78 research outputs found
zaplotnik/Hadley-cell-strength: Hadley cell strength
No full textTimeseries of Hadley cell strength in the period 1979-2018 in ERA5 and ERA-Interim reanalyses. The timeseries and their trends are derived from different measures of HC strength
Flow‐dependent wind extraction in strong‐constraint 4D‐Var
No full textIn the process of data assimilation for numerical weather prediction, biases in the model and observations can induce spurious analysis increments, which degrade the quality of the analyses. For this reason, the feedback of atmospheric composition (e.g., ozone and aerosols) observations on winds through dynamical adjustment is typically disabled in operational 4D-Var assimilation. This study investigates whether an increasing number of tracer observations could be exploited to constrain winds better in 4D-Var. For an idealized case study using analytical strong-constraint 4D-Var with the 1D advection model of Allen et al. and accurate background tracer field, it is shown that coupled wind–tracer assimilation always improves the tracer analysis. It also improves the wind analysis, but only if the magnitude of the error associated with unrepresented or misrepresented tracer physical forcings is smaller than the magnitude of the difference between the nature-run advection and the background-tracer advection. In other words, the model needs to be a good approximation of the truth for successful wind extraction. Based on this criterion, a method for flow-dependent 4D-Var wind extraction is developed, which selectively activates the coupling between winds and tracers locally and temporally by altering the tangent-linear tracer equation and the adjoint wind equation. The new method is implemented in the intermediate-complexity incremental 4D-Var model Moist Atmosphere Dynamics Data Assimilation Model (MADDAM) of Zaplotnik et al. Numerical experiments with MADDAM show that the new approach diminishes the occurrence of spurious wind-analysis increments and can improve the accuracy of wind analyses
Prijenos i licencija žiga u suvremenom hrvatskom žigovnom pravu
No full textThis paper analyses issues of licensing and transfer of trademark and license in contemporary Croatian law. The author frst discusses contemporary trends of trademark and license transfer and then analyses international aspects of this issue with special attention being paid to European countries, especially Germany, Switzerland, Great Britain, France, Italy and United States. This demanding subject is also discussed from the aspect of Croatian legislation in this area.U radu se analizira problematika licence i prenosa žiga i licence u savremenom hrvatskom pravu. Autor najpre govori o savremenim trendovima prenosa žiga i licence uopšte, a zatim i o odgovarajućim međunarodnopravnim aspektima, sa posebnim osvrtom na evropsko pravo, odnosno pojedine zemlje, kao što su Nemačka, Švajcarska, V.Britanija, Francuska, Italija, SAD. Obimna problematika razmatrana je i sa stanovišta hrvatskog zakonodavstva u ovoj oblasti
Charging processes of the network tariff and of other contributions in Elektro Gorenjska d.d.
No full textV diplomskem delu je opisana veljavna zakonodaja na področju oskrbe z električno energijo, na podlagi katere se izvajajo procesi obračuna omrežnine in drugih prispevkov v Sloveniji. Predstavljeni so vsi glavni akterji na elektroenergetskem trgu, ki so posredno ali neposredno vpleteni v ta proces, ter načini izmenjave podatkov med distribucijskimi podjetji in dobavitelji.
Na praktičnem primeru je razložena prenova informacijskega sistema v podjetju Elektro Gorenjska d.d., ki je nasledil predhodnega, ker je bil zastarel in neučinkovit. Podrobneje je opisan tudi celoten postopek obračunavanja omrežnine in prispevkov v novem programu. Ta zajema vse od merilnih in obračunskih podatkov, vrst obračuna, določanja tarifnih skupin, do kontrole obračuna, ki so potrebni za izstavitev računa.
V zaključku je podana ocena posodobljenega sistema in predstavljene možne izboljšave za nadaljnji razvoj in še boljšo učinkovitost programa.The thesis describes the legislation in force that regulates the field of electricity supply and the processes of charging network tariff and other contributions in Slovenia. It presents all the main actors in the electricity sector who are indirectly or directly involved in the process. It also touches on the ways of exchanging data between distribution companies and suppliers.
