The land based SYNOP messages measurements describe hourly observations from land stations distributed globally. The observations cumulate in around 60,000 reports a day, giving measurements of parameters such as wind speed and direction, maximum and minimum air temperature, sunshine duration, rainfall accumulation, and cloud type. The data are collected by observation stations worldwide and transmitted within the land SYNOP message.

Data are extracted from the Met Office's MetDB system before being sent to CEDA for archiving. These extractions occur at the 4 principal synoptic periods (00-06, 06-12, 12-18 and 18-00 UT).

The dataset contains a range of measurements including:

- Wind speed and wind direction

- Maximum and minimum air and grass temperature

- Horizontal and vertical visibility

- Snow depth

- Dew-point temperature

- Relative humidity

- 3 -hour pressure change

- Height and period of wind waves

- Cloud height and type

- Radiation in last 24 hours

- Maximum gust period

- Past and present weather

- Rainfall accumulation

- Precipitation amount

- Sunshine duration

The wind speed and vertical gust speed are given to the nearest metre per second, and the vertical gust acceleration to the nearest metre per second squared. The wind direction from which the wind blows is measured in Degrees (true). The entry for an east wind is 090, for a south wind it is 180 and so on clockwise. Note that zero values in both wind speed and wind direction fields indicate that there was no wind blowing at the time of observation.

The air temperature, grass temperature and dew-point temperature are measured in Kelvin.

The cloud height, visibility, snow depth, and wind-wave height are given in metres.

Sunshine duration is recorded over 24 hours and over one hour. For the former, the measurement is in hours, but for the latter the measurement is in minutes.

The past weather is recorded as a number between 0-9 which details what the weather has been like in the last 6 hours for observations at 00, 06, 12, 1800 UTC, the last 3 hours for observations at 03, 09, 15, 2100 UTC and the previous hour at any other times. The past weather is only recorded when a manual observation is done at the station.

The relative humidity is measured as a percentage.

Documentation and Links to further information and references (see linked documentation on this record):

Some general information about surface station readings can be obtained from the abridged version of "MIDAS Data Users Guide", provided by the Met Office. This document describes the meteorological surface data in the Met Office Database - MIDAS. This guide is rich in information and is aimed at those with little familiarity with observing methods or instrumentation.

Details of the WMO Meteorological codes used at weather observing stations (daily and hourly weather) explain the codes used in this dataset further.