Thermometer Variable temperature Units Degrees Celsius o C

Thermometer • • • Variable: temperature Units: Degrees Celsius (o. C) Accuracy: marked to 0. 5 o. C Cost: £ 10 Site: in the shade (e. g. a Stevenson Screen) • Mercury (or sometimes coloured alcohol) in the bulb expands and contracts up the calibrated tube with changes in the ambient air temperature

Max & Min Thermometer • Details as for thermometer, except an index marker is pushed up or down by the tube of mercury to indicate the maximum or minimum

Whirling hygrometer • Variables: temperature and wet bulb temperature • Units: Kelvin or Degrees Celsius • Accuracy: marked to 0. 5 o. C (range -5 to +50 o. C) • Cost: £ 45 • Site: in the shade • Whirl it round your head so thermometer bulbs are well ventilated and there is sufficient evaporation from the wet bulb to achieve lowest possible temperature.

Assman psychrometer • Similar to the whirling hygrometer, but uses a wind up fan to ventilated the dry and wet bulb thermometers.

Humidity slide rule • Variable: converts between water vapour content measures • Units: n/a • Accuracy: ~1 % • Cost: cheap! • Site: n/a • A ready-reckoner for conversion between, e. g. wet bulb temperature and relative humidity

Barograph (recording Barometer) • Variable: atmospheric pressure • Units: millibars (mb) or Pascals (Pa) • Accuracy: ~0. 1 mb • Cost: ? • Site: Anywhere • An aneroid barometer contains a partial vacuum in the sealed metal aneroid cell, hence changes in pressure amplified by movements of the arm attached to the cell.

Net radiometer • Variables: upwelling and downwelling radiation • Units: W m-2 • Accuracy: ? • Cost: ? • Site: Exposed site without shading • Dark surfaces absorb longwave or shortwave radiation, causing a change in voltage which can be measured electronically and converted to radiation.

Dome solarimeter • • • Variable: solar radiation Units: W m-2 Accuracy: ? Cost: ? Site: exposed As for net radiometers

Tipping bucket raingauge • • • Variable: rain rate and amount Units: mm Accuracy: 0. 2 mm Cost: £ 300 -£ 700 Site: exposed horizontal location • Rain falls into cone and tips a small bucket once full, with that time recorded, thus a rain rate can be observed. Cone amplifies signal.

Air meter • Variable: the “run of air” & hence wind speed • Units: m & m s-1 • Accuracy: dependent on the observation time • Cost: no longer available. • Site: away from buildings, etc • Impeller spun round by the wind, turning dials to measure the wind run.

Handheld anenometer • Variable: wind speed (instantaneous) • Units: m s-1 or equivalent • Accuracy: poor. • Cost: cheap • Site: handheld • Wind blows the cups around to give an instantaneous reading.

Sodar (Acoustic Radar) • • Variable: Backscatter Units: amplitude Accuracy: ? Site: away from buildings, people, & noise! • Cost: ~£ 1000 -10, 000 • Acoustic pulses are scattered back to the receiver, from small -scale density changes (e. g. turbulence), with the volume and time-lag measured to give amplitude and range.

Doppler sodar • Variable: Backscatter & derived wind profiles • Units: n/a and m/s • Accuracy: ~1 m/s • Site: remote! • Cost: £ 10, 000 • Acoustic beams fired in several directions, so scatters relative movement can be determined, and hence wind speed & direction in 3 D.

Radiosonde (Upper air sounding) • Variables: an atmospheric sounding (i. e. vertical profile) of, typically, pressure, temperature, relative humidity & wind • Units: various • Accuracy: various • Cost: £ 100 per sonde • Site: away from buildings, good spatial representation, often airports • Balloon is filled with Helium gas and released rising up few metres per second, the radiosonde measures and transmits data to a ground station

Radar • Variables: Backscatter, usually from hydrometeors, such as rain drops, hail, snow, etc. • Units: backscatter amplitude • Accuracy: ? • Site: away from buildings, good spatial distribution • Cost: £ 10, 000 -£ 1 millions • Radio waves emitted and reflected back, with return amplitude and time-lag giving backscatter intensity and range. These can be related to precipitation intensity. • Doppler radars also available.

Satellites! • Variable: Radiation & derived brightness temperature • Units: W & derived K • Resolution: down to < 1 km • Site: space! Either geostationary or polar orbits • Cost: millions & millions • Passive satellites measure upwelling radiation at various wavelengths (visible, infra red & microwave) • Active satellites work more like radars.

Observing scenarios: • You have been tasked with determining the structure & governing physics of the wind field over Greenland – discuss in groups how to achieve this challenge.