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

Chen

et al. 2021

Journal of Climate

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The reproducibility of climatology and the midwinter suppression of cold season North Pacific storm track (NPST) in historical runs of 18 CMIP6 models is evaluated against the NCEP reanalysis data. The results show that the position of the climatological peak area of 850 hPa meridional eddy heat flux (v′t′850) is well captured by these models. The spatial patterns of climatological v′t′850 are basically consistent with the NCEP reanalysis. Generally, NorESM2-LM and CESM2-WACCM present a relatively strong capability to reproduce the climatological amplitude of v′t′850 with lower RMSE than the other models. Compared with CMIP5 models, the inter-model spread of v′t′850 climatology among the CMIP6 models is smaller, and their multi-model ensemble is closer to the NCEP reanalysis. The geographical distribution in more than half of the selected models is further south and east. For the subseasonal variability of v′t′850, nearly half of the models exhibit a double-peak structure. In contrast, the apparent midwinter suppression in the NPST represented by the 250 hPa filtered meridional wind variance (v′v′250) is reproduced by all the selected models.In addition, the present study investigates the possible reasons for simulation biases regarding climatological NPST amplitude. It is found that a higher model horizontal resolution significantly intensifies the climatological v′v′250. There is a significant in-phase relationship between climatological v′t′250 and the intensity of the East Asian winter monsoon (EAWM). However, the climatological v′t′850 is not sensitive to the model grid spacing. Additionally, the climatological low-tropospheric atmospheric baroclinicity is uncorrelated with climatological v′v′250. The stronger climatological baroclinic energy conversion is associated with the stronger climatological v′t′850.

Section: Methodsmentioning

confidence: 99%

The Climatology and the Midwinter Suppression of the Cold Season North Pacific Storm Track in CMIP6 Models

Chen

et al. 2021

Journal of Climate

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“…To quantitatively describe the strength and meridional movement of WNPST, the storm track strength index (STSI) and meridional movement index (MMI) used in our research are the same as those used by Yang et al. (2020), which can be expressed as:

STSI = {140%true \sum}_{1}^{N} {WNPST}_{amp} \cos φ / N

MMI = {140%true \sum}_{1}^{N} {WNPST}_{lat} \cos φ / N

where

N

denotes the number of grid points on which the strengths exceed the median of the WNPST strength of all grid points within a domain (25°–65°N, 130°E−120°W), and

{WNPST}_{amp}

and

{WNPST}_{lat}

denote the amplitude and latitude at the grid point. The threshold is set each winter and applied to all grid points, and the main body of the WNPST can be dynamically captured in each calculation.…”

Section: Methodsmentioning

confidence: 99%

Section: The Strength Index and Meridional Movement Index Of The Wnpstmentioning

confidence: 99%

Are the Different Eddy Metrics Quantifying the Winter North Pacific Storm Track Consistent With Each Other?

et al. 2021

JGR Atmospheres

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symbiotic relationship between the transient eddy embedded in storm tracks and planetary-scale flow (Cai & Mak, 1990). Data and Methods DataThe daily atmospheric data used in the present study, including sea level pressure, horizontal winds, air temperature and geopotential height, are provided by the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) global atmospheric reanalysis datasets

“…These four eddy indicators are widely used in previous studies (e.g., Blackmon, 1976; Blackmon et al., 1977; Chang et al., 2002, 2012; Hoskins & Hodges, 2019; Jhun & Lee, 2004; Lee et al., 2010; Nakamura et al., 2002; Yang et al., 2020b) and represent the surface, lower‐tropospheric, middle‐tropospheric and upper‐tropospheric storm tracks, respectively. However, the second leading modes of slp′ and v ′ t ′850 exhibit a zonal dipole, while h ′500 and v ′ v ′300 only have a leading mode with a meridional dipole (figure not shown), which indicates that the zonal (meridional) displacement is more pronounced in surface and lower‐tropospheric storm tracks (middle‐tropospheric and upper‐tropospheric storm tracks).…”

Section: The Statistical Relationship Between the Eawm And Wnpst Zonamentioning

confidence: 99%

Association of the Zonal Migration of North Pacific Storm Track With the East Asian Monsoon in Boreal Wintertime

et al. 2021

JGR Atmospheres

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The change in atmospheric circulation in the midlatitudes is manifested as a conspicuous synoptic-scale disturbance, which is associated with the formation, evolution, and dissipation of daily weather systems. Located in areas where cyclones, anticyclones, and baroclinic waves occur frequently (Penny et al., 2013), the storm track refers to the region where the maximum variance of synoptic-scale (2.5-6 days) disturbance occurs (Blackmon, 1976; Blackmon et al., 1977) and indicates the synoptic-scale transient wave itself, which is called the "baroclinic waveguide" (Wallace et al., 1988). The storm track redistributes heat, moisture, and angular momentum (Mbengue & Schneider, 2018), helping to maintain the global temperature distribution and the basic characteristics of atmospheric circulation, as well as playing an important role in modulating extreme weather events in the midlatitudes (