The practical example explains the renovation of the information system in the company Elektro Gorenjska d.d., which replaced an outdated and ineffective system. Furthermore, it describes in more detail the entire process of charging network tariff and other contributions using the programme, which includes measurement and calculation data, types of calculations, determination of tariff groups, and calculation controls necessary for issuing an invoice.
The final part assess the renovated system and proposes improvements for its further development and greater effectiveness
Sklopitev aerosolov, vlage in vetra v 4D-variacijski asimilaciji opazovanj pri numeričnem napovedovanju vremena
No full textThe increasing amount of remotely sensed data on atmospheric trace constituents has been provided by satellites in recent years as well as numerous vertical temperature and moisture profiles in form of radiances. This trend is going to continue with the launch of the Aeolus and EarthCARE satellites. In spite of significant improvements in atmospheric wind analyses expected from the Aeolus mission, especially in the tropics, there will remain a large gap between the number of available wind field and mass field observations. The initialization of wind field will remain strongly dependent on the quality of the background state and the modeling assumptions regarding the background-error covariances.
The thesis addresses the potential of the four-dimensional variational data assimilation (4D-Var) to retrieve the unobserved wind field from the observations of atmospheric tracers and the mass field (temperature, moisture) through the 4D-Var internal model dynamics and the multivariate relationships in the background-error term. These mass-field data provide the information on advection. The presence of discontinuous and nonlinear moist dynamics as well as numerous non-mass conserving aerosol processes make the wind tracing very difficult and susceptible to errors. On the other hand, moisture observations were shown to influence wind in both tropics and midlatitudes.
The problem of wind retrieval is studied using a novel intermediate-complexity 4D-Var data assimilation system which simulates nonlinear interactions between wind, temperature, moisture and aerosols. The description of moist processes includes a simple representation of condensation and the impact of released latent heat on dynamics. The prognostic equation for the total aerosol mixing ratio describes the dominant processes affecting the aerosol spatial distribution: advection and wet deposition by precipitation. The 4D-Var assimilation applies the incremental approach and uses a transformed relative humidity as control variable. In contrast to the model dynamical variables, which are analyzed in the multivariate fashion, moisture and aerosol data are assimilated univariately.
The observing system simulation experiments are performed for the tropics, where the lack of wind information is most critical. Results show that the wind tracing from both aerosol and moisture data in unsaturated atmosphere largely depends on the spatial density and accuracy of the observations as well as the frequency of observation update and assimilation window length. The first two are needed to describe the spatial gradients of tracer and the last two provide information about the advection. In the case with linear flow, the spatial density of observations is more important than their update frequency while the opposite holds in nonlinear flow. There, the accuracy of wind tracing depends on the level of nonlinearity.
In saturated atmosphere, combined assimilation of moisture and temperature data is shown to significantly improve wind analyses, as the intensity of the condensation process is susceptible to slightest changes in saturation humidity and thus temperature. The perfect-model 4D-Var with moisture observations can extract wind information even in the precipitating regions and strongly non-linear flow provided sufficient observations of humidity gradients.
Wind tracing from aerosol data in saturated atmosphere is more complex, as the dominant aerosol process becomes deposition. As a result, small prior errors in thermodynamic fields (humidity, temperature) can amplify in a positive feedback loop, ruining the wind analysis. The results suggest that the assimilation of aerosols (and tracers in general) with feedback on winds is beneficial if the local rate of unmodeled or unknown aerosol sources and sinks (e.g. unmodeled wet deposition) is lower than the local magnitude of the wind advection rate, or else the analysis is ruined.
Last, an ensemble of assimilation experiments provided a quantified estimation of the wind tracing potential for various modeling choices regarding the background-error covariance model, observation availability and accuracy, and assimilation settings.V zadnjih letih se je močno povečala količina daljinskih satelitskih opazovanj (meritev), tako atmosferskih aerosolov in redkih plinov, katerih vsebnosti se prostorsko in časovno spreminjajo, kot tudi iz meritev sevalnosti izluščenih navpičnih profilov vlage in temperature. Ta trend povečevanja daljinskih opazovanj se bo nadaljeval z izstrelitvijo satelitov Aeolus in EarthCARE. Pričakovano je, da bo Aeolus še posebej v tropih precej izboljšal točnost vetra v analizi, t.j. začetnem pogoju za meteorološko napoved. Vseeno pa bo skupno meritev vetra še vedno mnogo manj kot ostalih meritev, zato bo ta v začetnem pogoju še vedno precej odvisen od natančnosti prejšnje kratkoročne napovedi, ozadja, in načina predstavitve kovarianc napak ozadja.
