Abbreviations

When you're beginning to study the weather or look at numerical weather prediction, one of the things you will come across is abbreviations. These abbreviations can be hard to figure out sometimes especially for beginners and this is what this page is designed for. This is meant to be the library of all the common abbreviations you will find along with definitions for each of them. Hope you find this page useful!

AO - Arctic Oscillation. An index that tells you the state of the atmosphere over the Arctic Circle in terms of sea level pressure. When the index is positive, it tells you there is low pressure over the Arctic Circle and when it's negative, it tells you there is high pressure over the Arctic Circle.

AMM - Atlantic Meridional Mode. A cycle that is the dominant source of ocean-atmosphere variability in the Atlantic Ocean. When the index is positive, the Atlantic Intertropical Convergence Zone is displaced northward and warmer than normal sea surface temperatures along with weak vertical wind shear leads to an enhancement in tropical cyclone development. It is the exact opposite when the index is negative.

AMO - Atlantic Multidecadal Oscillation. A climate cycle that affects the sea surface temperatures of the North Atlantic Ocean. When the majority of the North Atlantic is cold, the index tends to be negative whilst the reverse occurs when the majority of the North Atlantic is warm. It is prone to changes on a regular basis like the other indexes but it comes in cycles as an average overall. For example, negative AMO occurred from the early 1960s to the early 1990s but since the early 2000s up to at least 2017, the AMO has been positive.

AMOC - Atlantic Meridional Overturning Circulation. A system of currents in the North Atlantic Ocean which includes the infamous Gulf Stream.

CAPE - Convective Available Potential Energy. The measure of the amount of energy available in the atmosphere for convection like thunderstorms to occur.

CET - Central England Temperature. The longest dataset in the entire world with monthly mean temperatures going back to January 1659. It was originally published by English climatologist, Gordon Manley, in 1953. As the name suggests, the dataset is based on the Midlands of England.

CW - Canadian Warming. Canadian Warming events are warming of the stratosphere on the Canadian side of the Arctic and usually occur from mid November to early December.

ECMWF - European Centre for Medium-Range Weather Forecasts. An organisation that operates a European numerical weather prediction model. The model has a few different modes, one is the short range which runs twice a day and stretches out to 10 days. Another mode is the month ahead which the model predicts 30 days ahead via weekly anomalies. The other mode is long range in which it forecasts up to 12 months but of course, this is highly unreliable.

ENSO - El Niño Southern Oscillation. An irregular index with variation in winds and sea surface temperatures over the equatorial Pacific Ocean. The warming phase is known as El Niño whilst the cooling phase is known as La Niña. Southern Oscillation is the accompanying atmospheric component coupled with the sea temperature change, see SOI below.

EWP - England & Wales Precipitation. One of the longest datasets in the entire world with monthly precipitation amounts going back to January 1766.

GEM - Global Environmental Multiscale Model. A global numerical weather prediction model that runs twice a day and stretches out to 10 days. Like all the other models, resolution and accuracy decrease the further out the model goes most of the time.

GFS - Global Forecast System. A global numerical weather prediction model that runs four times a day and produces forecasts that stretch out to 16 days. However, resolution and accuracy decrease generally the further out the model goes.

MJO - Madden Julian Oscillation. A large scale coupling between atmospheric circulation and tropical deep convection. The MJO propagates eastward at around 4 to 8 m/s through the atmosphere above the warm parts of the Indian and Pacific Ocean. Each phase of the MJO is shown by anomalous rainfall. The anomalous rainfall is usually first evident over the western Indian Ocean and remains evident as it propagates over the very warm waters of the equatorial Pacific. Each cycle lasts around 30-60 days.

NAO - North Atlantic Oscillation. An index that tells you the difference in sea level pressure between the Icelandic Low and the Azores High which are the two core elements in how the Northern Hemisphere jet stream takes off. When the index is positive, it tells you the Azores High and Icelandic Low are strengthened but when it's negative, it tells you they're both or non-existent and the reverse happens (Azores Low and Icelandic High).

PDO - Pacific Decadal Oscillation. An index that tells you the state of the sea surface temperatures over the mid-latitude Pacific basin. When the index is positive, it tells you the west Pacific is cool and the east Pacific is warm whilst the reverse happens when the index is negative.

PV - Polar Vortex. A ribbon of air high up in the atmosphere that usually surrounds the Arctic Circle. It keeps cold air from descending down into the mid-latitudes. In Spring and Summer, the Polar Vortex is very weak the majority of the time and thus why certain patterns can last very long in the British Isles in comparison to Autumn and Winter when the weather tends to be more changeable on average. In Autumn and Winter, the Polar Vortex is strengthened and is why you see deeper depressions during those times of year as a result of more extreme temperature gradients.

QBO - Quasi Biennial Oscillation. An index that tells you the state of the equatorial zonal winds in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km per month until they are dissipated at the tropical tropopause. The amplitude of the easterly QBO phase is about twice as strong as that of the westerly phase. Historically, it's shown that the QBO can have an effect on the NAO. As shown by 2016 when a new band of westerly winds overtook the initial transition to easterly winds, the QBO is not always regular.

SOI - Southern Oscillation Index. An index that is computed from fluctuations in the difference of surface air pressure between Tahiti in the Pacific and Darwin, Australia. When the Pacific is in an El Niño phase, the SOI is negative meaning there is lower pressure over Tahiti and higher pressure over Darwin. When the Pacific is in a La Niña phase, the SOI is positive meaning there is higher pressure over Tahiti and lower pressure over Darwin.

SST - Sea surface temperature(s).

SSTA - Sea surface temperature anomaly(s).

SSW - Sudden stratospheric warming. An event in which stratospheric temperatures rise by several tens of degrees Celsius over the course of a few days or short period of time. A SSW event can occur in any month from November to April and usually disrupts the natural weather patterns majorly in the Northern Hemisphere though this depends on the type of SSW event. Types of SSW events include Major warming events, Minor warming events, Final warming events and Canadian Warming events. There also lies several Polar Vortex behaviours as a result of the warming; these include a Polar Vortex split, a Polar Vortex displacement and a Polar Vortex obliteration. The effects of SSW on the troposphere usually takes minimum 9-14 days.

UKMO - UK Met Office. An organisation that delivers forecasts for the United Kingdom as well as issue all weather warnings for events in the country. It is also a numerical weather prediction model that runs twice a day and stretches out to 6 days.

Wx - Weather.