pinecone/core-2020-05-10-deduplication huggingface dataset:
Met Office unified model high resolution simulations of a strong wind event in Antarctica

During winter much of the Antarctic coast is susceptible to severe and hazardous strong wind events (SWEs) associated with the enhancement of katabatic winds by synoptic weather systems. In this study a SWE which occurred at Mawson, East Antarctica involving a hurricane force wind speed of ~39 m s-1 is simulated by the Met Office Unified Model at high horizontal resolutions with grid lengths between 12 and 1.5 km. It is shown that all the simulations capture the qualitative evolution of the SWE but underestimate its peak wind speed. The extent of the underestimate is dependent on horizontal resolution, with the 4 and 1.5-km (12-km) models under-forecasting the peak wind speed by around 15% (36%). In addition to a strengthening of the katabatic flow, the simulated low-level cyclonic winds associated with the depression responsible for the SWE caused the formation of a barrier-type jet parallel to the coast, resulting in strong wind convergence/interaction at the coastline and suggesting a strong topographic influence on the dynamics responsible for SWE formation. Moreover, that Mawson is influenced by small-scale gravity waves which formed in response to the stronger winds, and that representation of this was particularly sensitive to horizontal resolution. Additional experiments suggest that the Met Office Unified Model simulation of the SWE is most sensitive to the representation of turbulent mixing under stable conditions. This study is important to identify shortcomings in the performance of the Met Office Unified Model near Antarctica's coastal regions as well as to improve understanding of the processes responsible for SWEs
Impact of a stochastic kinetic energy backscatter scheme across time-scales and resolutions

Copyright © 2014 Royal Meteorological SocietyStochastic physics is one of the preferred methods to represent model uncertainty in ensemble prediction systems of medium-range weather prediction and seasonal forecasting. These schemes increase the ensemble spread and improve probabilistic skill scores. However, little is known about how the stochastic perturbations interact with different atmospheric processes. In order to provide deeper insight into the impacts of stochastic physics on the representation of the atmosphere the stochastic kinetic energy backscatter (SKEB2) scheme has been used in the Met Office Unified Model (MetUM) across different time-scales. We use ‘classic’ verification techniques such as the Root Mean Error Square (RMSE) index in combination with novel ‘object-oriented’ verification metrics such as the Reading University Tracking system (RUTRACK) for extratropical cyclones. We find that the SKEB2 degrades the RMSE and Anomaly Correlation Coefficient (ACC) of individual short-range deterministic forecasts. On average the kinetic energy backscatter by the SKEB2 counteracts the excessive dissipation of extratropical cyclones, improving the model, but its forcing does not scale well across resolutions. Over the Tropics the SKEB2 improvements of the mean climatology and temporal variability are noteworthy, but driven by spurious Rossby waves. There are aspects of the SKEB2 that could be improved to create a more realistic stochastic representation of model uncertainty.Joint DECC/Defra Met Office Hadley Centre Climate Programm
On steady-state tropical cyclones

The article of record as published may be located at http://dx.doi.org/10.1002/qj.2329Weexamine the physical constraints thatmust be satisfied to allow for a steady-state tropical
cyclone in an isolated environment, paying particular attention to the need to replenish
absolute angularmomentum at exactly the rate at which it is consumed and to the vanishing
of the spin-up function above the frictional boundary layer. We conclude that it is unlikely
that these conditions will bemet simultaneously and question whether globally steady-state
tropical cyclone solutions have merit. The implications for previous studies are discussed.MTM acknowledges the support of NSF Grant AGS-0733380
On the computation of moist-air specific thermal enthalpy

