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A new procedure to obtain a longitudinally varying and slowly evolving atmospheric background state for the analysis of Rossby waveguides is described and discussed. The procedure is a rolling zonalization scheme, redistributing Ertel potential vorticity in a moving window to separate waves from the background. Waveguides are subsequently diagnosed from the gradient of the logarithm of potential vorticity. The effectiveness of the wave‐background separation, even in large‐amplitude conditions, is illustrated with reanalysis data. Established climatological‐mean waveguide structures are recovered from the rolling‐zonalized state in the limit of long‐term aggregation. Two contrasting episodes of Rossby wave packet propagation demonstrate how the evolution of waveguides derived from rolling zonalization can correspond to the development of superposed wave packets. The ability of the procedure to work with snapshots of the atmosphere provides new opportunities for waveguide research. Plain Language Summary: Rossby waves are meridional excursions of the jet stream, a strong band of wind in the extratropics. Stationary Rossby waves can cause extreme weather at the surface and traveling waves connect the weather of remote regions on the globe. Paths along which Rossby waves preferentially develop and travel are called waveguides. To detect the presence of a waveguide in atmospheric data, the waves have to be separated from their guiding atmospheric background state first. We introduce a new separation procedure for snapshots of the atmosphere that results in a slowly evolving and longitudinally varying background state. Our background state is a new source of local waveguide information, particularly in applications where no reliable information was available previously. Key Points: We construct a new atmospheric background state that is local in both space and timeWaveguide information can be extracted from the background state potential vorticity fieldOur scheme enables instantaneous waveguide analysis while also reproducing established waveguide patterns after long‐term aggregation [ABSTRACT FROM AUTHOR]

Banner clouds are clouds in the lee of steep mountains or sharp ridges on otherwise cloud-free days. Previous studies investigated various aspects of banner cloud formation in numerical simulations, most of which were based on idealized orography and a neutrally stratified ambient atmosphere. The present study extends these simulations in two important directions by 1) examining the impact of various types of orography ranging from an idealized pyramid to the realistic orography of Mount Matterhorn and 2) accounting for an ambient atmosphere that turns from neutral to stably stratified below the mountain summit. Not surprisingly, realistic orography introduces asymmetries in the spanwise direction. At the same time, banner cloud occurrence remains associated with a coherent area of strong uplift, although this region does not have to be located exclusively in the lee of the mountain any longer. In the case of Mount Matterhorn with a westerly ambient flow, a large fraction of air parcels rises along the southern face of the mountain, before they reach the lee and are lifted into the banner cloud. The presence of a shallow boundary layer with its top below the mountain summit introduces more complex behavior compared to a neutrally stratified boundary layer; in particular, it introduces a dependence on wind speed, because strong wind is associated with strong turbulence that is able to raise the boundary layer height and, thus, facilitates the formation of a banner cloud. [ABSTRACT FROM AUTHOR]

Recently, Nakamura and Huang proposed a theory of blocking onset based on the budget of finite-amplitude local wave activity on the midlatitude waveguide. Blocks form in their idealized model due to a mechanism that also describes the emergence of traffic jams in traffic theory. The current work investigates the development of a winter European block in terms of finite-amplitude local wave activity to evaluate the possible relevance of the "traffic jam" mechanism for the flow transition. Two hundred members of a medium-range ensemble forecast of the blocking onset period are analyzed with correlation- and cluster-based sensitivity techniques. Diagnostic evidence points to a traffic jam onset on 17 December 2016. Block development is sensitive to upstream Rossby wave activity up to 1.5 days prior to its initiation and consistent with expectations from the idealized theory. Eastward transport of finite-amplitude local wave activity in the southern part of the block is suppressed by nonlinear flux modification from the large-amplitude blocking pattern, consistent with the expected obstruction in the traffic jam model. The relationship of finite-amplitude local wave activity and its zonal flux as mapped by the ensemble exhibits established characteristics of a traffic jam. This study suggests that the traffic jam mechanism may play an important role in some cases of blocking onset and more generally that applying finite-amplitude local wave activity diagnostics to ensemble data is a promising approach for the further examination of individual onset events in light of the Nakamura and Huang theory. Significance Statement: Blocking is an occasional phenomenon in the mid- and high-latitude atmosphere characterized by the stalling of weather systems. Episodes of blocking are linked to extreme weather but their occurrence is not completely understood. A recent theory suggests that blocks may form in the jet stream like traffic jams on a highway. The onset mechanism contained in the theory could explain why forecasts of blocking are sometimes poor. In this work, we investigate the formation of a 2016 European winter block in the context of the traffic jam theory. Though questions remain regarding the implications for forecast uncertainty, our findings strongly support the notion of a traffic jam onset. [ABSTRACT FROM AUTHOR]

The Lagrangian representation of fluid flows offers a natural perspective to study many kinds of physical mechanisms. By contrast, the Eulerian representation is more convenient from a diagnostic point of view. This article attempts to combine elements of both worlds by proposing an Eulerian method that allows one to extract Lagrangian information about the atmospheric flow. The method is based on the offline advection of passive tracer fields and includes a relaxation term. The latter device allows one to run the integration in a continuous fashion without the need for reinitialization. As a result one obtains accumulated Lagrangian information, for example, about the recent parcel displacement or the recent parcel‐based diabatic heating, at each point of an Eulerian grid at any time step. The method is implemented with a pseudospectral algorithm suitable for gridded global atmospheric data and compared with the more traditional trajectory method. The method's utility is demonstrated on the basis of a few examples, which relate to cloud formation and the development of temperature anomalies. The examples highlight that the method provides a convenient diagnostic of parcel‐based changes, paving an intuitive way to explore the physical processes involved. Due to its gridpoint‐based nature, the proposed method can be applied to large data sets in a straightforward and computationally efficient manner, suggesting that the method is particularly useful for climatological analyses. [ABSTRACT FROM AUTHOR]

