pinecone/core-2020-05-10-deduplication huggingface dataset:
Combining an EKF soil analysis with a 3D-Var upper-air assimilation in a limited-area NWP model

In recent years, the Extended Kalman Filter (EKF) has been gaining more attention in the surface data assimilation (DA) community and has already replaced the older Optimal Interpolation (OI) scheme for the vertical component of the land surface DA system in a number of meteorological institutes. An EKF has been developed within the standalone land-surface modelling platform SURFace Externalisee (SURFEX) for the initialisation of soil temperature and soil water content based on screen-level temperature and relative humidity. In this article we present a new combination of the EKF with a basic (using conventional observations only) three-dimensional variational (3D-Var) upper-air assimilation for the limited-area model ALARO coupled to SURFEX. This new combination is compared to an Open Loop experiment where all initial conditions are interpolated from an analysis of the global numerical weather prediction model Action de Recherche Petite Echelle Grande Echelle (ARPEGE) and to an experiment where the surface is initialised using the EKF, while the upper-air initial conditions are interpolated from the ARPEGE analysis. The aim of this article is to examine whether the EKF surface assimilation coupled or not with a basic 3D-Var upper-air assimilation has an added value compared to the Open Loop, in which the more advanced upper-air data assimilation of ARPEGE with more observations used is interpolated onto the limited-area model grid. All set-ups are verified during a 1-year period 2013 against soil measurements, screen-level observations, radiosoundings and merged radar-rain-gauge precipitation observations. Results indicate that the EKF surface assimilation has positive effects on humidity scores and is able to produce similar or improved scores compared to the Open Loop. While the upper-air 3D-Var DA system of ALARO still needs improvements, the potential benefits of the combination of upper-air and surface assimilation are demonstrated through soil moisture and screen-level relative humidity verifications
A Model for Moist Convection in an Ascending Atmospheric Column

This paper presents a single-column model of moist atmospheric convection. The\ud
problem is formulated in terms of conservation laws for mass, moist potential\ud
temperature and specific humidity of air parcels. A numerical adjustment algorithm\ud
is devised to model the convective adjustment of the column to a statically stable\ud
equilibrium state for a number of test cases. The algorithm is shown to converge to\ud
a weak solution with saturated and unsaturated parcels interleaved in the column as\ud
the vertical spatial grid size decreases. Such weak solutions would not be obtainable via\ud
discrete PDE methods, such as finite differences or finite volumes, from the governing\ud
Eulerian PDEs. An equivalent variational formulation of the problem is presented and\ud
numerical results show equivalence with those of the adjustment algorithm. Results are\ud
also presented for numerical simulations of an ascending atmospheric column as a series\ud
of steady states. The adjustment algorithm developed in this paper is advantageous\ud
over similar algorithms because first it includes the latent heating of parcels due to\ud
the condensation of water vapour, and secondly it is computationally efficient making it\ud
implementable into current weather and climate models
Sedimentation analysis of small ice crystals by Lattice Boltzmann Method

Lattice Boltzmann Method (LBM) is used to simulate and analyze the
sedimentation of small ($15-80 \,\mu m$) columnar ice particles in the
atmosphere. We are specially interested in evaluating the terminal falling
velocity of columnar ice crystals with hexagonal cross section. The main
objective is to apply the LBM to solve ice crystal sedimentation problems. This
numerical method is evaluated as a powerful numerical tool to solve ice crystal
sedimentation problems in a variety of sizes. LBM results are presented in
comparison with laboratory experimental results and theoretical approaches well
known in the literature. The numerical results show good agreement with
experimental and theoretical results for the analyzed geometrical
configurations
An iterative ensemble Kalman filter in presence of additive model error

The iterative ensemble Kalman filter (IEnKF) in a deterministic framework was
introduced in Sakov et al. (2012) to extend the ensemble Kalman filter (EnKF)
and improve its performance in mildly up to strongly nonlinear cases.
  However, the IEnKF assumes that the model is perfect. This assumption
simplified the update of the system at a time different from the observation
time, which made it natural to apply the IEnKF for smoothing. In this study, we
generalise the IEnKF to the case of imperfect model with additive model error.
  The new method called IEnKF-Q conducts a Gauss-Newton minimisation in
ensemble space. It combines the propagated analysed ensemble anomalies from the
previous cycle and model noise ensemble anomalies into a single ensemble of
anomalies, and by doing so takes an algebraic form similar to that of the
IEnKF. The performance of the IEnKF-Q is tested in a number of experiments with
the Lorenz-96 model, which show that the method consistently outperforms both
the EnKF and the IEnKF naively modified to accommodate additive model noise.Comment: Accepted for publication in the Quarterly Journal of the Royal
  Meteorological Societ
Conservative finite volume schemes for the quasi-geostrophic equation on
  coastal-conforming unstructured primal-dual meshes