The specific thermal enthalpy of a moist-air parcel is defined analytically
following a method in which specific moist entropy is derived from the Third
Law of thermodynamics. Specific thermal enthalpy is computed by integrating
specific heat content with respect to absolute temperature and including the
impacts of various latent heats (i.e., solid condensation, sublimation,
melting, and evaporation). It is assumed that thermal enthalpies can be set to
zero at $0$ K for the solid form of the main chemically inactive components of
the atmosphere (solid-$\alpha$ oxygen and nitrogen, hexagonal ice). The moist
thermal enthalpy is compared to already existing formulations of moist static
energy (MSE). It is shown that the differences between thermal enthalpy and the
thermal part of MSE may be quite large. This prevents the use of MSE to
evaluate the enthalpy budget of a moist atmosphere accurately, a situation that
is particularly true when dry-air and cloud parcels mix because of
entrainment/detrainment processes along the edges of cloud. Other differences
are observed when MSE or moist-air thermal enthalpy is plotted on a
psychrometric diagram or when vertical profiles of surface deficit are plotted.Comment: Paper accepted for publication (January 2014) in the Quarterly
  Journal of the Royal Meteorological Society (39 pages, 12 Figures, 7 Tables
Aircraft-based observations of air-sea turbulent fluxes around the British Isles:Observations of Air-Sea Fluxes

Observations of turbulent fluxes of momentum, heat and moisture from low-level aircraft data are presented. Fluxes are calculated using the eddy covariance technique from flight legs typically ∼40 m above the sea surface. Over 400 runs of 2 min (∼12 km) from 26 flights are evaluated. Flight legs are mainly from around the British Isles although a small number are from around Iceland and Norway. Sea-surface temperature (SST) observations from two on-board sensors (the ARIES interferometer and a Heimann radiometer) and a satellite-based analysis (OSTIA) are used to determine an improved SST estimate. Most of the observations are from moderate to strong wind speed conditions, the latter being a regime short of validation data for the bulk flux algorithms that are necessary for numerical weather prediction and climate models. Observations from both statically stable and unstable atmospheric boundary-layer conditions are presented. There is a particular focus on several flights made as part of the DIAMET (Diabatic influence on mesoscale structures in extratropical storms) project. Observed neutral exchange coefficients are in the same range as previous studies, although higher for the momentum coefficient, and are broadly consistent with the COARE 3.0 bulk flux algorithm, as well as the surface exchange schemes used in the ECMWF and Met Office models. Examining the results as a function of aircraft heading shows higher fluxes and exchange coefficients in the across-wind direction, compared to along-wind (although this comparison is limited by the relatively small number of along-wind legs). A multi-resolution spectral decomposition technique demonstrates a lengthening of spatial scales in along-wind variances in along-wind legs, implying the boundary-layer eddies are elongated in the along-wind direction. The along-wind runs may not be able to adequately capture the full range of turbulent exchange that is occurring because elongation places the largest eddies outside of the run length
Impact of the inflow moisture on the evolution of a warm conveyor belt

This case study of a warm conveyor belt (WCB) event that was probed on a research flight during the THORPEX (The Observing-System Research and Predictability Experiment) Pacific Asian Regional Campaign (T-PARC) field experiment in 2008, investigates the sensitivity of the forecast of the WCB, the associated cyclone and the downstream waveguide to the moisture content in the inflow region of the WCB. By assimilating water vapour profiles of a differential absorption lidar (DIAL) into the European Centre for Medium Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS), the inflow moisture in the analysis fields is adjusted and humidity is reduced in a broad region around the flight track. The initial reduction of moisture in the WCB inflow affects the latent heat release along the WCB, as well as the potential vorticity (PV) production at lower levels. This change led to a substantially lower outflow height of the forecasted WCB. Further, the height of the tropopause was reduced up to 20 hPa, which caused a change in the jet stream wind speeds of up to 15% downstream. Although the impact on the developing surface cyclone was small, improvements of the PV structure as well as of the kinetic energy could be identified
Observation of the airflow over the Alps during a foehn event

