© George Anderson
Wokingham, England, United Kingdom of Great Britain and Northern Ireland
Latitude: 51° 25' 4'' N
Longitude: 0° 51' 48'' W
22 June 2016 0944 (Local Time)
Image P/S code: P.11.2.3
Image I.D.: 4977
This photograph shows drops of drizzle on a ruler and gives an illustration of the size of the drops. The ruler was exposed to falling drizzle for a period of a few minutes until a reasonable number of drops had accumulated. The large graduations at the top of the ruler are in centimetres and each small graduation is 1 mm. The large graduations at the bottom are inches and each of the smallest graduations is one sixteenth of an inch.
A frontal wave was crossing southern England, UK and the location was in a warm-sector airflow. All nearby weather stations reported drizzle and overcast Stratus cloud.
Drizzle falls from Stratus cloud and the drops are typically less than 0.5 mm in diameter, as shown in this picture at 6 and 7. Larger drops on the ruler are probably due to one or more drops merging together after landing.
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This photograph gives an illustration of the relative size of drops of rain and of drizzle. Each graduation on the ruler is 1 mm.
The ruler was exposed to moderate precipitation in the form of rain and drizzle mixed (present weather code 59) for about 1 minute during a period in which the rate of accumulation was about 0.6 mm/hr.
A wave on a cold front had recently passed east over the location in southern England, UK and had reintroduced the location to a warm-sector airflow. A 1200 UTC upper-air sounding from Camborne, England, UK (approximately 335 km to the west-south-west of the observing location and within the warm-sector airflow) indicates extensive low-level cloud of Stratus and Stratocumulus to a top of around 830 hPa, with further layers of medium-level cloud above. It is likely that the relatively few, larger rain drops originated in the medium-level cloud, while the more numerous drizzle drops would have fallen from the low Stratus layer.
Drizzle drops are usually less than 0.5 mm in diameter, while rain drops are larger than this and vary according to the intensity and nature of the precipitation. The relative sizes are illustrated well in this photograph, although it must be noted that due to the squashing of the larger raindrops on the ruler (caused by gravity and/or surface tension), these drops appear slightly larger than their true diameter when in freefall through the air. Nevertheless, the image illustrates how rain and drizzle drops would appear, for example, once they have fallen onto the lenses of an observer's spectacles – a useful aid to help determine whether precipitation is drizzle, rain, or a mixture of the two.
Links in the image description will highlight features on the image. Mouse over the features for more detail.