Albin Ullmann

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Papers by Albin Ullmann

Surcotes, tempêtes et risque d’inondation le long du littoral belge : variabilité contemporaine et future (1950-2100)

Précipitations intenses sur le Bassin Méditerranéen : quelles tendances entre 1950 et 2013 ?

by Florian Raymond and Albin Ullmann

Cybergeo, 2016

Surcotes marines dans le Golfe du Lion et forçages atmosphériques : variabilité contemporaine et future (1950-2100) (Sea surges in the Gulf of Lion and atmospheric forcing : contemporary and future variability)

Bulletin de l'Association de géographes français, 2010

ABSTRACT Les surcotes marines dans le Golfe du Lion se produisent principalement lorsque des fort... more ABSTRACT Les surcotes marines dans le Golfe du Lion se produisent principalement lorsque des forts vents d&#39;afflux de secteur sud à sud-est soufflent à l&#39;échelle du Golfe du Lion. Cette circulation atmosphérique régionale est associée à la présence d&#39;un fort gradient barométrique zonal sur la méditerranée occidentale entre un centre dépressionnaire autour du Golfe de Gascogne et des hautes pressions sur l&#39;Europe Centrale. Cette géographie barométrique est généralement associée au type de temps « Greenland Above ». Dans la deuxième moitié du 20ème siècle, la lente hausse de la pression de surface sur l&#39;Europe Centrale a augmenté le risque de fortes surcotes dans le Golfe du Lion durant les jours de « Greenland Above ». Un modèle de régression linéaire permet de simuler de façon robuste la variabilité interannuelle de la hauteur des surcotes dans le Golfe du Lion à partir de la pression atmosphériques de surface autour du Golfe de Gascogne comme prédicteur. Ce modèle statistique permet de montrer que la hauteur des fortes surcotes dans le Golfe du Lion pourrait rester stationnaire au 21ème siècle et pour le scénario A1b du changement climatique.

Extreme Dry Spell Detection And Climatology Over The Mediterranean Basin During The Wet Season

Geophysical Research Letters, 2016

A. Ullmann are surge-generating winds changing? AIR-SEA INTERACTION IN THE CENTRAL MEDITERRANEAN: ARE SURGE-GENERATING WINDS CHANGING?

Extreme sea levels in two northern Mediterranean areas

Mediterranee Revue Geographique Des Pays Mediterraneens Journal of Mediterranean Geography, 2007

Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO

Annales Geophysicae, Oct 25, 2010

The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological statio... more The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: until 1975, 1976-1992 and 1993-2008. Frequencies have been computed also for the "winter" (October to March) period, per quadrants, and for occurrences exceeding the speed of 15 m s-1. At Reykjavick a recent increase in the frequency of strong winds has occurred from various directions. Between 62° N (Thorshavn) and 59° N (Kirkwall) strong wind has been increasing since 1975. Minor changes can be observed at Stornoway, whereas at Malin Head the greatest increase for southerlies and westerlies is observed during the 1976-1992 period. At Belmullet, the frequency of strong southerlies has almost doubled since 1992, while at Shannon and Valentia it remains quite low. Finally at Brest and Belle-Ile, westerlies are predominant among winds >15 m s-1. Important changes in time and latitude appear in the correlation with the NAO (North Atlantic Oscillation) index. The highest correlation coefficients, calculated with monthly or seasonal means between the early 1950s and 1975, are observed from between 58° N (Stornoway) and Iceland, whereas low positive coefficients are reported more south. During the period 1976-1992, when increasing NAO index is predominant, positive correlation improves southwards as far as 54° (Belmullet) with some improvement also at Shannon and Valentia, while it remains low or even negative near the French Atlantic coast. Finally in the 1993-2008 period, correlation improves for all the stations south of 54° N (Belmullet), while it weakens more north.

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Impact of the Mediterranean Sea Surface Temperatures from a Weather Regimes Classification Approach

