Japan's south foehn on the Toyama Plain: Dynamical or thermodynamical mechanisms?

Kusaka, Hiroyuki; Nishi, Akifumi; Kakinuma, Ai; Doan, Quang‐Van; Onodera, Taira; Endo, S.

doi:10.1002/joc.7133

Cited by 15 publications

(28 citation statements)

References 56 publications

(109 reference statements)

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“…Hence, the analysis corroborates the distinction of a "Swiss foehn" and an "Austrian foehn" as proposed by Steinacker (2006), whereas the former more closely follows the thermodynamic foehn theory. Similarly, Kusaka et al (2021) investigated a multitude of south foehn events in Japan. According to their backward trajectory analysis, adiabatic compression (isentropic drawdown) governs the foehn air warming for most cases.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamics and airstreams of a south foehn event in different Alpine valleys

Jansing

Sprenger

2022

Quart J Royal Meteoro Soc

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Foehn flows are associated with a characteristic warming of the respective air in lee‐side valleys. Recent studies about the physical mechanisms question the traditional thermodynamic foehn theory, pointing out the potential role of adiabatic descent and other diabatic processes, besides upstream latent heating in clouds, for the warming. This study applies a kilometre‐scale simulation together with online trajectories and a Lagrangian heat budget to investigate the foehn air warming for an intense, long‐lasting Alpine south foehn period in November 2016. Thereby, the focus lies on the attribution of the warming to adiabatic descent and the different diabatic processes in six foehn valleys, as well as the linkage of the warming processes to different airstreams. Overall, adiabatic warming emerges as the most important process for 57% of all air parcels arriving in the foehn valleys. However, upstream latent heating in clouds is the dominant mechanism for a considerable amount of air parcels (35%). The heat budget analysis reveals a clear transition along the Alps from west to east, whereat diabatic warming constitutes the driving mechanism for western valleys during the central phase of the event, and adiabatic warming dominates the foehn air warming in eastern valleys. The foehn trajectories can be separated into different air‐stream categories according to their diabatic temperature change. Air parcels experiencing strong diabatic heating are transported in an easterly barrier jet in the Po Valley before crossing the Alpine crest. Air parcels experiencing diabatic cooling, in contrast, are advected quasi‐horizontally from the south towards the Alpine crest prior to their descent. The relative strength of the different airstreams therefore determines the dominating warming process. These findings strongly point to the combined importance of adiabatic and diabatic warming mechanisms, which co‐occur with varying relative contributions, depending on the valley and time period of the event.

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Section: Introductionmentioning

confidence: 99%

“…Similarly, Kusaka et al . (2021) investigated a multitude of south foehn events in Japan. According to their backward trajectory analysis, adiabatic compression (isentropic drawdown) governs the foehn air warming for most cases.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics and airstreams of a south foehn event in different Alpine valleys

Jansing

Sprenger

2022

Quart J Royal Meteoro Soc

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“…Chokai, foehn could occur in the white head area. According to Kusaka et al (2021), in the Hokuriku region, foehn caused by a typhoon is common in summer including the heading period.…”

Section: Resultsmentioning

confidence: 99%

“…Foehn has been observed worldwide, including the European Alps (Hoinka, 1985; Mayr et al, 2007; Seibert, 1990; Würsch & Sprenger, 2015), the Rocky Mountains (Baren, 1967; Durran, 1986; Klemp & Lilly, 1975), Antarctica (Elvidge et al, 2015; Elvidge et al, 2016; Elvidge & Renfrew, 2016), the Andes (Norte, 2015; Puliafito et al, 2015; Seluchi et al, 2003) and the South Island of New Zealand (McGowan et al, 2002; McGowan & Sturman, 1996). In the Hokuriku region of Japan, foehn is observed when cyclones or typhoons pass the Sea of Japan (Arakawa et al, 1982; Koyanagi & Kusaka, 2020; Kusaka et al, 2021; Nishi et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation study of the effects of foehn winds on white head incidences in Yamagata Prefecture, Japan

Asano

Kusaka

2021

Meteorological Applications

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Numerous studies have elucidated that white heads and chalky rice are caused by hot, dry and strong winds at night. However, these studies have only used synoptic weather charts and near‐surface observation data to confirm the role of foehn in white head occurrences. This study used a high‐resolution three‐dimensional numerical weather prediction model to show that strong foehn effects induced a significant number of white heads in rice in Yamagata Prefecture, Japan. The model accurately predicted and represented the location and timing of the observed white heads, occurring only in a limited area (87.1 ha) on the southwest side of Mt. Chokai during the nighttime. Specifically, the simulated nocturnal FTP (transpiration forcing) continuously exceeded 30 at that location. This high FTP was caused by high temperature (>24°C), strong wind speed (>8 m s−1) and low humidity (<65%) caused by the strong foehn winds descending over the southwest slope of the mountain. In the other areas, FTP did not exceed 30 because either wind speed, water vapour deficit or both were insufficiently high.

