Global climatology of synoptically‐forced downslope winds

Abstract

Downslope winds are mesoscale mountain meteorological phenomena that contribute to localized temperature extremes and contribute to numerous societal and environmental impacts. Whereas previous studies have examined local downslope winds, no known efforts have attempted to identify and characterize meso-to synoptic-scale downslope winds globally using a common approach. We use a conceptual model for downslope winds that employs cross-barrier wind speed, near-mountain top static stability, and downward vertical velocity using thresholds guided by a chronology of local downslope winds and meta-analysis of downslope wind case studies. This approach was applied to ERA-5 reanalysis during 1979-2018 to develop a global atlas of downslope winds. Downslope winds adhered to distinct geographic and seasonal patterns, with peak occurrence in north-south oriented midlatitude mountains in the winter hemisphere associated with strong cross-mountain winds and stability. However, we identify numerous locations from the tropics to the high-latitudes where downslope winds occur at least 60 days a year as a byproduct of the general circulation and local-scale circulation interacting with topography. The four-decade-long data set is also used to examine statistical relationships between the occurrence of downslope winds and El Niño-Southern Oscillation as well as long-term trends in downslope wind occurrence.

Spatio-Temporal Distribution of Deep Convection Observed along the Trans-Mexican Volcanic Belt

“…Along the TMVB, values between 600-1200 mm/year are shown. The area at the west of the Eastern Sierra Madre mountain range displays the minimum values (∼300 mm/year), coinciding with an area affected by the Föhn effect and the dryer portion of the domain [34]. In summary, the relationship between precipitation-terrain-land-use and vegetation is clear.…”

“…The high cloudiness over all of the Gulf of Mexico allows the identification of the possibly important role of sea breeze [52] and the position of the mountains (perpendicular to moisture advection) for the eastern portion of the Neotropical sub-region. Cold fronts and Föhn effects [34,55] influence the Nearctic sub-region; i.e., drylands in the north portion of the domain. The analysis of the behavior of convective events allowed the identification of similarities across the Transition sub-region.…”

A Shorter, Sharper Rainy Season Amplifies California Wildfire Risk

“…across southern California most common around December or January ( [Abatzoglou et al, 2021;Guzman-Morales et al, 2016]; Fig 1a). The onset of the rainy season from north to south across California exhibits a similar seasonality, beginning 1-2 months earlier in the north than across the south.…”

“…Autumn also heralds the arrival of “offshore wind” season, characterized by occasional bursts of land‐to‐sea winds (locally termed “Santa Ana” winds in southern California and “Diablo” winds near the San Francisco Bay Area) that represent a conspicuous reversal of the typically moist onshore (west‐to‐east) flow across coastal California. Offshore winds tend to occur during autumn and early winter, rather than summer (Abatzoglou et al., 2021), as they are primarily driven by strong surface pressure gradients arising from early season cold air masses over the Great Basin (Guzman‐Morales et al., 2016). These sometimes violent winds can result in dramatic drying and warming of the airmass as they descend the western slopes of California's mountains from the interior desert plateau toward the Pacific Ocean.…”

A Surrogate Model for Rapidly Assessing the Size of a Wildfire over Time

“…The fuel load was based on a Tasmania fire history data set allowing the time since the fire to be calculated and populated using Olson fuel load curves [54][55][56]. Our current study covered only the westerly winds as they are the most common winds in Tasmania [57,58]. The configuration and input files can be made available from the authors upon request.…”