pinecone/core-2020-05-10-deduplication huggingface dataset:
Spatial Verification Using Wavelet Transforms: A Review

Due to the emergence of new high resolution numerical weather prediction
(NWP) models and the availability of new or more reliable remote sensing data,
the importance of efficient spatial verification techniques is growing. Wavelet
transforms offer an effective framework to decompose spatial data into separate
(and possibly orthogonal) scales and directions. Most wavelet based spatial
verification techniques have been developed or refined in the last decade and
concentrate on assessing forecast performance (i.e. forecast skill or forecast
error) on distinct physical scales. Particularly during the last five years, a
significant growth in meteorological applications could be observed. However, a
comparison with other scientific fields such as feature detection, image
fusion, texture analysis, or facial and biometric recognition, shows that there
is still a considerable, currently unused potential to derive useful diagnostic
information. In order to tab the full potential of wavelet analysis, we revise
the state-of-the art in one- and two-dimensional wavelet analysis and its
application with emphasis on spatial verification. We further use a technique
developed for texture analysis in the context of high-resolution quantitative
precipitation forecasts, which is able to assess structural characteristics of
the precipitation fields and allows efficient clustering of ensemble data.Comment: Revised Manuscript submitted to Quarterly Journal of the Royal
  Meteorological Society (10 May 2016
Structure of a shear-line polar low

During March 2013 a series of polar lows originated in a high-vorticity (>10−3 s−1) shear zone that was associated with a prolonged marine cold-air outbreak over the Norwegian Sea. A detailed analysis of one shear-line polar low at the leading edge of the outbreak is presented using comprehensive observations from a well-instrumented aircraft, dropsondes, scatterometer and CloudSat data; and numerical modelling output from a convection-resolving configuration of the Met Office Unified Model. The maximum low-level wind gradient across the shear line was 25 m s−1 over 50 km. High windsto the north and west were within the cold-air mass and were associated with large surface turbulent heat fluxes and convective clouds. Low wind speed to the south and east of the shear line were associated with low heat fluxes and a clear ‘eye’ in the polarlow. Shear-line meso-γ-scale instabilities merging into the polar low appeared important to its structure and development. The model captured the shear line and the polar low structure very well — in particular the strength of the horizontal shear and the mesoscale thermodynamic fields.The spatialstructure of convective cloud bands around the polar low wassimulated reasonably well, but the modelsignificantly underestimated the liquid water content and height of the cloud layers compared to the observations. Shear-line polar lows are relatively common, however this case is arguably the first to be examined with a wide range of in-situ and remote observations allied with numerical model output
The dynamics of intensification in a Hurricane Weather Research and Forecasting simulation of Hurricane Earl

Quarterly Journal of the Royal Meteorological SocietyThe article of record as published may be found at http://dx.doi.org/10.1002/qj.2922We use a high-resolution numerical simulation of Atlantic Hurricane Earl (2010) to increase our understanding of Earl’s intensification in relatively strong vertical shear in the context of a recent paradigm for tropical cyclone intensification. The integrity of the simulation is judged by comparing analyses thereof with those of the unprecedented observational data gathered in Earl. Consistent with the classical view of spin-up, the amplification of the tangential wind field above the boundary layer is found to occur as the absolute angular momentum surfaces are drawn inwards by the aggregate heating of the rotating convective clouds in the interior of the vortex. In addition to this classical pathway, spin-up occurs within the inner-core boundary layer, where the maximum tangential winds occur. The latter is another element of the new paradigm. Despite the detrimental influence of the shear on the vortex alignment and in depressing the pseudo-equivalent potential temperature outside the developing eyewall, the combined eddy processes associated with the vortical plume structures in and around the developing eyewall region are shown to contribute to an enhanced overturning circulation and an intensifying storm. These eddy processes are distinctly agradient effects that are not features of the classical spin-up mechanism. It remains to be understood how the rotating convective updraughts combine to produce the diagnosed structures of the eddy terms themselves and how vortex Rossby waves and other eddies contribute to the alignment of the vortex during intensification.Funded by Naval Postgraduate SchoolOffice of Naval Research GlobalNational Aeronautics and Space AdministrationNational Oceanic and Atmospheric AdministrationDeutsche ForschungsgemeinschaftNational Science Foundatio
A unified view of tropical cyclogenesis and intensification

