Llansadwrn (Anglesey) Weather

Atmospheric depositions code

Most weather stations have their equipment set into a short grass sward. While it has been normal practice to make observations of the state of the soil on a bared plot, not much use has been made of the grass. One use, put forward by Terence Meaden ¹, is to observe the state of the grass as a means of recording the deposition of the various liquid and solid forms of water. Use is made of a 10-digit sequence for this purpose (Table 1).

I have been recording the state of the grass at Llansadwrn since 1996 and found it to be an informative addition to my observations. The grass code is a good discipline to adopt as it affords a means of accurately recording, in the weather diary, the types of water deposition observed. The code is simple to use and carried out over several years can form a valuable record at any weather station ².

The grass code is not a substitute for the state of the ground code (Table 2) as different information is recorded. For example the ground may be frozen, or more than 50% covered with snow. I have added also a concrete surface (a road surface or some other surface would also be interesting) and suggest a modified code which I use (Table 3). Some interesting differences can occur throughout the year, and often within a day, due to contrasting thermal regimes.

Table 1 State of the grass code (from Meaden, 1996)

0 Dry, no deposits
1 Wet from dew only
2 Wet from fog (some dew may be present too)
3 Wet from falling rain or drizzle
4 Wet from the melting of the frozen deposits listed as codes 5-9, or from sleet
5 Ice resulting from the freezing of 1-3 or the refreezing of 4, and also including silver frost (frozen supercooled dew)
6 Ice of glaze resulting from the direct fall of freezing rain or drizzle upon cold surfaces, or ice from hail or ice pellets
7 Hoar frost - the direct deposition of crystals from the air
8 Rime - the direct deposition of crystals from supercooled freezing fog or falling ice prisms or falling ice crystals
9 Snow
Addendum: Include snow pellets
Note: The highest code number takes precedence

Table 2 MO State of the ground code

0 Surface of ground dry
1 Surface of ground moist
2 Surface of ground wet (standing water)
3 Surface of ground frozen
4 Glaze or ice (without snow or melting snow) on the ground
5 Ice, snow or melting snow covering less than one-half of the ground
6 Ice, snow or melting snow covering more than one-half of the ground, but not completely
7 Ice, snow or melting snow covering the ground completely
8 Loose dry snow, dust or sand, covering more than one-half of the ground, but not completely
9 Loose dry snow, dust or sand, covering the ground completely
Note: The highest code number takes precedence
Addendum: Code =0 ground dry and cracked

Table 3 State of a concrete surface (from Perkins, 1997)

0 Dry, no deposits
1 Surface moist in patches, drying or wetting by any source
2 Surface completely moist by any source
3 Surface wet from rain falling at the time of observation (including sleet/snow, drizzle or fog)
4 Glaze of ice without snow
5 Ice, snow or melting snow covering less than one-half of the concrete
6 Ice, snow or melting snow covering more than one-half of the concrete, but not completely
7 Ice, snow of melting snow covering the concrete completely
8 Loose dry snow, dust or sand, covering more than one-half of the concrete, but not completely
9 Loose dry snow, dust or sand, covering the concrete completely
Note: The highest code number takes precedence

References

1: MEADEN, G.T. (1996) An atmospheric deposition code using observations of the state of the grass. Weather 51, 68-71.
2: PERKINS, D. (1997) Use of a state of the grass code to record atmospheric depositions. Journal of Meteorology 22(218), 121-125.

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Updated: 22 July 1999

Last updated 23 April 2014

Llansadwrn (Anglesey) Weather Atmospheric depositions code

Llansadwrn (Anglesey) Weather

Atmospheric depositions code