Regional boreal summer intraseasonal oscillation over Indian Ocean and Western Pacific: comparison and predictability study

2015 ◽  
Vol 46 (7-8) ◽  
pp. 2213-2229 ◽  
Author(s):  
Sun-Seon Lee ◽  
Bin Wang
Keyword(s):  
Indian Ocean ◽  
Intraseasonal Oscillation ◽  
Western Pacific ◽  
Boreal Summer ◽  
Boreal Summer Intraseasonal Oscillation

scholarly journals Impacts of atmospheric and oceanic initial conditions on boreal summer intraseasonal oscillation forecast in the BCC model

2020 ◽  
Vol 142 (1-2) ◽  
pp. 393-406
Author(s):  
Zhongkai Bo ◽  
Xiangwen Liu ◽  
Weizong Gu ◽  
Anning Huang ◽  
Yongjie Fang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
North Pacific ◽  
Western North Pacific ◽  
Initial Conditions ◽  
Intraseasonal Oscillation ◽  
Tropical Indian Ocean ◽  
Boreal Summer ◽  
Model Errors ◽  
Maritime Continent ◽  
Boreal Summer Intraseasonal Oscillation

Abstract In this paper, we evaluate the capability of the Beijing Climate Center Climate System Model (BCC-CSM) in simulating and forecasting the boreal summer intraseasonal oscillation (BSISO), using its simulation and sub-seasonal to seasonal (S2S) hindcast results. Results show that the model can generally simulate the spatial structure of the BSISO, but give relatively weaker strength, shorter period, and faster transition of BSISO phases when compared with the observations. This partially limits the model’s capability in forecasting the BSISO, with a useful skill of only 9 days. Two sets of hindcast experiments with improved atmospheric and atmosphere/ocean initial conditions (referred to as EXP1 and EXP2, respectively) are conducted to improve the BSISO forecast. The BSISO forecast skill is increased by 2 days with the optimization of atmospheric initial conditions only (EXP1), and is further increased by 1 day with the optimization of both atmospheric and oceanic initial conditions (EXP2). These changes lead to a final skill of 12 days, which is comparable to the skills of most models participated in the S2S Prediction Project. In EXP1 and EXP2, the BSISO forecast skills are improved for most initial phases, especially phases 1 and 2, denoting a better description for BSISO propagation from the tropical Indian Ocean to the western North Pacific. However, the skill is considerably low and insensitive to initial conditions for initial phase 6 and target phase 3, corresponding to the BSISO convection’s active-to-break transition over the western North Pacific and BSISO convection’s break-to-active transition over the tropical Indian Ocean and Maritime Continent. This prediction barrier also exists in many forecast models of the S2S Prediction Project. Our hindcast experiments with different initial conditions indicate that the remarkable model errors over the Maritime Continent and subtropical western North Pacific may largely account for the prediction barrier.

Reinitiation of the Boreal Summer Intraseasonal Oscillation in the Tropical Indian Ocean*

2005 ◽  
Vol 18 (18) ◽  
pp. 3777-3795 ◽  
Author(s):  
Xian-An Jiang ◽  
Tim Li
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Intraseasonal Oscillation ◽  
Circulation Model ◽  
Equatorial Indian Ocean ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Temperature Advection

Abstract The characteristic features of the boreal summer intraseasonal oscillation (BSISO) during its reinitiation period are studied using NCEP–NCAR reanalysis. Based on these observations and with the aid of an anomalous atmospheric general circulation model (AGCM), a possible mechanism responsible for the BSISO reinitiation is elucidated. The western equatorial Indian Ocean along the eastern African coast tends to be a key region for the phase transition of the BSISO from an enhanced to suppressed convective phase, or vise versa. The major precursory feature associated with reinitiation of suppressed convection is found in the divergence and reduced specific humidity in the boundary layer. Numerical experiments indicate that the low-level divergence is caused by the cold horizontal temperature advection and associated adiabatic warming (descending motion) in situ. The summer mean state is found to be important for the cold horizontal temperature advection through the modulation of a Gill-type response to an intraseasonal oscillation (ISO) heating in the eastern equatorial Indian Ocean. The results in this study suggest a self-sustained paradigm in the Indian Ocean for the BSISO; that is, the BSISO could be a basinwide phenomenon instead of a global circumstance system as hypothesized for the boreal winter ISO (i.e., the Madden–Julian oscillation).