In this paper we propose finite volume schemes for solving the inviscid and
viscous quasi-geostrophic equations on coastal-conforming unstructured
primal-dual meshes. Several approaches for enforcing the boundary conditions
are also explored along with these schemes. The pure transport part in these
schemes are shown to conserve the potential vorticity along fluid paths in an
averaged sense, and conserve the potential enstrophy up to the time truncation
errors. Numerical tests based on the centroidal Voronoi-Delaunay meshes are
performed to confirm these properties, and to distinguish the dynamical
behaviors of these schemes. Finally some potential applications of these
schemes in different situations are discussed
A nestable, multigrid-friendly grid on a sphere for global spectral
  models based on Clenshaw-Curtis quadrature

A new grid system on a sphere is proposed that allows for straight-forward
implementation of both spherical-harmonics-based spectral methods and
gridpoint-based multigrid methods. The latitudinal gridpoints in the new grid
are equidistant and spectral transforms in the latitudinal direction are
performed using Clenshaw-Curtis quadrature. The spectral transforms with this
new grid and quadrature are shown to be exact within the machine precision
provided that the grid truncation is such that there are at least 2N + 1
latitudinal gridpoints for the total truncation wavenumber of N. The new grid
and quadrature is implemented and tested on a shallow-water equations model and
the hydrostatic dry dynamical core of the global NWP model JMA-GSM. The
integration results obtained with the new quadrature are shown to be almost
identical to those obtained with the conventional Gaussian quadrature on
Gaussian grid.Comment: 32 pages, 8 figures; submitted to Quarterly Journal of the Royal
  Meteorological Societ
Assessment of algorithms for computing moist available potential energy

Atmospheric moist available potential energy (MAPE) has been traditionally
defined as the potential energy of a moist atmosphere relative to that of the
adiabatically sorted reference state defining a global potential energy
minimum. Finding such a reference state was recently shown to be a linear
assignment problem, and therefore exactly solvable. However, this is
computationally extremely expensive, so there has been much interest in
developing heuristic methods for computing MAPE in practice. Comparisons of the
accuracy of such approximate algorithms have so far been limited to a small
number of test cases; this work provides an assessment of the algorithms'
performance across a wide range of atmospheric soundings, in two different
locations. We determine that the divide-and-conquer algorithm is the best
suited to practical application, but suffers from the previously overlooked
shortcoming that it can produce a reference state with higher potential energy
than the actual state, resulting in a negative value of MAPE. Additionally, we
show that it is possible to construct an algorithm exploiting a theoretical
expression linking MAPE to Convective Available Potential Energy (CAPE)
previously derived by Kerry Emanuel. This approach has a similar accuracy to
existing approximate sorting algorithms, whilst providing greater insight into
the physical source of MAPE. In light of these results, we discuss how to make
progress towards constructing a satisfactory moist APE theory for the
atmosphere. We also outline a method for vectorising the adiabatic lifting of
moist air parcels, which increases the computational efficiency of algorithms
for calculating MAPE, and could be used for other applications such as
convection schemes.Comment: 12 pages, submitted to QJRM
Filtering properties of wavelets for local background-error correlations

International audienceBackground-error covariances can be estimated from an ensemble of forecast differences. The finite size of the ensemble induces a sampling noise in the calculated statistics. It is shown formally that a wavelet diagonal approach amounts to locally averaging the correlations, and its ability to spatially filter this sampling noise is thus investigated experimentally. This is first studied in a simple analytical one-dimensional framework. The capacity of a wavelet diagonal approach to model the scale variations over the domain is illustrated. Moreover, the sampling noise appears to be better filtered than when only using a Schur filter, in particular for small ensembles. The filtering properties are then illustrated for an ensemble of Meteo-France Arpege forecasts. This is done both for the ‘time-averaged correlations', and for the ‘correlations of the day'. It is shown that the wavelets are able to extract some length-scale variations that are related to the meteorological situation
The moist parcel-in-cell method for modelling moist convection

