scholarly journals Sensitivity of western north Pacific summertime tropical synoptic- scale disturbances to extratropical forcing – A regional climate model study

2021 ◽  
Author(s):  
Ying Lung Liu ◽  
Chi-Yung Tam ◽  
Andie Yee Man Au-Yeung
Keyword(s):  
Regional Climate Model ◽  
North Pacific ◽  
Western North Pacific ◽  
Climate Model ◽  
Regional Climate ◽  
Wave Activity ◽  
Synoptic Scale ◽  
Low Level ◽  
Zonal Wavenumber ◽  
Extratropical Forcing

Abstract The role of extratropical forcing on the summertime tropical synoptic-scale disturbances (TSDs) in the western north Pacific has been investigated, by conducting parallel integrations of the Regional Climate Model (RegCM). The suite of experiments consists of a control run (CTRL) with European Centre for Medium Range Forecasts (ECMWF) Reanalysis data as boundary conditions, and an experimental run (EXPT) with the same setting, except that signals with zonal wavenumber > 6 were suppressed at the northern boundary (located at 42°N) of the model domain. Comparison between CTRL and EXPT showed that, without extratropical forcing, there is weaker TSD activity in the June-to-August season, with reduced precipitation over the TSD pathway. Associated with suppressed TSD, southeastward-directed wave activity is also reduced, leading to less active mixed Rossby gravity (MRG) waves in the equatorial western Pacific area. Further analysis revealed that extratropical forcing and associated circulation changes can modulate the TSD wavetrain and its coherence structure, in relation to low-level vorticity in far western north Pacific. In CTRL, west of about 140°E, TSD-related circulation tends to be stronger; in EXPT, vorticity signals and vertical motions are found to be slightly more coherent in the more eastern portion of the TSD wavetrain. The latter enhanced coherency of TSD east of 140°E, from the EXPT simulations, might be due to changes in wave activity transport channelled by modulated upper-level mid-latitude westerlies in EXPT. Energetics indicate that changes in low-level background circulation itself can also influence TSD characteristics. Our results serve to quantify how extratropical forcing and related general circulation features influence western north Pacific summertime TSD activities. Implications on understanding the initiation of TSD, as well as their variability on longer time scales, are discussed.

scholarly journals Boreal Summer Synoptic-Scale Waves over the Western North Pacific in Multimodel Simulations

2016 ◽  
Vol 29 (12) ◽  
pp. 4487-4508 ◽  
Author(s):  
Haikun Zhao ◽  
Xianan Jiang ◽  
Liguang Wu
Keyword(s):  
Spatial Pattern ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
Climate Model ◽  
Climate Modeling ◽  
Active Role ◽  
General Circulation Models ◽  
Boreal Summer ◽  
Synoptic Scale

During boreal summer, vigorous synoptic-scale wave (SSW) activity, often evident as southeast–northwest-oriented wave trains, prevails over the western North Pacific (WNP). In spite of their active role for regional weather and climate, modeling studies on SSWs are rather limited. In this study, a comprehensive survey on climate model capability in representing the WNP SSWs is conducted by analyzing simulations from 27 recent general circulation models (GCMs). Results suggest that it is challenging for GCMs to realistically represent the observed SSWs. Only 2 models out of the 27 GCMs generally well simulate both the intensity and spatial pattern of the observed SSW mode. Plausible key processes for realistic simulations of SSW activity are further explored. It is illustrated that GCM skill in representing the spatial pattern of the SSW is highly correlated to its skill in simulating the summer mean patterns of the low-level convergence associated with the WNP monsoon trough and conversion from eddy available potential energy (EAPE) to eddy kinetic energy (EKE). Meanwhile, simulated SSW intensity is found to be significantly correlated to the amplitude of 850-hPa vorticity, divergence, and conversion from EAPE to EKE over the WNP. The observed modulations of SSW activity by the Madden–Julian oscillation are able to be captured in several model simulations.

Influence of cumulus convection schemes on winter North Pacific storm tracks in the regional climate model RegCM4.5

2019 ◽  
Vol 40 (2) ◽  
pp. 1294-1305 ◽  
Author(s):  
Minghao Yang ◽  
Yanke Tan ◽  
Xin Li ◽  
Xiong Chen ◽  
Chao Zhang ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
North Pacific ◽  
Climate Model ◽  
Regional Climate ◽  
Storm Tracks ◽  
Cumulus Convection ◽  
Convection Schemes

scholarly journals The effect of topography on east African rainfall based on regional climate model

MAUSAM ◽  
2021 ◽  
Vol 67 (2) ◽  
pp. 431-440
Author(s):  
BOB ALEX OGWANG ◽  
HAISHAN CHEN ◽  
L. I. XING
Keyword(s):  
Regional Climate Model ◽  
East Africa ◽  
Climate Model ◽  
Regional Climate ◽  
Research Unit ◽  
Theoretical Physics ◽  
East African ◽  
Maximum Rainfall ◽  
Low Level ◽  
The Mean

The effect of topography on June to August (JJA) rainfall over east Africa is investigated using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM4.0). Grell convection scheme with Fritsch-Chappell closure assumption is used. The control simulation is done with actual topography and sensitivity experiments are carried out with topography reduced to 75%, 25% and to zero. The model output was evaluated against Climate Research Unit (CRU) dataset, gridded at 0.5 degree resolution and ERA-interim datasets, gridded at 0.75 degree resolution. Results show that the mean JJA rainfall significantly reduces over the region when topography elevation is reduced. Based on the model, when the topography over the selected region (KTU) is reduced to 25%, the mean JJA rainfall over east Africa is reduced by roughly half. The maximum rainfall reduction is however observed around the region over which topography is reduced. The reduction in topography resulted into an anomalous moisture divergence over the region at low level (850 hPa). Divergence at low level results in vertical shrinking which suppresses convection due to subsidence. The strength of moisture transport and the zonal wind speed at 850hpa increased with decrease in topography, which may be responsible for the observed shift in moisture convergence zone from western Kenya to northern Uganda. The findings from this study would provide insight into the effect of topography on the east African climate and call for more detailed investigative research, particularly in the region. The results may motivate researchers and modeling centers to further improve on the performance of the model over the region.

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