A detailed analysis is presented of the large-scale, mesoscale and local features of a south-foehn event\ud
in the Alps on 8 November 1982. On this day, with a substantial cross-mountain flow, instrumented aircraft\ud
made programmed flights back and forth across the Alps between southern Germany and northern Italy.\ud
Rawinsonde observations were used to complete the data set. A mesoscale double mountain wave with an\ud
amplitude of 1 km was found in the upper troposphere, In the mid troposphere above the Inn valley a rather\ud
pronounced wave with an amplitude of 2 km and a wavelength of 50 km was analysed. This wave was close\ud
to overturning. The foehn turned out to be accompanied by low wave drag at high levels and with strong wave\ud
drag at lower levels. Downward southerly (westerly) momentum flux was evaluated to be 0.3 (0.1) Pa. Mountain\ud
drag was estimated to be between 1.6 and 6.7Pa. Light to moderate turbulence was observed immediately to\ud
the lee in a low-level turbulence zone over the region of strong gusty surface winds. Finally, special attention\ud
has been devoted to the similarities and possible differences between foehn in the Alps and chinook in the\ud
Rocky Mountains
Prospects for decadal climate prediction in the Mediterranean region

The Mediterranean region stands as one of the most sensitive to climate change, both in terms of warming and drying. On shorter time-scales, internal variability has substantially affected the observed climate and in the next decade might enhance or compensate long-term trends. Here we compare the multi-model climate predictions produced within the framework of the CMIP5 (Coupled Model Intercomparison Project Phase 5) project with historical simulations to assess the level of multi-year climate prediction skill in the Mediterranean region beyond that originating from the model accumulated response to the external radiative forcings. We obtain a high and significant skill in predicting 4-year averaged annual and summer mean temperature over most of the study domain and in predicting precipitation for the same seasons over northern Europe and sub-Saharan Africa. A lower skill is found during the winter season but still positive for temperature. Although most of this high skill originates from the model response to the external radiative forcings, the initialization contributes to the temperature skill over the Mediterranean Sea and surrounding land areas. The high and significant correlations between the observed Mediterranean temperatures and the observed Atlantic multidecadal oscillation (AMO) in the summer and annual means are captured by the CMIP5 ensemble which suggests that the added skill is related to the ability of the CMIP5 ensemble to predict the AMO. Such a link to the AMO seems restricted to western Africa and summer means only for the precipitation case
Diagnosing the vertical structure of the eddy diffusivity in real and idealized atmospheres

The Earth's extratropical troposphere is equilibrated by turbulent eddy fluxes of potential temperature and momentum. The equilibrated state has the remarkable characteristic that isentropic slopes leaving the surface in the subtropics reach the tropopause near the Poles. It has been speculated that turbulent eddy fluxes maintain this state for a wide range of radiative forcing and planetary parameters. In a previous study, the authors showed that this state needs to be associated with an eddy diffusivity of Ertel potential vorticity that is largest at the surface and decays through the troposphere to approximately zero at the tropopause. This result is confirmed in this study using atmospheric reanalysis and idealized numerical simulations. However, it is also shown that the vertical profile of the eddy diffusivity can change, resulting in different isentropic slopes and climates. This is illustrated with a series of idealized numerical simulations with varying planetary scales and rotation rates.National Science Foundation (U.S.) (Award OCE-0849233
Global Seasonal forecast system version 5 (GloSea5): a high-resolution seasonal forecast system

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This article describes the UK Met Office Global Seasonal forecast system version 5 (GloSea5). GloSea5 upgrades include an increase in horizontal resolution in the atmosphere (N216–0.7°) and the ocean (0.25°), and implementation of a 3D-Var assimilation system for ocean and sea-ice conditions. GloSea5 shows improved year-to-year predictions of the major modes of variability. In the Tropics, predictions of the El Niño–Southern Oscillation are improved with reduced errors in the West Pacific. In the Extratropics, GloSea5 shows unprecedented levels of forecast skill and reliability for both the North Atlantic Oscillation and the Arctic Oscillation. We also find useful levels of skill for the western North Pacific Subtropical High which largely determines summer precipitation over East Asia
The predictability of the extratropical stratosphere on monthly time-scales and its impact on the skill of tropospheric forecasts

