pinecone/core-2020-05-10-deduplication huggingface dataset:
Modelling the vertical structure of the atmospheric boundary layer over Arctic fjords in Svalbard

The vertical structure of the atmospheric boundary layer (ABL), simulated with the\ud
mesoscale modelWeather Research and Forecasting (WRF) as well as with its polar\ud
optimized version Polar WRF, was compared to tethered balloon soundings and\ud
mast observations taken in March and April 2009 from two Arctic fjords in Svalbard.\ud
From twelve short (48 h) simulations, the Quasi-Normal Scale Elimination scheme\ud
for the ABL and the NOAH land surface scheme for the surface were found to\ud
perform best and were selected for one long (16 day) simulation. The differences\ud
in performance of the standard WRF and Polar WRF were marginal. A warm\ud
bias, especially near the surface, was found in the modelled temperature profiles\ud
related to underestimated temperature inversion strength and depth. The modelled\ud
humidity inversions were generally deeper but weaker than the observed, and often\ud
occurred independently of temperature inversions. The largest errors in temperature\ud
and humidity occurred under high pressure conditions. Multiple temperature and\ud
humidity inversions were usually not captured byWRF. Compared to the compact\ud
sea ice east of Svalbard, the modelled temperature and humidity inversions were\ud
weaker and less frequent over the fjords. The biases in modelled wind speed profiles\ud
were closely related to low-level jets (LLJs); the modelled LLJs were stronger and\ud
deeper, and typically located at higher altitudes than the observed LLJs. Errors in the\ud
near-surface variables were notably reduced by applying post-processing equations\ud
based on othermodelled variables
A bias-corrected decomposition of the Brier score

Copyright © 2012 Royal Meteorological SocietyThe Brier score is a widely used measure of performance for probabilistic forecasts of event occurrences and is often decomposed additively into three terms that quantify the reliability and resolution of the forecasts and the uncertainty of the forecast events. The standard decomposition yields biased estimates of the large-sample values of these three quantities: reliability is overestimated and uncertainty is underestimated, while resolution may be either overestimated or underestimated. An unbiased decomposition is shown to be unattainable but a new decomposition is proposed that has smaller biases and therefore provides a more accurate measure of forecast performance. The implications for the Brier skill score and the attributes diagram are discussed and results are illustrated with seasonal forecasts of sea-surface temperatures
Factors influencing Northern Hemisphere winter mean atmospheric circulation anomalies during the period 1960/61 to 2001/02

Influences from the Tropics, the stratosphere and the specification of observed sea\ud
surface temperature and sea-ice (SSTSI) on Northern Hemisphere winter mean\ud
circulation anomalies during the period 1960/61 to 2001/02 are studied using a\ud
relaxation technique applied to the ECMWF model. On interannual time-scales,\ud
the Tropics strongly influence the Pacific sector but also the North Atlantic sector,\ud
although weakly. The stratosphere is found to be influential on the North Atlantic\ud
Oscillation (NAO) on interannual time-scales but is less important over the Pacific\ud
sector. Adding the observed SSTSI to the tropical relaxation runs generally improves\ud
the model performance on interannual time-scales but degrades/enhances the\ud
model’s ability to capture the 42-year trend over the Pacific/Atlantic sector. While\ud
relaxing the stratosphere to the reanalysis fails to capture the trend over the whole\ud
42-year period, the stratosphere is shown to be influential on the upward trend of the\ud
NAO index from 1965 to 1995, but with reduced amplitude compared to previous\ud
studies. Influence from the Tropics is found to be important for the trend over both\ud
time periods and over both sectors although, across all experiments, we can account\ud
for only 30% of the amplitude of the hemispheric trend. Copyright c� 2012 Royal\ud
Meteorological Societ
On a general definition of the squared Brunt-V\"{a}is\"{a}l\"{a}
  Frequency associated with the specific moist entropy potential temperature

