitro</i> cell exposure conditions can influence the end result, therefore experimental methodology should include a description of the cells lines and whether synchronised, in suspension, or a mono-layer of cells attached to vessel surface were used. Details of the medium should include the volume within the insonation chamber, its temperature and pressure, and whether it is aerated or contains nuclei for cavitation and whether radical scavengers are present. Important information about the ultrasound exposure would include the pulsing conditions, degree of focussing, presence of travelling waves, standing waves or stationary waves and internal reflections. An attempt should be made to identify the physical mechanisms of action, whether thermal, transient or stable cavitation, or other mechanical effects. Experimental design directly influences the interactive mechanism involved during <i>in vitro</i> exposures and is particularly important for non-thermal effects such as cavitation. Within an ultrasound beam passing through a cell suspension in a plastic tube, cells and bubbles are segregated by the presence of a stationary wave pattern such that cells collect in the pressure nodes whilst bubbles are held in the antinodes of the pressure wave. When the tube is rotated cells are swept in the fluid past arrays of bubbles trapped at the pressure maxima (Church & Miller, 1983) and lysis occurs at about 1 W/cm² SATA. However, if the tube remains stationary the cells are unaffected. The possibility of gas bubbles existing <i>in vivo</i> has not been resolved and needs further investigation. The importance of proper statistical interpretation of experimental results was stressed. Conclusions cannot be drawn from an <i>a posteriori</i> statistical analysis which can only lead to a hypothesis. Studies should start with a hypothesis of what is expected and the results analysed to test this hypothesis. Sound statistical analysis should be employed to avoid statements such as "the results were not significantly different, but a trend was noted." Finally, it was noted that safety of diagnostic ultrasound cannot be directly demonstrated by studies which only show absence of effects. The value of <i>in vitro</i> experiments to health and safety assessment is that they allow examination of the physical mechanisms of ultrasound interaction in biologically relevant systems.

Another look at the index cycle

Relationships between the zonal index, as defined by Rossby, the hemispheric circulation pattern, the amplitude of the zonally asymmetric or “eddy” component of the hemispheric circulation, and the amplitude of the stationary wave pattern during northern hemisphere winter are investigated using 27 years of gridded 5-day mean 500 mb height data from the US National Meteorological Center. In agreement with preliminary results reported in Rossby, the major stationary wave features appear to be displaced to the east of their climatological mean positions during periods of strong zonal flow, and vice versa . The zonal index shows only a weak negative temporal correlation with an index designed to monitor the hemispherically averaged variance of the eddy component of the 500 mb height field. Eddy amplitude is much more strongly correlated with the amplitude of the climatological mean stationary wave pattern. Hence, the notion of an “index cycle”, interpreted in terms of amplitude vacillation, does not appear to have much relevance to the northern hemisphere winter-time circulation. The situation may be different in the southern hemisphere, where the stationary waves are much weaker. DOI: 10.1111/j.1600-0870.1985.tb00445.x

Baroclinic generation of planetary transient and stationary waves from forced stationary waves

The linear instability of forced stationary waves in a baroclinic zonal flow is examined with a two‐level quasi‐geostrophic beta plane model. Realistic zonal topography and diabatic forcings produce a steady state solution of planetary‐scale stationary waves. Baroclinic instability of the forced waves gives rise to transient perturbation modes of planetary zonal scale and a preferred meridional scale of about twice the radius of deformation. One of the dominant planetary modes is stationary and resembles the observed stationary wave pattern. In the steady state model this form can be obtained only for certain values of the meridional scale of the forcings. It is suggested that this stationary mode could contribute to the time average stationary wave distribution. Applications to blocking are also considered. Interference of stationary and quasi‐stationary modes can apparently produce regional as well as global blocking patterns.

Reduction of systematic forecast errors in the ECMWF model through the introduction of an envelope orography

AbstractDay 1 forecast errors in the ECMWF model geopotential height fields during wintertime show a distinctive and highly reproducible signature with negative biases over the major mountain barriers. These biases are largest on days when the 500mb flow over the mountains is strong and they tend to shift position from day to day so as to remain close to the region where the jet stream crosses the mountain barrier. These systematic errors evolve through the forecast interval until by day 10 they assume an equivalent barotropic structure which strongly resembles the upper‐level stationary wave pattern, but has the opposite sign, which indicates that the model does not have sufficient (presumably orographic) forcing to maintain the stationary waves.The time evolution of the systematic error pattern is investigated by means of a series of experiments with a barotropic model, in which the observed mean wintertime 300 mb flow is perturbed by a steady forcing derived from the day 1 forecast error pattern. The day 10 error patterns, as simulated by the barotropic model, bear a strong similarity to the observed ones. The forcing in the vicinity of the northern Rockies makes a particularly large contribution to the simulated day 10 error pattern whereas that in the Himalaya region appears to be relatively less important.The impact of an enhanced orography upon the climate of the ECMWF model is investigated by carrying out a pair of extended integrations out to 50 days. The control run is based on the conventional average‐type orography used for operational forecasting; the other run is based on an ‘envelope orography’ constructed by adding to the conventional, grid‐square averaged, orography an increment proportional to the standard deviation of the sub‐grid scale variance. Results for this one, rather short pair of integrations suggest that the envelope orography may be capable of yielding a more realistic simulation of the observed wintertime flow pattern, particularly with respect to features in the Pacific and western North American sectors. Certain aspects of the zonally averaged circulation are also more realistic in this envelope simulation.A series of 21 successive ten‐day forecast integrations has also been carried out with this envelope orography from February 1982 data. Results indicate that the introduction of the envelope orography results in a slight degradation of the short‐range forecasts together with a distinct improvement of the forecast beyond four days. The beneficial impact towards the end of the forecast interval appears to be large enough to increase the forecast usefulness by perhaps as much as half a day.

The interaction of zonal currents with topography with applications to the Southern Ocean

An analytical model for the interaction of a broad, eastward baroclinic current with shallow topographic features in an unbounded β-plane ocean is developed and solved for three types of topography: a meridionally oriented ridge as is found in the central South Pacific and South Atlantic sectors of the Southern Ocean, a zonally oriented ridge as is found south of Australia and Africa, and an isolated plateau or seamount. The meridional ridge causes a stationary wave pattern similar to that believed to occur in the southeast Pacific Ocean. The zonal ridge causes a current intensification on the equatorward side of the ridge crest, with intermittent slowed or reversed flow and a string of stationary warm core eddies on the poleward side. Comparison is made to Callahan's (1971, Journal of Geophysics Research, 76, 5859–5870) observations of the flow along the ridge south of Australia. The isolated seamount forces a Taylor column (warm core anticyclonic eddy) above it, and has a stationary meandering wake downstream, sometimes with embedded eddies.