The authors gratefully acknowledge support for this research from the EPSRC Maths Foresees Network. The numerical model development was carried out under the grant “A prototype vortex-in-cell algorithm for modelling moist convection” from March to October 2016. Steven Böing is partially funded through the NERC/Met Office Joint Programme on Understanding and Representing Atmospheric Convection across Scales (GENESIS, grant number NE/N013840/1). Doug Parker is supported by a Royal Society Wolfson Research Merit Award.We describe a promising alternative approach to modelling moist convection and cloud development in the atmosphere. Rather than using a conventional grid‐based approach, we use Lagrangian “parcels” to represent key dynamical and thermodynamical variables. In the prototype model considered, parcels carry vorticity, mass, specific humidity, and liquid‐water potential temperature. In this first study, we ignore precipitation, and many of these parcel “attributes” remain unchanged (i.e. are materially conserved). While the vorticity does change following the parcel motion, the vorticity tendency is readily computed and, crucially, unwanted numerical diffusion can be avoided. The model, called “Moist Parcel‐In‐Cell” (MPIC), is a hybrid approach which uses both parcels and a fixed underlying grid for efficiency: advection (here moving parcels) is Lagrangian whereas inversion (determining the velocity field) is Eulerian. The parcel‐based representation of key variables has several advantages: (a) it allows an explicit subgrid representation; (b) it provides a velocity field which is undamped by numerical diffusion all the way down to the grid scale; (c) it does away with the need for eddy viscosity parametrizations and, in their place, it provides for a natural subgrid parcel mixing; (d) it is exactly conservative (i.e. there can be no net loss or gain of any theoretically conserved attribute); and (e) it dispenses with the need to have separate equations for each conserved parcel attribute; attributes are simply labels carried by each parcel. Moreover, the latter advantage increases as more attributes are added, such as the distributions of microphysical properties, chemical composition and aerosol loading.    Publisher PDFPeer reviewe
On the use of the saddle formulation in weakly-constrained 4D-VAR data
  assimilation

This paper discusses the practical use of the saddle variational formulation
for the weakly-constrained 4D-VAR method in data assimilation. It is shown that
the method, in its original form, may produce erratic results or diverge
because of the inherent lack of monotonicity of the produced objective function
values. Convergent, variationaly coherent variants of the algorithm are then
proposed whose practical performance is compared to that of other formulations.
This comparison is conducted on two data assimilation instances (Burgers
equation and the Quasi-Geostrophic model), using two different assumptions on
parallel computing environment. Because these variants essentially retain the
parallelization advantages of the original proposal, they often --- but not
always --- perform best, even for moderate numbers of computing processes
A relationship between all Atlantic hurricanes and those that make landfall in the USA

The interannual prediction of the number of hurricanes to strike the US coastline is of vital interest to those who live on the coast, those who insure property along the coast and policy makers who make decisions about infrastructure and mitigation measures. Here it is shown that these predictions can be made more accurate when information about the total number of Atlantic Basin hurricanes is considered. The proportion of Atlantic hurricanes that make landfall in the USA is a measure of the relationship between landfalling and basin hurricane numbers. In order to use basin numbers to help make predictions of landfalling numbers, we must first investigate the nature of this relationship. Here we run a number of statistical tests and find that there is a significant change in the relative proportion of Atlantic hurricanes that hit the US coastline between the first and second halves of the 20th century. This difference is ostensibly due to the lack of basin observations in the earlier period. However, after 1948, the proportion of Atlantic hurricanes that hit the US coast shows no evidence of change. By assuming that the proportion is constant, we are able to then use information about the total number of hurricanes in the Atlantic Basin and make more accurate estimates of landfalling hurricane activity
REAL - Ensemble radar precipitation estimation for hydrology in a mountainous region

An elegant solution to characterise the residual errors in radar precipitation estimates is to generate an ensemble of precipitation fields. The paper proposes a radar ensemble generator designed for usage in the Alps using LU decomposition (REAL), and presents first results from a real-time implementation coupling the radar ensemble with a semi-distributed rainfall–runoff model for flash flood modelling in a steep Alpine catchment. Each member of the radar\ud
ensemble is a possible realisation of the unknown true precipitation field given the observed radar field and knowledge of the space–time error structure of radar precipitation estimates. Feeding the alternative realisations into a hydrological\ud
model yields a distribution of response values, the spread of which represents the sensitivity of runoff to uncertainties in\ud
the input radar precipitation field.\ud
The presented ensemble generator is based on singular value decomposition of the error covariance matrix, stochastic simulation using the LU decomposition algorithm, and autoregressive filtering. It allows full representation of spatial dependence of the mean and covariances of radar errors. This is of particular importance in a mountainous region with large uncertainty in radar precipitation estimates and strong dependence of error structure on location. The real-time implementation of the radar ensemble generator coupled with a semi-distributed hydrological model in the framework of the forecast demonstration project MAP D-PHASE is one of the first experiments of this type worldwide, and is a fully novel contribution to this evolving area of applied research.Peer ReviewedPostprint (published version
Life cycle of the QBO modulated 11-year solar cycle signals in the northern hemispheric winter

