scholarly journals Assessment of the Ability of CMIP6 GCMS to Simulate the Boreal Summer Intraseasonal Oscillation Over Southeast Asia

2021 ◽  
Vol 3 ◽  
Author(s):  
Abayomi A. Abatan ◽  
Matthew Collins ◽  
Mukand S. Babel ◽  
Dibesh Khadka ◽  
Yenushi K. De Silva
Keyword(s):  
Southeast Asia ◽  
Asian Summer Monsoon ◽  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Study Region ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Good Ability ◽  
Wide Range ◽  
Static Energy

The boreal summer intraseasonal oscillation (BSISO) plays an important role in the intraseasonal variability of a wide range of weather and climate phenomena across the region modulated by the Asian summer monsoon system. This study evaluates the strengths and weaknesses of 19 Coupled Model Intercomparison Project Phase 6 (CMIP6) models to reproduce the basic characteristics of BSISO. The models' rainfall and largescale climates are evaluated against GPCP and ERA5 reanalysis datasets. All models exhibit intraseasonal variance of 30–60-day bandpass-filtered rainfall and convection anomalies but with diverse magnitude when compared with observations. The CMIP6 models capture the structure of the eastward/northward propagating BSISO at wavenumbers 1 and 2 but struggle with the intensity and location of the convection signal. Nevertheless, the models show a good ability to simulate the power spectrum and coherence squared of the principal components of the combined empirical orthogonal function (CEOF) and can capture the distinction between the CEOF modes and red noise. Also, the result shows that some CMIP6 models can capture the coherent intraseasonal propagating features of the BSISO as indicated by the Hovmöller diagram. The contribution of latent static energy to the relationship between the moist static energy and intraseasonal rainfall over Southeast Asia is also simulated by the selected models, albeit the signals are weak. Taking together, some of the CMIP6 models can represent the summertime climate and intraseasonal variability over the study region, and can also simulate the propagating features of BSISO, but biases still exist.

Impact of the Boreal Summer Intraseasonal Oscillation on the Diurnal Cycle of Precipitation near and over the Island of Luzon

2020 ◽  
Vol 148 (5) ◽  
pp. 1805-1827
Author(s):  
Kyle Chudler ◽  
Weixin Xu ◽  
Steven A. Rutledge
Keyword(s):  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Vertical Wind Shear ◽  
The Philippines ◽  
Heat Fluxes ◽  
Boreal Summer ◽  
Diurnal Variability ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Precipitation Estimates ◽  
Monsoon Winds

Abstract During the boreal summer, satellite-based precipitation estimates indicate a distinct maximum in rainfall off the west coast of the island of Luzon in the Philippines. Also occurring during the summer months is the boreal summer intraseasonal oscillation (BSISO), a main driver of intraseasonal variability in the region. This study investigates the diurnal variability of convective intensity, morphology, and precipitation coverage offshore and over the island of Luzon. The results are then composited by BSISO activity. Results of this study indicate that offshore precipitation is markedly increased during active BSISO phases, when strong low-level southwesterly monsoon winds bring increased moisture and enhanced convergence upwind of the island’s high terrain. A key finding of this work is the existence of an afternoon maximum in convection over Luzon even during active BSISO phases, when solar heating and instability are apparently reduced due to enhanced cloud cover. This result is important, as previous studies have shown in other areas of the tropics afternoon convection over landmasses is a key component to offshore precipitation. Although offshore precipitation is maximized in the evening hours during active phases, results indicate that precipitation frequently occurs over the ocean around the clock (both as organized systems and isolated, shallow showers), possibly owing to an increase in sensible and latent heat fluxes, vertical wind shear, and convergence of the monsoon flow with land features.

scholarly journals Subseasonal Variability Associated with Asian Summer Monsoon Simulated by 14 IPCC AR4 Coupled GCMs