This is the final version of the article. Available from Wiley via the DOI in this record.Extreme variability of the winter- and spring-time stratospheric polar vortex has been shown to affect extratropical tropospheric weather. Therefore, reducing stratospheric forecast error may be one way to improve the skill of tropospheric weather forecasts. In this review, the basis for this idea is examined. A range of studies of different stratospheric extreme vortex events shows that they can be skilfully forecasted beyond 5 days and into the sub-seasonal range (0–30 days) in some cases. Separate studies show that typical errors in forecasting a stratospheric extreme vortex event can alter tropospheric forecast skill by 5–7% in the extratropics on sub-seasonal time-scales. Thus understanding what limits stratospheric predictability is of significant interest to operational forecasting centres. Both limitations in forecasting tropospheric planetary waves and stratospheric model biases have been shown to be important in this context.This work is supported by the Natural Environmental Research Council (NERC) funded project Stratospheric Network for the Assessment of Predictability (SNAP) (Grant H5147600) and partially supported by the SPARC. ACP and RGH acknowledge funding through the EU ARISE project (Grant 284387) (EU-FP7). We also acknowledge Steven Pawson and Lawrence Coy from NASA for providing Figure 1. We wish to thank Lorenzo Polvani from Columbia University for providing Figure 4 and Amy Butler from NOAA for her contribution to Figure 5. We thank Adrian Simmons of ECMWF for his insightful review and two anonymous reviewers for their comments and suggestions that improved the quality of the manuscript
Island precipitation enhancement and the diurnal cycle in radiative-convective equilibrium

To understand why tropical islands are rainier than nearby ocean areas, we explore how a highly idealized island, which differs from the surrounding ocean only in heat capacity, might respond to the diurnal cycle and influence the tropical climate, especially the spatial distribution of rainfall and the thermal structure of the troposphere. We perform simulations of three-dimensional radiative-convective equilibrium with the System for Atmospheric Modeling (SAM) cloud-system-resolving model, with interactive surface temperature, where a highly idealized, low heat capacity circular island is embedded in a slab-ocean domain. The calculated precipitation rate over the island can be more than double the domain average value, with island rainfall occurring primarily in an intense, regular thunderstorm system that forms in the afternoon to early evening each day. Island size affects the magnitude of simulated island rainfall enhancement, the intensity of the convection, and the timing of the rainfall maximum relative to solar noon. A combination of dynamic and thermodynamic mechanisms leads to a monotonic enhancement of domain-averaged tropospheric temperature with increasing fraction of island surface, which may contribute to localization of ascent over the Maritime Continent and its relationship to the Walker Circulation.National Science Foundation (U.S.) (Grant AGS 1136466)National Science Foundation (U.S.) (Grant AGS 1136480
Response of the large-scale structure of the atmosphere to global warming

This is the peer reviewed version of the following article: Vallis, G. K., Zurita-Gotor, P., Cairns, C. and Kidston, J. (2015), Response of the large-scale structure of the atmosphere to global warming. Q.J.R. Meteorol. Soc., 141: 1479–1501, which has been published in final form at 10.1002/qj.2456. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving: http://olabout.wiley.com/WileyCDA/Section/id-820227.html#termsThis article discusses the possible response of the large-scale atmospheric structure to a warmer climate. Using integrations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) in conjunction with physical arguments, we try to identify what changes are likely to be robust and what the underlying mechanisms might be. We focus on the large-scale zonally averaged circulation, in particular on height of the tropopause, the strength and position of the surface westerlies and the strength and extent of the Hadley Cell. We present analytic arguments and numerical calculations which suggest that under global warming the height of the tropopause will increase in both the transient response and final equilibrium state, and an increase is clearly found in all the comprehensive models in CMIP5. Upper stratospheric cooling is also found in the comprehensive models, and this too can be explained by a radiative argument. Regarding the circulation, most models show a slight expansion and weakening of the Hadley Cell, depending on season and hemisphere. The expansion is small and largely confined to winter but with some expansion in Southern Hemisphere summer. The weakening occurs principally in the Northern Hemisphere but the intermodel scatter is large. There is also a general polewards shift in surface westerlies, but the changes are small and again are little larger than the intermodel variability in the change. This shift is positively correlated with the Hadley Cell expansion to a degree that depends somewhat on the metric chosen for the latter. There is a robust strengthening in the Southern Hemisphere surface winds across seasons. In the Northern Hemisphere there is a slight strengthening in the westerlies in most models in winter but a consistent weakening of the westerlies in summer. We present various physical arguments concerning these circulation changes but none that are both demonstrably correct and that account for the model results. We conclude that the above-mentioned large-scale thermodynamic/radiative changes in the large-scale atmospheric structure are generally robust, in the sense of being both well understood and consistently reproduced by comprehensive models. In that sense the dynamical changes are less robust given the current state of knowledge and simulation, although one cannot conclude that they are, in principle, unknowable or less predictable.National Science FoundationRoyal SocietyWolfson FoundationMarie Curie fellowshipMinistry of Science and Innovation of Spai
A conservative adaptive wavelet method for the shallow water equations
  on the sphere