V tej študiji ocenjujejmo možnost luščenja polja vetra iz meritev koncentracije vlage in aerosolov ter opazovanj ostalih masnih spremenljivk (npr. temperature) s pomočjo štiridimenzionalne variacijske asimilacije opazovanj (4D-Var). V 4D-Var se namreč z integracijo enačb atmosferskega modela znotraj asimilacijskega okna informacija o opazovani količini prostorsko in časovno porazdeli ter vpliva tudi na ostale spremenljivke. Točneje, opazovanja mase vsebujejo tudi informacijo o advekciji z vetrom. Z dobrim poznavanjem količin, ki se z vetrom advektirajo, lahko torej vetru “sledimo” (ang. wind tracing). V praksi je zaradi nezvezne, nelinearne dinamike vlažnih procesov ter mnogih procesov aerosolov, ki ne ohranjajo skupne mase, luščenje vetra zahtevno in podvrženo napakam. Kljub temu so nekatere pretekle študije že pokazale, da v 4D-Var asimilaciji opazovanja vlage močno vplivajo na polje vetra tako v tropskih predelih kot v zmernih širinah.
Problem luščenja vetra v 4D-Var študiramo s srednje zahtevnim prognostičnim modelom s predpisanim vertikalnim profilom, ki simulira nelinearne interakcije med vetrom, temperaturo, vlago in aerosoli. Model vključuje preprost fizikalni opis kondenzacije in vpliv pri tem sproščene latentne toplote na atmosfersko dinamiko, nasičena vlažnost pa je temperaturno odvisna. Prognostična enačba za skupno razmerje mešanosti aerosolov opisuje zgolj procesa, ki najbolj vplivata na spreminjanje prostorske porazdelitve aerosolov: advekcijo in izpiranje aerosolov s padavinami. 4D-Var asimilacija je formulirana v inkrementalnem načinu. Kontrolna spremenljivka za vlago je transformirana relativna vlažnost. Dinamične spremenljivke (horizontalni komponenti vetra in temperatura) so projicirane na ekvatorialne valove in asimilirane multivariatno, vlaga in aerosoli pa so asimilirani univariatno.
Vsi eksperimenti v študiji so tipa OSSE (ang. observing system simulation experiment, t.j. eksperiment, kjer so opazovanja simulirana) in so pripravljeni v tropski domeni, kjer je negotovost vetra v analizi operativnih prognostičnih modelov največja. Rezultati študije kažejo, da je luščenje vetra v nenasičeni atmosferi tako iz opazovanj vlage kot aerosolov najbolj odvisno od prostorske gostote in natančnosti opazovanj ter časovne pogostosti opazovanj in dolžine asimilacijskega okna. Prvi dve opišeta gradiente v poljih snovi, drugi dve pa dajeta informacijo o advekciji. Če je atmosferski tok linearen, potem je prostorska gostota opazovanj bolj pomembna kot njihova pogostost, obratno pa velja v nelinearnem toku. Izkaže se, da je uspešnost luščenja vetra funkcija nelinearnosti asimilacijskega problema.
V nasičeni atmosferi se analiza vetra, pridobljena z asimilacijo opazovanj vlage, močno izboljša, če asimiliramo še opazovanja temperature. Intenziteta kondenzacije je namreč odvisna od najmanjše spremembe nasičene vlažnosti, torej tudi od temperature. 4D-Var s perfektnim modelom atmosfere lahko v primeru, ko opazovanja zadosti dobro opišejo prostorske gradiente, izlušči informacijo o vetru tudi v območjih s padavinami in močno nelinearno dinamiko.