2008 ◽  
Vol 21 (18) ◽  
pp. 4541-4567 ◽  
Author(s):  
Jia-Lin Lin ◽  
Klaus M. Weickman ◽  
George N. Kiladis ◽  
Brian E. Mapes ◽  
Siegfried D. Schubert ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Climate Simulation ◽  
Boreal Summer ◽  
Subseasonal Variability ◽  
Wide Range ◽  
Northward Propagation ◽  
Asian Summer

Abstract This study evaluates the subseasonal variability associated with the Asian summer monsoon in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The authors focus on the three major components of Asian summer monsoon: the Indian summer monsoon (ISM), the western North Pacific summer monsoon (WNPSM), and the East Asian summer monsoon (EASM), together with the two dominant subseasonal modes: the eastward- and northward-propagating boreal summer intraseasonal oscillation (BSIO) and the westward-propagating 12–24-day mode. The results show that current state-of-the-art GCMs still have difficulties and display a wide range of skill in simulating the subseasonal variability associated with Asian summer monsoon. During boreal summer (May–October), most of the models produce reasonable seasonal-mean precipitation over the ISM region, but excessive precipitation over the WNPSM region and insufficient precipitation over the EASM region. In other words, models concentrate their rain too close to the equator in the western Pacific. Most of the models simulate overly weak total subseasonal (2–128 day) variance, as well as too little variance for BSIO and the 12–24-day mode. Only 4–5 models produce spectral peaks in the BSIO and 12–24-day frequency bands; instead, most of the models display too red a spectrum, that is, an overly strong persistence of precipitation. For the seven models with three-dimensional data available, five reproduce the preconditioning of moisture in BSIO but often with a too late starting time, and only three simulate the phase lead of low-level convergence. Interestingly, although models often have difficulty in simulating the eastward propagation of BSIO, they tend to simulate well the northward propagation of BSIO, together with the westward propagation of the 12–24-day mode. The northward propagation in these models is thus not simply a NW–SE-tilted tail protruding off of an eastward-moving deep-tropical intraseasonal oscillation.

scholarly journals Atmospheric Rivers over the Indo-Pacific and its Associations with Boreal Summer Intraseasonal Oscillation

2021 ◽  
pp. 1-46
Author(s):  
Xiaojun Guo ◽  
Ning Zhao ◽  
Kazuyoshi Kikuchi ◽  
Tomoe Nasuno ◽  
Masuo Nakano ◽  
...  
Keyword(s):  
North Pacific ◽  
Moisture Transport ◽  
Western North Pacific ◽  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Reanalysis Dataset ◽  
Convective Envelope ◽  
Atmospheric Rivers ◽  
Boreal Summer Intraseasonal Oscillation

AbstractRecent works have revealed that the wintertime atmospheric river (AR) activity is closely related to the 30–60-day tropical intraseasonal variability, yet it remains unclear whether summertime AR activity is also significantly influenced by the intraseasonal variability, often referred to as the boreal summer intraseasonal oscillation (BSISO). Diagnosing the 40-year (1979–2018) ERA5 reanalysis dataset, the present study examines the climatological features of ARs over the Indo-Pacific region during June to October and its associations with the BSISO. Results suggest that the western North Pacific Subtropical High (WNPSH) provides a favorable circulation background for the summertime AR activity, which conveys the moisture from the tropics to midlatitude North Pacific along its periphery. Our analysis reveals that the BSISO has substantial impacts on the occurrence and distribution of ARs. More ARs are found over the western North Pacific (WNP) when the BSISO convective envelope propagates northward to the subtropical regions, while fewer ARs can be seen when convection is suppressed there. Specifically, in phases 7–8, the active BSISO convection over the Philippine Sea induces a low-pressure anomaly and the corresponding anomalous cyclonic circulation, leading to the enhanced poleward moisture transport and more frequent AR activity over the WNP. Moreover, the WNP ARs tend to be longer and have larger sizes during these two phases. It is also found that more frequent occurrence of tropical cyclones in phases 7–8 can significantly enhance the moisture transport and AR occurrence over the WNP.

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.

Sign in / Sign up

Export Citation Format

Share Document