Glossary and Acronyms: E

E:

Eye number. Acronym used for the analysis of a tropical system with the Dvorak Technique.

EA :

Eye Adjustment Number. Acronym used for the analysis of a tropical system with the Dvorak Technique.

Easterly trough:

trough in a belt of trade winds, usually oriented at right angles to the air flow and moving from east to west, at a lower scale than the easterly waves (synoptic-scale disturbance which moves from east to west, superimposed on the basic easterly flow of the tropics (trade winds zone).

ECMWF:

European Centre for Medium-range Weather Forecasts.
Forecast centre located in Reading (England) and formed in 1975 by a group of European countries as a joint venture to carry out research into improving weather forecasting for up to 10 days in advance and to produce such forecasts on an operational basis. 170 persons from the 18 members states work at the Centre, which has concluded co-operations agreements with 12 others countries.
The principal objectives of the Centre are:

the development of numerical methods for medium-range weather forecasting;
the preparation, on a regular basis, of medium-range weather forecasts for distribution to the meteorological services of the Member States;
scientific and technical research directed at the improvement of these forecasts;
collection and storage of appropriate meteorological data.

ECMWF model is a global model that runs twice a day, at 00 and 12 UTC, up to 240h.
For further details, see http://www.ecmwf.int

Ekman:

(pumping): convection and friction are two physic process leading to convergence in lower troposphere. This low levels convergence produces vertical transport within the boundary layer named "Ekman pumping". The top of the "Ekman layer" is located at about 1000 m.

EIR:

Enhanced InfraRed image. An enhanced image is an image that has had processing (e.g., contrast stretching, pseudocoloring, unsharp masking) applied to improve information presentation.
For the enhanced infrared imagery, temperature ranges are associated to a color palette. This product is particularly used for the analysis of the tropical systems with the Dvorak Technique.

El Niño :

a significant increase in sea surface temperature over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years. El Niño conditions, which are often characterized by "warm events", most often develop during the early months of the year and decay during the following year. The term was originally applied by fishermen of northern Peru to a warm annual southward coastal current that develops shortly after the Christmas season; hence the Spanish name referring to "the Christ Child". The name subsequently became more commonly used in reference to the occasional very strong coastal warmings that are associated with torrential rains in the desert coastal regions of southern Ecuador- northern Peru. The current definition of El Niño developed following the discovery that the coastal warmings are simply part of a larger-scale phenomenon arising from coupled ocean-atmosphere interactions across a broad expanse of the equatorial Pacific. See also La Niña, Southern Oscillation, ENSO.

El Niño is a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. Among these consequences are catastrophic impacts on essential fisheries along the Pacific coast of South America, increased rainfall across the southern parts of the United States and in Peru, causing destructive flooding. Other consequenses are drought in the west Pacific region with devastating bush fires in Australia and widespread forest fires in Indonesia.

The phenomena is characterised by changes in the wind flow and temperature of the tropical Pacific - large changes observed here relating to significant weather impacts both in the immediate area and more generally. Observations of conditions in the tropical Pacific are therefore considered essential for the prediction of short-term climate variations over a few months up a year.

In normal years the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 0.5 metres higher at Indonesia than at Ecuador. The sea surface temperature is about 8°C higher in the west, with cool temperatures off South America due to an upwelling of cold, nutrient-rich, water from deeper levels. These nutrients normally feed the fish that are an important food source in the coastal regions of western South America. During El Niño, the trade winds relax in the central and western Pacific leading to a rise in sea surface temperature and a drastic decline in primary fisheries productivity.

The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific. These anomalies include severe rainfall events over the west coast of the United States and Peru, together with droughts in many other locations. The droughts have occurred in Brazil, Mexico, Australia and South East Asia, and are often associated with devastating forest fires, together with the ensuing damage and pollution. The global economic impact can be measured in billions of dollars.

EMZPCOI :

Etat-Major de Zone et de Protection Civile de l'Océan Indien. Headquarter for the area and Civil Protection for the Indian Ocean region.

Ensemble forecasting:

Ensemble forecasting is a technique using numerical forecasting models, which is suitable for the period extending beyond 3 days from the day of the observation. Actually the reliability of the numerical models calculations decreases as their outcomes recedes from the day of the observation: at the present time, the "raw" predictability of a model is about 3 days; ensemble forecasting technique is used to forecast the weather beyond this three days limit and is exploited with a confidence index scale.
One of the sources of error of weather forecasting, limiting predictability, is the inaccuracy of the observational data that define the initial state of the atmosphere used for the calculation onset. In order to lessen the impact of these inaccuracies, several initial states are realized, obtained by forcing small variations on the observed data, smaller than the normal measuring errors or interpolation errors. Then, based on each of this initial states, calculations of the future states of the atmosphere are run: for a given forecast day, there are as many future states as variations of the initial state.
First, an average forecast is deduced from this, then numerical model outcomes are compared to the average forecast for a same date at the same hour, using a method of clusters: all the forecasts close to the average make a central cluster which will be used as a basis for the forecast, whereas the forecasts diverging from the average are grouped in "tubes"; zero to several tubes are possible (2, 3 or sometimes 4). The variations are sometimes very different of the central cluster forecast.
The forecaster determine a confidence index of the forecast according to objective quantizations: the number of tubes, number of forecasts in a same cluster, difference of forecast between the tube and the central forecast.
This ensemble forecasting system has been finalized after 1992 at the European Centre for Medium-Range Weather Forecasts (ECMWF). The version used in 2004 dates from 1996 and provides 50 variations of the basic model until 10 days of forecast (240 hours). These variations are obtained from identical models but less precise -in order to reduce the calculation time- as the basic one; according to this, 51 forecasts are compared among themselves. Since august 1998, not only the errors due to the initial conditions are taken into account, but those which are due to the transcription of the physical phenomena governing the atmosphere behaviour. Another research axis of ensemble forecasting is a "multi-models approach", which consists in combining the solutions proposed by different numerical models for a same day of forecast.
Since the 17th of May 1998, Météo-France daily issues a weather trend between the 4th and the 7th day of forecast with a confidence index. Others ensemble forecasts exist in the United States and Canada (the British one is not issued towards the public); each of these ensemble forecasts uses others methods than the ECMWF to create the initial state variations and the variations taken into account by the numerical model to transcribe the physical phenomena. (source : www.meteo.fr).