Luščenje vetra iz opazovanj aerosolov v nasičeni atmosferi je precej zahtevnejše. V tem primeru je glavni proces, ki spreminja porazdelitev aerosolov, izpiranje. Majhna začetna napaka v termodinamičnih poljih (vlaga, temperatura) ozadja se v procesu asimilacije še poveča. Ta pozitivna povratna zanka povsem uniči analizo vetra. Rezultati kažejo tudi, da je asimilacija aerosolov z učinkom na polje vetra smiselna, če je magnituda neznanih izvirov/ponorov aerosolov manjša od magnitude advekcije.
Nazadnje je potencial luščenja vetra ocenjen še kvantitativno z ansamblom eksperimentov in asimilacijskim modelom z modelsko napako, pri čemer variiramo model kovarianc napak, razpoložljivost in natančnost opazovanj ter druge asimilacijske nastavitve
Johann Siegmund Valentin Popowitsch (Janez Žiga Valentin Popovič), Vocabula Austriaca et Stiriaca 1-2 (Frankfurt am Main 2004)
No full textThe Austrian dictionary composed by the Slovenian scho-lar Janez Žiga Valentin Popovič (1705-1774) in the third quarter of the 18th century was only published in 2004, and edited by Richard Reutner, who wrote an extensive introduction to it. The dictionary comprises many language-geographical data for the German language, excellent explanations and many comparisons with much information provided regarding Popovic's mother tongue. The author broad horizon is admirable, especially with regard to the German language area and the linguistic literature of that time.Avstrijski slovar, ki ga je v tretji četrtini 18. stoletja sestavil slovenski učenjak Janez Žiga Valentin Popovič (1705-1774), je izšel šele leta 2004 v uredništvu Richarda Reutnerja, kije k njemu napisal obsežen uvod. Slovar vsebuje mnogo jezikovnogeografskih podatkov za nemščino, odlične razlage in marsikaj primerjalnega, veliko pa se najde tudi v zvezi s Popovičevo materinščino. Občudovanja vredna je avtorjeva razgledanost predvsem po nemškem jezikoslovnem prostoru in po takratni jezikoslovni literaturi
3D-Var Data Assimilation using a Variational Autoencoder
No full textData assimilation of atmospheric observations traditionally relies on
variational and Kalman filter methods. Here, an alternative neural-network data
assimilation (NNDA) with variational autoencoder (VAE) is proposed. The
three-dimensional variational (3D-Var) data assimilation cost function is
utilised to determine the analysis that optimally fuses simulated observations
and the encoded short-range persistence forecast (background), accounting for
their errors. The minimisation is performed in the reduced-order latent space,
discovered by the VAE. The variational problem is auto-differentiable,
simplifying the computation of the cost function gradient necessary for
efficient minimisation. We demonstrate that the background-error covariance
() matrix measured and represented in the latent space is
quasi-diagonal. The background-error covariances in the grid-point space are
flow-dependent, evolving seasonally and depending on the current state of the
atmosphere. Data assimilation experiments with a single temperature observation
in the lower troposphere indicate that the -matrix simultaneously
describes both tropical and extratropical background-error covariances.Comment: Peer-reviewed version of this paper has been published in QJRMS
(https://doi.org/10.1002/qj.4708). The uploaded version in this repository is
not the same as the peer-reviewed versio
Indices of Pacific Walker Circulation Strength
No full textThe Pacific Walker circulation (PWC) significantly affects the global weather patterns, the distribution of mean precipitation, and modulates the rate of global warming. In this study, we review and compare 10 different indices measuring the strength of the PWC using data from the ERA5 reanalyses for the period 1951–2020. We propose a revised velocity potential index, while we also discuss two streamfunction indices. We show that the normalized PWC indices largely agree on the annual-mean strength of the PWC, with the highest correlations observed between indices that measure closely linked physical processes. The indices tend to disagree the most during the periods of strong El Niño. Therefore, the trends in PWC strength vary depending on the chosen time frame. While trends for 1981–2010 show PWC strengthening, trends for 1951–2020 are mostly neutral, and the recent trends (2000–2020) show (insignificant) weakening of the PWC. The results hint at the multidecadal variability in the PWC strength with a period of approximately 35 years, which would result in continued weakening of the PWC in the coming decade
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