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95th AMS Annual Meeting13th Symposium on the Coastal Environment
Coastal clouds along northern Chile: climatology and trends
Ricardo C. MuñozDept. Geophysics, University of Chile
Juan QuintanaChilean National Weather Service (DMC)
Mark FalveyDept. Geophysics, University of Chile
Acknowledgment: Partial funding by Project Fondecyt-Chile 1130111
Arica
Iquique
Antofagasta
Key geographic/climate elements:
• Andes Cordillera (Z>5000 m)• Atacama Desert• SE Pacific Anticyclone• Cold Chile-Peru surface current• Extensive Sc cloud layer
from: www.nrlmry.navy.mil/nexsat-bin/
taken from Mechoso et al., BAMS, 2014.
Importance of SE Pacific Sc clouds:
• local: coastal clouds affect transport and local weather• global: impact in Earth´s radiation budget (e.g. Exp. VOCALS-REx 2008)
Objective of this presentation:
• to document climatology and trends of coastal clouds based on long-term databases:
• hourly surface observations (SYNOP/METAR): 1969-2013• T, RH, WS, WD, P• clouds: layers, type, fraction, height• sunshine hours (Campbell-Stokes heliograph)
• upper air: 1979-2013• 12 UTC ( 8 AM LT ) radiosondes
Thermodynamic structure of this coastal boundary layer:
full description in Muñoz et al., J.Climate, 2011, p. 1013-1033
Subsidenceinversion
cool and humidboundary layer
Cloud observations:
• most typical conditions: 1-layer Sc clouds with bases below 1 km and various cloud fractions
Annual/Diurnal cycles of cloud properties:
• frequency: time fraction with low clouds• fraction: spatial coverage of low clouds (oktas)• height: cloud base height
Trends of low clouds:
cloud frequency:slight increase
cloud fraction:slight decrease
cloud height:significant decrease
Inversion Base
Cloud base
Surface LCL
Divergence in trendsof inversion and cloud basessuggests cloud deepening
Convergence in trendsof cloud base and LCLsuggests ABL coupling
Increase in correlationbetween LCL and cloudbase reaffirms coupling
Consistent trends:
decrease in AM sunshine hours
decrease in cloud base heights in other stations along the coast
Antofagasta
Iquique
Arica
Not-as-consistent trends:
slight decrease in winds not consistent with mechanical coupling of ABL:
decrease of radiosonde relative humidity not consistent with cloud deepening:
RH in ABL
RH aloft
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