El próximo 23 de marzo "Día Meteorológico Mundial 2013"

Todos los años, el 23 de marzo, la Organización Meteorológica Mundial, sus 191 Miembros y la comunidad meteorológica internacional celebran el Día Meteorológico Mundial con la elección de un tema oportuno. Este día conmemora la entrada en vigor, en 1950, del Convenio por el que se estableció la Organización. Posteriormente, en 1951, la OMM fue designada organismo especializado del sistema de las Naciones Unidas.

El tema de este año es "Vigilar el tiempo para proteger las vidas y los bienes"

 

Página de la OMM dedicada a ese día

Invitaciones a los actos que los servicios eteorológicos celebrane:

Data: 

Dissabte, 23 Març, 2013

March 23 "World Meteorological Day 2013"

Each year, on 23 March, the World Meteorological Organization, its 191 Members and the worldwide meteorological community celebrate World Meteorological Day around a chosen theme. This day commemorates the entry into force, on that date in 1950, of the WMO Convention creating the Organization. Subsequently, in 1951, WMO was designated a specialized agency of the United Nations System.

This year, the theme is “Watching the weather to protect life and property"

OMM page dedicated to this day

Invitations to the events that meteorological services celebrate:

Data: 

Dissabte, 23 Març, 2013

El proper 23 de març "Dia Meteorològic Mundial 2013"

Tots els anys, el 23 de març, l'Organització Meteorològica Mundial, els seus 191 membres i la comunitat meteorològica internacional celebren el Dia Meteorològic Mundial amb l'elecció d'un tema oportú. Aquest dia conmemora l'entrada en vigor, el 1950 del Conveni per el que es va establir l'Organització. Posteriorment, al 1951, la OMM va ser designada organisme especialitzat del Sistema de les Nacions Unides.

El tema d'aquest any és "Vigilar el temps per a protegir les vides i els bens"

 

Pàgina de l'OMM dedicada a aquest dia

Invitacions als actes que els serveis meteorològics celebren aquest dia:

Data: 

Dissabte, 23 Març, 2013

Solar Irradiance Variations Induced by Faculae and Small Magnetic Elements in the Photosphere

The aim of this thesis is the study of the total and spectral solar irradiance variability induced by the presence of small magnetic elements that emerge into the solar photosphere. It is important to study changes in the solar energy output because they reflect the existence of several physical processes in the solar interior, their interpretation helps to understand the solar cycle and because of their influence on the terrestrial climate. The work presented in this thesis is exclusively based on data provided by the SOHO spacecraft, specifically by the VIRGO and MDI instruments.

Irradiance variations produced on the solar rotation time-scale are due to the passage of active regions across the solar disk. However, the origin of variations on the solar cycle time-scale is under debate. One of the most controversial aspects is the long-term contribution of the small magnetic elements conforming faculae and the network. Their identification and contrast measurement is difficult and, consequently, their contrast center-to-limb variation (CLV) remains poorly defined in spite of the fact that its knowledge is essential to determine their contribution to variability.

In this work we have studied the contribution of small photospheric magnetic elements (those with a positive contribution to variability), both on short, i.e. solar rotation, and long, i.e. solar cycle, time-scales. By analyzing the evolution of an isolated active region (NOAA AR 7978) during several Carrington rotations, we have evaluated the variations in luminosity induced by this facular region during the 1996 minimum of activity. Simultaneous photometric and magnetic data from the MDI instrument have been combined in order to study the contrast of small scale magnetic features and its dependence both on position and magnetic field, as well as its evolution along the rising phase of solar cycle 23.

The study of the solar variability has required reduction and analysis of the employed MDI and VIRGO data. These data had to be converted from level 0 (raw data) to level 2 (scientifically useful data), since solar variations were hidden by instrumental effects. We developed original algorithms to correct instrument-related effects from the data, such as filter degradation and the variation of the limb darkening with distance. The determination of the contrast of magnetic features also required the development of an algorithm in order to identify the surface distribution of those small features present over the solar disk.

