Aircraft Observations of the Aircraft Observations of the Atmospheric Boundary Layer over Atmospheric Boundary Layer over the Ronne Polynya, Southern the Ronne Polynya, Southern Weddell Sea, AntarcticaWeddell Sea, Antarctica
Emma FiedlerEmma Fiedler
Ian Renfrew (UEA)
Tom Lachlan-Cope (BAS)
John King (BAS)
(Open University 1998)
sensible heatsensible heat
Antarctic Peninsula
Study areaStudy area
AVHRRAVHRR
Aircraft ObservationsAircraft Observations
3 flights between3 flights between February 25February 25thth-28-28thth 2007 2007
Cold air outbreak off Cold air outbreak off
Ronne Ice ShelfRonne Ice Shelf
High frequency High frequency measurements u, v, w, Tmeasurements u, v, w, T
3 flights over Ronne Polynya3 flights over Ronne Polynya
4 ~120 km low altitude legs4 ~120 km low altitude legs
2 at ~15 m, 2 at ~30 m (within 2 at ~15 m, 2 at ~30 m (within surface layer)surface layer)
Quality control:Quality control: - spectral analysis, cospectra, etc - spectral analysis, cospectra, etc (c.f. French et al. 2007; Drennan et al. 2007)(c.f. French et al. 2007; Drennan et al. 2007)
– – averaging period (run) of 140 sec for averaging period (run) of 140 sec for turbulent fluxes appropriateturbulent fluxes appropriate
– – 6 runs rejected out of 49 runs 6 runs rejected out of 49 runs
– – 1 run rejected due to instrument malfunction1 run rejected due to instrument malfunction
ResultsResults
Decrease in sensible heat flux Decrease in sensible heat flux with fetch due to reduction in air-with fetch due to reduction in air-surface temperature differencesurface temperature difference
– – CIBL warmingCIBL warming
– – surface temperature decreasesurface temperature decrease
ResultsResults
Decrease in sensible heat flux Decrease in sensible heat flux with fetch due to reduction in air-with fetch due to reduction in air-surface temperature differencesurface temperature difference
– – CIBL warmingCIBL warming
– – surface temperature decreasesurface temperature decrease
ResultsResults
Only values from Only values from 15 m legs used due 15 m legs used due to increased scatter to increased scatter at 30 mat 30 m
Mean values same Mean values same (flights 24hrs apart)(flights 24hrs apart)
CCDN10DN10 = 1.1 x 10 = 1.1 x 10-3-3
CCHN10HN10 = 0.7 x 10 = 0.7 x 10-3-3
No obvious trend No obvious trend with fetch, no with fetch, no difference between difference between means for different means for different regimes regimes
Transfer coefficientsTransfer coefficients
Is there a variation with Is there a variation with surface characteristics?surface characteristics?
Relationships between CRelationships between CDD and and
CCH H with albedo and Twith albedo and Tsurfacesurface
examined as indicator of surface examined as indicator of surface ice typeice type
Modelling of sensible heat fluxesModelling of sensible heat fluxes Validation of CIBL model (Renfrew and Validation of CIBL model (Renfrew and King, 2000)King, 2000)
– – designed for use over polynyas designed for use over polynyas
– – 1-D, zero-order jump model1-D, zero-order jump model
– – QQss, h and , h and θθmm vary with fetch vary with fetch
Model changes:Model changes:
Ice covered surface observed rather Ice covered surface observed rather than open waterthan open water
– – surface roughness length not surface roughness length not dependent on wind speeddependent on wind speed
– – two-regime initial Ttwo-regime initial Tsurfacesurface
– – revised Crevised CHH and C and CDD
Sensible heat fluxesSensible heat fluxes
Ts = -7.8 oC
Ts = -11.7 oC
Sensible heat fluxesSensible heat fluxes
Ts = -7.8 oC
Ts = -11.7 oC
Ts = -1.9 oCCHN10= 1.14 x 10-3
(DeCosmo et al., 1996)
CHN10= 0.70 x 10-3
(Ronne Polynya observations)
Sensible heat fluxesSensible heat fluxes
Ts = -7.8 oC
Ts = -11.7 oC
Ts = -1.9 oC
Ts = -1.9 oC
AMSR-EAMSR-E
http://iup.physik.uni-http://iup.physik.uni-bremen.de:8084/archive.htmlbremen.de:8084/archive.html
Conclusions : ObservationsConclusions : Observations
Low-level, aircraft-based turbulence observations Low-level, aircraft-based turbulence observations successfully collected over Ronne Polynyasuccessfully collected over Ronne Polynya
Decrease in QDecrease in Qss with fetch with fetch Polynya thin ice, rather than open waterPolynya thin ice, rather than open water
Ice surface type can be split into two regimesIce surface type can be split into two regimes Both regimes considered part of polynya due to large heat Both regimes considered part of polynya due to large heat
fluxesfluxes
New values of CNew values of CHH and C and CDD to add to limited data sets to add to limited data sets CCDN10DN10 = 1.1 x 10-3 = 1.1 x 10-3 CCHN10HN10 = 0.7 x 10-3 = 0.7 x 10-3
No significant difference in CNo significant difference in CHH and C and CDD between between regimesregimes
Conclusions : ModellingConclusions : Modelling For these cases the Ronne Polynya was thin ice (not For these cases the Ronne Polynya was thin ice (not
open water)open water) Modelling of QModelling of QSS requires appropriate requires appropriate
– – CCH10NH10N and C and CD10ND10N
– – TTsurfacesurface
– – no Charnock parameterno Charnock parameter Other coastal polynyas can be modelled in same Other coastal polynyas can be modelled in same
wayway unless large areas of open waterunless large areas of open water
Implications for polynya satellite ice concentration Implications for polynya satellite ice concentration algorithms & modellingalgorithms & modelling Should Should thin icethin ice be considered in the same way as be considered in the same way as thicker icethicker ice or or
open wateropen water?? This study suggests This study suggests thin icethin ice similar to similar to thicker icethicker ice
Similarity of CSimilarity of CHH and C and CDD between regimes between regimes Reduced QReduced QSS compared to open water compared to open water