ENSO:

El Niño Southern Oscillation . Acronym for El Niño-Southern Oscillation, coined in the early 1980s in recognition of the intimate linkage between El Niño events and the Southern Oscillation, which prior to the late 1960s had been viewed as two unrelated phenomena. The global ocean-atmosphere phenomenon to which this term applies is sometimes referred to as the "ENSO cycle". See also El Niño, La Niña, Southern Oscillation.

EOS :

Earth Observing System.

EP_10:

mean of the forecasts of the ECMWF model 10 best runs. These 10 best runs are the runs for which the forecast at range 12 is the closest of the analysis done 12 hours after. See also EPS.

EP_51 :

mean of the 51 runs of the ECMWF EPS (50 perturbed members + 1 control run). See also EPS.

EPS :

Ensemble Prediction System / Ensemble forecast (or in another topic: Eumetsat Polar System). A set of different forecasts all valid at the same forecast time(s).
The differences between the forecasts can provide information on the probability distribution of the predicted variables. The forecasts in the ensemble may have different initial conditions, boundary conditions, parameter settings, or may even be from entirely independent NWP models.
For the ECMWF EPS, the weather prediction model is run 51 times from slightly different initial conditions. One forecast, called the EPS control forecast, is run from the operational ECMWF analysis. 50 additional integrations, the perturbed members, are made from slightly different initial conditions which are designed to represent the uncertainties inherent in the operational analysis.

ERS :

European Remote Sensing satellite. European Remote Sensing satellite, ERS-1, launched in 1991, was ESA's first Earth Observation satellite; it carried a comprehensive payload including an imaging Synthetic Aperture Radar (SAR), a radar altimeter and other powerful instruments to measure ocean surface temperature and winds at sea. ERS-2, which overlapped with ERS-1, was launched in 1995 with an additional sensor for atmospheric ozone research.

ESA :

European Space Agency.

Eumetnet:

Network of European Meteorological Services.

Eumetsat :

European Organisation for the Exploitation of Meteorological Satellites.

Extratropical depression:

system that primarily gets its energy from the horizontal temperature contrasts that exist in the atmosphere. Extra-tropical systems (also known as mid-latitude or baroclinic systems) are low pressure systems with associated cold fronts, warm fronts, and occluded fronts. (See FAQ A5)).

Extra-tropical transition:

as a tropical system moves within the extra-tropical zone, it enters in the mid latitudes baroclinic environment and is confronted with cooler sea surface temperatures. The system undergoes a complicated evolution stage within that cooler air enters in the west part of the cyclonic wind circulation, whereas convection still exists- temporarily at least- in the system core. Within this change's stage, named "extra-tropical transition", the depression, appearing with a very moving structure mixing tropical and extra-tropical features, is very tricky to analyse.
The baroclinic environment due to the interaction with the mid-latitudes disturbed westerly current is often associated with an increasing vertical wind shear, bringing generally to a rapid weakening of the system (eventually combined with the weakening due to the cooler SSTs according to the latitude of the extra-tropical transition). The system is then in the extra-tropical dissipation stage. However the vertical wind shear is not always a bar during the extra-tropical transition. In this situation of relatively homogeneous vertical flow, the tropical system digs into the southern latitudes and keeps for a longer time its tropical features: this is named an extra-tropical "capture". Then this system will become either a mid latitudes disturbance, or merge with an existing baroclinic depression (and generally deepen it by bringing humidity and diabatic process), or interact with a frontal zone and create an undulation.

Eye (of a tropical cyclone):

the roughly circular area of comparatively light winds found at the center of a severe tropical cyclone and surrounded by the eyewall. The winds increase gradually outward from the center but can remain very light up to the inner edge of the eyewall. No rain occurs and in intense tropical cyclones the eye is clear with blue sky overhead. Most, but not all, tropical cyclones with maximum winds in excess of 40 ms^-1; (78 knots) have eyes visible on satellite imagery. Eye diameters vary from 10 to more than 100 km.

Eyewall / Wall Cloud :

An organized band or ring of cumulonimbus clouds that surround the eye, or light-wind center of a tropical cyclone. Eyewall and wall cloud are used synonymously.