Observations and comparisons of cloud microphysical properties in spring and summertime Arctic stratocumulus during the ACCACIA campaign

• Main Authors: Lloyd, G., Choularton, Thomas, Bower, Keith, Crosier, Jonathan, Jones, H., Dorsey, James, Gallagher, M. W., Connolly, Paul, Kirchgaessner, A. C. R., Lachlan-Cope, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Arctic clouds; cloud microphysics; ACCACIA; airborne; cloud spectrometers; CDP; CAPS; CIP; FAAM. Hallet Mossop; Ice; Stratocumulus; Antarctic; Arctic; Hallet; Hallett; The Antarctic; Antarc*
• Online Access: https://research.manchester.ac.uk/en/publications/a8688e59-54c3-42de-b9ac-821f652ca4d8; https://doi.org/10.5194/acpd-14-28757-2014

Measurements from four case studies in spring and summer-time Arctic stratocumulus clouds during the Aerosol–Cloud Coupling And Climate Interactions in the Arctic (AC- CACIA) campaign are presented. We compare microphysics observations between 5 cases and with previous measurements made in the Arctic and Antarctic. During AC- CACIA, stratocumulus clouds were observed to consist of liquid at cloud tops, often at distinct temperature inversions. The cloud top regions precipitated low concentrations of ice into the cloud below. During the spring cases median ice number concentra- tions (∼0.5L−1) were found to be lower by about a factor of 5 than observations from 10 the summer campaign (∼3L−1). Cloud layers in the summer spanned a warmer tem- perature regime than in the spring and enhancement of ice concentrations in these cases was found to be due to secondary ice production through the Hallett–Mossop (H–M) process. Aerosol concentrations during spring ranged from ∼ 300–400 cm−3 in one case to lower values of ∼50–100 cm−3 in the other. The concentration of aerosol 15 with sizes, Dp > 0.5 μm, was used in a primary ice nucleus (IN) prediction scheme, DeMott et al. (2010). Predicted IN values varied depending on aerosol measurement periods, but were generally greater than maximum observed median values of ice crys- tal concentrations in the spring cases, and less than the observed ice concentrations in the summer due to the influence of secondary ice production. Comparison with re- 20 cent cloud observations in the Antarctic summer (Grosvenor et al., 2012), reveals lower ice concentrations in Antarctic clouds in comparable seasons. An enhancement of ice crystal number concentrations (when compared with predicted IN numbers) was also found in Antarctic stratocumulus clouds spanning the Hallett–Mossop (H–M) temper- ature zone, but concentrations were about an order of magnitude lower than those 25 observed in the Arctic summer cases, but were similar to the peak values observed in the colder Arctic spring cases, ...