The waveguidability of an upper-tropospheric zonal jet quantifies its propensity to duct Rossby waves in the zonal direction. This property has played a central role in previous attempts to explain large wave amplitudes and the subsequent occurrence of extreme weather. In these studies, waveguidability was diagnosed with the help of ray tracing arguments using the zonal average of the observed flow as the relevant background state. Here, it is argued that this method is problematic both conceptually and mathematically. The issue is investigated in the framework of the nondivergent barotropic model. This model allows the straightforward computation of an alternative "zonalized" background state, which is obtained through conservative symmetrization of potential vorticity contours and that is argued to be superior to the zonal average. Using an idealized prototypical flow configuration with large-amplitude eddies, it is shown that the two different choices for the background state yield very different results; in particular, the zonal-mean background state diagnoses a zonal waveguide, while the zonalized background state does not. This result suggests that the existence of a waveguide in the zonal-mean background state is a consequence of, rather than a precondition for, large wave amplitudes, and it would mean that the direction of causality is opposite to the usual argument. The analysis is applied to two heatwave episodes from summer 2003 and 2010, yielding essentially the same result. It is concluded that previous arguments about the role of waveguidability for extreme weather need to be carefully reevaluated to prevent misinterpretation in the future. Significance Statement: Understanding strong undulations of the midlatitude jet stream is important, because these undulations are sometimes associated with extreme weather. Several previous publications have suggested that episodes with strong undulations can be caused by a jet that acts as a circumglobal waveguide. In the current paper we argue that these results are likely to be based on a misinterpretation and that the causality may be almost the other way around: large jet undulations can render the traditional waveguide diagnostic inappropriate and, thereby, fake strong circumglobal waveguidability. We suggest a novel diagnostic that tries to circumvent the problem. Our work implies that the results from previous publications need to be carefully reevaluated in order to avoid misinterpretation in the future. [ABSTRACT FROM AUTHOR]

Transient Rossby wave packets (RWPs) are a prominent feature of the synoptic to planetary upper-tropospheric flow at the midlatitudes. Their demonstrated role in various aspects of weather and climate prompts the investigation of characteristic properties like their amplitude, phase speed, and group velocity. Traditional frameworks for the diagnosis of the two latter have so far remained nonlocal in space or time, thus preventing a detailed view on the spatiotemporal evolution of RWPs. The present work proposes a method for the diagnosis of horizontal Rossby wave phase speed and group velocity locally in space and time. The approach is based on the analytic signal of upper-tropospheric meridional wind velocity and RWP amplitude, respectively. The new diagnostics are first applied to illustrative examples from a barotropic model simulation and the real atmosphere. The main seasonal and interregional variability features of RWP amplitude, phase speed, and group velocity are then explored using ERA5 reanalysis data for the time period 1979-2018. Apparent differences and similarities in these respects between the Northern and Southern Hemispheres are also discussed. Finally, the role of RWP amplitude and phase speed during central European short-lived and persistent temperature extremes is investigated based on changes of their distribution compared to the climatology of the region. The proposed diagnostics offer insight into the spatiotemporal variability of RWP properties and allow the evaluation of their implications at low computational demands. [ABSTRACT FROM AUTHOR]

Banner clouds are clouds that appear to be attached to the leeward face of a steep mountain. This paper investigates the role of wind speed and wind shear for the formation of banner clouds. Large-eddy simulations are performed to simulate the flow of dry air past an idealized pyramid-shaped mountain. The potential for cloud formation is diagnosed through the Lagrangian vertical parcel displacement, which in the case of a banner cloud shows a plume of large values in the lee of the mountain. In addition, vortical structures are visualized through streamlines and their curvature. A series of sensitivity experiments indicates that both the flow and the banner cloud occurrence are largely independent of the ambient wind speed U. On the other hand, the shear of the ambient wind has a profound impact on the location of the stagnation point on the windward face as well as on the flow geometry in the lee of the mountain. The relevant measure for shear is H/Hs, where H denotes the height of the mountain and Hs = U/Uz is the scale height of the shear (with Uz denoting the scale of the shear). The simulations are also used to compute the line-of-sight velocity component seen by a hypothetical Doppler wind lidar positioned in the lee of the mountain; the analysis suggests that such sensitivities can potentially be detected using modern wind lidar technology. [ABSTRACT FROM AUTHOR]

Rossby wave packets (RWPs) are Rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances. This review focuses on upper-tropospheric transient RWPs along the midlatitude jet stream. Their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor, a process called "downstream development." These RWPs sometimes act as long-range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems. The paper reviews research progress in this area with an emphasis on developments during the last 15 years. The current state of knowledge is summarized including a discussion of the RWP life cycle as well as Rossby waveguides. Recent progress in the dynamical understanding of RWPs has been based, in part, on the development of diagnostic methods. These methods include algorithms to identify and track RWPs in an automated manner, which can be used to extract the climatological properties of RWPs. RWP dynamics have traditionally been investigated using the eddy kinetic energy framework; alternative approaches based on potential vorticity and wave activity fluxes are discussed and put into perspective with the more traditional approach. The different diagnostics are compared to each other and the strengths and weaknesses of individual methods are highlighted. A recurrent theme is the role of diabatic processes, which can be a source for forecast errors. Finally, the paper points to important open research questions and suggests avenues for future research. [ABSTRACT FROM AUTHOR]

It has been suggested that upper-tropospheric Rossby wave packets propagating along the midlatitude waveguide may play a role for triggering severe weather. This motivates the search for robust methods to detect and track Rossby wave packets and to diagnose their properties. In the framework of several observed cases, this paper compares different methods that have been proposed for these tasks, with an emphasis on horizontal propagation and on a particular formulation of a wave activity flux previously suggested by Takaya and Nakamura. The utility of this flux is compromised by the semigeostrophic nature of upper-tropospheric Rossby waves, but this problem can partly be overcome by a semigeostrophic coordinate transformation. The wave activity flux allows one to obtain information from a single snapshot about the meridional propagation, in particular propagation from or into polar and subtropical latitudes, as well as about the onset of wave breaking. This helps to clarify the dynamics of individual wave packets in cases where other, more conventional methods provide ambiguous or even misleading information. In some cases, the 'true dynamics' of the Rossby wave packet turns out to be more complex than apparent from the more conventional diagnostics, and this may have important implications for the predictability of the wave packet. [ABSTRACT FROM AUTHOR]

There is still a high diversity of lichen-forming fungi that remains undescribed, especially cryptic lineages at the species level. Integrating morphological, chemical, and DNA sequence data has proved useful in corroborating species descriptions and delimitations. Here we reviewed morphological features, secondary metabolites and the DNA sequences of ITS, mtSSU and nuLSU markers to study the diversity of Xanthoparmelia in southern Africa. A total of 37 species were recorded. Three of these appear undescribed, and we therefore describe them here as new: Xanthoparmelia nimisii , with a sorediate thallus and broad lobes, is well supported as a clade separate from X. annexa ; X. pseudochalybaeizans with a white medulla is phylogenetically distinct from the otherwise similar X. chalybaeizans ; and X. sipmaniana , well supported as a separate clade from the similar X. hypoprocetrarica. In addition, the separation of Xanthoparmelia capensis and X. tinctina requires further studies. [ABSTRACT FROM AUTHOR]

