pinecone/core-2020-05-10-deduplication huggingface dataset:
An inherently mass-conserving semi-implicit semi-Lagrangian discretisation of the shallow-water equations on the sphere

Copyright © 2009 Royal Meteorological SocietyFor the shallow-water equations on the sphere, an inherently mass-conserving semi-Lagrangian discretisation (SLICE) of the continuity equation is coupled with a semi-implicit semi-Lagrangian discretisation of the momentum equations. Various tests from the literature (two with analytical nonlinear solutions) are used to assess the model's performance and also to compare it with that of a variant model that instead employs a standard non-conserving semi-implicit semi-Lagrangian discretisation of the continuity equation. The mass-conserving version gives results that are overall somewhat better than the non-conserving one
Real-time localised forecasting of the Madden-Julian Oscillation using neural network models

Existing statistical forecast models of the Madden-Julian Oscillation (MJO) are generally of very low order and predict the evolution of a small number (typically two) of principal components (PCs). While such models are skilful up to 25 days lead time, by design they only predict the very largest-scale features of the MJO. Here we present a higher-order MJO statistical forecast model that is able to predict MJO variability on smaller, more localised scales, that will be of more direct benefit to national weather agencies and regional government planning. The model is based on daily outgoing long-wave radiation (OLR) data that are intraseasonally filtered using a recently developed technique of empirical mode decomposition that can be used in real time. A standard truncated PC analysis is then used to isolate the maximum amount of variance in a finite number of modes. The evolution of these modes is then forecast using a neural network model, which does not suffer from the parametrisation problems of other statistical forecast techniques when applied to a higher number of modes. Compared to a standard 2-PC model, the higher-order PC model showed improved skill over the whole MJO domain, with substantial improvements over the western Pacific, Arabian Sea, Bay of Bengal, South China Sea and Phillipine Sea
Addressing model uncertainty in seasonal and annual dynamical ensemble forecasts

The relative merits of three forecast systems addressing the impact of model uncertainty on seasonal/annual forecasts are described. One system consists of a multi-model, whereas two other systems sample uncertainties by perturbing the parametrization of reference models through perturbed parameter and stochastic physics techniques. Ensemble re-forecasts over 1991 to 2001 were performed with coupled climate models started from realistic initial conditions. Forecast quality varies due to the different strategies for sampling uncertainties, but also to differences in initialisation methods and in the reference forecast system. Both the stochastic-physics and perturbed-parameter ensembles improve the reliability with respect to their reference forecast systems, but not the discrimination ability. Although the multi-model experiment has an ensemble size larger than the other two experiments, most of the assessment was done using equally-sized ensembles. The three ensembles show similar levels of skill: significant differences in performance typically range between 5 and 20%. However, a nine-member multi-model shows better results for seasonal predictions with lead times shorter than five months, followed by the stochastic-physics and perturbed-parameter ensembles. Conversely, for seasonal predictions with lead times longer than four months, the perturbed-parameter ensemble gives more often better results. All systems suggest that spread cannot be considered a useful predictor of skill. Annual-mean predictions showed lower forecast quality than seasonal predictions. Only small differences between the systems were found. The full multi-model ensemble has improved quality with respect to all other systems, mainly from the larger ensemble size for lead times longer than four months and annual predictions
Structure and dynamics of the Saharan atmospheric boundary layer during the West African Monsoon onset: Observations and analyses from research flights of 14 and 17 July 2006