Quarterly Journal of the Royal Meteorological SocietyThe article of record as published may be found at http://dx.doi.org/10.1002/qj.2934Idealized high-resolution numerical simulations of tropical cyclogenesis are presented in a model that represents deep convection by a warm rain process only. Starting with an initially weak, cloud-free, axisymmetric warm-cored vortex (maximum wind speed 5 m s−1 at a radius of 100 km), rapid vortex intensification begins after a gestation period on the order of 2 days. From a three-dimensional perspective, the genesis process is similar to that in the rotating convection paradigm for vortex intensification starting with a much stronger initial vortex (Vmax = 15 m s−1). The patterns of deep convection and convectively amplified cyclonic relative vorticity are far from axisymmetric during the genesis period. Moreover, the organization of the cyclonic relative vorticity into a monopole structure occurs at relatively low wind speeds, before the maximum local wind speed has increased appreciably. Barotropic processes are shown to play an important role in helping to consolidate a single-signed vorticity monopole within a few hours near the intensification begin time. The rotating convection paradigm appears adequate to explain the basic genesis process within the weak initial vortex, providing strong support for a hypothesis of Montgomery and Smith that the genesis process is not fundamentally different from that of vortex intensification. In particular, genesis does not require a ‘trigger’ and does not depend on the prior existence of a mid-level vortex.Funded by Naval Postgraduate SchoolOffice of Naval Research GlobalNOAA HFIPNational Aeronautics and Space AdministrationDeutsche ForschungsgemeinschaftNational Science Foundatio
Numerical instabilities of vector invariant momentum equations on rectangular C-grids

This is the author accepted manuscript. Version of record to be made available by the publisher via the DOI in this record.This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which
may lead to differences between this version and the Version of Record.The linear stability of two well known energy and enstrophy conserving schemes for
the vector invariant hydrostatic primitive equations is examined. The problem is analysed for a
stably stratified Boussinesq fluid on an f -plane, with a constant velocity field, in height and
isopycnal coordinates, by separation of variables into vertical normal modes and a linearised
form of the shallow water equations (SWEs). As found by [Hollingsworth
~al.(1983)Hollingsworth, Kallberg, Renner and Burridge], (HKRB hereafter) the schemes are
linearly unstable in height coordinate models, due to a non-cancellation of terms in the
momentum equations. The schemes with the modified formulations of the kinetic energy
proposed by HKRB are shown to have Hermitain stability matrices and hence to be stable to all
perturbations. All perturbations in isopycnal models are also shown to be neutrally stable, even
with the original formulations for kinetic energy. Analytical expressions are derived for the
smallest equivalent depths obtained using Charney-Phillips and Lorenz vertical grids, which
show that the Lorenz grid has larger growth rates for the unstable schemes than the CharneyPhillips
grid. Test cases are proposed for assessing the stability of new numerical schemes using
the SWEs.We gratefully acknowledge inputs from Nicolas Ducousso,
Gurvan Madec, Julien le Sommer, David Storkey, Andy
White and Nigel Wood. Bell was supported by the
Joint UK DECC/Defra Met Office Hadley Centre Climate
Programme (GA01101), Peixoto acknowledges the Sao
Paulo Research Foundation (FAPESP), under the grant
number 2014/10750-0 and Thuburn was supported by the
Natural Environment Research Council under grant number
NE/K006762/1
Remote control on NAO predictability via the stratosphere

The phase and the amplitude of the North Atlantic Oscillation (NAO) are influenced by numerous factors, which include Sea Surface Temperature (SST) anomalies in both the Tropics and extratropics and stratospheric extreme events like Stratospheric Sudden Warmings (SSWs). Analyzing seasonal forecast experiments, which cover the winters from 1979/80–2013/14, with the European Centre for Medium-Range Weather Forecast model, we investigate how these factors affect NAO variability and predictability. Building on the idea that the tropical influence might happen via the stratosphere, special emphasis is placed on the role of major SSWs. Relaxation experiments are performed, where different regions of the atmosphere are relaxed towards ERA-Interim to obtain perfect forecasts in those regions. By comparing experiments with relaxation in the tropical atmosphere, performed with an atmosphere-only model on the one hand and a coupled atmosphere–ocean model version on the other, the importance of extratropical atmosphere–ocean interaction is addressed.\ud
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Interannual variability of the NAO is best reproduced when perfect knowledge about the NH stratosphere is available together with perfect knowledge of SSTs and sea ice, in which case 64% of the variance of the winter mean NAO is projected to be accounted for with a forecast ensemble of infinite size. The coupled experiment shows a strong bias in the stratospheric polar night jet (PNJ) which might be associated with a drift in the modelled SSTs resembling the North Atlantic cold bias and an underestimation of blockings in the North Atlantic/Europe sector. Consistent with the stronger PNJ, the lowest frequency of major SSWs is found in this experiment. However, after statistically removing the bias, a perfect forecast of the tropical atmosphere and allowing two-way atmosphere–ocean coupling in the extratropics seem to be key ingredients for successful SSW predictions. In combination with SSW occurrence, a clear shift of the predicted NAO towards lower values occurs
Tropical low formation and intensification over land as seen in ECMWF analyses