We introduce an innovative wavelet-based approach to dynamically adjust the
local grid resolution to maintain a uniform specified error tolerance.
Extending the work of Dubos and Kevlahan (2013), a wavelet multi-scale
approximation is used to make dynamically adaptive the TRiSK model (Ringler et
al. 2010) for the rotating shallow water equations on the sphere. This paper
focuses on the challenges encountered when extending the adaptive wavelet
method to the sphere and ensuring an efficient parallel implementation using
MPI. The wavelet method is implemented in Fortran95 with an emphasis on
computational efficiency and scales well up to O(10^2) processors for
load-unbalanced scenarios and up to at least O(10^3) processors for
load-balanced scenarios. The method is verified using standard smooth test
cases (Williamson et al. 1992) and a nonlinear test case proposed by (Galewsky
te al. 2004). The dynamical grid adaption provides compression ratios of up to
50 times in a challenging homogenous turbulence test case. The adaptive code is
about three times slower per active grid point than the equivalent non-adaptive
TRiSK code and about four times slower per active grid point than an equivalent
spectral code. This computationally efficient adaptive dynamical core could
serve as the foundation on which to build a complete climate or weather model
Simulation of shallow-water jets with a unified element-based continuous/discontinuous Galerkin model with grid flexibility on the sphere

The article of record as published may be located at http://dx.doi.org/10.1002/qj.2474We test the behaviour of a unified continuous/discontinuous Galerkin (CG/DG) shallowwater
model in spherical geometry with curved elements on three different grids
of ubiquitous use in atmospheric modelling: (i) the cubed-sphere, (ii) the reduced
latitude–longitude, and (iii) the icosahedral grid. Both conforming and non-conforming
grids are adopted including static and dynamically adaptive grids for a total of twelve mesh
configurations. The behaviour of CG and DG on the different grids are compared for a
nonlinear midlatitude perturbed jet and for a linear case that admits an analytic solution.
Because the inviscid solution on certain grids shows a high sensitivity to the resolution,
the viscous counterpart of the governing equations is also solved and the results compared.
The logically unstructured element-based CG/DG model described in this article is flexible
with respect to arbitrary grids. However, we were unable to define a best grid configuration
that could possiblyminimize the error regardless of the characteristic geometry of the flow.
This is especially true if the governing equations are not regularized by the addition of a
sufficiently large, fully artificial, diffusion mechanism, as will be shown. The main novelty
of this study lies in the unified implementation of two element-based Galerkin methods
that share the same numericalmachinery and do not rely on any specific grid configuration
to solve the shallow-water equation on the sphere.The authors gratefully acknowledge the support of the Office of Naval Research through program element PE-0602435N, the National Science Foundation (Division ofMathematical Sciences) through program element 121670, and the Air Force Office of Scientific Research through the Computational Mathematics program