The Science:

The Lews Castle radar offers a temporal and spatial resolution of weather systems (and their precipitation) at least one order of magnitude (or more) greater than conventional observational systems.

The radar operates at a frequency of 24GHz, at a vertical resolution of 30m x 100 steps, giving a maximum height penetration of up to 3100m above the surface. The radar sends a vertical pulse of radiation, which is back-scattered (reflected) by any hydrometeors (snow, hail, sleet, rain) present in the atmosphere. The radar data are averaged over time bins of 1 minute in duration.

As the wavelength of the radiation (approx. 1.3cm) is larger than the droplet size, then the amount of back scatter of the radiation is proportional to the 6^th power of the droplet radius Thus, large raindrops or hailstones reflect significantly more radiation than do drizzle or small ice crystals. Sleet or melting snow (snowflakes covered with a thin layer of water) reflect anomalously strongly, leading to a phenomena known as the 'bright band' (see below).

The enhanced reflectivity of the bright band approximates to the height of the freezing level in the atmosphere. Over Stornoway during summertime, the height of this level ranges from perhaps ~900m to ~2400m, and from the surface to ~1500m in winter.

Further reading / resources:

Fukao, S., Hamazu, K. and Doviak, R.J. (2014). Radar for meteorological and atmospheric observations. Springer.

Rutgers University (2016). Remote Sensing of the Atmosphere and Ocean [online] [13 June 2016]

Micro Rain Radar (MRR) at Lews Castle College Energy Croft

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