Quarterly Journal of the Royal Meteorological SocietyThe article of record as published may be found at http://dx.doi.org/10.1002/qj.2963Case studies of the formation and intensification over land of three tropical lows in northern Australia are described. The case studies are based on European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. The aim is to investigate the generality of recent results concerning the dynamics and thermodynamics of tropical lows. Consistent with these results, it is found that the processes of low formation and intensification are the same over land as over the ocean. An important element of the intensification process is the need for bursts of deep convection to persist near the circulation centre, which, in turn, requires that convective instability be maintained by surface moisture fluxes. The moist monsoonal environment locally surrounding the storm provides a shield against the adverse effects of dry-air intrusion from the Australian continent.Funded by Naval Postgraduate SchoolNSFOffice of Naval Research GlobalNOAA HFIPNational Aeronautics and Space AdministrationDeutsche Forschungsgemeinschaf
Estimating model evidence using data assimilation

We review the field of data assimilation (DA) from a Bayesian perspective and
show that, in addition to its by now common application to state estimation, DA
may be used for model selection. An important special case of the latter is the
discrimination between a factual model --- which corresponds, to the best of
the modeler's knowledge, to the situation in the actual world in which a
sequence of events has occurred --- and a counterfactual model, in which a
particular forcing or process might be absent or just quantitatively different
from the actual world. Three different ensemble-DA methods are reviewed for
this purpose: the ensemble Kalman filter (EnKF), the ensemble four-dimensional
variational smoother (En-4D-Var), and the iterative ensemble Kalman smoother
(IEnKS). An original contextual formulation of model evidence (CME) is
introduced. It is shown how to apply these three methods to compute CME, using
the approximated time-dependent probability distribution functions (pdfs) each
of them provide in the process of state estimation. The theoretical formulae so
derived are applied to two simplified nonlinear and chaotic models: (i) the
Lorenz three-variable convection (L63) model, and (ii) the Lorenz 40-variable
mid-latitude atmospheric dynamics model (L95). The numerical results of these
three DA-based methods and those of an integration based on importance sampling
are compared. It is found that better CME estimates are obtained by using DA,
and the IEnKS method appears to be best among the DA methods. Differences among
the performance of the three DA-based methods are discussed as a function of
model properties. Finally, the methodology is implemented for parameter
estimation and for event attribution
Stochastic parameterization of subgrid-scale processes in coupled
  ocean-atmosphere systems: Benefits and limitations of response theory

A stochastic subgrid-scale parameterization based on the Ruelle's response
theory and proposed in Wouters and Lucarini [2012] is tested in the context of
a low-order coupled ocean-atmosphere model for which a part of the atmospheric
modes are considered as unresolved. A natural separation of the phase-space
into an invariant set and its complement allows for an analytical derivation of
the different terms involved in the parameterization, namely the average, the
fluctuation and the long memory terms. In this case, the fluctuation term is an
additive stochastic noise. Its application to the low-order system reveals that
a considerable correction of the low-frequency variability along the invariant
subset can be obtained, provided that the coupling is sufficiently weak. This
new approach of scale separation opens new avenues of subgrid-scale
parameterizations in multiscale systems used for climate forecasts.Comment: 26 pages, 12 figures, 2 tables. Accepted for publication in the
  Quarterly Journal of the Royal Meteorological Societ
A Cirrus cloud scheme for general circulation models

A statistical cloud scheme for non-convective cirrus formed by homogeneous freezing of supercooled aerosols is presented. As large-scale cirrus clouds exhibit metastable thermodynamic states and have long lifetimes, a fully prognostic approach is developed. The scheme is based on separate probability distribution functions of total water representing clear-sky and in-cloud conditions. These distributions are based on  in situ observations and have few degrees of freedom so that they can be used in forecast and climate models. Predictive equations are derived for horizontal cloud fraction and mixing ratios of grid-mean water vapour and ice water, in-cloud water vapour and ice crystal number. The scheme allows sub- and supersaturations with respect to ice to occur in cloud-free air and inside cirrus, and produces nucleated ice crystal concentrations and sizes in good agreement with observations, an important prerequisite for an improved treatment of cirrus cloud radiative properties. Implementation in general circulation models, open issues and future research avenues are discussed
Rain retrieval from dual-frequency radar Doppler spectra: validation and potential for a midlatitude precipitating case-study

