scholarly journals Improving the Northeast Asian Monsoon Simulation: Remote Impact of Tropical Heating Bias Correction

2009 ◽  
Vol 137 (2) ◽  
pp. 797-803 ◽  
Author(s):  
Kyong-Hee An ◽  
Chi-Yung Tam ◽  
Chung-Kyu Park
Keyword(s):  
General Circulation ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Western Pacific ◽  
Boreal Summer ◽  
Simple Method ◽  
Northeast Asian ◽  
The Western Pacific

Abstract This study investigates the role of model tropical diabatic heating error on the boreal summer northeast Asian monsoon (NEAM) simulation given by a general circulation model (GCM). A numerical experiment is carried out in which the GCM diabatic heating is adjusted toward more realistic values in the tropics. It is found that the seasonal mean NEAM circulation and rainfall are improved in the GCM. This can be attributed to the reduced positive heating bias in the western Pacific Ocean around 10°–15°N in the model, which in turn leads to better-simulated low-level southerly winds over eastern Asia and more moisture supply to the NEAM region. The GCM’s ability in capturing the year-to-year variation of NEAM rainfall is also markedly improved in the experiment. These results show that the diabatic heating error over the western Pacific can be one reason for poor NEAM simulations in GCMs. The authors also suggest a simple method to reduce model heating biases that can be readily applied to dynamical seasonal prediction systems.

The Dynamics of Quasi-Stationary Atmospheric Rivers and Their Implications for Monsoon Onset

2021 ◽  
Author(s):  
Hung-I Lee ◽  
Jonathan L. Mitchell
Keyword(s):  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Monsoon Onset ◽  
Western Pacific ◽  
Eastern Pacific ◽  
The Tibetan Plateau ◽  
Atmospheric Rivers ◽  
Upper Level ◽  
The Western Pacific

AbstractA global Hovmöller diagram of column water vapor (CWV) at 30°N from daily ERA-Interim reanalysis data shows seasonally migrating North Pacific/Atlantic quasi-stationary atmospheric rivers (QSARs) located in the Eastern Pacific/Atlantic in winter and propagate to the Western Pacific/Atlantic in summer. Simplified general circulation model (GCM) experiments produce QSAR-like features if the boundary conditions include (1) the sea surface temperature contrast from the tropical warm pool-cold tongue and (2) topographic contrast similar to the Tibetan plateau. Simulated QSARs form downstream of topographic contrast during winter and coincide with it in summer. Two models of baroclinic instability demonstrate that QSARs coincide with the location where the most unstable mode phase speed equals that of the upper-level zonal winds. A consistent interpretation is that the waves become quasi-stationary at this location and break. The location of quasistationarity migrates from the Eastern Pacific/Atlantic in the winter, when upper-level winds are strong and extended over the basin, to the Western Pacific/Atlantic when winds are weak and contracted. Low-level wind convergence and moist static energy coincide with QSARs, and since the former two are essential ingredients to monsoon formation, this implies an important role for QSARs in monsoon onset. This connection opens a new window into the dynamics of subtropical monsoon extensions.

scholarly journals Precipitation in Boreal Summer Simulated by a GCM with Two Convective Parameterization Schemes: Implications of the Intraseasonal Oscillation for Dynamic Seasonal Prediction

2010 ◽  
Vol 23 (10) ◽  
pp. 2801-2816 ◽  
Author(s):  
Suhee Park ◽  
Song-You Hong ◽  
Young-Hwa Byun
Keyword(s):  
General Circulation ◽  
Intraseasonal Oscillation ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Boreal Summer ◽  
Convection Scheme ◽  
Seasonal Predictability ◽  
Model Framework ◽  
Wave Characteristics ◽  
Skill Scores