Banner clouds are clouds that are attached to the leeward slope of a steep mountain. Their formation is essentially due to strong Lagrangian uplift of air in the lee of the mountain. However, little is known about the flow regime in which banner clouds can be expected to occur. The present study addresses this question through numerical simulations of flow past idealized orography. Systematic sets of simulations are carried out exploring the parameter space spanned by two dimensionless numbers, which represent the aspect ratio of the mountain and the stratification of the flow. The simulations include both two-dimensional flow past two-dimensional orography and three-dimensional flow past three-dimensional orography. Regarding flow separation from the surface, both the two- and the three-dimensional simulations show the characteristic regime behavior that has previously been found in laboratory experiments for two-dimensional orography. Flow separation is observed in two of the three regimes, namely in the 'leeside separation regime,' which occurs preferably for steep mountains in weakly stratified flow, and in the 'postwave separation regime,' which requires increased stratification. The physical mechanism for the former is boundary layer friction, while the latter may also occur for inviscid flow. However, flow separation is only a necessary, not sufficient condition for banner cloud formation. The vertical uplift and its leeward-windward asymmetry show that banner clouds cannot form in the two-dimensional simulations. In addition, even in the three-dimensional simulations they can only be expected in a small part of the parameter space corresponding to steep three-dimensional orography in weakly stratified flow. [ABSTRACT FROM AUTHOR]

Banner clouds are clouds in the lee of steep mountains or sharp ridges. Previous work suggests that the main formation mechanism is vertical uplift in the lee of the mountain. On the other hand, little is known about the Lagrangian behavior of air parcels as they pass the mountain, which motivates the current investigation. Three different diagnostics are applied in the framework of large-eddy simulations of airflow past an isolated pyramid-shaped obstacle: Eulerian tracers indicating the initial positions of the parcels, streamlines along the time-averaged wind field, and online trajectories computed from the instantaneous wind field. All three methods diagnose a plume of large vertical uplift in the immediate lee of the mountain. According to the time-mean Eulerian tracers, the cloudy parcels originated within a fairly small coherent area at the inflow boundary. In contrast, the time-mean streamlines indicate a bifurcation into two distinct classes of air parcels with very different characteristics. The parcels in the first class originate at intermediate altitudes, pass the obstacle close to its summit, and proceed directly into the cloud. By contrast, the parcels in the second class start at low altitude and take a fairly long time before they reach the cloud on a spiraling path. A humidity tracer quantifies mixing, revealing partial moistening for the first class of parcels and drying for the second class of parcels. For the online trajectories, the originating location of parcels is more scattered, but the results are still consistent with the basic features revealed by the other two diagnostics. [ABSTRACT FROM AUTHOR]

Upper-tropospheric Rossby wave packets have received increased attention recently. In most previous studies wave packets have been detected by computing the envelope of the meridional wind field using either complex demodulation or a Hilbert transform. The latter requires fewer choices to be made and appears, therefore, preferable. However, the Hilbert transform is fraught with a significant problem, namely, a tendency that fragments a single wave packet into several parts. The problem arises because Rossby wave packets show substantial deviations from the almost-plane wave paradigm, a feature that is well represented by semigeostrophic dynamics. As a consequence, higher harmonics interfere with the reconstruction of the wave envelope leading to undesirable wiggles. A possible cure lies in additional smoothing (e.g., by means of a filter) or resorting to complex demodulation (which implies smoothing, too). Another possibility, which does not imply any smoothing, lies in applying the Hilbert transform in semigeostrophic coordinate space. It turns out beneficial to exclude planetary-scale wavenumbers from this transformation in order to avoid problems in cases when the wave packet travels on a low wavenumber quasi-stationary background flow. [ABSTRACT FROM AUTHOR]

A novel method is introduced to automatically identify upper-level Rossby wave trains and to objectively diagnose their properties. Based on the envelope of the upper tropospheric meridional wind represented in a Hovmöller diagram, the algorithm identifies individual Rossby wave trains as objects. These depend to some extent on user defined parameters. The utility of the method is demonstrated in two areas of application. First, the skill of a particular numerical weather prediction model is analysed for a specific case of a long-lived Rossby wave train. For this purpose, a novel diagnostic is designed based on a Hovmöller diagram of the Rossby wave train objects that contains forecast data with the same lead time throughout the diagram. Automatically calculated properties of the different forecast Rossby wave trains are compared. Second, the climatological behaviour of Rossby wave train objects is investigated in long time series from reanalysis data. There are preferred regions for the generation and the decay of Rossby wave trains, and these regions show significant differences for Rossby wave trains of different minimum lifetimes; in addition there are substantial differences between the seasons. [ABSTRACT FROM AUTHOR]

Banner clouds are clouds in the lee of steep mountains or sharp ridges. Their formation has previously been hypothesized as due to three different mechanisms: (i) vertical uplift in a lee vortex (which has a horizontal axis), (ii) adiabatic expansion along quasi-horizontal trajectories (the so-called Bernoulli effect), and (iii) a mixing cloud (i.e., condensation through mixing of two unsaturated air masses). In the present work, these hypotheses are tested and quantitatively evaluated against each other by means of large-eddy simulation. The model setup is chosen such as to represent idealized but prototypical conditions for banner cloud formation. In this setup the lee-vortex mechanism is clearly the dominant mechanism for banner cloud formation. An essential aspect is the pronounced windward-leeward asymmetry in the Lagrangian vertical uplift with a plume of large positive values in the immediate lee of the mountain; this allows the region in the lee to tap moister air from closer to the surface. By comparison, the horizontal pressure perturbation is more than two orders of magnitude smaller than the pressure drop along a trajectory in the rising branch of the lee vortex; the 'Bernoulli mechanism' is, therefore, very unlikely to be a primary mechanism. Banner clouds are unlikely to be 'mixing clouds' in the strict sense of their definition. However, turbulent mixing may lead to small but nonnegligible moistening of parcels along time-mean trajectories; although not of primary importance, the latter may be considered as a modifying factor to existing banner clouds. [ABSTRACT FROM AUTHOR]