This paper presents the results of co-ordinated research flights over the Saharan heat-low, conducted during July 2006 as part of the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Periods. The flights consisted of a morning transect on 14 July 2006 with the Falcon F20 aircraft of the Deutsches Zentrum für Luft- und Raumfahrt (DLR), using the Doppler lidar WIND to observe the tropospheric winds, followed by an afternoon flight on 17 July with the BAe146 aircraft of the Facility for Airborne Atmospheric Measurements (FAAM) releasing a curtain of 16 dropsondes. Measurements from radiosondes at the Algerian stations of Tamanrasset and In Salah, as well as the CALIPSO spaceborne lidar, are analysed also. It is shown that the daytime Saharan atmospheric boundary layer exhibits a remarkable split structure, with a well-mixed convective layer lying beneath a residual layer whose dynamics appear to be more nearly laminar. Observations from Saharan radiosonde stations confirm that the Saharan residual boundary layer is, on some days, a persistent rather than a transient feature, and that on occasion the residual layer can last right through the day.
The broad features of the Saharan heat-low thermodynamics and winds are successfully captured by the ECMWF operational analyses and the discrepancies are quantified here. The lidar winds of 14 July confirm that the analysis represents the main airflows accurately, apart from the zone to the southeast of a mid-level trough, for which the southerly component of winds was underestimated by some 8 m s-1. On 17 July, the strengths of both the southwesterly monsoon and the northeasterly Harmattan winds were slightly underestimated also. The region of maximum boundary-layer temperature over the desert was around 1 degree too far north, and too broad in the analysis, while the equivalent potential temperature in the Saharan convective boundary layer was around 2 K lower than observed. The near-saturated layer observed at the top of the Saharan atmospheric boundary layer was underestimated also in the analysis, in horizontal extent and altitude. The intertropical front of 17 July was coincident with strong surface contrasts in vegetation and fluxes. On each study day the intertropical front in the analyses was around 1 degree further north than observed
Solar heating of the oceans-diurnal, seasonal and meridional variation

Solar heating is an important factor in modelling the upper boundary layer of the ocean. It influences not only the temperature, but also the depth of the mixed layer and must be taken into account in circulation dynamics. The study reported in this paper was designed to reveal the principal features of the global climatology of solar heating in the ocean, with such applications in mind. The meridional, seasonal and diurnal variations of the vertical distribution of solar heating inside the ocean, expressed in terms of I(z), the rate of heat accumulation below depth z, and †(z) = (1/c). dzI(z), the rate of temperature rise, are calculated for given values of cloud cover and seawater turbidity (expressed in terms of Jerlov's water types) using a model that incorporates a new parametrization of I(z)/I(0), which is shown to be more accurate than previous versions. At present there exist no reliable global climatologies of cloud cover and seawater turbidity, so the values of the corresponding parameters are held constant in each computation, which is then repeated using parameter sets covering the full ranges from clear to overcast sky, clear to turbid ocean water. It is found that uncertainty in cloud cover is more important in the mixed layer, and uncertainty in seawater turbidity is more important below. The results presented in this paper are mainly concerned with solar heating below the mixed layer. It is calculated that the annual temperature rise can exceed 1 K and the annual heat accumulation can exceed 100 MJ/m2 below the mixed layer in the tropics. At higher latitudes solar heating produces similar heating rates in summer, but the stored heat is extracted locally in winter when the mixed layer depth exceeds the maximum depth of solar heating, defined here by a daily temperature rise of 1 mK or a heat flux of 86.4 KJ/m2d (=1 W/m2). The sensitivity of the seasonal and meridional variations of the maximum depth of solar heating to cloud cover and seawater turbidity is investigated. The actual change of temperature due to solar heating in the seasonal thermocline at Ocean Weather Station ‘C’ is calculated using Bunker's monthly mean cloud cover and Jerlov's seawater turbidity. Extension of such calculations to the whole of the World Ocean must await the publication of global climatologies of cloud cover and seawater turbidity, which are expected to be derived from satellite observations during the next decade.\ud
A solar heating climatology is a prerequisite for computation of the thermal response of the ocean to CO2 pollution of the atmosphere. The implications of the results obtained from the present study are discussed. An early rise in tropical sea surface temperature seems likely, but exact prediction will be hindered by uncertainty in the turbidity of the tropical ocean
The response of the upper ocean to solar heating. I: The mixed layer

