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Rainfall characteristics predictability by NARI

This Maprooms explores the predictability of weather-within-climate variability of rainfall by the North Atlantic SST Relative Index

The map shows the 1983-2015 historical probability of seasonal weather-within-climate characteristics of precipitation (see Options tab for details) to fall within the upper (Above Normal), middle (Near Normal), or bottom (Below Normal) tercile given the phase of the North Atlantic SST Relative Index (nari -- Above-/Near-/Below-Normal) during that same 3-month long season (see Index definition below).

By default, the map shows the likelihood of Below Normal Total Rainfall in July-September season during Below Normal nari. Mouse over the map to explore the other rainfall and sst categories. Menus in the top control bar allows to change the 3-month season of interest, the years to span, and the weather-within-climate variable.

Clicking on the map will then display local yearly seasonal weather-within-climate characteristics time series. The color of the bars depicting what nari Phase it was that year for that season, and the horizontal lines depicting the historical terciles limits for the historical rainfall characteristics. This allows to quickly picture what years fell into what what nari Phase and into what Rainfall Tercile category.

This analysis is not a forecast and is solely based on historical observations of rainfall and SST. Variability at inter-annual and decadal time scales of North Atlantic sea surface temperatures proved to be a driver of rainfall pattern in West Africa. The nari index is defined as the difference between the spatial average of SST over the North Atlantic (75˚W-15˚W, 10˚N-40˚N) and over the Global Tropics (20˚S-20˚N). The categories, Below, Near and Above Normal are defined according to their distance to the historical mean, respectively lesser than 0.5 standard deviation, within 0.5 standard deviation, or greater than 0.5 standard deviation. This Maprooms allows to explore and better understand this relationship, with the prospect to then design better climate forecast for West Africa.

Options

Data Source: Merged TAMSAT v3, Merged CHIRPS and Merged ARC2 are available.
Resolution: local analysis is available at 0.0375˚ (TAMSAT resolution) and 0.05˚ (CHIRPS and ARC2 resolution). Note that if you pick the resolution that doesn't correspond to the data resolution, the analysis will be spatially weighted-averaged.
Years and Season: Specify the range of years over which to perform the analysis (CHIRPS and ARC2 start in 1981) and choose the 3-month long season of interest over which the weather-within-climate diagnostics are to be computed.
Weather-within-climate: Choose the seasonal diagnostic quantity (i.e the statistic of the daily data) to be computed for each season, from the following choices.
Total Rainfall: total cumulative precipitation (in mm) falling in the season.
Number of Wet Days: the number of wet days (as defined below) during the season.
Rainfall Intensity: the average daily precipitation over the season considering only wet days.
Number of Wet (Dry) Spells: the number of wet (dry) spells during the season according to the definitions below. For example, if a wet spell is defined as 5 contiguous wet days, 10 contiguous wet days are counted as 1 wet spell, not 2. Note that a spell, according to the definitions below, that is overlapping the start or end of the season will be counted only if the part of the spell that falls within the season reaches the minimal length of consecutive days.
Wet/Dry Day/Spell Definitions: These define the amount in millimeters (non inclusive) above which a day is considered to be a wet day (as opposed to dry), and the minimum number (inclusive) of consecutive wet (dry) days to define a wet (dry) spell.

Dataset Documentation

Precipitation
Data Source: Daily merged precipitation data products from AGRHYMET.

North Atlantic SST Relative Index
Data Source: Extended reconstructed sea surface temperature data from NOAA.

Helpdesk

Contact help@iri.columbia.edu with any questions about or problems with this Map Room.