Evidence of a Diurnal Cycle in Precipitation over the Southern Ocean as Observed at Macquarie Island

• Main Authors: Francisco Lang, Yi Huang, Steven T. Siems, Michael J. Manton
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Atmosphere
• Subjects: precipitation; diurnal cycle; southern ocean; macquarie island; marine boundary layer clouds
• Online Access: https://www.mdpi.com/2073-4433/11/2/181

Due to a lack of observations, relatively large discrepancies exist between precipitation products over the Southern Ocean. In this manuscript, surface hourly precipitation observations from Macquarie Island (54.62<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>&#176;</mo> </msup> </semantics> </math> </inline-formula> S, 158.85<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>&#176;</mo> </msup> </semantics> </math> </inline-formula> E) are analysed (1998&#8722;2016) to reveal a diurnal cycle. The precipitation rate is at a maximum during night/early morning and a minimum in the afternoon at Macquarie Island station. Seasonally, the diurnal cycle is strongest in summer and negligible over winter. Such a cycle is consistent with precipitation arising from marine boundary layer clouds, suggesting that such clouds are making a substantial contribution to total precipitation over Macquarie Island and the Southern Ocean. Using twice daily upper air soundings (1995&#8722;2011), lower troposphere stability parameters show a stronger inversion at night, again consistent with precipitation arising from marine boundary layer clouds. The ERA-Interim precipitation is dominated by a 12 hourly cycle, year around, which is likely to be a consequence of the twice-daily initialisation. The implication of a diurnal cycle in boundary layer clouds over the Southern Ocean to derived A-Train satellite precipitation products is also discussed.