The squared Brunt-V\"{a}is\"{a}l\"{a} Frequency (BVF) is computed in terms of
the moist entropy potential temperature recently defined in Marquet (2011).
Both homogeneously saturated and non-saturated versions of $N^2$ (the squared
BVF) are derived. The method employed for computing these special homogeneous
cases relies on the expression of density written as a function of pressure,
total water content and specific moist entropy only. The associated
conservative variable diagrams are discussed and compared with existing ones.
Despite being obtained without any simplification, the formulations for $N^2$
remain nicely compact and are clearly linked with the squared BVF expressed in
terms of the adiabatic non-saturated and saturated lapse rates. As in previous
similar expressions, the extreme homogeneous solutions for $N^2$ are of course
different, but they are not analytically discontinuous. This allows us to
define a simple bridging expression for a single general shape of $N^2$,
depending only on the basic mean atmospheric quantities and on a transition
parameter, to be defined (or parameterized) in connection with the type of
application sought. This integrated result remains a linear combination (with
complex but purely local weights) of two terms only, namely the environmental
gradient of the moist entropy potential temperature and the environmental
gradient of the total water content. Simplified versions of the various
equations are also proposed for the case in which the moist entropy potential
temperature is approximated by a function of both so-called moist-conservative
variables of Betts (1973).Comment: Paper submitted in July 2011 to the Quarterly Journal of the Royal
  Meteorological Society. Published: Volume 139, Issue 670, pages 85-100,
  January 2013 Part A.
  http://onlinelibrary.wiley.com/doi/10.1002/qj.1957/abstract (27 pages / 10
  black and white Figures). V2: add arXiv link to Marquet (2011
Absolute or Convective instability in the equatorial Pacific and implications for ENSO

International audienceThe El Niño-Southern Oscillation (ENSO) is driven by ocean-atmosphere interactions in the equatorial Pacific, and this variability is often attributed to coupled modes that are evidenced by the temporal stability analysis of anomaly models. Here, the further diagnostic of absolute/convective instability is considered, which assesses whether small perturbations localized in space and time (e.g. random wind disturbances) lead to instabilities that develop in-place or propagate away from the perturbed region. It is shown that boundary conditions play a secondary role for this approach and that the development of large-scale wave packets in the equatorial Pacific basin is possible, as in the case of an infinite domain. As an illustration, two simple coupled models are diagnosed that rely either on thermocline processes or zonal advective processes. The model with thermocline processes is 'absolutely unstable' and therefore develops intrinsic oscillations, while the model with zonal advective processes is 'convectively unstable' and therefore acts as a noise amplifier. The identification of the two instability regimes may characterize different ENSO formation mechanisms as a response to random wind disturbances. For the absolutely unstable regime, a standing ENSO-like oscillation can develop in the equatorial Pacific without involving boundary reflections, while for the convectively unstable regime boundary reflections are essential. Copyright © 2012 Royal Meteorological Societ
Multivariate probabilistic forecasting using Bayesian model averaging
  and copulas

We propose a method for post-processing an ensemble of multivariate forecasts
in order to obtain a joint predictive distribution of weather. Our method
utilizes existing univariate post-processing techniques, in this case ensemble
Bayesian model averaging (BMA), to obtain estimated marginal distributions.
However, implementing these methods individually offers no information
regarding the joint distribution. To correct this, we propose the use of a
Gaussian copula, which offers a simple procedure for recovering the dependence
that is lost in the estimation of the ensemble BMA marginals. Our method is
applied to 48-h forecasts of a set of five weather quantities using the
8-member University of Washington mesoscale ensemble. We show that our method
recovers many well-understood dependencies between weather quantities and
subsequently improves calibration and sharpness over both the raw ensemble and
a method which does not incorporate joint distributional information.Comment: 17 pages, 4 figure
Sensitivity of tropical cyclone intensification to perturbations in the surface drag coefficient