Abstract In this paper, the intraseasonal oscillation (ISO) and its possible link to dynamical seasonal predictability within a general circulation model framework is investigated. Two experiments with different convection scheme algorithms, namely, the simplified Arakawa–Schubert (SAS) and the relaxed Arakawa–Schubert (RAS) convection algorithms, were designed to compare seasonal simulations from 1979 to 2002 on a seasonal model intercomparison project (SMIP)-type simulation test bed. Furthermore, the wave characteristics (wave intensity, period, and propagation) of the simulated ISO signal provided by the model with two different convection schemes for extended boreal summers from 1997 to 2004 were compared to the observational ISO signal. Precipitation in the boreal summer was fairly well simulated by the model irrespective of the convection scheme used, but the RAS run outperformed the SAS run with respect to tabulated skill scores. Decomposition of the interannual variability of boreal summer precipitation based on observations and model results demonstrates that the seasonal predictability of precipitation is dominated by the intraseasonal component over the warm pool area and the SST-forced signal over the equatorial Pacific Ocean, implying that the seasonal mean anomalies are more predictable under active ISO conditions as well as strong ENSO conditions. Comparison of the ISO simulations with the observations revealed that the main features, such as the intensity of precipitation variance in the intraseasonal time scale and the evolution of propagating ISOs, were reproduced fairly well by the model; however, the wave characteristics associated with the ISO signals were better captured by the experiment with the RAS scheme than the SAS scheme. This study further suggests that accurate simulation of the ISO can improve the seasonal predictability of dynamical seasonal prediction systems.

Simulation of the Southern Oscillation in an atmospheric general circulation model

1989 ◽  
Vol 329 (1604) ◽  
pp. 179-188 ◽  
Keyword(s):  
General Circulation Model ◽  
Wind Stress ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Circulation Model ◽  
Western Pacific ◽  
Atmospheric General Circulation ◽  
The Western Pacific

An atmospheric general circulation model (GCM) was forced with the observed near-global sea surface temperature (SST) pattern for the period January 1970-December 1985. Its response over the Pacific Ocean is compared with Tahiti and Darwin station sea-level pressure and wind stress analyses obtained from Florida State University. The time-dependent SST clearly induces in the model run a Southern Oscillation that is apparent in the time series of all considered variables. The phase of the GCM Southern Oscillation is as observed but its low-frequency variance is too low and the spatial pattern is confined mainly to the western Pacific. The model is successful in reproducing the warm events of 1972—73 and 1982—83 and the cold event 1970—71, but fails with the cold events 1973-74 and 1975-76 and with the warm event 1976-77. Because the GCM is used as the atmospheric component in a coupled model, the response of an equatorial oceanic primitive equation model to both the modelled and observed wind stress is examined. The ocean model responds in essentially the same way to forcing with the observed wind stress and to forcing that corresponds to the first two low-frequency empirical orthogonal functions (EOFS) of the wind variations. These first two EOFS describe a regular eastward propagation of the so signal from the western Pacific to the central Pacific within about one year. The ocean model’s response to the modelled wind stress is too weak. It is similar to the response to the first observed wind stress EOF only. That is, the observed Southern Oscillation appears as a sequence of propagating patterns but the simulated Southern Oscillation appears as one standing pattern. The nature of the deviation of simulated wind stress from observations is further analysed by means of model output statistics.

scholarly journals A Source of AGCM Bias in Simulating the Western Pacific Subtropical High: Different Sensitivities to the Two Types of ENSO

2015 ◽  
Vol 143 (6) ◽  
pp. 2348-2362 ◽  
Author(s):  
Houk Paek ◽  
Jin-Yi Yu ◽  
Jyh-Wen Hwu ◽  
Mong-Ming Lu ◽  
Tao Gao
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Western Pacific Subtropical High ◽  
Western Pacific ◽  
Subtropical High ◽  
Boreal Summer ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
The Western Pacific

Abstract This study reveals a possible cause of model bias in simulating the western Pacific subtropical high (WPSH) variability via an examination of an Atmospheric Model Intercomparison Project (AMIP) simulation produced by the atmospheric general circulation model (AGCM) developed at Taiwan’s Central Weather Bureau (CWB). During boreal summer, the model overestimates the quasi-biennial (2–3 yr) band of WPSH variability but underestimates the low-frequency (3–5 yr) band of variability. The overestimation of the quasi-biennial WPSH sensitivity is found to be due to the model’s stronger sensitivity to the central Pacific El Niño–Southern Oscillation (CP ENSO) that has a leading periodicity in the quasi-biennial band. The model underestimates the low-frequency WPSH variability because of its weaker sensitivity to the eastern Pacific (EP) ENSO that has a leading periodicity in the 3–5-yr band. These different model sensitivities are shown to be related to the relative strengths of the mean Hadley and Walker circulations simulated in the model. An overly strong Hadley circulation causes the CWB AGCM to be overly sensitive to the CP ENSO, while an overly weak Walker circulation results in a weak sensitivity to the EP ENSO. The relative strengths of the simulated mean Hadley and Walker circulations are critical to a realistic simulation of the summer WPSH variability in AGCMs. This conclusion is further supported using AMIP simulations produced by three other AGCMs, including the CanAM4, GISS-E2-R, and IPSL-CM5A-MR models.