The tropopause inversion layer (TIL) is a region of enhanced static stability just above the WMO-defined thermal tropopause. It is a ubiquitous feature in midlatitudes and is well characterized by observations. However, it is still lacking a satisfactory theoretical explanation. This study utilizes adiabatic baroclinic life cycle experiments to investigate dynamical mechanisms that lead to TIL formation. As the baroclinic wave grows, a strong TIL forms above anticyclonic anomalies, while no TIL is found above cyclonic anomalies; this is consistent with previous results. However, during the early growth phase there is no TIL in the global or zonal average: positive and negative anomalies cancel out exactly. The zonal and global mean TIL only emerges during the mature stage of the life cycle, after the onset of wave breaking. The TIL predominantly occurs equatorward of the jet and the vertical structure bears resemblance to the TIL in midlatitudes; there is no equivalent to the subpolar TIL. Life cycles without significant wave breaking develop neither a global nor a zonal mean TIL. No global mean TIL is found in any life cycle if the dynamical tropopause definition is used. In addition, a new mechanism of dynamical TIL formation is presented, suggesting that the TIL in the global and zonal mean is linked to a strongly skewed distribution of relative vorticity after wave breaking. [ABSTRACT FROM AUTHOR]

Based on findings in vascular plants showing that the capacity to provide enough carbon skeletons for rapid ammonium assimilation into amino acids is a prerequisite for tolerance to eutrophication, we tested the hypothesis that lichens from shady habitats are particularly sensitive to nitrogen pollution. We tested this hypothesis using published ecological indicator values (estimates of eutrophication tolerance and light preferences on an ordinal scale) for more than 500 central European lichen species. Our results show that shade-adapted lichens are indeed at the same time intolerant to eutrophication. However, not all eutrophication-sensitive lichens inhabit shady environments, suggesting the existence of several independent mechanisms causing intolerance of high nitrogen levels in lichens. The correlation of shade adaptation with nitrogen intolerance is limited to epiphytic and saxicolous species, since terricolous lichens are out-competed by vascular plants in dense vegetation. Our results suggest that lichen communities of shady bark, wood and rock are particularly sensitive to eutrophication. [ABSTRACT FROM AUTHOR]

This paper investigates the occurrence, formation, and maintenance of eyes in idealized axisymmetric balanced vortices with diabatic forcing. Two key elements of the model setup are temperature relaxation toward a specified equilibrium temperature Te and Ekman pumping from a turbulent boundary layer. Furthermore, the flow is assumed to be almost inviscid in the interior. The model does not attempt any closure for moist convection. Previous work by the authors has shown that there is a continuous transition from monsoonlike vortices to hurricane-like vortices. This transition is governed by the ratio F = αT/cD, where αT is the thermal relaxation rate and cD the surface drag coefficient. An eye is defined in terms of the vertical wind with maximum upwelling occurring at some finite radius rather than at the origin. It is possible to obtain an eye even though Te maximizes at the origin, that is, even though Te does not directly predispose upwelling at some finite radius. The occurrence of an eye is controlled by F, and the transition between vortices without any eye and vortices with a clearly defined eye is rather sudden. These results are robust with respect to the amplitude of the forcing or the specific shape of Te. The key role of F is corroborated through a systematic nondimensionalization. In a steady-state hurricane-like vortex, mechanical forcing from Ekman pumping maximizes at some finite radius and is instrumental for the maintenance of an eyelike secondary circulation. On the other hand, eye formation during spinup is a purely inviscid process. The results imply that eye formation is a robust and general feature in vortices with strong diabatic forcing. [ABSTRACT FROM AUTHOR]

This note investigates the dependence of the extratropical tropopause inversion layer (TIL) on numerical resolution in an idealized modeling framework. Axisymmetric upper-tropospheric anticyclones are constructed by specifying potential vorticity (PV) and solving the nonlinear PV-inversion problem. The PV distribution has a smooth but near-discontinuous change of PV across the tropopause in a transition zone with vertical depth δ. For fixed δ the strength of the TIL changes with changing resolution until the transition zone is resolved by a fairly large number of grid points. The quality-controlled numerical solutions are used to study the behavior for δ → 0. This limit can lead to very strong TILs, but no indications for divergent behavior were found. [ABSTRACT FROM AUTHOR]

This paper presents the dry version of a new large-eddy simulation (LES) model, which is designed to simulate air flow and clouds above highly complex terrain. The model is three-dimensional and nonhydrostatic, and the governing equations are sound filtered by use of the anelastic approximation. A fractional step method is applied to solve the equations on a staggered Cartesian grid. Arbitrarily steep and complex orography can be accounted for through the method of viscous topography. The dynamical model core is validated by comparing the results for a spreading density current against a benchmark solution. The model accuracy is further assessed through the simulation of turbulent flow across a quasi two-dimensional ridge. The results are compared with wind-tunnel data. The method of viscous topography is not restricted to moderately sloped terrain. Compared to models using curvilinear grids, it allows this model to be applied to a much wider range of flows. This is illustrated through the simulation of an atmospheric boundary-layer flow over a surface mounted cube. The results show that the dry model version is able to accurately represent the complex flow in the vicinity of three-dimensional obstacles. It is concluded that the method of viscous topography was successfully implemented into a micrometeorological LES model. As will be shown in Part II, this allows the detailed study of clouds in highly complex terrain. [ABSTRACT FROM AUTHOR]

Buellia peregrina is described as new to science from small limestone pebbles on exposed ground of the coastal Namib Desert, Namibia. The species is unusual for two reasons: (I) it is the only species in Buellia s.l. currently known to grow euendolithically, i.e., establishing a thallus entirely within its rock substratum, and (2) its apothecia contain a previously unknown blue pigment, here described as peregrina-blue according to its colour and characteristic reactions with HNO33, KOH and HCI. [ABSTRACT FROM AUTHOR]

This paper provides a unified perspective on the dynamics of hurricane- and monsoonlike vortices by identifying them as specific limiting cases of a more general flow system. This more general system is defined as stationary axisymmetric balanced flow of a stably stratified non-Boussinesq atmosphere on the f plane. The model is based on the primitive equations assuming gradient wind balance in the radial momentum equation. The flow is forced by heating in the vortex center, which is implemented as relaxation toward a specified equilibrium temperature Te. The flow is dissipated through surface friction, and it is assumed to be almost inviscid in the interior. The heating is assumed supercritical, which means that Te does not allow a regular thermal equilibrium solution with zero surface wind, and which gives rise to a cross-vortex secondary circulation. Numerical solutions are obtained using time stepping to a steady state, where at each step the Eliassen secondary circulation is diagnosed as part of the solution strategy. Reality and regularity of the solution is discussed, putting this work in relation to previous work. Scaling analysis suggests that for a given geometry, essential vortex properties are controlled by the ratio F = αT/cD, where αT is the rate of thermal relaxation and cD quantifies the strength of surface friction for a given surface wind. For large F, the temperature is close to Te and the vortex shows properties that can be associated with a hurricane including strong cyclonic surface winds. On the other hand, for small F, the vortex shows properties that can be associated with a monsoon; that is, the surface winds are small and the secondary circulation keeps the temperature significantly away from Te. The scaling analysis is verified by numerical solutions spanning a wide range of the parameter space. It is shown how the two limiting cases correspond with the respective approximate semianalytical theories presented previously. The results imply an important role of αT for hurricane formation. [ABSTRACT FROM AUTHOR]