The article of record as published may be located at http://dx.doi.org/10.1002/qj.2048The recent studies of the sensitivity of tropical-cyclone intensification to the surface
drag coefficient in a three-dimensional model by Montgomery et al. and Smith
et al. are extended to include perturbations of the surface drag coefficient in one
of four boundary-layer parametrization schemes: the bulk scheme, the Blackadar
scheme, the MRF scheme, and the Gayno–Seaman scheme. The schemes are slightly
modified to have the same drag coefficient formulation and the same constant
exchange coefficients for sensible heat and moisture.We find that the intensification
rate and mature intensity are essentially unaltered when the drag coefficient is
perturbed randomly by variations of up to 60%. The results, in conjunction with
an analysis of coherent drag coefficient variations for a moving vortex, question
the notion that coupled wind–wave models are necessary to accurately forecast
tropical-cyclone intensification and mature intensity.MTM acknowledges the support of grant no. N00014-03-
1-0185 from the US Office of Naval Research, and the US
National Science Foundation grant ATM-0715426
Sensitivity of tropical-cyclone models to the surface drag coefficient in different boundary-later schemes

The article of record as published may be found at http://dx.doi.org/10.1002/qj.2057The recent study of the sensitivity of tropical-cyclone intensification to the surface drag coefficient in a three-dimensional model by Montgomery et al. is extended to include a wind-speed-dependent drag coefficient and one of four boundary-layer parametrization schemes: the bulk, Blackadar, MRF and Gayno–Seaman schemes.  The schemes are slightly modified to have the same drag coefficient formulation and the same constant exchange coefficients for sensible heat and moisture. Interest
is focused on the change in intensity of the azimuthally-averaged tangential wind speed and change in the low-level vortex structure when the standard value of the drag coefficient is halved or doubled. Changing the drag coefficient provides insight into unbalanced effects in the boundary layer and their impact on the vortex evolution and structure. The changes in vortex behaviour with changing drag coefficient are qualitatively similar for all schemes, the maximum intensification occurring for a
value somewhere near the standard value of the drag coefficient. The interpretation given to explain this behaviour underlines the intrinsically unbalanced nature of the boundary-layer dynamics, although, for reasons discussed, a complete theory for the behaviour does not exist. The behaviour found is at odds with the predictions of Emanuel’s (balance) theory for the maximum intensity of a tropical-cyclone, which
predicts a monotonic decrease in intensity with the drag coefficient if the enthalpy exchange coefficient is held fixed. It is at odds also with a recent numerical study of the maximum intensity by Bryan and Rotunno.  The study underscores the importance of boundary-layer dynamics in models for forecasting tropical-cyclone intensity and the need for care in choosing a boundary layer scheme.  However, it is not yet known which boundary-layer formulation is the most appropriate for this purpose, highlighting the need for a concerted research effort in this direction.German Research CouncilU.S. Office of Naval ResearchNational Science FoundationNOAA hurrican Research DivisionNASAGrant No. SM30/23-1 (GRC)Grant No. N0001411Wx20095 (ONR)AGS-0733380 and AGS-0851077 (NSF)Grants NNH09AK561 and NNG09HG031 (NASA
On the onset of bora and the formation of rotors and jumps near a mountain gap