The results of two earlier papers on convection in the mixed layer and on the solar heating profile are here introduced into a one-dimensional model in order to investigate the following consequences of the daily cycle of solar heating in the upper ocean:\ud
\ud
1. the daytime convection depth becomes less than the turbocline depth;\ud
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2. the convective power supply to turbulence in the mixed layer is reduced;\ud
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3. the mixed layer below the convection layer becomes stably stratified;\ud
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4. the depth of the turbocline is reduced, leaving a diurnal thermocline between it and the top of the seasonal thermocline;\ud
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5. the heat content and potential energy of the diurnal and seasonal thermoclines are increased, slowing down the subsequent nocturnal descent of the turbocline.\ud
\ud
These diurnal changes are illustrated by integrating a one-dimensional model forced by the astronomical cycle of solar heating and seasonal variation of surface meteorology derived from Bunker's climatology. The model is integrated for 18 months to show the seasonal modulation of the diurnal cycle. Nocturnal convection plays a dominant role. The convection depth closely follows the thermal compensation depth during the day when they are less than the turbocline depth. Integrating the model with a 24-hour time step leads to large errors in the seasonal variation of mixed layer temperature and depth, and in the source term of isopycnic potential vorticity. The errors are reduced by using two time steps per day, one for the daytime when convection is quenched, the other for the night when it is active. A novel parametrization based on tuning the daily equivalent solar elevation to surface temperature further reduces the error. This parametrization is used to investigate the sensitivity of the seasonal cycles of mixed layer depth and temperature to: (1) seasonality in the surface fluxes; (2) systematic changes in the net annual solar heating; (3) random changes in the seasonal cycles of solar heating induced (i) monthly and (ii) daily. The sensitivity to uncertainty in seawater turbidity is investigated in the same way. The profile of isopycnic potential vorticity subducted into the thermocline depends on the vernal correlation of mixed layer depth and density, so gyre circulation is sensitive to solar heating in spring
The response of the upper ocean to solar heating II: The wind-driven current

The current profile generated by a steady wind stress is disturbed by the diurnal variation of mixed layer depth forced by solar heating. Momentum diffused deep at night is abandoned to rotate inertially during the day when the mixed layer is shallow and then re-entrained next night when it deepens. The resulting variation of current profile has been calculated with a one-dimensional model in which power supply to turbulence determines the profile of eddy viscosity. The resulting variations of current velocity at fixed depths are so complicated that it is not surprising that current meter measurements have seldom yielded the classical Ekman solution. However, the progressive vector diagrams do exhibit an Ekman-like response (albeit with superimposed inertial disturbances) suggesting that the model might be tested by tracking drifters designed to follow the flow at fixed depths. The inertial rotation of the current in the diurnal thermocline leads to a diurnal jet, the dynamical equivalent of the nocturnal jet in the atmospheric boundary layer over land. The role of inertial currents in deepening the mixed layer is clarified, leading to proposals for improving the turbulence parametrizations used in models of the upper ocean. The model predicts that the diurnal thermocline contains two layers of persistent vigorous turbulence separated by a thicker band of patchy turbulence in otherwise laminar flow
Large-Eddy Simulation of the Up-slope Boundary Layer

Large-eddy simulation (LES) is used to determine the turbulent structure of the steady-state up-slope boundary layer (UBL) which forms at a uniformly heated inclined or vertical plane surface below a stratified atmosphere at rest. At proper scales, the problem depends solely on the slope angle a and the surface roughness height z<sub>0</sub> a relative to a length scale H which is a function of stratification and surface heating. We cover 2° ≤ α  ≤ 90° and 3 × 10<sup>-5</sup> ≤ z<sub>0</sub>/H ≤ 3 × 10<sup>-2</sup> by a series of LESs. Simulations using different grids show that the results are only weakly sensitive to truncation errors. the UBL approaches a steady-state mean-profile by slowly decaying oscillations; its frequency equals the Brunt-Väisälä frequency times sin α. In the LES, convergence towards steady state has been enforced by adjusting the fields according to integral steady-state conditions. For α ≤ 10°, a well-mixed layer is formed which causes a strong temperature inversion and strong down-slope flow at the outer edge of the UBL. Large-scale coherence is weak with some indications of cross-slope rolls for small inclination angles and longitudinal rolls for steep slopes. Several mean quantities have been tabulated as a function of slope angle and surface roughness and approximating power laws are given. the dependence of mean quantities on the slope angle is difficult to explain with simple models, but the influence of surface roughness closely follows earlier results
On the concept of exergy and available enthalpy: Application to
  atmospheric energetics

