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Cloud, Drizzle and Turbulence Observations in Azores
Jasmine Rémillard1, Pavlos Kollias1, and Edward Luke2
1McGill University 2Brookhaven National Laboratory
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CAP-MBL campaign
• unprecedented data set focused on the marine boundary layer (radia5on and microphysics)
• 20‐month deployment of the AMF1 on Graciosa Island
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Data set
• WACR: hydrometeors boundaries, intensity, ver5cal veloci5es
• Vaisala ceilometer: liquid cloud base (up to 7.5 km)
• MWR: column‐integrated amount of water (liquid and vapor)
• Radiosondes: in situ measurements of the thermodynamic state and winds
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Example
• WACR reflec5vity (colors) and ceilometer bases (black dots) – Radar echoes below lidar base indicate precipita5on
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Example
• Regions containing only precipita5on (blue), and those with cloud par5cles (red)
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Cloud and precipitation
Type High Middle Extending Cu Sc Other
CB > 7km > 3km < 3km — — —
CT — — > 3km < 3km < 3km < 3km
Dura5on — — — < 20min > 20min > 20min
CT variability — — — — < 100m > 100m
Type Virga Light Intense
Echo base > 200m < 200m < 200m
Base reflec5vity — < 0dBZ > 0dBZ
Echo below CB Yes Yes Possible
Precipita5on iden5fica5on done profile by profile
Cloud iden5fica5on done daily by cloud clusters (each analyzed by hours)
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Example
• Iden5fica5on of cloud and precipita5on types (showing only in the BL)
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Minimum cloud coverage in late summer / early fall, and around half of the cloudy profiles had also liquid precipita5ons
Full results
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Full results
BL clouds dominate the atmosphere, especially in spring and summer, while higher clouds have minima occurrences in summer5me.
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Full results
BL clouds are mostly Cu or Sc, and they o_en coexist within an hour (especially in spring and summer)
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Full results
Most precipita5on evaporates before reaching the ground, and intense precipita5on at the ground occurs mainly in winter.
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Detection of decoupling in the BL
• Mul5ple cloud layers are most likely forming in a decoupled BL – Decoupled/coupled hours selected based on the mul5‐layer sta5s5cs in the BL (> 10% vs. 0%) and the cloud base variability in the BL (> 300m vs. < 100m)
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Thermodynamic state
• Layer‐by‐layer averaging was performed on the soundings linked to decoupled/coupled hours – Both usually have a transi5on layer – Coupled cloud layer found either at the inversion or the transi5on (about 50‐50, resul5ng in lower averaged RH)
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Selection of good Sc cases
• Persis5ng for the most part of a day (> 50%)
• Most of the Sc is single‐layer (> 90%)
35 days selected
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Non-drizzling vs. Drizzling
The Sc coverage can be divided into periods when drizzle is falling from the cloud, and periods without virga (or very limited).
Precipita5ng periods are characterized by thicker clouds, and stronger liquid water paths.
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Composited daily cycle
Composi5ng the hourly sta5s5cs from the 35 selected days, a daily cycle is obtained. ‐ blue: falling drizzle
detected ‐ black: no virga detected
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Turbulence
Hourly sta5s5cs of the radar veloci5es during the Sc periods without radar echoes below the ceilometer base provide informa5on about the turbulence and dra_s.
cloud base
cloud top
many small updra_s
few strong updra_s
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Updrafts and mass fluxes
• 3 different views – Direct sampling – Coherent structures – Sta5s5cal method (Randall et al., 1992)
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Summary
• The Azores are cloudy, with many BL clouds, including a lot of Sc clouds.
• It is hard to detect real coupled BL periods using only cloudiness measurements.
• Drizzling Sc clouds are thicker and higher, and contain more liquid than their non‐drizzling counterparts.
• Sc clouds have a propensity to precipitate, although it doesn’t reach the ground o_en.
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Summary
• Sc clouds are linked to the inversion at the BL top.
• The marine Sc observed were rather calm.
• Coherent structures account for about half of the mass flux in those marine Sc, with a maximum observed around sunrise.
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(Near) future work
• Retrieval of drizzle microphysics and cloud dynamics from the WACR Doppler spectra
• Characteriza5on of the factors influencing drizzle produc5on and growth in marine Sc clouds