Inter-basin and Multi-time Scale Interactions in generating the 2019 Extreme Indian Ocean Dipole

2021 ◽  
pp. 1-39
Author(s):  
Lei Zhang ◽  
Weiqing Han ◽  
Zeng-Zhen Hu
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Intraseasonal Oscillation ◽  
Tropical Indian Ocean ◽  
Forecast Model ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Indian Ocean Dipole Event ◽  
Easterly Wind ◽  
Western Tropical Pacific

AbstractAn unprecedented extreme positive Indian Ocean Dipole event (pIOD) occurred in 2019, which has caused widespread disastrous impacts on countries bordering the Indian Ocean, including the East African floods and vast bushfires in Australia. Here we investigate the causes for the 2019 pIOD by analyzing multiple observational datasets and performing numerical model experiments. We find that the 2019 pIOD is triggered in May by easterly wind bursts over the tropical Indian Ocean associated with the dry phase of the boreal summer intraseasonal oscillation, and sustained by the local atmosphere-ocean interaction thereafter. During September-November, warm sea surface temperature anomalies (SSTA) in the central-western tropical Pacific further enhance the Indian Ocean’s easterly winds, bringing the pIOD to an extreme magnitude. The central-western tropical Pacific warm SSTA is strengthened by two consecutive Madden Julian Oscillation (MJO) events that originate from the tropical Indian Ocean. Our results highlight the important roles of cross-basin and cross-timescale interactions in generating extreme IOD events. The lack of accurate representation of these interactions may be the root for a short lead time in predicting this extreme pIOD with a state-of-the-art climate forecast model.

Cloud and radiative heating profiles associated with the boreal summer intraseasonal oscillation

2017 ◽  
Vol 50 (5-6) ◽  
pp. 1485-1494 ◽  
Author(s):  
Jinwon Kim ◽  
Duane E. Waliser ◽  
Gregory V. Cesana ◽  
Xianan Jiang ◽  
Tristan L’Ecuyer ◽  
...  
Keyword(s):  
Intraseasonal Oscillation ◽  
Radiative Heating ◽  
Boreal Summer ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Heating Profiles

scholarly journals Initiation of Boreal Summer Intraseasonal Oscillation: Dynamic Contribution by Potential Vorticity

2012 ◽  
Vol 140 (6) ◽  
pp. 1748-1760 ◽  
Author(s):  
Kyong-Hwan Seo ◽  
Eun-Ji Song
Keyword(s):  
Potential Vorticity ◽  
Intraseasonal Oscillation ◽  
Vertical Wind Shear ◽  
Boreal Summer ◽  
Dynamical Process ◽  
Initiation Mechanism ◽  
Middle Troposphere ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Low Level ◽  
The Tropics

Abstract Potential vorticity (PV) thinking conceptually connects the upper-level (upper troposphere in the extratropics and middle troposphere for the tropics) dynamical process to the lower-level process. Here, the initiation mechanism of the boreal summer intraseasonal oscillation (BSISO) in the tropics is investigated using PV thinking. The authors demonstrate that the midtropospheric PV anomaly produces a dynamical environment favorable for the BSISO initiation. Under seasonal easterly vertical wind shear, the PV anomaly enhances low-level convergence and upward motion at its western edge. Tropical PV forcing in the middle troposphere produces balanced mass and circulation fields that spread horizontally and vertically so that its effect can reach even the lowest troposphere. The downward influence of the midtropospheric PV forcing is one of the key aspects of the PV thinking. Direct piecewise PV inversions confirm that the anomalous lower-level zonal wind and its convergence necessary for the initiation of BSISO convection do not arise solely from the response to the lower-level PV forcing but from the summed contribution by PV forcing at all levels. About 50% of the low-level circulation variations result from PV forcing from 700 to 450 hPa, with the largest contribution from the 600–650-hPa PV anomalies for the convection initiation region over the western Indian Ocean. The current study is compared with and incorporated into the thermodynamic recharge process and the frictional moisture flux convergence mechanism for the BSISO initiation. This study is the first qualitative application of the PV thinking approach that reveals the BSISO dynamics.

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