Editing IPCC:AR6/WGI/Chapter-10 (section)

===== 10.3.3.4.2 Mountain wind systems =====

<div id="h4-9-siblings" class="h4-siblings"></div>

Mountain slope and valley winds are localized thermally generated diurnal circulations that have a strong influence on temperature and precipitation patterns in mountain regions. During the day, heating of mountain slopes induces upslope winds; during the night this circulation reverses. This phenomenon is not realistically represented by global models and coarse-resolution RCMs. RCM simulations at 4 km resolution showed good skill in simulating the diurnal cycle of temperature and wind on days of weak synoptic forcing in the Rocky Mountains ( [[#Letcher--2017|Letcher and Minder, 2017]] ) as well as in simulating the mountain-plain wind circulation over the Tianshan mountains in central Asia ( [[#Cai--2019|Cai et al., 2019]] ), while in the Alps, a 1 km resolution has been required ( [[#Zängl--2004|Zängl, 2004]] ).

Föhn winds are synoptically-driven winds across a mountain range that are warm and dry due to adiabatic warming in the downwind side. In an RCM study for the Japanese Alps, [[#Ishizaki--2009|Ishizaki and Takayabu (2009)]] found that at least 10 km resolution was required to realistically simulate the basic characteristics of Föhn events.

Synoptically-forced winds may be channelled and accelerated in long valleys. For instance, the Tramontana, Mistral and Bora are northerly winds blowing down-valley from central France and the Balkans into the Mediterranean ( [[#Flaounas--2013|Flaounas et al., 2013]] ). In winter, these winds may cause severe cold air outbreaks along the coast. [[#Flaounas--2013|Flaounas et al. (2013)]] have shown that a GCM with a horizontal resolution of roughly 3.75° longitude/1.875° latitude (roughly 400 km × 200 km depending on latitude) is unable to reproduce these winds because of the coarse representation of orography. Fifty-kilometre RCM simulations did not realistically represent the Mistral ( [[#Obermann--2018|Obermann et al., 2018]] ) and Bora winds ( [[#Belušić--2018|Belušić et al., 2018]] ), but simulations at 12 km added substantial value. Similarly, [[#Cholette--2015|Cholette et al. (2015)]] found that a 30 km RCM resolution was not sufficient to adequately simulate the channelling of winds in the St Lawrence River Valley in eastern Canada, whereas a 10 km resolution was.

There is ''high confidence'' that climate models with resolutions of around 10 km or finer are necessary for realistically simulating mountain wind systems such as slope and valley winds and the channelling of winds in valleys.

<div id="10.3.3.4.3" class="h4-container"></div>

<span id="coastal-winds-and-lake-effects"></span>