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

Acoustic wave generation by turbulence in the stratified, moist atmosphere is
studied. It is shown that in the saturated moist air turbulence in addition to
the Lighthill's quadrupole and the dipole sources of sound related to
stratification and temperature fluctuations, there exist monopole sources
related to heat and mass production during the condensation of moisture. We
determine acoustic power of these monopole sources. Performed analysis shows
that the monopole radiation is dominant for typical parameters of strong
convective storms. Obtained results are in good qualitative agreement with the
main observed characteristics of infrasound radiation by strong convective
storms such as total acoustic power and characteristic frequency
Super-Droplet Method for the Numerical Simulation of Clouds and
  Precipitation: a Particle-Based Microphysics Model Coupled with
  Non-hydrostatic Model

A novel simulation model of cloud microphysics is developed, which is named
Super-Droplet Method (SDM). SDM enables accurate calculation of cloud
microphysics with reasonable cost in computation. A simple SDM for warm rain,
which incorporates sedimentation, condensation/evaporation, stochastic
coalescence, is developed. The methodology to couple SDM and a non-hydrostatic
model is also developed. It is confirmed that the result of our Monte Carlo
scheme for the coalescence of super-droplets agrees fairly well with the
solution of stochastic coalescence equation. A preliminary simulation of a
shallow maritime cumulus formation initiated by a warm bubble is presented to
demonstrate the practicality of SDM. Further discussions are devoted for the
extension and the computational efficiency of SDM to incorporate various
properties of clouds, such as, several types of ice crystals, several sorts of
soluble/insoluble CCNs, their chemical reactions, electrification, and the
breakup of droplets. It is suggested that the computational cost of SDM becomes
lower than spectral (bin) method when the number of attributes $d$ becomes
larger than some critical value, which may be $2\sim4$
A comparison of aircraft-based surface-layer observations over Denmark Strait and the Irminger sea with meteorological analyses and QuikSCAT winds

A compilation of aircraft observations of the atmospheric surface layer is compared with several meteorological analyses and QuikSCAT wind products. The observations are taken during the Greenland Flow Distortion Experiment, in February and March 2007, during cold-air outbreak conditions and moderate to high wind speeds. About 150 data points spread over six days are used, with each data point derived from a 2-min run (equivalent to a 12 km spatial average). The observations were taken 30–50 m above the sea surface and are adjusted to standard heights. Surface-layer temperature, humidity and wind, as well as sea-surface temperature (SST) and surface turbulent fluxes are compared against co-located data from the ECMWF operational analyses, NCEP Global Reanalyses, NCEP North American Regional Reanalyses (NARR), Met Office North Atlantic European (NAE) operational analyses, two MM5 hindcasts, and two QuikSCAT products. In general, the limited-area models are better at capturing the mesoscale high wind speed features and their associated structure; often the models underestimate the highest wind speeds and gradients. The most significant discrepancies are: a poor simulation of relative humidity by the NCEP global and MM5 models, a cold bias in 2 m air temperature near the sea-ice edge in the NAE model, and an overestimation of wind speed above 20 m s-1 in the QuikSCAT wind products. In addition, the NCEP global, NARR and MM5 models all have significant discrepancies associated with the parametrisation of surface turbulent heat fluxes. A high-resolution prescription of the SST field is crucial in this region, although these were not generally used at this time
An overview of barrier winds off southeastern Greenland during the Greenland Flow Distortion experiment

During the Greenland Flow Distortion experiment, barrier flow was observed by an instrumented aircraft on 1, 2, 5 and 6 March 2007 off southeastern Greenland. During this time period the barrier flow increased from a narrow jet, ~15 m s-1, to a jet filling almost the whole of the Denmark Strait with maximum wind speed exceeding 40 m s-1. Dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height. Below the inversion was a cold and dry jet, with a larger northerly wind component than that of the flow above, which was also warmer and more moist. Thus, the observations indicate two air masses below mountain height: a cold and dry barrier jet of northern origin and, above this, a warmer and moister air mass that was of cyclonic origin. Numerical simulations emphasize the non-stationarity of the Greenland barrier flow and its dependence on the synoptic situation in the Greenland--Iceland region. They show that the barrier jet originated north of the Denmark Strait and was drawn southward by a synoptic-scale cyclone, with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of Greenland. Experiments without Greenland's orography suggest a ~20 m s-1 enhancement of the low-level peak wind speeds due to the presence of the barrier. Thus, the Greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are precisely controlled by synoptic-scale systems