The new species Arthothelium desertorum is described from the Namib desert. It is characterized by its saxicolous habit and areolate thallus containing divaricatic acid. [ABSTRACT FROM AUTHOR]

The new species Arthothelium desertorum is described from the Namib desert. It is characterized by its saxicolous habit and areolate thallus containing divaricatic acid. [ABSTRACT FROM AUTHOR]

Idealized axisymmetric anomalies of potential vorticity (PV) on a midlatitude f plane and their related response in terms of balanced wind and temperature are investigated with special focus on the static stability in the tropopause region. The PV anomalies are specified such that they can be interpreted as the result of conservative advection in the tropopause region across the gradients of a prescribed background atmosphere with piecewise constant buoyancy frequency squared N[SUP2]. Related cyclones and anticyclones are treated identically except for the sign of the tropopause potential temperature anomaly. Composite profiles of N[SUP2] are computed, for which the thermal tropopause is used as a common reference level and where the number of cyclones in the composite equals the number of anticyclones. One obtains a pronounced peak of N[SUP2] just above the tropopause and slightly enhanced values below the tropopause in comparison with the background profile. Within the framework of PV inversion various mechanisms are identified. Important contributions to the peak in N[SUP2] are due to the pronounced cyclone-anticyclone asymmetry in the vertical structure of the tangential wind, and to the poleward advection of high values of PV from the subtropical lower stratosphere. Qualitatively, the key features of the composite profiles are in good agreement with observations above southern Germany that have recently been compiled. [ABSTRACT FROM AUTHOR]

Examines the impact of the parameterization for Rossby wave breaking to obtain an improved representation of wave damping throughout the stratosphere through the Matsuno model. Overview of the Rossby wave breaking; Discussion on the application of the Matsuno model in wave damping; Details on the testing of the model.

Presents information on a study which investigated the differences between upper-tropospheric cyclones and anticyclones regarding the height of the thermal and dynamical tropopause. Methodology; Results of the study; Summary and conclusions.

Presents a study which investigated the flow of the Rayleigh friction parameter, with reference to the stationary axisymmetric balanced flow of stably stratified dry non-Boussinesq atmosphere in the f plane. Examination of the threshold behavior in the frictionless limit and the subcritical regime; Use of model to investigate the nonlinear dependence of the secondary circulation of the Rayleigh friction; Findings of the study.

The quasi-horizontal roll-up of unstable stratospheric intrusions into isolated vortices is known to result in specific structures on satellite water vapor images that are characterized by intermingling dark and light filaments. The current paper investigates how these features are generated and how they relate to partly similar features found on concurrent maps of the tropopause height or potential vorticity (PV). The roll-up of a stratospheric intrusion is simulated numerically with an idealized quasigeostrophic model, which focuses on the dynamics induced by anomalies in the height of the tropopause. The upper-tropospheric adiabatic vertical wind is calculated explicitly and is used to simulate water vapor images in the model. These images show qualitatively the same characteristic features as observed. They are generated through a combination of horizontal advection of initial moisture anomalies and the creation of additional moisture anomalies resulting from the upper-tropospheric vertical air motion. The latter is, in turn, induced by the quasi-horizontal motion of the tropopause anomaly. It is suggested that a substantial portion of the spiral-like structures on the water vapor images is likely to reflect the vertical wind induced by the evolution of the intrusion itself. When the tropopause is defined through a fairly low value of PV, it may acquire similar spiraling structures, as it is being advected almost like a passive tracer. On the other hand, for the dynamically active core part of the intrusion, which is located at higher values of PV, one may expect an evolution leading to more compact vortex cores and less structure overall. [ABSTRACT FROM AUTHOR]

Comments on the paper by Wei Ming-Ying in 1987 entitled: `A new formulations of the exchange of mass and trace constituents between the stratosphere and troposphere.' Potential vorticity (PV) as vertical coordinate; Vagueness of Wei's formulations.

Upper tropospheric Rossby wave packets (RWPs) have implications for the predictability of the atmosphere. Recently it has been shown that there is a link between high forecast skills in the medium and long range and long lived RWPs propagating from the Pacific region towards Europe across North America and the North Atlantic. On the other hand, this was not the case for such wave packets that deeply interacted with mesoscale phenomena in the lower and mid-troposphere over the North American continent. This contribution presents a novel diagnostic for RWPs based on local finite amplitude wave activity (LWA) in the primitive equations/isentropic coordinates framework and its application to an episode in which a propagating RWP was associated with a reduced predictability horizon. LWA is proportional to the local (in longitude) meridional displacement of contours of potential vorticity (PV) from zonal symmetry. The advantage of using LWA consists in the fact that its formulation does not make any small amplitude assumption and it is able to identify nonlinear phenomena such as Rossby wave breaking, blocking, PV streamers, or cutoffs. Furthermore, LWA has an exact conservation relation which allows one to formulate a budget equation for its evolution, distinguishing between conservative propagation and the impact of non-conservative processes. The latter is quantified as a residual from the LWA budget equation. In addition, the conservative propagation is partitioned into the tropopause near, tropopause deep and divergent wind contribution using the Helmholtz partitioning and a piecewise potential vorticity inversion technique.This new diagnostic is applied first to RWPs simulated in a dry general circulation model (the Portable University Model of the Atmosphere, PUMA) showing that nonconservative processes in general play a non-negligible role in their evolution. The LWA diagnostic and its budget are also applied to a specific episode containing a large amplitude wave packet propagating from North America towards Europe which was associated to very low forecast skills. This was done by using the forecasts from the European Center for Medium range Weather Forecast and the respective analyses and comparing the two. The results show that nonconservative processes played a considerable role in the RWP dynamics. In particular the operational model misrepresented the wave packet amplitude during its growth stage, leading to a wrong amplitude throughout the whole episode. This fact was associated to the very low forecast skills during that episode. [ABSTRACT FROM AUTHOR]

