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

Conclusions

Work in progress:

• continuous measurements of cloud properties:• CL31 Ceilometer• Total Sky Imager• 3 Automatic weather stations• additional 16 UTC radiosoundings

• WRF modeling and validation

TSI image

see Poster 314