Surface Meteorological charts Maps of sealevel pressure Surface

Surface Meteorological charts Maps of sea-level pressure

Surface weather chart for 3 January 2007 (UK Met Office) 1110 km: 1° lat = 111 km http: //www. wetterzentrale. de/topkarten/tknfax. html

Salient features 1 • Map shows sea-level pressure. Over land the measured pressure is adjusted to what it would be at sea level.

Salient features 1 • Map shows sea-level pressure. Over land the measured pressure is adjusted to what it would be at sea level. • Surface pressure pattern dominated by highs and lows, on a scale ~ 103 km. We call this the synoptic scale

Salient features 2 • Isobars give an indication of the wind speed by the geostrophic relation: wind tends to flow along isobars and its strength is proportional to pressure gradient

Salient features 2 • Isobars give an indication of the wind speed by the geostrophic relation: wind tends to flow along isobars and its strength is proportional to pressure gradient • Pressure excursions around ± 30 mb – much smaller than the total pressure of ~1000 mb. Pressure is the weight of air above you

Time scale 00 h 3/1/07 Weather system takes ~ 1 day to pass over the UK – so synoptic timescale is around a day (105 s) 00 h 4/1/07

Fronts: areas of cloud and rain AVHRR IR image 2317 2/1/07 http: //www. sat. dundee. ac. uk

Warm airfronts Cold and warm Cold Air Motion of front Warm air Cold front: narrow (~100 km), steep, can get line convection particularly on leading edge www. quora. com Cold Air Warm front: broad (~300 km), layer cloud due to gentle upglide. Convection unusual.

Occluded front Warm air Cold, unstable air Cold, stable air