Improved boreal summer intraseasonal oscillation simulations over the Indian Ocean by modifying moist parameterizations in climate models

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.

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

Climate Dynamics ◽

10.1007/s00382-015-2698-7 ◽

2015 ◽

Vol 46 (7-8) ◽

pp. 2213-2229 ◽

Cited By ~ 13

Author(s):

Sun-Seon Lee ◽

Bin Wang

Keyword(s):

Indian Ocean ◽

Intraseasonal Oscillation ◽

Western Pacific ◽

Boreal Summer ◽

Boreal Summer Intraseasonal Oscillation

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The Boreal Summer Intraseasonal Oscillation Simulated in the NCEP Climate Forecast System: The Effect of Sea Surface Temperature

Monthly Weather Review ◽

10.1175/mwr3369.1 ◽

2007 ◽

Vol 135 (5) ◽

pp. 1807-1827 ◽

Cited By ~ 90

Author(s):

Kyong-Hwan Seo ◽

Jae-Kyung E. Schemm ◽

Wanqiu Wang ◽

Arun Kumar

Keyword(s):

Indian Ocean ◽

Wind Shear ◽

Intraseasonal Oscillation ◽

Vertical Wind Shear ◽

Sea Surface ◽

Boreal Summer ◽

Forecast System ◽

Climate Forecast System ◽

Northward Propagation ◽

The Indian Ocean

Abstract Observational evidence has indicated the important role of the interaction of the atmosphere with the sea surface in the development and maintenance of the tropical intraseasonal oscillation (ISO). However, improvements in ISO simulations with fully coupled atmosphere–ocean general circulation models are limited and model dependent. This study further examines the effect of air–sea coupling and the basic-state sea surface temperature (SST) associated with the boreal summer intraseasonal oscillation (BSISO) in a 21-yr free run with the recently developed NCEP coupled Climate Forecast System (CFS) model. For this, the CFS run is compared with an Atmospheric Model Intercomparison Project–type long-term simulation forced by prescribed SST in the NCEP Global Forecast System (GFS) model and flux-corrected version of CFS (referred to as CFSA). The GFS run simulates significantly unorganized BSISO convection anomalies, which exhibit an erroneous standing oscillation. The CFS run with interactive air–sea coupling has limited improvements, including the generation of intraseasonal SST variation preceding the convection anomaly by ∼10 days. However, this simulation still does not show the observed continuous northward propagation over the Indian Ocean due to a cold model bias. The CFSA run removes the cold bias in the Indian Ocean and the simulation of the development and propagation of BSISO anomalies are significantly improved. Enhanced and suppressed convection anomalies exhibit the observed quadrupole-like configuration, and phase relationships between precipitation and surface dynamic and thermodynamic variables for the northward propagation are shown to be coherent and consistent with the observations. It is shown that the surface meridional moisture convergence is an important factor for the northward propagation of the BSISO. On the other hand, both the GFS and CFS runs do not realistically simulate an eastward-propagating equatorial mode. The CFSA run produces a more realistic eastward-propagation mode only over the Indian Ocean and Java Sea due to the improved mean state in SST, low-level winds, and vertical wind shear. Reasons for the failure of farther eastward propagation into the west Pacific in CFSA are discussed. This study reconfirms the significance of air–sea interactions. More importantly, however, the results suggest that in order for the influence of the coupled air–sea interaction to be properly communicated, the mean state SST in the coupled model should be reasonably simulated. This is because the basic-state SST itself acts to sustain BSISO convection and it makes the large-scale dynamical environment (i.e., easterly vertical wind shear or low-level westerly zonal wind) more favorable for the propagation of the moist Rossby–Kelvin wave packet.

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Boreal summer intraseasonal oscillation in a superparameterized GCM: effects of air-sea coupling and ocean mean state

10.5194/gmd-2020-63 ◽

2020 ◽

Author(s):

Yingxia Gao ◽

Nicholas P. Klingaman ◽

Charlotte A. DeMott ◽

Pang-Chi Hsu

Keyword(s):

