IOP 4 – 5 March 2010
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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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Investigating the typical occurrence of cold-air-pools during the COLd air Pool Experiment (COLPEX) Bradley Jemmett-Smith COLPEX meeting 15 October 2012. IOP 4 – 5 March 2010. Δ T/ Δ z = 7 o C/200 m Most within bottom 100 m. Temperature time series for the month of March - PowerPoint PPT Presentation
Transcript of IOP 4 – 5 March 2010
Investigating the typical occurrence of cold-air-pools during the COLd air Pool Experiment
(COLPEX)
Bradley Jemmett-Smith
COLPEX meeting 15 October 2012
IOP 4 – 5 March 2010
Temperature time series for the month of March
Green Δz = 95 m Blue Δz = 200 m
ΔT/Δz = 7 oC/200 m
Most within bottom 100 m
IOP 4 – 5 March 2010Synoptic conditions
IR sat image 00:00 UTC 5 March 2010
Analysis 00:00 UTC 5 March 2010
IOP 4 – 5 March 2010
Potential temp
Valley Env. Lapse
rateRH
IOP 4 – 5 March 2010
Radiosonde profiles
Potential temp
Mixing ratio
Drying of layer
IOP 4 – 5 March 2010
Radiosonde profiles
Wind DirectionWind Speed
Nocturnal Jet formed SW wind seen
IOP 4 – 5 March 2010CP formation
17:05 18:05 18:35
Sunset 18:00
IOP 4 – 5 March 2010CP evolution
22:45 23:15 03:45
Sunset 18:00
AWS 3 warming
Valley Jet
04:05
AWS 7, 5 warming
23:45
IOP 4 – 5 March 2010
LIDAR
Anomalies
Vertical velocities
Backscatter
IOP 4 – 5 March 2010Anomalies
Tower
IOP 4 – 5 March 2010
Potential temp
Env. Lapse rate
RH
WarmingCooling
IOP 4 – 5 March 2010Anomalies
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
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.
IOP 4 – 5 March 2010Summary 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.
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?
Cold-air-pool occurrence
Nights with an inversion >= 4oC occur 23% of the time.
