TY - JOUR
T1 - Mountain waves, downslope jets, and boundary layer interactions during the Sundowner Winds Experiment (SWEX) - IOP2
AU - Seto, Daisuke
AU - Carvalho, Leila M.V.
AU - Duine, Gert Jan
AU - De Wekker, Stephan
AU - Wang, Zhien
AU - Jones, Charles
AU - Emmitt, David
AU - Greco, Steve
AU - Fernando, Harindra J.S.
AU - Modjeski, Griffin
AU - Clements, Craig B.
AU - de Orla-Barile, Marian
AU - Thompson, Callum
AU - Liu, Zhixing
AU - Bucholtz, Anthony
AU - Brown, William
AU - Oncley, Steven
AU - Vӧmel, Holger
N1 - Publisher Copyright:
© 2026 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/
PY - 2026/7
Y1 - 2026/7
N2 - Sundowner winds are downslope windstorms occurring along the lee of the Santa Ynez Mountains (SYM) in Santa Barbara County, California, and are recognized as the region's most critical fire-weather condition. The Sundowner Winds Experiment (SWEX) provided a rare opportunity to integrate airborne and ground-based observations to examine interactions between continental and marine atmospheric boundary layers (ABLs), and their modulation by mountain waves. This study focuses on an eastern Sundowner event (IOP2) observed on the evening of 5–6 April 2022, driven by strong mean sea-level pressure gradients. Multi-platform observations revealed sharp elevated temperature inversions near the SYM and San Rafael Mountains (SRM), with mountain waves propagating across these layers. The free atmosphere was extremely dry, and strong horizontal winds were confined near the inversion height. On the lee side of the SYM, a large-amplitude lee wave evolved into a hydraulic jump, followed by wave breaking and a downslope jet. Despite strong offshore forcing, a shallow sea breeze developed over eastern SYM foothills, while nighttime marine boundary layer (MBL) intrusion—capped by a strong inversion—played a key role in the Sundowner cycle. Mountain waves strongly influenced the timing and intensity of the Sundowner event, with descending waves and rotor circulations producing reversed flows and enhanced surface winds. A cyclonic atmospheric eddy that formed in the eastern Santa Barbara Channel at night further stratified the MBL, decoupling it from the downslope jet. WRF simulations at 1-km grid spacing underestimated ridgetop and lee slope winds and overestimated winds at hoothill and coastal sites.
AB - Sundowner winds are downslope windstorms occurring along the lee of the Santa Ynez Mountains (SYM) in Santa Barbara County, California, and are recognized as the region's most critical fire-weather condition. The Sundowner Winds Experiment (SWEX) provided a rare opportunity to integrate airborne and ground-based observations to examine interactions between continental and marine atmospheric boundary layers (ABLs), and their modulation by mountain waves. This study focuses on an eastern Sundowner event (IOP2) observed on the evening of 5–6 April 2022, driven by strong mean sea-level pressure gradients. Multi-platform observations revealed sharp elevated temperature inversions near the SYM and San Rafael Mountains (SRM), with mountain waves propagating across these layers. The free atmosphere was extremely dry, and strong horizontal winds were confined near the inversion height. On the lee side of the SYM, a large-amplitude lee wave evolved into a hydraulic jump, followed by wave breaking and a downslope jet. Despite strong offshore forcing, a shallow sea breeze developed over eastern SYM foothills, while nighttime marine boundary layer (MBL) intrusion—capped by a strong inversion—played a key role in the Sundowner cycle. Mountain waves strongly influenced the timing and intensity of the Sundowner event, with descending waves and rotor circulations producing reversed flows and enhanced surface winds. A cyclonic atmospheric eddy that formed in the eastern Santa Barbara Channel at night further stratified the MBL, decoupling it from the downslope jet. WRF simulations at 1-km grid spacing underestimated ridgetop and lee slope winds and overestimated winds at hoothill and coastal sites.
KW - Aircraft observations
KW - Boundary layer
KW - Coastal meteorology
KW - Downslope winds
KW - Lidar observations
KW - Mountain waves
UR - https://www.scopus.com/pages/publications/105034619732
U2 - 10.1016/j.atmosres.2026.108920
DO - 10.1016/j.atmosres.2026.108920
M3 - Article
AN - SCOPUS:105034619732
SN - 0169-8095
VL - 337
JO - Atmospheric Research
JF - Atmospheric Research
M1 - 108920
ER -