Two diagnostics based on potential vorticity and the envelope of Rossby waves are used to investigate upscale error growth from a dynamical perspective. The diagnostics are applied to several cases of global, real-case ensemble simulations, in which the only difference between the ensemble members lies in the random seed of the stochastic convection scheme. Based on a tendency equation for the enstrophy error, the relative importance of individual processes to enstrophy-error growth near the tropopause is quantified. After the enstrophy error is saturated on the synoptic scale, the envelope diagnostic is used to investigate error growth up to the planetary scale. The diagnostics reveal distinct stages of the error growth: in the first 12 h, error growth is dominated by differences in the convection scheme. Differences in the upper-tropospheric divergent wind then project these diabatic errors into the tropopause region (day 0.5–2). The subsequent error growth (day 2–14.5) is governed by differences in the nonlinear near-tropopause dynamics. A fourth stage of the error growth is found up to 18 days when the envelope diagnostic indicates error growth from the synoptic up to the planetary scale. Previous ideas of the multiscale nature of upscale error growth are confirmed in general. However, a novel interpretation of the governing processes is provided. The insight obtained into the dynamics of upscale error growth may help to design representations of uncertainty in operational forecast models and to identify atmospheric conditions that are intrinsically prone to large error amplification. [ABSTRACT FROM AUTHOR]

The lichen flora in the German Federal State of Mecklenburg-Western Pomerania was analysed with special focus on its occurrence in habitats. We distinguished the following habitats: coasts, waters, peatlands, forests (collectively subsumed under natural landscape), semi-cultivated land, cultivated land and settlement area (collectively subsumed under cultivated landscape). Presence and conservation status of lichen species were analysed with respect to their habitats, substrates and distribution patterns and compared with the correspondending traits of the lichen flora in all of Germany (Litterski et al. 2019) and of higher plants in Mecklenburg-Western Pomerania. The number of lichens (39 %) growing in forests is high in Mecklenburg-Western Pomerania, similar to entire Germany, whereas the proportion of extinct and threatened lichen species in forests (Mecklenburg-Western Pomerania: 64 %, Germany: 56 %) is much higher than the proportion of extinct and threatened higher plant species in forests (Mecklenburg-Western Pomerania: 20 %, Germany: 14 %). In contrast, the proportion of threatened lichens and higher plants in dry semi-cultivated land is equal (lichens in both areas: 52 %, higher plants in Mecklenburg-Western Pomerania: 61 %, Germany: 42 %). We found a conservation status of high concern in terricolous and epiphytic lichens in both study areas. The proportion of extinct and threatened lichen species was around 60 % in each case. The proportion of threatened lichen species of distribution type I (temp/mo-alp-arct) in Mecklenburg-Western Pomerania is significantly higher compared to Germany as a whole (Mecklenburg-Western Pomerania: 75 % of 83 species, Germany: 46 % of 459 species). Among the endangered lichens of distribution type V (med-temp·subatl) there are many species that depend on old-growth forests and have limited dispersal ability (Mecklenburg-Western Pomerania: 69 % of 108 species, Germany: 67 % of 251 species being extinct or endangered). [ABSTRACT FROM AUTHOR]

Upper-tropospheric Rossby wave packets (RWPs) are important dynamical features, because they are often associated with weather systems and sometimes act as precursors to high-impact weather. The present work introduces a novel diagnostic to identify RWPs and to quantify their amplitude. It is based on the local finite-amplitude wave activity (LWA) of Huang and Nakamura, which is generalized to the primitive equations in isentropic coordinates. The new diagnostic is applied to a specific episode containing large-amplitude RWPs and compared with a more traditional diagnostic based on the envelope of the meridional wind. In this case, LWA provides a more coherent picture of the RWPs and their zonal propagation. This difference in performance is demonstrated more explicitly in the framework of an idealized barotropic model simulation, where LWA is able to follow an RWP into its fully nonlinear stage, including cutoff formation and wave breaking, while the envelope diagnostic yields reduced amplitudes in such situations. [ABSTRACT FROM AUTHOR]

Synoptic-scale error growth near the tropopause is investigated from a process-based perspective. Following previous work, a potential vorticity (PV) error tendency equation is derived and partitioned into individual contributions to yield insight into the processes governing error growth near the tropopause. Importantly, we focus here on the further amplification of preexisting errors and not on the origin of errors. The individual contributions to error growth are quantified in a case study of a 6-day forecast. In this case, localized mesoscale error maxima have formed by forecast day 2. These maxima organize into a wavelike pattern and reach the Rossby wave scale around forecast day 6. Error growth occurs most prominently within the Atlantic and Pacific Rossby wave patterns. In our PV framework, the error growth is dominated by the contribution of upper-level, near-tropopause PV anomalies (near-tropopause dynamics). Significant contributions from upper-tropospheric divergent flow (prominently associated with latent heat release below) and lower-tropospheric anomalies [tropospheric-deep (i.e., baroclinic) interaction] are associated with a misrepresentation of the surface cyclone development in the forecast. These contributions are, in general, of smaller importance to error growth than near-tropopause dynamics. This result indicates that the mesoscale errors generated near the tropopause do not primarily project on differences in the subsequent baroclinic growth, but instead directly project on the tropopause evolution and amplify because of differences in the nonlinear Rossby wave dynamics. [ABSTRACT FROM AUTHOR]

A notable number of high-impact weather extremes have occurred in recent years, often associated with persistent, strongly meandering atmospheric circulation patterns known as Rossby waves. Because of the high societal and ecosystem impacts, it is of great interest to be able to accurately project how such extreme events will change with climate change, and to predict these events on seasonal-to-subseasonal (S2S) time scales. There are multiple physical links connecting upper-atmosphere circulation patterns to surface weather extremes, and it is asking a lot of our dynamical models to accurately simulate all of these. Subsequently, our confidence in future projections and S2S forecasts of extreme events connected to Rossby waves remains relatively low. We also lack full fundamental theories for the growth and propagation of Rossby waves on the spatial and temporal scales relevant to extreme events, particularly under strongly nonlinear conditions. By focusing on one of the first links in the chain from upper-atmospheric conditions to surface extremes—the Rossby waveguide—it may be possible to circumvent some model biases in later links. To further our understanding of the nature of waveguides, links to persistent surface weather events and their representation in models, we recommend exploring these links in model hierarchies of increasing complexity, developing fundamental theory, exploiting novel large ensemble datasets, harnessing deep learning, and increased community collaboration. This would help increase understanding and confidence in both S2S predictions of extremes and of projections of the impact of climate change on extreme weather events. [ABSTRACT FROM AUTHOR]