Egu General Assembly Conference Abstracts, May 1, 2010

Weather Regimes (WR) have been defined over the Euro-Mediterranean region [60W-60E; 15N-70N] from... more Weather Regimes (WR) have been defined over the Euro-Mediterranean region [60W-60E; 15N-70N] from May to October season using the daily Sea Level Pressure, 700 hPa geopotential height and specific humidity from ERA-interim dataset over the period 1989-2008. Computations are based on a neural network classification technique referred to as Self Organizing Maps and the WR produced can be used by the community for comparison with other periods, projection onto model outputs, seasonal prediction, or teleconnection studies. This work particularly examines the relationship between Mediterranean Sea Surface Temperatures and West African rainfall through the WR classification. Our results suggest that changes in particular WR frequencies associated with anomalous Mediterranean SST can account for part of interannual rainfall variability. Thus during anomalous wet (dry) years in West Africa, both higher frequencies of occurrence of WR related to negative (positive) summer NAO-like pattern and less frequent WR related to positive (negative) summer NAO-like pattern are attested in July and August (hereafter SN- and SN+). This is associated with a zonal symmetric pattern, consistent along the middle troposphere, i.e. a low pressure anomaly centered over 50N-20W and Eurasia (Greenland) and a high pressure anomaly centered over Iceland (central Europe) for SN- (SN+) WR. Another striking characteristic of SN- (SN+) WR is southeastward (southwestward) surface anomalous winds flowing from (to) the Atlantic ocean at 20N and therefore able to enhance (weaken) wet convection. Sea Surface Temperature associated with SN- WR shows a warming of the Mediterranean in July and the opposite with SN+ WR in August, suggesting that temperature anomalies could be a precursor in the change of frequency of SN- and SN+ WR and therefore impacts on WA rainfall.

Configurations atmosphériques de vastes échelles spatiales et variabilité des surcotes dans le Golfe du Lion

Cybergeo European Journal of Geography, Jul 22, 2007

ABSTRACT This paper is based on the analysis of sea-surge variations in the Gulf of Lions. A sea ... more ABSTRACT This paper is based on the analysis of sea-surge variations in the Gulf of Lions. A sea surge is defined as the difference between the observed sea level and the astronomical tide. It corresponds to the sea-level height only forced by meteorological conditions. The main goal of our study is to analyse broad-scale climatic conditions linked to the regional and local-scale sea-surges formation in the Golfe du Lion. Around this gulf, daily variations of sea-surge heights are mostly linked with the sea-level pressure variation over the Bay of Biscay. Surge peaks almost always occured during “Greenland Above” and “Blocking” Weather Regimes. These weather regimes are potentially associated with local meteorological conditions enable to lead to a surge peak.

Recent evolution of extreme sea surge-related meteorological conditions and assessment of coastal flooding risk on the gulf of Lions

Mediterranee, Dec 15, 2006

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Les types de temps associés aux risques d’inondations et d’érosions en Camargue : éléments de diagnostic et de prospectives pour le 21e siècle (1993-2100)

Echogeo, Dec 16, 2010

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Méditerranée et mousson africaine : mécanismes et évolution dans l’actuel et le futur

Harmattan dust events over the Western Sahel: synoptic analysis

by Albin Ullmann, Alice Favre, and N. Martiny

Dust events are a natural hazard which affects the Western Sahel region. These episodes can happe... more Dust events are a natural hazard which affects the Western Sahel region. These episodes can happen in summer as winter but are different in nature according to the season (e.g. Morales 1986). During the rainy season, dust storms are generally associated with mesoscale convective systems while in winter they are more likely induced by synoptic wind. The winter wind, called Harmattan, blows south of the Sahara during the dry season from November to March. Mineral particles, coming from the desert, are thus transported toward the Sahel and can sometimes attempt the Guinean Gulf. The purpose of this study is to investigate synoptic features of Harmattan dust events occurring over the Western Sahel. Firstly, a systematic detection of dust events has been performed from ground-based measurements of aerosol optical thickness, supplied by the AErosol RObotic NETwork, and Aerosol Index derived from Aura Ozone Monitoring Instrument satellite data. Next, using the ERA Interim Reanalysis datase...

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Types de temps et risque d'inondation et d'érosion en Camargue : diagnostique et prévision au 21ème siècle (1993-2100)

Les fortes surcotes marines et les fortes vagues sont les principaux aléas météo-marins associés ... more Les fortes surcotes marines et les fortes vagues sont les principaux aléas météo-marins associés aux risques de submersion et d'érosion du littoral camarguais. Sur la période 1993-2002, une forte fréquence mensuelle de très hautes surcotes est généralement associée à une forte fréquence de très hautes vagues. Ces deux phénomènes locaux se produisent principalement durant le type de temps associé à une dépression autour du Golfe de Gascogne associé à des hautes pressions sur l'Europe Centrale. La fréquence mensuelle de ce type de temps nous renseigne de la probabilité d'occurrence de fortes surcotes et vagues en Camargue. Au 21ème siècle, la fréquence du type de temps associé aux plus fortes surcotes et vagues en Camargue pourrait rester stationnaire dans le scénario A1b su changement climatique.