By analyzing irradiance variations induced by the small magnetic features that emerge into the solar photosphere we have concluded that:

· active region faculae and the magnetic network present very different contrast CLV's, therefore, their contributions to irradiance variability are distinct; as a consequence, both contributions need to be taken into account separately when reconstructing variations of the solar irradiance.

· the functional dependence on position and magnetic signal of the facular contrast is time independent; this suggests that the physical properties of the underlying flux tubes do not vary with time.

· network elements are bright over the whole solar disk and have proved to be the dominant population along the solar cycle; this implies that their contribution to long-term irradiance variations is significant and needs to be taken into account.

Autor/Doctorant: 

Ortiz Carbonell, Ada Natalia

Directors/Tutors: 

Blai Sanahuja Parera i Vicente Domingo Codoñer

Fitxer Tesis: 

Dia: 

Divendres, 10 Octubre, 2003

Lloc: 

SALA DE GRAUS DE FÍSICA

Tribunal: 

Dr. José Luis Ballester Mortes. Catedràtic d'Universitat. Universitat d'Illes Balears. (President). Javier Labay Aguirre. Professor Titular d'Universitat.Universitat de Barcelona. (Secretari). Manuel Vázquez Abeledo. Investigador del Instituto de Astrofísica de Canarias. (Vocal).

Hora: 

11:30

Wind Field Retrieval from Satellite Radar Systems

Wind observations are essential for determining the atmospheric flow. In particular, sea-surface wind observations are very useful for many meteorological and oceanographic applications. In this respect, most of the satellite remote-sensing radar systems can provide sea-surface wind information. This thesis reviews the current wind retrieval procedures for such systems, identifies the most significant unresolved problems, and proposes new methods to overcome such problems.
In order to invert the geophysical model function (GMF), which relates the radar backscatter measurement with the wind speed and direction (unknowns), two independent measurements over the same scene (wind cell) are at least needed. The degree of independence of such measurements is given by the azimuth (view) angle separation among them. This thesis is focused on improving the wind retrieval for determined systems (two or more measurements) with poor azimuth diversity and for underdetermined systems (one single measurement). For such purpose, observations from two different radar systems, i.e., SeaWinds and SAR (Synthetic Aperture Radar), are used.
The wind retrieval methods proposed in this book for determined (Multiple Solution Scheme, denoted MSS) and underdetermined (SAR Wind Retrieval Algorithm, denoted SWRA) systems are based on Bayesian methodology, that is, on maximizing the probability of obtaining the "true" wind given the radar measurements and the a priori wind information (often provided by numerical weather prediction models), assuming that all wind information sources contain errors. In contrast with the standard procedure for determined systems, the MSS fully uses the information obtained from inversion, which turns out to positively impact the wind retrieval when poor azimuth diversity. On the other hand, in contrast with the various algorithms used nowadays to resolve the wind vector for underdetermined systems, the SWRA assumes not only that the system can not be solved without additional information (underdetermination assumption) but also that both the algorithms and the additional information (which are combined to retrieved the wind vector) contain errors and these should be well characterized. The MSS and the SWRA give promising results, improving the wind retrieval quality as compared to the methods used up to now.
Finally, a generic quality control is proposed for determined systems. In general, high-quality retrieved wind fields can be obtained from scatterometer (determined systems) measurements. However, geophysical conditions other than wind (e.g., rain, confused sea state or sea ice) can distort the radar signal and, in turn, substantially decrease the wind retrieval quality. The quality control method uses the inversion residual (which is sensitive to inconsistencies between observations and the geophysical model function that are mainly produced when conditions other than wind dominate the radar backscatter signal) to detect and reject the poor-quality retrievals. The method gives good results, minimizing the rejection of good-quality data and maximizing the rejection of poor-quality data, including rain contamination

Autor/Doctorant: 

Portabella Arnús, Marcos

Directors/Tutors: 

Ad Stoffelen, i Àngel Redaño i Xipell

Fitxer Tesis: 

Dia: 

Dilluns, 18 Novembre, 2002

Lloc: 

SALA DE GRAUS DE FÍSICA

Hora: 

12:00

Pàgines

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