Prediction of weather is a main goal of atmospheric science. Its importance to society is growing continuously due to factors such as vulnerability to natural disasters, the move to renewable energy sources, and the risks of climate change. But prediction is also a major scientific challenge due to the inherently limited predictability of a chaotic atmosphere, and has led to a revolution in forecasting methods as we have moved to probabilistic prediction. These changes provide the motivation for Waves to Weather (W2W), a major national research program in Germany with three main university partners in Munich, Mainz, and Karlsruhe. We are currently in the second 4-yr phase of our planned duration of 12 years and employ 36 doctoral and postdoctoral scientists. In the context of this large program, we address what we have identified to be the most important and challenging scientific questions in predictability of weather, namely, upscale error growth, errors associated with cloud processes, and probabilistic prediction of high-impact weather. This paper presents some key results of the first phase of W2W and discusses how they have influenced our understanding of predictability. The key role of interdisciplinary research linking atmospheric scientists with experts in visualization, statistics, numerical analysis, and inverse methods will be highlighted. To ensure a lasting impact on research in our field in Germany and internationally, we have instituted innovative programs for training and support of early-career scientists, and to support education, equal opportunities, and outreach, which are also described here. [ABSTRACT FROM AUTHOR]

An obituary for lichenologist Antonín Vězda is presented.

Part II. Focuses on wind observations in the Kali Gandaki Valley, Nepal. Presentation of a simulation model of the diurnal upvalley flow; Significance of gravity waves on the flow structure; Role of humidity in the simulation.

The connection between weather extremes and Rossby wave packets (RWP) has been increasingly documented in recent years. RWP propagation and characteristics can modulate the midlatitude weather, setting the scene for temperature and precipitation extremes and controlling the geographical area affected. Several studies on extreme precipitation events (EPEs) in the Alpine area reported, as the main triggering factor, a meridionally elongated upper-level trough as part of an incoming Rossby wave packet. In this work, we investigate a wide number of EPEs occurring between 1979 and 2015 in northern-central Italy. The EPEs are subdivided into three categories (Cat1, Cat2, Cat3) according to thermodynamic conditions over the affected region. It is found that the three categories differ not only in terms of the local meteorological conditions, but also in terms of the evolution and properties of precursor RWPs. These differences cannot be solely explained by the apparent seasonality of the flow; therefore, the relevant physical processes in the RWP propagation of each case are further investigated. In particular, we show that RWPs associated with the strongest EPEs, namely the ones falling in Cat2, undergo a substantial amplification over the western North Atlantic due to anomalous ridge-building 2 days before the event; arguably due to diabatic heating sources. This type of development induces a downstream trough which is highly effective in focusing water vapour transport toward the main orographic barriers of northern-central Italy and favouring the occurrence of EPEs. [ABSTRACT FROM AUTHOR]

Recently, the authors proposed a novel diagnostic to quantify the amplitude of Rossby wave packets. This diagnostic extends the local finite-amplitude wave activity (LWA) of N. Nakamura and collaborators to the primitive-equations framework and combines it with a zonal filter to remove the phase dependence. In the present work, this diagnostic is used to investigate the dynamics of upper-tropospheric Rossby wave packets, with a particular focus on distinguishing between conservative dynamics and nonconservative processes. For this purpose, a budget equation for filtered LWA is derived and its utility is tested in a hierarchy of models. Idealized simulations with a barotropic and a dry primitive-equation model confirm the ability of the LWA diagnostic to identify nonconservative local sources or sinks of wave activity. In addition, the LWA budget is applied to forecast data for an episode in which the amplitude of an upper-tropospheric Rossby wave packet was poorly represented. The analysis attributes deficiencies in the Rossby wave packet amplitude to the misrepresentation of diabatic processes and illuminates the importance of the upper-level divergent outflow as a source for the error in the wave packet amplitude. [ABSTRACT FROM AUTHOR]

The connection between extreme events and Rossby wave packets (RWP) has been increasingly documented in recent years. Rossby waves modulate mid-latitude weather, generating main precipitation spells and controlling geographical area affected. In the Mediterranean region, several case studies of extreme precipitation event (EPE) reported, as a main triggering factor, a meridionally elongated upper-level trough (i.e a breaking Rossby wave) as part of an incoming RWP. In this study we investigate the RWP characteristics leading to a very large number of EPEs that occurred between 1979 and 2015 over Northern Italy. EPE cases (more than 800) are subdivided in three categories; this allows to test the hypothesis that different EPEs are driven by different RWP dynamical evolution, which in turn, controls the interplay between large-scale vs mesoscale precipitation. We also investigate the strong seasonality of the waveguide which produces, in Spring and Autumn, a peculiar positioning of the Rossby wave which favours EPEs over target area (N-Italy). This synoptic setting is in fact highly effective in focusing water vapour transport (atmospheric river) towards the main orographic barriers of the Apennines and the Alps. [ABSTRACT FROM AUTHOR]

In 2011, the German Federal Ministry of Transport, Building and Urban Development laid the foundation of the Hans-Ertel Centre for Weather Research [Hans-Ertel-Zentrum für Wetterforschung (HErZ)] in order to better connect fundamental meteorological research and teaching at German universities and atmospheric research centers with the needs of the German national weather service Deutscher Wetterdienst (DWD). The concept for HErZ was developed by DWD and its scientific advisory board with input from the entire German meteorological community. It foresees core research funding of about €2,000,000 yr−1 over a 12-yr period, during which time permanent research groups must be established and DWD subjects strengthened in the university curriculum. Five priority research areas were identified: atmospheric dynamics and predictability, data assimilation, model development, climate monitoring and diagnostics, and the optimal use of information from weather forecasting and climate monitoring for the benefit of society. Following an open call, five groups were selected for funding for the first 4-yr phase by an international review panel. A dual project leadership with one leader employed by the academic institute and the other by DWD ensures that research and teaching in HErZ is attuned to DWD needs and priorities, fosters a close collaboration with DWD, and facilitates the transfer of fundamental research into operations. In this article, we describe the rationale behind HErZ and the road to its establishment, present some scientific highlights from the initial five research groups, and discuss the merits and future development of this new concept to better link academic research with the needs and challenges of a national weather service. [ABSTRACT FROM AUTHOR]