Intraseasonal Oscillation ◽

Phase Relationship ◽

Atmospheric Model ◽

Boreal Summer ◽

Coupled Models ◽

Boreal Summer Intraseasonal Oscillation ◽

Taylor Diagram ◽

The Indian Ocean ◽

The Mean ◽

Mean State

Abstract. The effect of air-sea coupling on the simulated boreal summer intraseasonal oscillation (BSISO) is examined using atmosphere—ocean-mixed-layer coupled (SPCAM3-KPP) and uncoupled configurations of the Super-Parameterized (SP) Community Atmospheric Model, version 3 (SPCAM3). The coupled configuration is constrained to either the 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 in the latter. 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. Constraining SPCAM3-KPP to the SPCCSM3 mean state reduces the overestimated BSISO variability, but also weakens BSISO propagation. Using the SPCCSM3 mean state also introduces a one-month delay to the BSISO seasonal cycle compared to SPCAM3-KPP with the observed ocean mean state, which matches well with the reanalysis. The phase relationship between intraseasonal rainfall and sea surface temperature (SST) is captured by all coupled models, but with a shorter delay between suppressed convection and warm SST relative to the reanalysis. Prescribing the 31-day smoothed SSTs from the SPCAM3-KPP simulations in SPCAM3 worsens the overestimated BSISO variance. This suggests that air-sea coupling improves the amplitude of the simulated BSISO. Based on a Taylor diagram, SPCCSM3 mean state SST biases and air-sea coupling both lead to higher simulated BSISO fidelity, largely due to their ability to suppress the overestimated subtropical BSISO variance.

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

Journal of Climate ◽

10.1175/jcli3516.1 ◽

2005 ◽

Vol 18 (18) ◽

pp. 3777-3795 ◽

Cited By ~ 75

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).

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Diagnosing ISO Forecast from GloSea5 Using Dynamic-Oriented ISO Theory

Atmosphere ◽

10.3390/atmos12010114 ◽

2021 ◽

Vol 12 (1) ◽

pp. 114

Author(s):

Young-Min Yang ◽

Taehyoun Shim ◽

Ja-Yeon Moon ◽

Ki-Young Kim ◽

Yu-Kyung Hyun

Keyword(s):

Indian Ocean ◽

Deep Convection ◽

Intraseasonal Oscillation ◽

Lower Troposphere ◽

Moisture Convergence ◽

Lower Atmosphere ◽

Vertical Shear ◽

Boreal Summer ◽

Kelvin Wave ◽

The Indian Ocean

A Madden–Jillian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) are important climate variabilities, which affect a forecast of weather and climate. In this study, the MJO and the BSISO hindcasts from the Global Seasonal Forecast System, version 5 (GS5) were diagnosed using dynamic-oriented theories. We additionally analyzed the GS5 climatological run to identify whether the weakness of the GS5 hindcast results from the model physics or initialization processes. The GS5 hindcast captures three-dimensional dynamics and thermodynamics structure of MJO eastward propagation well in the Indian Ocean. The model produces the boundary layer (BL) moisture convergence anomalies to the east of the MJO deep precipitation with easterly anomalies associated with the Kelvin wave. The enhanced BL moisture convergence increases upward transport of moisture from the surface to the lower troposphere, inducing the moist lower troposphere and the positive convective instability by destabilization of the lower atmosphere and, thus, generating the next convection to the east of MJO deep convection and promoting MJO eastward propagation. However, the signal for eastward propagation is relatively weak in the Maritime Continent (MC) and the Western Pacific (WP). To improve the MJO eastward propagation in the MC and WP, improved heating induced by shallow (or congestus) clouds interacting with enhanced BL dynamics may be required. On the other hand, the GS5 hindcast reproduces the BSISO northward propagation reasonably well in the Indian Ocean, which is attributed to positive vorticity anomalies induced by strong vertical shear.

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

Journal of Climate ◽

10.1175/jcli-d-20-0760.1 ◽

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.

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Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-11973-2018 ◽

2018 ◽

Vol 18 (16) ◽

pp. 11973-11990 ◽

Cited By ~ 5

Author(s):

Alina Fiehn ◽

Birgit Quack ◽

Irene Stemmler ◽

Franziska Ziska ◽

Kirstin Krüger

Keyword(s):

Indian Ocean ◽

Summer Monsoon ◽

Tropical Indian Ocean ◽

Boreal Summer ◽

Boreal Winter ◽

The West ◽

West Pacific ◽

Mixing Ratios ◽

The Indian Ocean ◽

Oceanic Emissions

Abstract. Oceanic very short-lived substances (VSLSs), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Indian summer monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly averaged and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean reasonably well. Using monthly resolved emissions, the main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric injection in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric injection of bromoform is in the same range whether using monthly averaged or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in the highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary by up to 50 % between using monthly averaged and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depend on the seasonality and spatial distribution of the VSLS emissions.

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

Climate Dynamics ◽

10.1007/s00382-017-3700-3 ◽

2017 ◽

Vol 50 (5-6) ◽

pp. 1485-1494 ◽

Cited By ~ 4

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

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

Monthly Weather Review ◽

10.1175/mwr-d-11-00105.1 ◽

2012 ◽

Vol 140 (6) ◽

pp. 1748-1760 ◽

Cited By ~ 10

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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