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High resolution rainfall variability in the vineyard: first results from a local scale network in Burgundy

by Albin Ullmann, Basile Pauthier, and Alice Favre

Rainfall is a major component of Vitivinicultural Terroirs. In many regions, it controls a large ... more Rainfall is a major component of Vitivinicultural Terroirs. In many regions, it controls a large part of water intake by vine and it has an important role in diseases occurrence. Winegrowers often record rainfall with only one or a couple of rain gauges. Such a sparse coverage might not be accurate enough to capture efficiently the spatial variability of rainfall, which is a necessary prerequisite for efficient crop management (e.g. for irrigation or spraying decisions, etc.). In order to study high resolution variability of rainfall, we implemented a 40 tipping bucket rain gauges network over an area of 28 km² in the hilly region of Beaune (France). The mesh size of the network varies from 300 meters to 1,000 meters. Between the 19 th and the 22 nd of January 2012, a rain sequence was recorded in the studied area. Using Convective Available Potential Energy (CAPE) data and analysing atmospheric circulation patterns, this sequence has been classified as a stratiform precipitation event. During this 4-day span, rain accumulations varied from 11 mm to 21 mm. Geostatistical analysis of the rainfall field indicates that variability increases with distance, in an east-to-west pattern mainly according with topography. Such a variation of about 100% on a four day stratiform rain accumulation event was unexpected. These observations, if confirmed by further measurements, might confirm that rain gauges network, as usually developed for rainfall monitoring in winegrowing regions, might not be tight enough to capture a strong local variability. Consequently, water intake and parasites monitoring at the vineyard scale might be strongly biased when assessed by a single rain gauge.

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Time evolution of observed July-September SST-Sahel climate teleconnection with removed quasi-global effect (1900-2008)

Using SST, precipitation and atmospheric information, this statistical study revisits the questio... more Using SST, precipitation and atmospheric information, this statistical study revisits the questions of the July-September SST-Sahel teleconnection variability after removing impact of quasi-global SSTs over the period 1900-2008. The eastern Mediterranean and the Indian Ocean dominate the relationship, both in terms of intensity and time stability, with significant values in 52% and 47% of years, respectively. More than two thirds of the rainy seasons classified as dry (wet) and 16/18 (12/15) of those classified as very dry (very wet) are concomitant of negative (positive) differences between the Mediterranean and the Indian Ocean. Correlations with the tropical Atlantic, the Nino area and the western Pacific region are generally lower and less robust, although, in some periods, they can be high with the southern tropical Atlantic. Telecconnection observed with continental precipitation and the 950 hPa moisture flux field confirmed these results. Positive SST differences between the ...

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Types De Configurations Pluviométriques Sur Le Bassin Méditerranéen, Forçages Atmosphériques et Événements Intenses (1979-2013)

by Albin Ullmann and Florian Raymond

Résumé - 6 régimes de pluie redondants et récurrents sont observés sur le bassin Méditerranéen po... more Résumé - 6 régimes de pluie redondants et récurrents sont observés sur le bassin Méditerranéen pour la période 1979-2013 : 5 sont associés à des excédents pluvieux régionaux (sud-ouest méditerranéen, centre-nord méditerranéen, est méditerranéen, ouest méditerranéen et nord-ouest méditerranéen) et 1 à un déficit généralisé. Chacun de ces régimes pluviométriques est associé à une géographie barométrique particulière générant des vents de composante sud mais de directions différentes selon la région considérée, à l’origine des surplus de précipitations. Ces 6 régimes sont un bon indicateur de la géographie et de la probabilité d’occurrence des évènements intenses. Par exemple, le régime « ouest méditerranéen » montre des probabilités d’occurrence des précipitations journalières intenses élevées sur la partie ouest de la Péninsule Ibérique où plus de 20% des jours de pluie sont associés à des dépassements locaux de percentiles à 95%. Abstract - Typical rainfall patterns in Mediterranean...

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Surcotes, tempêtes et risque d’inondation le long du littoral belge : variabilité contemporaine et future (1950-2100)

by Albin Ullmann and Jaak Monbaliu

Les types de temps associés aux risques d’inondations et d’érosions en Camargue : éléments de diagnostic et de prospectives pour le 21e siècle (1993-2100)

EchoGéo, 2010

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Tool kit helps digitize tide gauge records

by Albin Ullmann and F. Pons

Eos, Transactions American Geophysical Union, 2005

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