Urban valleys can experience serious air pollution problems as a combined result of their limited ventilation and the high emission of pollutants from the urban areas. Idealized simulations were analyzed to elucidate the breakup of an inversion layer in urban valleys subject to a strong low-level temperature inversion and topographic effects on surface heating such as topographic shading, as well as the associated air pollution transport mechanisms. The results indicate that the presence and evolution in time of the inversion layer and its interplay with an urban heat island within the valley strongly influence the venting of pollutants out of urban valleys. Three mechanisms of air pollution transport were identified. These are transport by upslope winds, transport by an urban heat island-induced circulation, and transport within a closed slope-flow circulation below an inversion layer. [ABSTRACT FROM AUTHOR]

We investigate the evolution of the early-morning boundary layer in a low-mountain valley in south-western Germany during COPS (convective and orographically induced precipitation study) in summer 2007. The term low-mountain refers to a mountainous region with a relief of gentle slopes and with an absolute altitude that remains under a specified height (usually 1,500 m a.s.l.). A subset of 23 fair weather days from the campaign was selected to study the transition of the boundary-layer flow in the early morning. The typical valley atmosphere in the morning hours was characterized by a stable temperature stratification and a pronounced valley wind system. During the reversal period-called the low wind period-of the valley wind system (duration of 1-2 h), the horizontal flow was very weak and the conditions for free convection were fulfilled close to the ground. Ground-based sodar observations of the vertical wind show enhanced values of upward motion, and the corresponding statistical properties differ from those observed under windless convective conditions over flat terrain. Large-eddy simulations of the boundary-layer transition in the valley were conducted, and statistical properties of the simulated flow agree with the observed quantities. Spatially coherent turbulence structures are present in the temporal as well as in the ensemble mean analysis. Thus, the complex orography induces coherent convective structures at predictable, specific locations during the early-morning low wind situations. These coherent updrafts, found in both the sodar observations and the simulation, lead to a flux counter to the gradient of the stably stratified valley atmosphere and reach up to the heights of the surrounding ridges. Furthermore, the energy balance in the surface layer during the low wind periods is closed. However, it becomes unclosed after the onset of the valley wind. The partition into the sensible and the latent heat fluxes indicates that missing flux components of sensible heat are the main reason for the unclosed energy balance in the considered situations. This result supports previously published investigations on the energy balance closure. [ABSTRACT FROM AUTHOR]

Many cities located in valleys with limited ventilation experience serious air pollution problems. The ventilation of an urban valley can be limited not only by orographic barriers, but also by urban heat island-induced circulations and/or the capping effect of temperature inversions. Furthermore, land-use/-cover changes caused by urbanization alter the dynamics of temperature inversions and urban heat islands, thereby affecting air quality in an urban valley. By means of idealized numerical simulations, it is shown that in a mountain valley subject to temperature inversions urbanization can have an important influence on air quality through effects on the inversion breakup. Depending on the urban area fraction in the simulations, the breakup time changes, the cross-valley wind system can evolve from a confined to an open system during the daytime, the slope winds can be reversed by the interplay between the urban heat island and the temperature inversion, and the breakup pattern can migrate from one dominated by the growth of the convective boundary layer to one also involving the removal of mass from the valley floor by the upslope winds. The analysis suggests that the influence of urbanization on the air quality of an urban valley may lead to contrasting and possibly counterintuitive effects when considering temperature inversions. More urban land does not necessarily imply worse air quality, even when considering that the amount of pollutants emitted grows with increased urbanization. [ABSTRACT FROM AUTHOR]

Abstract: Adaptive mesh refinement generally aims to increase computational efficiency without compromising the accuracy of the numerical solution. However it is an open question in which regions the spatial resolution can actually be coarsened without affecting the accuracy of the result. This question is investigated for a specific example of dry atmospheric convection, namely the simulation of warm air bubbles. For this purpose a novel numerical model is developed that is tailored towards this specific application. The compressible Euler equations are solved with a discontinuous Galerkin method. Time integration is done with an IMEX-method and the dynamic grid adaptivity uses space filling curves via the AMATOS function library. So far the model is able to simulate dry flow in two-dimensional geometry without subgrid-scale modeling. The model is tested with three standard test cases. An error indicator is introduced for a warm air bubble test case which allows one to compare the accuracy between different choices of refinement regions without knowing the exact solution. Essentially this is done by comparing features of the solution that are strongly sensitive to spatial resolution. For the rising warm air bubble the additional error by using adaptivity is smaller than 1% of the total numerical error if the average number of elements used for the adaptive simulation is about a factor of two times smaller than the number used for the simulation with the uniform fine-resolution grid. Correspondingly the adaptive simulation is almost two times faster than the uniform simulation. Furthermore the adaptive simulation is more accurate than a uniform simulation when both use the same CPU-time. [Copyright &y& Elsevier]

ABSTRACT The study investigates and compares various methods that aim to diagnose Rossby wave trains with the help of Hovmöller diagrams. Three groups of methods are distinguished: The first group contains trough-and-ridge Hovmöller diagrams of the meridional wind; they provide full phase information, but differ in the method for latitudinal averaging or weighting. The second group aims to identify Rossby wave trains as a whole, discounting individual troughs and ridges. The third group contains diagnostics which focus on physical mechanisms during the different phases of a Rossby wave train life cycle; they include the analysis of eddy kinetic energy and methods for quantifying Rossby wave breaking. The different methods are analysed and systematically compared with each other in the framework of a two-month period in fall 2008. Each method more or less serves its designed purpose, but they all have their own strengths and weaknesses. Notable differences between the individual methods render an objective identification of a Rossby wave train somewhat elusive. Nevertheless, the combination of several techniques provides a rather comprehensive picture of the Rossby wave train life cycle, being broadly consistent with the expected behaviour from previous theoretical analysis. [ABSTRACT FROM AUTHOR]

The diurnal wind system of the Kali Gandaki Valley in Nepal was explored in September and October 1998 in a field campaign using pilot balloons as the main observational tool. This valley connects the Plateau of Tibet with the Indian plains. The river crosses the Himalayas forming the deepest valley on Earth. Intense upvalley winds blow up this valley during the day. Observations were made along the river at various spots selected between the exit point from the Himalayas and the source close to the Plateau of Tibet. The strongest upvalley winds were found between Marpha and Chuksang with typical speeds of 15–20 m s[sup -1] . The upvalley wind sets in first at the ground but an upvalley wind layer of 1000–2000-m depth forms quickly after the onset. This deep inflow layer persists up to Lo Manthang, a town located a few kilometers south of the Plateau of Tibet. Deceleration in the late afternoon and evening also appears to commence near the ground. Weak drainage flow forms late in the night. The causes of these phenomena are discussed. [ABSTRACT FROM AUTHOR]