scholarly journals Predictability of the California Niño/Niña*

2015 ◽  
Vol 28 (18) ◽  
pp. 7237-7249 ◽  
Author(s):  
Takeshi Doi ◽  
Chaoxia Yuan ◽  
Swadhin K. Behera ◽  
Toshio Yamagata
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Regional Climate ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
La Niña ◽  
Boreal Summer ◽  
La Nina ◽  
Basin Scale

Abstract Predictability of a recently discovered regional coupled climate mode called the California Niño (Niña) off Baja California and California is explored using a seasonal prediction system based on the Scale Interaction Experiment-Frontier, version 1 (SINTEX-F1) coupled ocean–atmosphere general circulation model. Because of the skillful prediction of basin-scale El Niño (La Niña), the California Niño (Niña) that co-occurs with El Niño (La Niña) with a peak in boreal winter is found to be predictable at least a couple of seasons ahead. On the other hand, the regional coupled phenomenon peaking in boreal summer without co-occurrence with El Niño (La Niña) is difficult to predict. The difficulty in predicting such an intrinsic regional climate phenomenon may be due to model deficiency in resolving the regional air–sea–land positive feedback processes. The model may also underestimate coastal Kelvin waves with a small offshore scale, which may play an important role in the generation of the California Niño/Niña. It may be improved by increasing horizontal resolution of the ocean component of the coupled model. The present study may provide a guideline to improve seasonal prediction of regional climate modes for important industrial as well as social applications.

Impact of Subdaily Air–Sea Interaction on Simulating Intraseasonal Oscillations over the Tropical Asian Monsoon Region

2015 ◽  
Vol 28 (3) ◽  
pp. 1057-1073 ◽  
Author(s):  
Wenting Hu ◽  
Anmin Duan ◽  
Guoxiong Wu
Keyword(s):  
General Circulation ◽  
Asian Monsoon ◽  
Intraseasonal Oscillation ◽  
Phase Relationship ◽  
Coupled Model ◽  
Circulation Model ◽  
Boreal Summer ◽  
Lag Phase ◽  
Asian Monsoon Region ◽  
Coupling Frequency

Abstract The off-equatorial boreal summer intraseasonal oscillation (ISO) is closely linked to the onset, active, and break phases of the tropical Asian monsoon, but the accurate simulation of the eastward-propagating low-frequency ISO by current models remains a challenge. In this study, an atmospheric general circulation model (AGCM)–ocean mixed layer coupled model with high (10 min) coupling frequency (DC_10m) shows improved skill in simulating the ISO signal in terms of period, intensity, and propagation direction, compared with the coupled runs with low (1 and 12 h) coupling frequency and a stand-alone AGCM driven by the daily sea surface temperature (SST) fields. In particular, only the DC_10m is able to recreate the observed lead–lag phase relationship between SST (SST tendency) and precipitation at intraseasonal time scales, indicating that the ISO signal is closely linked to the subdaily air–sea interaction. During the ISO life cycle, air–sea interaction reduces the SST underlying the convection via wind–evaporation and cloud–radiation feedbacks, as well as wind-induced oceanic mixing, which in turn restrains convection. However, to the east of the convection, the heat-induced atmospheric Gill-type response leads to downward motion and a reduced surface westerly background flow because of the easterly anomalies. The resultant decreased oceanic mixing, together with the increased shortwave flux, tends to warm the SST and subsequently trigger convection. Therefore, the eastward-propagating ISO may result from an asymmetric east–west change in SST induced mainly by multiscale air–sea interactions.

scholarly journals Impacts of the Tropical Pacific–Indian Ocean Associated Mode on Madden–Julian Oscillation over the Maritime Continent in Boreal Winter

