Convective initiation by topographically induced convergence forcing over the Dabie Mountains on 24 June 2010

Abstract

The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local data assimilation. A primary convergence line is found over the ridge of the Dabie Mountains, and along the ridge line several locally enhanced convergence centers preferentially initiate convection. Three processes responsible for creating the overall convergence pattern are identified. First, thermally-driven upslope winds induce convergence zones over the main mountain peaks along the ridge, which are shifted slightly downwind in location by the moderate low-level easterly flow found on the north side of a Mei-yu front. Second, flows around the main mountain peaks along the ridge create further convergence on the lee side of the peaks. Third, upslope winds develop along the roughly north-south oriented valleys on both sides of the ridge due to thermal and dynamic channeling effects, and create additional convergence between the peaks along the ridge. The superposition of the above convergence features creates the primary convergence line along the ridge line of the Dabie Mountains. Locally enhanced convergence centers on the primary line cause the initiation of the first convection cells along the ridge. These conclusions are supported by two sensitivity experiments in which the environmental wind (dynamic forcing) or radiative and land surface thermal forcing are removed, respectively. Overall, the thermal forcing effects are stronger than dynamic forcing given the relatively weak environmental flow.

The Importance of Soil‐Type Contrast in Modulating August Precipitation Distribution Near the Edwards Plateau and Balcones Escarpment in Texas

“…Mountains have been reported to affect precipitation in many places around the world through the mountains' thermal effect or orographic forcing effect (e.g., Bao & Zhang, 2013;Carbone & Tuttle, 2008;Gao et al, 1981;He & Zhang, 2010;Liu et al, 2009;Sun & Zhang, 2012;Tripoli & Cotton, 1989b;Wang et al, 2016;Wolyn & Mckee, 1994;Zhang et al, 2014). On a clear summer afternoon, because of absorption of strong shortwave radiation, elevated terrain acts as a heat source, warming the near-surface air over the higher terrain as compared to adjacent, low-lying areas and producing a baroclinicity.…”

“…As summarized previously (e.g., Fernando et al, 2015;, the dynamic effects of mountainous terrain can cause different atmospheric processes, including barrier winds Lee & Xue, 2013;McCauley & Sturman, 1999;Parish, 1982;Schwerdtfeger, 1979;Xu, 1990), flow around and over mountains (Chen & Feng, 2001;Hu & Liu, 2005;Jeglum et al, 2017;Malkus, 1955;Pierrehumbert & Wyman, 1985;Smith, 1982;Takane et al, 2017;Yang & Chen, 2008), wave motions (Armi & Mayr, 2011;Brown et al, 2003;Grubisic et al, 2008;Jackson et al, 2013;Reinecke & Durran, 2009;Serafin et al, 2017;Smith, 2004), wakes (Epifanio & Rotunno, 2005), gap winds (Hitzl et al, 2014;Pan & Smith, 1999;Wang et al, 2016;Whiteman & Doran, 1993), and flow separation (Sheridan et al, 2007;Vosper et al, 2006), to name a few examples. Dynamic effects generated by barriers to atmospheric flow have been shown to play important roles in development of precipitation (Chen et al, 2013;Dettinger et al, 2004;Lee & Xue, 2013;Medina et al, 2005;Pedgley, 1970;Rotunno & Ferretti, 2001).…”

“…Dynamic effects generated by barriers to atmospheric flow have been shown to play important roles in development of precipitation (Chen et al, ; Dettinger et al, ; Houze & Medina, ; Lee & Xue, ; Medina et al, ; Pedgley, ; Rotunno & Ferretti, ). In Wang et al (), several effects, including thermal upslope flows, lee‐side convergence between around‐mountain flows, and up‐valley channeling flows, worked together in determining the preferred locations of convective initiation over the Dabie Mountains.…”

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“…Those models are referred to as convection‐permitting or convection‐allowing models showing better performance compared to coarser‐resolution models employing convective parameterization. In general, there have been climatological studies on modeling of convective precipitation (Bukovsky & Karoly, ; Gao et al, ; Li et al, ; Ratna et al, ; Schwartz et al, ; Sun et al, , ) and studies focusing on individual storms leading to severe weather events, that is, case studies (Barthlotta et al, ; Chan et al, ; Coniglio et al, ; Mcmillen & Steenburgh, ; Pieri et al, ; Stratman et al, ; Wang et al, ). A comprehensive review on convection‐permitting climate modeling was presented by Prein et al ().…”

Simulation and Analysis of the Initiation of a Squall Line within a Meiyu Frontal System in East China

“…The model resolution, initial condition, and initial forecast time can lead to such errors, but the propagation of the cold outflow associated with the earlier rainfall systems is believed to be the direct cause for this case. Moreover, such forecast errors can also be found in Wang and Xue [19] and Wang et al [42]. As the aim of this study is to examine the mesoscale structures and associated physical processes responsible for the CIs, further analyses based on the simulated results in CTRL have relatively higher reliability.…”