Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output where shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

ecCharts

ecCharts is a web-based presentation system developed to show a very wide range of ECMWF IFS model output worldwide in chart form, and in a very flexible way under the control of the user.  This allows ECMWF's medium-range forecasts to be viewed in far greater detail than was previously possible on the web, with panning and zooming being key functionalities that are not provided by the standard web charts.  ecCharts allows several forecast fields to be superimposed for ease of inter-comparison.  These charts may be animated throughout the forecast period as an aid to understanding the forecast structure of the atmosphere.  Ensemble output may be displayed in probabilistic form or as several derived fields (e.g.vorticity, divergence, CAPE, CAPE-shear, etc).  Also are simulated IR and WV images derived using the control member (CTRL) of the medium range ensemble.   A probe tool is provided to allow display of values at a selected point at the chart time.  Results from the latest and previous forecast runs are also readily available.  Time sequences of variables at a selected point can also be displayed in graph form.  

ecCharts documentation gives a clear and comprehensive description of options and practical use of ecCharts.

Simulated imagery

These products display cloud-related fields from the model in a format that is very familiar to forecasters and that they are used to interpreting.  They can easily be compared to actual satellite imagery.

Simulated visible imagery

These show simulations of the upward flux of visible radiation (as would be detected by a weather satellite).   This is derived from the model representation of reflectances derived from underlying model forecast cloud tops and surfaces.  The brightness reflectances can then be used to produce pictures equivalent to the visible images available from geostationary satellites.

Note:

• The area of coverage includes high latitudes but every pixel is assumed to be an overhead (nadir) view.
• The solar illumination is always assumed to be directly overhead.  This means that cloud structures can still be seen at times and locations even when in reality it is dark.
• Unlike on real visible images, shadowing from clouds is never represented.
• The displayed cloud reflectance is a function of the total column cloud liquid water.  When this is modelled too low the low clouds do not stand out well.  The reflectance can be close to the reflectance from the surface and then clouds can’t be distinguished from terrain.

Simulated infra-red imagery

These show simulation of the upward flux of infra-red radiation (as would be detected by a weather satellite).  This is derived from the model representation of temperatures from underlying model forecast cloud tops and surfaces.  The brightness temperatures can then be used to produce pictures equivalent to the infra-red images available from geostationary satellites.

Note:

• The area of coverage includes high latitudes and every pixel is assumed to be an overhead (nadir) view. 

Simulated water vapour imagery

These show simulation of the upward flux of radiation (as would be detected by a weather satellite) derived from a radiative transfer model dealing with emission from model forecasts of water vapour through a vertical column.

The model radiation value can then be used to produce pictures equivalent to the water-vapour images available from geostationary satellites.

Note:

• The area of coverage includes high latitudes and every pixel is assumed to be an overhead (nadir) view. 

Comparing fields for consistency

Ideally, simulated water vapour images can be compared with water vapour imagery to allow an assessment of any departure of the analysed and forecast fields from reality.  The structure of the IFS model atmosphere may also be explored by comparing the water vapour imagery with the potential vorticity fields.  Currently satellite imagery is not available on ecCharts and comparison of observed and simulated imagery cannot be done directly.

As the distribution of moisture is governed by ascent, areas that are coloured light grey by convention (=low temperature emissions) commonly tally with regions of current or past ascent, and regions coloured dark grey commonly tally with current or past descent.  The potential vorticity (PV=2) pattern is essentially governed by the dynamics of the upper flow and variations induce ascent or descent at around the level of the tropopause (conventionally taken as indicated by 2 PV units; higher values represent stratospheric air as shown here by shades of purple).  In the vicinity of developing depressions it would be expected that descending air (here shown by stratospheric air at 300hPa) would match the confinement of moisture to lower levels.  Comparing the detail of these patterns with satellite imagery can provide a powerful method of identifying discrepancies between the modelled atmosphere and reality.

Fig10.2-1: ecChart DT 00Z 8 August 2017 T+00 VT 00Z 8 August 2017 from HRES showing the simulated water vapour image and 300hPa potential vorticity.  These can be compared with WV satellite imagery to highlight discrepancies between the modelled atmosphere and reality.  Stratospheric air (PV=2 taken as near the tropopause, greater PV values (shown purple)) imply stratospheric air has descended to 300hPa.  Descent is also implied by the darker areas of the simulated water vapour image.  Comparing WV imagery with simulated imagery and PV charts can provide a powerful method of identifying discrepancies between the modelled atmosphere and reality.

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output where shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

Considerations when using ecCharts

Although comprehensive and detailed investigations and presentations are possible with ecCharts, a few points should be considered when interpreting the data:

• The values of isopleths of several parameters (e.g. CAPE, probabilities) are not marked on the charts but values are shown by colouring as shown in the legends window.  Use of the probe tool can be helpful.
• Some of the isopleth intervals on the pre-defined chart styles are non-uniform (e.g. some probabilities have isopleths at 5%, 30%, 60%, 70%, 80%, 90%; others are different).  Use of the probe tool can be helpful.
• There is no way to directly compare charts for a given time from different forecast runs.
• There is no way to compare IFS model analyses and short-term forecasts directly with observational data such as imagery.
• Some fields are only available at low temporal resolution (e.g. CAPE EFI is for 24h periods);  if these are selected then other parameters will not be displayed at their intervening steps (e.g. 3h precipitation would only be displayed for 21-24UTC each day if included with CAPE EFI).
  

(FUG Associated with Cy49r1)