A Novel Temperature Anomaly Source Diagnostic: Method and Application to the 2021 Heatwave in the Pacific Northwest
Lukas Papritz, Matthias Röthlisberger
Abstract
Abstract Quantitative methods to pinpoint the origin of atmospheric temperature anomalies ( T ′) associated with heatwaves are pivotal for the construction of physically plausible synoptic storylines of heatwave formation and their evaluation in models. Here, we combine a Lagrangian T ′ decomposition with concepts from moisture tracking techniques to identify where and when the principal physical processes generate T ′ and to attribute these sources to synoptic weather systems. Applying this framework to near‐surface and free‐tropospheric T ′ associated with the record‐shattering 2021 heatwave in the Pacific Northwest shows that ascending, diabatic air streams in North Pacific cyclones contribute more than 50% of free‐tropospheric T ′, whereas near‐surface T ′ is mainly produced by local subsidence and diabatic heating with only marginal upstream contributions. Since free‐tropospheric T ′ facilitates near‐surface accumulation of locally produced T ′ by rendering the atmosphere stable to moist convection, our findings corroborate the notion of top‐down induced heatwave formation fueled by upstream diabatic processes.