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Published byAbigayle Hampton Modified over 9 years ago
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Investigating the typical occurrence of cold-air-pools during the COLd air Pool Experiment (COLPEX) Bradley Jemmett-Smith COLPEX meeting 15 October 2012
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IOP 4 – 5 March 2010 Temperature time series for the month of March Green Δz = 95 mBlue Δz = 200 m ΔT/Δz = 7 o C/200 m Most within bottom 100 m
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IOP 4 – 5 March 2010 Synoptic conditions IR sat image 00:00 UTC 5 March 2010 Analysis 00:00 UTC 5 March 2010
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IOP 4 – 5 March 2010 Potential temp Valley Env. Lapse rate RH
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IOP 4 – 5 March 2010 Radiosonde profiles Potential tempMixing ratio Drying of layer
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IOP 4 – 5 March 2010 Radiosonde profiles Wind DirectionWind Speed Nocturnal Jet formed SW wind seen
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IOP 4 – 5 March 2010 CP formation 17:0518:05 18:35 Sunset 18:00
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IOP 4 – 5 March 2010 CP evolution 22:4523:15 03:45 Sunset 18:00 AWS 3 warmingValley Jet 04:05 AWS 7, 5 warming 23:45
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IOP 4 – 5 March 2010 LIDAR Anomalies Vertical velocitiesBackscatter
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IOP 4 – 5 March 2010 Anomalies Tower
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IOP 4 – 5 March 2010 Potential tempEnv. Lapse rateRH Warming Cooling
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IOP 4 – 5 March 2010 Anomalies 21:15 Cooling at same rate, undisturbed growth. 01:45 Warmer flow at 50m Duffryn from the NNW. 04:45 Warming at AWS 3. SSW flow seen at 50m Duffryn. 05:45 ‘Extra’ cooling at some AWS. Up-valley flow seen! N flow seen at Duffryn 50m! Valley flow 50 m
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Mixing events - explanation A mixing/warming events can: occur across a number of sites, caused by an external source. be caused internally, by a disturbance at a neighbouring site. KH instability – potentially dependent on valley orientation and IVJ. Change in wind direction will change the source of advection towards the valley.
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IOP 4 – 5 March 2010 Summary CAP begins to form before sunset, with change in wind direction at valley sites. Development of Internal Valley Jet (IVJ) soon after sunset. Disturbances seen in the cold pool growth after 23:00 UTC: 1.Warming seen to coincide with a change in the wind-direction. 2.Layered erosion caused by Nocturnal Jet above the valley, which disrupts the IVJ. Layered structure: 1.Very cold undisturbed layer; light winds, reversal in wind dir can occur. 2.Cold layer, higher 2 m wind speeds, susceptible to warming events. 3.IVJ/mixed layer region, very sensitive to changes in synoptic wind conditions. Possible evidence for side valley drainage at Duffryn, layered structure. Accelerated cooling at AWS 5, 05:30, accompanied with a reverse in wind dir. CAP elevated during break-up, seen at Duffryn. Cold-air-pool persists up to 2 hrs after sunset at Clun Castle.
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Future work Writing up March case at the moment. Need to explain the rapid cooling towards the end of the night; synoptic, local or both? Model comparison and investigations. Climatology studys: Wind climatology; forcing mechanisms. Importance of; Nocturnal Jet, IVJ, diurnal change in atmospheric water vapour content (LW in), pressure situation (wind speed, direction), KH instability?
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Cold-air-pool occurrence Nights with an inversion >= 4 o C occur 23% of the time.
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