This study investigates the onset phase of a strong Adriatic bora windstorm that occurred on 4 April 2002. The target area is a gap about 20 km wide embedded in the coastal mountain barrier of the Dinaric Alps that favours strong jet-like winds. Airborne-aerosol back-scatter lidar measurements on board the DLR Falcon research aircraft, together with surface and upper-air observations, are used to verify high-resolution numerical experiments conducted with the mesoscale atmospheric model RAMS and a single-layer shallow-water model (SWM). Especially during the breakthrough phase of the bora, the flow at the gap exit exhibits a complex spatial structure and temporal evolution. On a transect through the centre of the gap, a hydraulic jump forms; this is located close to the coast throughout the night, and starts to propagate downstream in the early morning. On a transect through the edge of the gap, a lee-wave-induced rotor becomes established, due to boundary-layer separation. It starts to propagate downstream about two hours after the jump. This flow evolution implies that the onset of strong winds at the coast occurs several hours earlier downstream of the centre of the gap than downwind of the edge of the gap. Consequently, the wind field in the vicinity of Rijeka airport, located downwind of the gap, is strongly inhomogeneous and transient, and represents a potential hazard to aviation. Measured bora winds at the surface exceed 20 ms<sup>-1</sup>, and the simulated wind speed in the gap wind layer exceeds 30 ms<sup>-1</sup>. The simulated turbulent kinetic energy exceeds 10 m<sup>2</sup> s<sup>-2</sup>.\ud
RAMS indicates that wave-breaking near a critical level is the dominant mechanism for the generation of the windstorm. Gap jets can be identified downstream of several mountain passes. The simulated wave pattern above the Dinaric Alps, the wave decay with height due to directional wind shear and the strong flow descent on the leeward side of the barrier are supported by measured back-scatter intensities. Basic bora flow features, including gap jets and jumps, are remarkably well reproduced by SWM simulations. The RAMS reference run captures observed flow phenomena and the temporal flow evolution qualitatively well. A cold low-level bias, an overestimated bora inversion strength, and a slightly too-early bora onset are probably related to insufficient turbulent mixing in the boundary layer. The amplitude of trapped gravity waves, the time of the bora breakthrough and the inversion strength are found to be quite sensitive to the turbulence parametrization
Impact of soil moisture and convectively generated waves on the initiation of a West African mesoscale convective system

A mesoscale convective system (MCS) case study was observed over northeast Mali as part of the African Monsoon Multidisciplinary Analysis (AMMA) on 31 July 2006. Observations of this case suggest that the soil-moisture heterogeneity and atmospheric gravity waves emitted from a ‘parent’ MCS were important trigger mechanisms for this system. This study uses high-resolution Met Office Unified Model (MetUM) simulations to assess the importance of the synoptic circulation, land-surface and gravity waves in the initiation and development of the MCS. During the early afternoon shallow convection developed over a region of dry soil within a synoptic-scale convergence zone, which was caused by the confluence of the southerly monsoon flow with winds associated with the circulation around the Saharan heat low. Two pronounced waves were emitted from a nearby ‘parent’ storm and propagated towards the convergence zone. When the second wave reached the location of the shallow convection, deep convection was immediately initiated. Further convective cells developed later in the afternoon over dry soil, many adjacent to strong soil moisture gradients; these aggregated with the main storm, which later developed into the case study MCS. A comparison of model simulations with/without the soil-moisture heterogeneity and gravity waves shows that the synoptic-scale circulation and convergence zones, specified by the atmospheric analysis, were the most important factors for the successful simulation of the MCS. If the location of the initiation of the system is to be forecast accurately, the land-surface, that is, the soil moisture, must be represented adequately. In order to reproduce the timing of the secondary initiation of convection correctly the model must be able to capture gravity waves that are emitted by existing systems
A critical revision of the estimation of the latent heat ﬂux from two-wavelength scintillometry

Simultaneous scintillometer measurements at multiple wavelengths (pairing visible\ud
or infrared with millimetre or radio waves) have the potential to provide estimates of\ud
path-averaged surface ﬂuxes of sensible and latent heat. Traditionally, the equations\ud
to deduce ﬂuxes from measurements of the refractive index structure parameter at\ud
the two wavelengths have been formulated in terms of absolute humidity. Here, it is\ud
shown that formulation in terms of speciﬁc humidity has several advantages. Speciﬁc\ud
humidity satisﬁes the requirement for a conserved variable in similarity theory and\ud
inherently accounts for density effects misapportioned through the use of absolute\ud
humidity. The validity and interpretation of both formulations are assessed and\ud
the analogy with open-path infrared gas analyser density corrections is discussed.\ud
Original derivations using absolute humidity to represent the inﬂuence of water\ud
vapour are shown to misrepresent the latent heat ﬂux. The errors in the ﬂux, which\ud
depend on the Bowen ratio (larger for drier conditions), may be of the order of 10%.\ud
The sensible heat ﬂux is shown to remain unchanged. It is also veriﬁed that use of\ud
a single scintillometer at optical wavelengths is essentially unaffected by these new\ud
formulations. Where it may not be possible to reprocess two-wavelength results, a\ud
density correction to the latent heat ﬂux is proposed for scintillometry, which can be\ud
applied retrospectively to reduce the error
The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010