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1049
Author(s):  
Xin Li ◽  
Ming Yin ◽  
Xiong Chen ◽  
Minghao Yang ◽  
Fei Xia ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
The Western Pacific ◽  
The Tropical Pacific

Based on the observation and reanalysis data, the relationship between the Madden–Julian Oscillation (MJO) over the Maritime Continent (MC) and the tropical Pacific–Indian Ocean associated mode was analyzed. The results showed that the MJO over the MC region (95°–150° E, 10° S–10° N) (referred to as the MC–MJO) possesses prominent interannual and interdecadal variations and seasonally “phase-locked” features. MC–MJO is strongest in the boreal winter and weakest in the boreal summer. Winter MC–MJO kinetic energy variation has significant relationships with the El Niño–Southern Oscillation (ENSO) in winter and the Indian Ocean Dipole (IOD) in autumn, but it correlates better with the tropical Pacific–Indian Ocean associated mode (PIOAM). The correlation coefficient between the winter MC–MJO kinetic energy index and the autumn PIOAM index is as high as −0.5. This means that when the positive (negative) autumn PIOAM anomaly strengthens, the MJO kinetic energy over the winter MC region weakens (strengthens). However, the correlation between the MC–MJO convection and PIOAM in winter is significantly weaker. The propagation of MJO over the Maritime Continent differs significantly in the contrast phases of PIOAM. During the positive phase of the PIOAM, the eastward propagation of the winter MJO kinetic energy always fails to move across the MC region and cannot enter the western Pacific. However, during the negative phase of the PIOAM, the anomalies of MJO kinetic energy over the MC is not significantly weakened, and MJO can propagate farther eastward and enter the western Pacific. It should be noted that MJO convection is more likely to extend to the western Pacific in the positive phases of PIOAM than in the negative phases. This is significant different with the propagation of the MJO kinetic energy.

Role of Abnormally Enhanced MJO over the Western Pacific in the Formation and Subseasonal Predictability of the Record-Breaking Northeast Asian Heatwave in the Summer of 2018

2020 ◽  
Vol 33 (8) ◽  
pp. 3333-3349 ◽  
Author(s):  
Pang-Chi Hsu ◽  
Yitian Qian ◽  
Yu Liu ◽  
Hiroyuki Murakami ◽  
Yingxia Gao
Keyword(s):  
Real Time ◽  
Time Scale ◽  
Wave Train ◽  
Northeast Asia ◽  
Warm Pool ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
Pacific Warm Pool ◽  
Northeast Asian ◽  
The Western Pacific

AbstractIn the summer of 2018, Northeast Asia experienced a heatwave event that broke the existing high-temperature records in several locations in Japan, the Korean Peninsula, and northeastern China. At the same time, an unusually strong Madden–Julian oscillation (MJO) was observed to stay over the western Pacific warm pool. Based on reanalysis diagnosis, numerical experiments, and assessments of real-time forecast data from two subseasonal-to-seasonal (S2S) models, we discovered the importance of the western Pacific MJO in the generation of this heatwave event, as well as its predictability at the subseasonal time scale. During the prolonged extreme heat period (11 July–14 August), a high pressure anomaly with variability at the intraseasonal (30–90 days) time scale appeared over Northeast Asia, causing persistent adiabatic heating and clear skies in this region. As shown in the composites of MJO-related convection and circulation anomalies, the occurrence of this 30–90-day high anomaly over Northeast Asia was linked with an anomalous wave train induced by tropical heating associated with the western tropical Pacific MJO. The impact of the MJO on the heatwave was further confirmed by sensitivity experiments with a coupled GCM. As the western Pacific MJO-related components were removed by nudging prognostic variables over the tropics toward their annual cycle and longer time scales (>90 days) in the coupled GCM, the anomalous wave train along the East Asian coast disappeared and the surface air temperature in Northeast Asia lowered. The MJO over the western Pacific warm pool also influenced the predictability of the extratropical heatwave. Our assessments of two S2S models’ real-time forecasts suggest that the extremity of this Northeast Asian heatwave can be better predicted 1–4 weeks in advance if the enhancement of MJO convection over the western Pacific warm pool is predicted well.

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