A recently developed technique retrieving the binned raindrop size distributions (DSDs) and air state parameters from ground-based Ka and W-band radars Doppler spectra profiles is improved and applied to a typical midlatitude rain event. The retrievals are thoroughly validated against DSD observations of a 2D video disdrometer and independent X-band observations. For this case-study, profiles of rain rate, R, mean volume diameter and concentration parameter are retrieved, with low bias and standard deviations. In light rain (0.1 < R < 1 mm h−1), the radar reflectivities must be calibrated with a collocated disdrometer which introduces random errors due to sampling mismatch between the two instruments. The best performances are obtained in moderate rain (1 < R < 20 mm h−1) where the retrieval is providing self-consistent estimates of the absolute calibration and of the attenuation caused by antenna or radome wetness for both radars.Peer-reviewedPublisher Versio
On the Calibration of Multilevel Monte Carlo Ensemble Forecasts

Multilevel Monte Carlo can efficiently compute statistical estimates of
discretized random variables, for a given error tolerance. Traditionally, only
a certain statistic is computed from a particular implementation of multilevel
Monte Carlo. This paper considers the multilevel case when one wants to verify
and evaluate a single ensemble that forms an empirical approximation to many
different statistics, namely an ensemble forecast. We propose a simple
algorithm that, in the univariate case, allows one to derive a statistically
consistent single ensemble forecast from the hierarchy of ensembles that are
formed during an implementation of multilevel Monte Carlo. This ensemble
forecast then allows the entire multilevel hierarchy of ensembles to be
evaluated using standard ensemble forecast verification techniques. We
demonstrate the case of evaluating the calibration of the forecast in this
paper.Comment: 6 pages, 2 figures. Accepted to Quarterly Journal of the Royal
  Meteorological Societ
Scale-selective dissipation in energy-conserving finite element schemes
  for two-dimensional turbulence

We analyse the multiscale properties of energy-conserving upwind-stabilised
finite element discretisations of the two-dimensional incompressible Euler
equations. We focus our attention on two particular methods: the Lie derivative
discretisation introduced in Natale and Cotter (2016a) and the Streamline
Upwind/Petrov-Galerkin (SUPG) discretisation of the vorticity advection
equation. Such discretisations provide control on enstrophy by modelling
different types of scale interactions. We quantify the performance of the
schemes in reproducing the non-local energy backscatter that characterises
two-dimensional turbulent flows
Measurements and models of the temperature change of water samples in Sea Surface Temperature buckets

Uncertainty in the bias adjustments applied to historical sea surface temperature (SST) measurements made using buckets are thought to make the largest contribution to uncertainty in global surface temperature trends. Measurements of the change in temperature of water samples in wooden and canvas buckets used before World War 2 are compared with the predictions of models that have been used to estimate bias adjustments applied in widely-used gridded analyses of SST. The results show that the models are broadly able to predict the dependence of the temperature change of the water over time on the thermal forcing and the bucket characteristics: volume and geometry; structure and material. However, assumptions inherent in the derivation of the models are likely to affect their applicability. We observed that the water sample needed to be fairly vigorously stirred to agree with results from the model, which assumes well-mixed conditions. There were inconsistences between the model results and previous measurements made in a wind tunnel in 1951. The model assumes non turbulent incident flow and consequently predicts an approximately square-root dependence on airflow speed. The wind tunnel measurements, taken over a wide range of airflows, showed a much stronger dependence. In the presence of turbulence the heat transfer will increase with the turbulent intensity: for measurements made on ships the incident airflow is likely to be turbulent and the intensity of the turbulence is always unknown. Taken together these uncertainties are expected to be substantial and may represent the limiting factor for the direct application of these models to adjust historical SST observations. However, both the models and the observations indicate that the most important parameter driving temperature biases in historical bucket measurements is the difference between the water temperature and the wet-bulb temperature. Solar radiation is also important, but not examined in this paper
A local ensemble transform Kalman particle filter for convective scale
  data assimilation

Ensemble data assimilation methods such as the Ensemble Kalman Filter (EnKF)
are a key component of probabilistic weather forecasting. They represent the
uncertainty in the initial conditions by an ensemble which incorporates
information coming from the physical model with the latest observations.
High-resolution numerical weather prediction models ran at operational centers
are able to resolve non-linear and non-Gaussian physical phenomena such as
convection. There is therefore a growing need to develop ensemble assimilation
algorithms able to deal with non-Gaussianity while staying computationally
feasible. In the present paper we address some of these needs by proposing a
new hybrid algorithm based on the Ensemble Kalman Particle Filter. It is fully
formulated in ensemble space and uses a deterministic scheme such that it has
the ensemble transform Kalman filter (ETKF) instead of the stochastic EnKF as a
limiting case. A new criterion for choosing the proportion of particle filter
and ETKF update is also proposed. The new algorithm is implemented in the COSMO
framework and numerical experiments in a quasi-operational convective-scale
setup are conducted. The results show the feasibility of the new algorithm in
practice and indicate a strong potential for such local hybrid methods, in
particular for forecasting non-Gaussian variables such as wind and hourly
precipitation.Comment: submitte