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“…Air parcel trajectories are frequently used in foehn research to assess the origin and thermodynamic evolution of the foehn air in various regions of the world (e.g. Elvidge and Renfrew, 2016;Kusaka et al, 2021), as well as the Alps (e.g. Würsch and Sprenger, 2015;Miltenberger et al, 2016;Saigger and Gohm, 2022).…”

Section: Trajectory Calculationsmentioning

confidence: 99%

Classification of Alpine south foehn based on 5 years of kilometre-scale analysis data

Jansing¹,

Papritz²,

Dürr³

et al. 2022

Weather Clim. Dynam.

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Abstract. It has long been recognized that a rich variety of Alpine south-foehn flavours exist that are related to varying flow conditions above crest level, the presence and intensity of orographic precipitation on the Alpine south side, and the Po Valley stratification. This study presents a systematic 5-year climatology of different foehn types. The classification relies on 2329 foehn hours, which are diagnosed using a station-based foehn index for Altdorf in the Swiss Reuss Valley. Operational analyses at 1 km horizontal resolution are employed to classify foehn hours with a decision tree that is based on foehn forecasting experience. Mean wind direction and speed in a circle with 100 km radius centred around Altdorf are considered to differentiate between three main foehn types (deep foehn, shallow foehn, gegenstrom foehn). In addition, upstream precipitation and its extent beyond the Alpine crest are used to distinguish three deep-foehn subtypes (dry foehn, moist foehn, dimmer foehn). The main foehn types differ distinctively in the synoptic conditions over the Alps. During deep foehn, pronounced southwesterlies ahead of an upper-level trough induce upstream orographic precipitation. Shallow foehn, in turn, is associated with cross-Alpine temperature differences that provoke a gap flow. The gegenstrom-foehn type is also restricted to major gaps, but a strong westerly flow prevails above crest level. The deep-foehn subtypes primarily differ in terms of the upper-level trough. While a weaker trough and the influence of an upper-level ridge over the Mediterranean inhibit precipitation (dry foehn), a deeper trough which is closer to the Alps induces stronger crest-level winds and intense precipitation on the Alpine south side (dimmer foehn). The different foehn types are found to strongly affect the local characteristics at Altdorf, which are investigated using station measurements. Backward trajectories from Altdorf are calculated for each of the foehn hours and used to define three clusters of air parcels depending upon their upstream thermodynamic evolution. Trajectories in cluster 1 are diabatically heated and transported within a low-level easterly barrier jet in the Po Valley prior to their ascent to crest level. They constitute the main precipitating airstream and, hence, are of key importance for moist foehn and dimmer foehn. Cluster-2 and cluster-3 trajectories are subject to weak diabatic heating or even diabatic cooling. They originate from southerly to southwesterly regions and from either slightly below or above crest level. Accordingly, these air parcels are associated with little to no precipitation, and as such, they take a key role for dry foehn, shallow foehn and gegenstrom foehn. Furthermore, these three foehn types feature a pronounced stable layer over the Po Valley, which, to some extent, inhibits air parcels to ascend from lower levels. In summary, the study introduces a systematic classification of south foehn using state-of-the-art data sets. It concludes by setting the new classification into a historic context and revisiting the rich body of literature with respect to different Alpine south-foehn types. In particular, analogies to and discrepancies with the existing conceptual models of “Swiss foehn” and “Austrian foehn” are discussed.

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Japan's south foehn on the Toyama Plain: Dynamical or thermodynamical mechanisms?

Cited by 15 publications

References 56 publications

Thermodynamics and airstreams of a south foehn event in different Alpine valleys

Thermodynamics and airstreams of a south foehn event in different Alpine valleys

Numerical simulation study of the effects of foehn winds on white head incidences in Yamagata Prefecture, Japan

Classification of Alpine south foehn based on 5 years of kilometre-scale analysis data

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