The available enthalpy is an early form of the modern thermodynamic concept
of exergy, which is the generic name for the amount of work obtainable when
some matter is brought to a state of equilibrium with its surroundings by means
of reversible processes.
  It is shown in this paper that a study of the hydrodynamic properties of
available enthalpy leads to a generalization of the global meteorological
available energies previously introduced by Lorenz, Dutton and Pearce. A local
energy cycle is derived without approximation. Moreover, static instabilities
or topography do not prevent this theory from having practical applications.
The concept of available enthalpy is also presented in terms of the potential
change in total entropy. Using the hydrostatic assumption, limited-area
energetics is then rigorously defined, including new boundary fluxes and new
energy components. This innovative approach is especially suitable for the
study of energy conversions between isobaric layers of an open limited
atmospheric domain.
  Numerical evaluations of various energy components are presented for a
hemispheric field of zonal-average temperature. It is further shown that this
new energetic scheme realizes a hierarchical partition of the components so
that the smallest of those available enthalpy reservoirs are almost of the same
magnitude as the kinetic energy. This is actually the fundamental property that
induced Margules to define the primary concept of available kinetic energy in
meteorology.Comment: Corrected and augmented version of a paper submitted in April 1990 to
  the Quarterly Journal of the Royal Meteorological Society. Published in
  Vol.117 (499), p.449-475, April 1991 (41 pages, 14 Figures
Large-Eddy Simulation of a Neutrally Stratified Boundary Layer: A Comparison of Four Computer Codes

A neutrally stratified Ekman layer limited in depth by a stress-free rigid lid has been simulated using four different large-eddy simulation computer codes. This is the second large-eddy simulation intercomparison study\ud
in a series of simulations of different flows aimed at a systematic analysis of large-eddy simulation sensitivity to subgrid scale model assumptions and numerical methods. The resolution was chosen to be coarse so that\ud
the results might be sensitive to the details of the various subgrid scale model formulations. Stochastic backscatter of subgrid kinetic energy and scalar variance was included in one subgrid scale model.\ud
Profiles of first and second moments, budgets of resolved-scale second moments, and spectra have been analyzed. It is found that significant differences in the lowest third of the boundary layer result from moderate\ud
changes in subgrid scale eddy diffusivities or from the inclusion of backscatter.\ud
To isolate effects of the various numerical methods, a set of tests with a fixed subgrid scale K-profile were made. When run with a common subgrid scale model the results from the four large-eddy simulation codes converge. This test indicates that the large-eddy simulation results are more sensitive to the subgrid scale model formulations than to the various numerics
On the concept of pseudo-energy of T. G. Shepherd. A close link with
  exergy functions