In July and August 2010 floods of unprecedented impact afflicted Pakistan. The floods resulted from a series of intense multi-day precipitation events in July and early August. At the same time a series of blocking anticyclones dominated the upper-level flow over western Russia and breaking waves i.e. equatorward extrusions of stratospheric high potential vorticity (PV) air formed along the downstream flank of the blocks. Previous studies suggested that these extratropical upper-level breaking waves were crucial for instigating the precipitation events in Pakistan. Here a detailed analysis is provided of the extratropical forcing of the precipitation. Piecewise PV inversion is used to quantify the extratropical upper-level forcing associated with the wave breaking and trajectories are calculated to study the pathways and source regions of the moisture that precipitated over Pakistan. Limited-area model simulations are carried out to complement the Lagrangian analysis.\ud
\ud
The precipitation events over Pakistan resulted from a combination of favourable boundary conditions with strong extratropical and monsoonal forcing factors. Above-normal sea-surface temperatures in the Indian Ocean led to an elevated lower-tropospheric moisture content. Surface monsoonal depressions ensured the transport of moist air from the ocean towards northeastern Pakistan. Along this pathway the air parcel humidity increased substantially (60–90% of precipitated moisture) via evapotranspiration from the land surface. Extratropical breaking waves influenced the surface wind field substantially by enhancing the wind component directed towards the mountains which reinforced the precipitation
Can aerosols influence deep tropical convection? :
                    Aerosol indirect effects in the Hector island thunderstorm

This article addresses the effects of cloud condensation nuclei on the evolution of an intense tropical convective system, known as Hector, using data taken from the ACTIVE and TWP-ICE field campaigns, which were conducted in 2005 and 2006. The Hector thunderstorms were observed in a variety of aerosol conditions so the data serve as an ideal dataset to test whether aerosols have a significant impact on the evolution of convective clouds and precipitation. We find evidence for an aerosol effect on the storm's properties, which are reproduced with a state-of-the-art mesoscale cloud-resolving model. Including the measured aerosol concentration within the model is shown to improve the fractions skill-score metric for every case presented in the article, thus giving us confidence that the deep convection observed during the period was indeed influenced by the aerosol entering the storm's inflow. However, we do not find a general relationship for the way aerosols affect properties such as cloud-top height, precipitation or radiative properties, as has been suggested in previous work. The reasons for this appear to be because of the nonlinearity of interactions between neighbouring cells and because of the variability in the meteorological profiles of temperature, wind and humidity
Impact of different ozone sounding networks on a 4D-Var stratospheric data assimilation system

Observing system simulation experiments (OSSEs) are performed to examine the impact of ozonesonde observations on a data assimilation system during a simulated satellite data gap during February 2003. Using the four-dimensional variational chemical data assimilation system SACADA, the relative influence of launch rates and station coverage is investigated. Starting with the VINTERSOL/MATCH campaign, different network and sounding configurations are evaluated. To quantify the performance of assimilation experiments in the lower stratosphere, analysis skill and linear pattern correlation with respect to ERA-Interim reference data are assessed for the 20 km altitude level. Using first-guess and analysis minus observation error statistics, a priori error settings are tuned to optimise the assimilation of simulated and real-world ozone soundings. In summary, it is found that, during satellite data gaps, ozonesonde data can have a significant positive impact on the mean analysis skill depending both on the number of observations and the network layout. A better distributed network based on the GAW system, with 28 stations and three soundings bi-weekly, proves clearly superior to VINTERSOL/MATCH, showing a positive gain in skill of 0.26 compared to a free-running model