Quick Guide to Using Cyclone Database Ensemble Products

Getting Started

1. North Atlantic Cyclone Database products (in real-time test mode) can be found HERE (from 29/5/2009). The archive of older North Pacific products, provided for the TPARC experiment, can be found via this TPARC web page: there is one link for Winter TPARC (2009), and one for Summer TPARC (2008).

2. On reaching a ‘Cyclone Database’ page, there are two drop down menus, one for selecting the DT and NWP centre, the other for selecting product type to view.

3. The default settings for (2) above are the Latest available forecast, and a ‘Clickable control T+0 image’.

General Principles

These web page products aim to represent, objectively, the location and behaviour of near-surface synoptic scale features in ensembles, in a variety of ways. The features represented are those typically associated with adverse weather:

-fronts, warm and cold (red and blue respectively)

and cyclonic features, consisting of:
-Barotropic Lows (black)
-Frontal Waves (orange)
-Diminutive Waves (green)

‘Smaller spot’ versions of Frontal waves and Diminutive waves denote when the related fronts are themselves associated with a less pronounced thermal gradient.

Co-location masking, using a feature type hierarchy and a minimum separation threshold, helps to keep all cyclonic features 300km or more apart.

Mean sea level pressure, as estimated from 1000mb geopotential height and temperature, is also shown as a reference point on many plots.

A new tracking algorithm has been used to follow the cyclonic features as they evolve in each ensemble member.

Products and How to Use Them

‘Clickable control T+0 image’

• This is akin to a synoptic analysis chart.
• The user can click on any cyclonic feature spot, to see how that feature behaves within the ensemble.
• This brings up a track map, and five feature plume diagrams relating to feature intensity (explained HERE).
• Take care to note the percentage of EPS members in which the feature has been tracked (tabulated).
• Subsequently clicking on the track map will show an animated version of that product (not available for Pacific domain T-PARC products). When running this animation, the bar on the right denotes percentage of members in which the feature has been tracked. At a given time if this is >50% then the bar is green - probably OK. For 10-50% it becomes orange - caution required, feature unlikely to persist to this point. For <10% it becomes red - considerable caution required - feature very unlikely to persist to this point.
• Do not neglect the smaller spots - sometimes these evolve into substantial cyclones.

‘Animation of fronts’

• Objective warm and cold fronts (meeting standard thermal gradient threshold criteria) from each ensemble member are overlaid (red and blue respectively)
• Control run fronts are plotted on top (warm in gold, cold in green)
• Animating tends to show increasing spread with increasing leads, and also how some features are more predictable than others at a given time
• The degree of spread can be used to attach confidence to any deterministic point forecast of front-related weather
• A new predictability limit could be defined to be where all synchroneity between EPS members’ fronts is lost
• The degree of agreement between the control run and the rest of the ensemble indicates the extent to which the control might be used as a first guess, at least for placing fronts

‘Animation of features’

• Feature points from all the ensemble members are overlaid, with the control run on top (highlighted with yellow)
• Legend below the plot denotes the meaning of each symbol type:
• Green is used for diminutive waves, Orange for frontal waves and Black for barotropic lows
• Blue spots denote features on cold fronts, Red denotes features on warm fronts
• Animating shows increasing spread with increasing lead, and also how some features are more predictable than others at a given time
• The degree of spread can be used to attach confidence to any deterministic point forecast of feature-related weather
• A 'feature predictability limit' could be defined to be where all synchroneity between EPS members’ features is lost
• The degree of agreement between the control run and the rest of the ensemble indicates the extent to which the control might be used as a first guess, at least for placing cyclonic features

‘Postage stamps’

• Self-explanatory. Can be animated. Weak fronts and weaker (small spot) frontal waves and diminutive waves have been omitted

‘Postage stamps (detailed)’

• A large volume of data; can take time to load. Every time frame from every ensemble member is shown in postage stamp format.
• All synoptic features, and both weak and standard fronts are shown.
• There are three types of link from here (though all are also available from the drop down menu):
• (1) Clicking on a stamp brings up a full size image in a separate window
• (2) Clicking on a member number (LHS) reverts the current window to show an animation of that member
• (3) Clicking on a lead time (TOP) opens up a new tab showing clickable postage stamps from all members for that lead time only (see next item..)

‘Postage stamps (detailed, times)’

• Clickable, relatively large T+0 postage stamps from each member, showing all synoptic features
• Page size designed to fit neatly onto a standard large screen (19’, 1280x1024), without needing scroll bars (works provided number of menu bars used is not excessive)
• No animation, but navigation buttons in lower right corner assist with moving between time frames

‘Strike probs (1km wind > 60kn)’ and other thresholds

• Show strike probabilities of a cyclonic feature track passing within 300km, within a time window of +/-12 hours relative to frame time
• Based on diagnosed cyclonic feature tracks, at all times, in all members
• No minimum track time threshold is applied - so an untracked (single time) feature will contribute a circle (on this projection) to the strike probability
• Thresholding is applied based on the time window -12 to +12h, specifically the maximum-300km-radius-wind, 1km up, registered within this. Hence the ‘>60kn’ threshold nominally represents ‘cyclonic windstorms’. Moderately vigorous features are denoted by the ‘>34kn’ threshold.
• The ‘all features’ option uses no thresholding.

‘Animation of control’, ‘Animation of member 1’, ..etc..

• Fairly self explanatory. All cyclonic features and fronts are shown, from one EPS member, in animation format.
• Try increasing the speed. ‘Toggle’ is also useful in static mode.