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.

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).

The Role of Coupled Sea Surface Temperatures in the Simulation of the Tropical Intraseasonal Oscillation

2004 ◽  
Vol 17 (21) ◽  
pp. 4109-4134 ◽  
Author(s):  
Y. Zheng ◽  
D. E. Waliser ◽  
W. F. Stern ◽  
C. Jones
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Intraseasonal Oscillation ◽  
Circulation Model ◽  
Sea Surface ◽  
Boreal Summer ◽  
Phase Lag ◽  
Sea Surface Temperatures ◽  
Tropical Intraseasonal Oscillation ◽  
Sst Anomalies

Abstract This study compares the tropical intraseasonal oscillation (TISO) variability in the Geophysical Fluid Dynamics Laboratory (GFDL) coupled general circulation model (CGCM) and the stand-alone atmospheric general circulation model (AGCM). For the AGCM simulation, the sea surface temperatures (SSTs) were specified using those from the CGCM simulation. This was done so that any differences in the TISO that emerged from the two simulations could be attributed to the coupling process and not to a difference in the mean background state. The comparison focused on analysis of the rainfall, 200-mb velocity potential, and 850-mb zonal wind data from the two simulations, for both summer and winter periods, and included comparisons to analogous diagnostics using NCEP–NCAR reanalysis and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) rainfall data. The results of the analysis showed three principal differences in the TISO variability between the coupled and uncoupled simulations. The first was that the CGCM showed an improvement in the spatial variability associated with the TISO mode, particularly for boreal summer. Specifically, the AGCM exhibited almost no TISO variability in the Indian Ocean during boreal summer—a common shortcoming among AGCMs. The CGCM, on the other hand, did show a considerable enhancement in TISO variability in this region for this season. The second was that the wavenumber–frequency spectra of the AGCM exhibited an unrealistic peak in variability at low wavenumbers (1–3, depending on the variable) and about 3 cycles yr−1 (cpy). This unrealistic peak of variability was absent in the CGCM, which otherwise tended to show good agreement with the observations. The third difference was that the AGCM showed a less realistic phase lag between the TISO-related convection and SST anomalies. In particular, the CGCM exhibited a near-quadrature relation between precipitation and SST anomalies, which is consistent with observations, while the phase lag was reduced in the AGCM by about 1.5 pentads (∼1 week). The implications of the above results, including those for the notions of “perfect SST” and “two tier” experiments, are discussed, as are the caveats associated with the study's modeling framework and analysis.

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 Boreal summer intraseasonal oscillation in a superparameterized general circulation model: effects of air–sea coupling and ocean mean state

2020 ◽  
Vol 13 (11) ◽  
pp. 5191-5209
Author(s):  
Yingxia Gao ◽  
Nicholas P. Klingaman ◽  
Charlotte A. DeMott ◽  
Pang-Chi Hsu
Keyword(s):  
General Circulation ◽  
Intraseasonal Oscillation ◽  
Phase Relationship ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Boreal Summer ◽  
Coupled Models ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Taylor Diagram ◽  
Mean State

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.

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.

scholarly journals Variability of Tropical Cyclone Frequency Over the Western North Pacific in 2018–2020

2021 ◽  
Vol 3 ◽  
Author(s):  
Tomomichi Ogata ◽  
Yuya Baba
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Circulation Model ◽  
Atmospheric Variability ◽  
Convection Scheme ◽  
Planetary Scale ◽  
Ensemble Simulations ◽  
Potential Index

In this study, we examine the tropical cyclone (TC) activity over the western North Pacific (WNP) in 2018–2020 and its relationship with planetary scale convection and circulation anomalies, which play an important role for TC genesis. To determine the sea surface temperature (SST)-forced atmospheric variability, atmospheric general circulation model (AGCM) ensemble simulations are executed along with the observed SST. For AGCM experiments, we use two different convection schemes to examine uncertainty in convective parameterization and robustness of simulated atmospheric response. The observed TC activity and genesis potential demonstrated consistent features. In our AGCM ensemble simulations, the updated convection scheme improves the simulation ability of observed genesis potential as well as planetary scale convection and circulation features, e.g., in September–October–November (SON), a considerable increase in the genesis potential index over the WNP in SON 2018, WNP in SON 2019, and South China Sea (SCS) in SON 2020, which were not captured in the Emanuel scheme, have been simulated in the updated convection scheme.

Eastward-Propagating Intraseasonal Oscillation Represented by Chikira–Sugiyama Cumulus Parameterization. Part II: Understanding Moisture Variation under Weak Temperature Gradient Balance

2014 ◽  
Vol 71 (2) ◽  
pp. 615-639 ◽  
Author(s):  
Minoru Chikira
Keyword(s):  
Temperature Gradient ◽  
Vertical Velocity ◽  
General Circulation ◽  
Intraseasonal Oscillation ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Velocity Anomaly ◽  
Mature Phase ◽  
Moisture Variation ◽  
Heating Profile

Abstract The eastward-propagating intraseasonal oscillation represented by the Chikira–Sugiyama cumulus scheme in a general circulation model was investigated focusing on the variation of the free-tropospheric humidity. The net effect of the vertical advection and cloud process amplifies the positive moisture anomaly in the mature phase, supporting the moisture-mode theory. The horizontal advection causes the eastward propagation of the field. The variation of the moisture profile is accurately understood by using environmental vertical velocity outside cumuli. The velocity is regulated by a thermodynamic balance under a weak temperature gradient. A nondimensional parameter α plays an important role in the moisture variation, which characterizes the efficiency of moistening (drying) induced by external heating (cooling). In the middle and lower troposphere, the major moistening factor is the radiative warming anomaly, which induces the upward environmental vertical velocity anomaly. The reevaporation of the precipitation works as drying, since its cooling effect induces the downward environmental vertical velocity anomaly. Snow melting significantly cools and thereby dries the midtroposphere. The moistening of the midtroposphere is important for moistening the lower troposphere through the reduction of α. The efficiency of moistening depends on the heating profile, and congestus clouds play an important role in it. The heating profile, which maximizes the moistening of the free troposphere, is realized in the mature phase. The atmosphere is marginally unstable even in the mature phase, which is a favorable condition for the congestus clouds to occur.

Sign in / Sign up

Export Citation Format

Share Document