Abstract
Abstract. The effect of air–sea coupling on simulated boreal summer intraseasonal oscillation (BSISO) is examined using atmosphere–ocean-mixed-layer coupled (SPCAM3-KPP, referred to as SPK throughout) and uncoupled configurations of the superparameterized (SP) Community Atmospheric Model, version 3 (SPCAM3, referred to as SPA throughout). The coupled configuration is constrained to either observed ocean mean state or the mean state from the SP coupled configuration with a dynamic ocean (SPCCSM3), to understand the effect of mean-state biases on the BSISO. All configurations overestimate summer mean subtropical rainfall and its intraseasonal variance. All configurations simulate realistic BSISO northward propagation over the Indian Ocean and western Pacific, in common with other SP configurations. Prescribing the 31 d smoothed sea surface temperature (SST) from the SPK simulation in SPA worsens the overestimated BSISO variance. In both coupled models, the phase relationship between intraseasonal rainfall and SST is well captured. This suggests that air–sea coupling improves the amplitude of simulated BSISO and contributes to the propagation of convection. Constraining SPK to the SPCCSM3 mean state also reduces the overestimated BSISO variability but weakens BSISO propagation. Using the SPCCSM3 mean state also introduces a 1-month delay to the BSISO seasonal cycle compared to SPK with the observed ocean mean state, which matches well with observation. Based on a Taylor diagram, both air–sea coupling and SPCCSM3 mean-state SST biases generally lead to higher simulated BSISO fidelity, largely due to their abilities to suppress the overestimated subtropical BSISO variance.
Highlights
The intraseasonal oscillation (ISO) is the most vigorous subseasonal signal in the tropics (Zhang, 2005)
We examine the roles of air–sea interaction and mean-state biases in simulated boreal summer ISO (BSISO) using a configuration of SP CAM (SPA) coupled to a mixed-layer ocean model, constrained to observed ocean mean state and simulated ocean mean state from the SP Community Climate System Model (CCSM), version 3 (SPCCSM3; Stan et al, 2010)
We investigate the roles of ocean mean-state biases and air– sea coupling in simulating the BSISO by coupling the SPA to the Multi-Column K Profile Parameterization (MC-KPP) mixed-layer ocean
Summary
The intraseasonal oscillation (ISO) is the most vigorous subseasonal signal in the tropics (Zhang, 2005). It interacts with other tropical climate and weather systems, such as the El Niño–Southern Oscillation (ENSO) and tropical cyclones (Kessler et al, 1995; Zhang and Gottschalck, 2002; McPhaden, 2004; Wu et al, 2007), and even the mid-latitude systems (Ding and Wang, 2007; Moon et al, 2013). Compared to the boreal winter ISO (i.e. the Madden and Julian Oscillation, or MJO; Madden and Julian, 1971, 1972), the boreal summer ISO (BSISO) shifts away from the Equator to the Asian summer monsoon (ASM) region (Wang et al, 2006; Lau and Waliser, 2012). The frequency of extreme events over the ASM region is highly related to BSISO activity (Ren et al, 2013; Li et al, 2015; Hsu et al, 2016, 2017, 2020; Liu and Hsu, 2019).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
