Page History

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• dark green are land points and HTESSEL will supply 90-100% of the flux information.
• mid-green are land points (but with 10-20% water surface) so HTESSEL will supply 80-90% and FLake 10-20% of the flux information.
• light green are land points (but with 20-30% water surface) so HTESSEL will supply 70-80% and FLake 20-30% of the flux information.
• turquoise are land points (but with 30-40% water surface) so HTESSEL will supply 50-60% and FLake 30-40% of the flux information.
• cyan are land points (but with 40-50% water surface) so HTESSEL will supply 50-60% and FLake 40-50% of the flux information.
• blue are sea points (i.e. >50% water surface) so FLake will supply 100% of the flux information in coastal waters.  NEMO will supply 100% of the flux information in oceanic waters.
  

Users should note, for flux information: 

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• The nearest ENS grid point is selected from among the four ENS grid points surrounding the selected location.  Within these four grid points:
  • if there is at least one land grid point then the nearest land grid point is chosen (even though a sea grid point may be nearer).  A land grid point is one where the "fraction of land cover"  is greater than 50%.   
  • if there is no land grid point then the nearest ENS grid point is chosen (which will be a sea grid point).

For sea locations:

• The nearest ENS grid point is selected from among the four ENS grid points surrounding the selected location.  

The process of selecting which gridpoints ENS that are used on meteograms is illustrated below, using relatively complex but informative examples.

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Example sites are shown on the diagram:

A coastal
• An inland location -
Bembridge
• Newport (location
B
• N).  The ENS grid is scanned for the grid points surrounding the location (ENS grid points
EFGH).  None is a
• NPJR) and the nearest land point
and a sea point
• is chosen (Point
E
• J).
 At this point
•   This is a land point where the "fraction of land cover" is
less than 50%
• 100% and the surface energy fluxes are determined by
FLake.  There will be no influence of land energy fluxes.  In fact any land location within grid box EFGH will be treated similarly, no matter how far away from the coast. 
• HTESSEL.
• A coastal city location -
Freshwater
• Portsmouth (location
F
• P).
 The
•   The ENS grid is scanned for the grid points surrounding the location (ENS grid points
MNRS
• ABCD) and the nearest land point is chosen (Point
R
• A).  This is a land point where the "fraction of land cover" is
60%-70%.  Surface
• 100% and the surface energy fluxes are determined
60%-70% by HTESSEL and 30%-40% by FLake.
• by HTESSEL.  There will be no influence of a water surface.  HTESSEL does not take into account the urban nature of the city. 
• A coastal
city
• location -
Portsmouth
• Freshwater (location
P
• F).
  The
•  The ENS grid is scanned for the grid points surrounding the location (ENS grid points
ABCD
• MNRS) and the nearest land point is chosen (Point
A
• R).  This is a land point where the "fraction of land cover" is
100% and the surface
• 60%-70%.  Surface energy fluxes are determined
by HTESSEL.  There will be no influence of a water surface.  HTESSEL does not take into account the urban nature of the city. 
• 60%-70% by HTESSEL and 30%-40% by FLake.
• A coastal location - Bembridge (location BAn inland location - Newport (location N).  The ENS grid is scanned for the grid points surrounding the location (ENS grid points NPJR) and the nearest land EFGH).  None is a land point and a sea point is chosen (Point JE).   This is a land point where  At this point the "fraction of land cover" is 100% less than 50% and the surface energy fluxes are determined by HTESSEL.FLake.  There will be no influence of land energy fluxes.  In fact any land location within grid box EFGH will be treated similarly, no matter how far away from the coast. 
• A coastal location - Ventnor (location V).  The ENS grid is scanned for the grid points surrounding the location (ENS grid points JHLK) and the nearest land point is chosen (Point J).  This is a land point where the "fraction of land cover" is 100% and the surface energy fluxes are determined by HTESSEL.  No adjustment is made for the influence of the sea and the effect of the sea and the effect of the sea may not be evident on ENS meteograms.the sea may not be evident on ENS meteograms.  This grid point is the same as selected for the inland town of Newport (location N) even though the town of Ventnor (location V) is right on the coast. 
• A location near land - offshore of Ventnor (location S).  The ENS grid is scanned for the grid points surrounding the location (ENS grid points JHLK) and the nearest sea point is chosen (Point L).  The surface energy fluxes are determined by FLake.  The influence of the sea will be more evident on ENS meteograms for location S than at location V. 

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• Inspection of meteograms for nearby offshore locations (e.g. location S) may add useful information for nearby coastal locations (e.g. location V).
• The same ENS grid point is used for both locations N and V (even though location N is inland and location V is coastal).  Differences between the inland location N and the coastal location V will not be apparent.  
• Temperature is adjusted to reflect the differences in height between the altitude of each location and the corresponding ENS orography, using a lapse rate of 6.5K/km.   Despite being on the coast, location V is at greater altitude than location N and will consequently appear cooler.
  

In the above example, if winds were light and from the East (i.e. wind blowing from sea to land at Ventnor) the influence of the sea point S is helpful in the derivation of temperatures.  However, if the winds were from the north (i.e. wind blowing from land to sea at Ventnor) then the influence of the sea point S may not be relevant.

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• a local effect (e.g. onset of a sea breeze).
• the local prevalence of persistent cloud (e.g.sea fog and low cloud drifting onshore).
• the influence of turbulent mixing with stronger winds.
• the effect of altitude.

It is for the user to assess critically the representativeness of the Meteogram displayed and to make adjustments in the light of local knowledge and experience.  Disentangling coastal effects from altitude effects can be difficult. 

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