Shepherd (1993) derived a general expression for the available potential
energy for compressible, hydrostatic flow, where the sum of this available
energy and the kinetic energy is called pseudo-energy. He demonstrated that for
a special basic state the small-amplitude limit of the generalized available
potential energy reduces to the well-known approximate form of Lorenz (1955)
expressed in a pressure vertical coordinate.
  Other forms of available energies exist in atmospheric energetics and in
thermodynamics, where the name exergy has been coined by Rant (1956) to denote
the maximum work that can be extracted from any system when it is subject to
some constraints (adiabatic transformations or constant total energy for
instance).
  The purpose of this note is to show that the specific available enthalpy
function denoted by $a_h = (h - h_r) - T_r \: (s - s_r)$ in Marquet (1991) can
be obtained from the generalized approach of Shepherd for another basic state.
This special form of pseudo-energy also leads to the global hydrostatic
concepts of Dutton (1973) and Pichler (1977). The function $a_h$ only depends
on the specific enthalpy $h$ and entropy $s$ at any point, the values $h_r$ and
$s_r$ refer to the special dead state at temperature $T_r$ and pressure $p_r$.
  It is explained that for another choice of the basic state, the generalized
expression of Shepherd reduces with a good accuracy to the approximate
functions introduced by Pearce (1978) or Blackburn (1983) in meteorology and
Thomson (1853, Lord Kelvin) in thermodynamics.Comment: An annotated, corrected and augmented copy of a Note submitted in
  January 1994 to the Quarterly Journal of the Royal Meteorological Society.
  Published in Volume 121, Issue 522, pages 455--459, January 1995 Part B.
  http://onlinelibrary.wiley.com/doi/10.1002/qj.49712152212/abstract (9 pages,
  1 Figure
Extremal principle of entropy production in the climate system

Paltridge found reasonable values for the most significant climatic variables through maximizing the material transport part of entropy production by using a simple box model. Here, we analyse Paltridge's box model to obtain the energy and the entropy balance equations separately. Derived expressions for global entropy production, which is a function of the radiation field, and even its material transport component, are shown to be different from those used by Paltridge. Plausible climatic states are found at extrema of these parameters. Feasible results are also obtained by minimizing the radiation part of entropy production, in agreement with one of Planck's results, Finally, globally averaged values of the entropy flux of radiation and material entropy production are obtained for two dynamical extreme cases: an earth with uniform temperature, and an earth in radiative equilibrium at each latitudinal poin
Second differential of the entropy as a criterion for the stability in low-dimensional climate models

The second differential of the entropy is used for analysing the stability of a thermodynamic climatic model. A delay time for the heat flux is introduced whereby it becomes an independent variable. Two different expressions for the second differential of the entropy are used: one follows classical irreversible thermodynamics theory; the second is related to the introduction of response time and is due to the extended irreversible thermodynamics theory. the second differential of the classical entropy leads to unstable solutions for high values of delay times. the extended expression always implies stable states for an ice-free earth. When the ice-albedo feedback is included, a discontinuous distribution of stable states is found for high response times. Following the thermodynamic analysis of the model, the maximum rates of entropy production at the steady state are obtained. A latitudinally isothermal earth produces the extremum in global entropy production. the material contribution to entropy production (by which we mean the production of entropy by material transport of heat) is a maximum when the latitudinal distribution of temperatures becomes less homogeneous than present value
Atmospheric response to sea surface temperature anomalies during El Niño 1997/98 as simulated by ECHAM4

One of the strongest El-Niño events on record was observed in 1997/98, a time period characterized by many strong climate anomalies all over the globe. To study the origin of these climate anomalies, ensemble experiments have been performed with the ECHAM4 atmospheric general circulation model at T42 resolution forced by observed sea surface temperatures (SSTs). Many of the observed climate anomalies and the well known El Niño Southern Oscillation teleconnection patterns could be reproduced by the ensemble integrations. In particular, the model reproduces the observed weakening of the trade winds, although it fails to simulate the early decline of the Southern Oscillation Index in November 1997. The observed climate anomalies over the Pacific, the Americas, and the Atlantic were successfully simulated. The model also reproduces the observed splitting of the jet over the North Atlantic which caused a very mild winter in western Europe. Our results do not indicate that the intense 1997 summer rainfalls leading to severe flooding in eastern central Europe were related to El Niño. With respect to the Indian Ocean, India, Australia, and southern Africa, the results were less satisfying. For example, the model yields reduced Indian monsoon rainfall which has not been observed. Additional experiments with SST anomalies restricted to particular ocean basins reveal that most of the atmospheric climate anomalies in 1997/98 were related to SST anomalies in the tropical Pacific. In particular, Atlantic SST anomalies had only a marginal impact on the atmosphere