Effects of the diurnal cycle in solar radiation on the tropical Indian Ocean mixed layer variability during wintertime Madden‐Julian Oscillations. Issue 10 (3rd October 2013)

• Record Type: Journal Article
• Authors: Li, Yuanlong; Han, Weiqing; Shinoda, Toshiaki; Wang, Chunzai; Lien, Ren‐Chieh; Moum, James N.; Wang, Jih‐Wang
• Is Part Of: Journal of geophysical research. Volume 118:Issue 10(2013:Oct.)
• Page Start: 4945
• Page End: 4964
• Publication Date: 2013-10-03
• Subjects: diurnal cycle -- sea surface temperature -- Madden‐Julian Oscillation -- CINDY/DYNAMO; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/jgrc.20395
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract : [1] The effects of solar radiation diurnal cycle on intraseasonal mixed layer variability in the tropical Indian Ocean during boreal wintertime Madden‐Julian Oscillation (MJO) events are examined using the HYbrid Coordinate Ocean Model. Two parallel experiments, the main run and the experimental run, are performed for the period of 2005–2011 with daily atmospheric forcing except that an idealized hourly shortwave radiation diurnal cycle is included in the main run. The results show that the diurnal cycle of solar radiation generally warms the Indian Ocean sea surface temperature (SST) north of 10°S, particularly during the calm phase of the MJO when sea surface wind is weak, mixed layer is thin, and the SST diurnal cycle amplitude ( dSST ) is large. The diurnal cycle enhances the MJO‐forced intraseasonal SST variability by about 20% in key regions like the Seychelles‐Chagos Thermocline Ridge (SCTR; 55°–70°E, 12°–4°S) and the central equatorial Indian Ocean (CEIO; 65°–95°E, 3°S–3°N) primarily through nonlinear rectification. The model also well reproduced the upper‐ocean variations monitored by the CINDY/DYNAMO field campaign between September‐November 2011. During this period, dSST reaches 0.7°C in the CEIO region, and intraseasonal SST variability is significantly amplified. In the SCTR region where mean easterly winds are strong during this period, diurnal SST variation and its impact on intraseasonal ocean variability are much weaker. In both regions, the diurnal cycle also has a large impact on the upward surface turbulent heat flux QT and induces diurnal variation of QT with a peak‐to‐peak difference of O (10 W m −2 ). Key Points: The diurnal cycle enhances intraseasonal SST variability by 20%. Impact of diurnal cycle on the Indian ocean is mainly through nonlinear effect. The diurnal cycle leads to significant change in surface heat flux.