Organisation of orographic convection by mountain waves above Cross Fell and Wales

Worthington, R. M.

doi:10.1002/wea.2475

Cited by 4 publications

(2 citation statements)

References 16 publications

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“…Complex terrain plays important roles in the initiation and organization of convection (e.g., Rotunno and Houze, 2007;Wulfmeyer et al, 2008;Houze, 2012;Kain et al, 2013;Trier et al, 2015;Worthington, 2015;Zhao, 2015). For strong airflows encountering complex terrain, dynamic forcing can be strong enough to cause convective initiation (CI).…”

Section: Introductionmentioning

confidence: 99%

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

2016

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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.

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Section: Introductionmentioning

confidence: 99%

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

2016

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“…Since this topography is "plateau-like", it is missed by our ridgefinding algorithm (not shown). It is also possible that these waves were excited by orographically linked convection, which was observed by, e.g., Worthington (2002) and Worthington (2015). These processes are currently not accounted for in the MWM.…”

Section: Residual Temperature As Compared To Ecmwf Operational Analys...mentioning

confidence: 99%

A mountain ridge model for quantifying oblique mountain wave propagation and distribution

Rhode¹,

Preusse²,

Ern³

et al. 2023

Atmos. Chem. Phys.

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Abstract. Following the current understanding of gravity waves (GWs) and especially mountain waves (MWs), they have a high potential for horizontal propagation from their source. This horizontal propagation and therefore the transport of energy is usually not well represented in MW parameterizations of numerical weather prediction and general circulation models. In this study, we present a mountain wave model (MWM) for the quantification of horizontal propagation of orographic gravity waves. This model determines MW source locations from topography data and estimates MW parameters from a fit of idealized Gaussian-shaped mountains to the elevation. Propagation and refraction of these MWs in the atmosphere are modeled using the Gravity-wave Regional Or Global Ray Tracer (GROGRAT). Ray tracing of each MW individually allows for an estimation of momentum transport due to both vertical and horizontal propagation. The MWM is a capable tool for the analysis of MW propagation and global MW activity and can support the understanding of observations and improvement of MW parameterizations in GCMs. This study presents the model itself and gives validations of MW-induced temperature perturbations to ECMWF Integrated Forecast System (IFS) numerical weather prediction data and estimations of GW momentum flux (GWMF) compared to HIgh Resolution Dynamics Limb Sounder (HIRDLS) satellite observations. The MWM is capable of reproducing the general features and amplitudes of both of these data sets and, in addition, is used to explain some observational features by investigating MW parameters along their trajectories.

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The Meteorology of the Tathra Bushfire

Wilke

Kepert

Tory

2022

Weather and Forecasting

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The meteorological conditions over the South Coast of New South Wales, Australia, are investigated on 18 March 2018, the day of the Tathra bushfire. We present an analysis of the event based on high-resolution (100-m and 400-m grid-length) simulations with the Bureau of Meteorology’s ACCESS numerical weather prediction system and available observations. Through this analysis we find several mesoscale features that likely contributed to the extreme fire event. Key among these was the development of horizontal convective rolls, which emanated from inland and aided the fire’s spread toward Tathra. The rolls interacted with the terrain to produce complex regions of strongly ascending and descending air, likely accelerating the lofting of firebrands and potentially contributing to the significant lee slope fire behaviour observed. Mountain waves, specifically trapped lee waves, occurred on the day and are hypothesised to have contributed to the strong winds around the time the fire began. These waves may also have influenced conditions during the period of peak fire activity when the fire spotted across the Bega River and impacted Tathra. Finally, the passage of the cold front through the fireground was complex, with frontal regression observed at a nearby station and likely also through Tathra. We postulate that interactions between the strong prefrontal flow and the initially weak change resulted in highly variable and dangerous fire weather across the fireground for a significant period after the change initially occurred.

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Organisation of orographic convection by mountain waves above Cross Fell and Wales

Cited by 4 publications

References 16 publications

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

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

A mountain ridge model for quantifying oblique mountain wave propagation and distribution

The Meteorology of the Tathra Bushfire

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