Extraordinary Persistence of Foehn Observed in the Hokuriku District of Japan in the 1999 Summer.

Abstract

An unusually prolonged foehn was observed at Toyama in the Hokuriku district, located on the coast of the Sea of Japan of central Japan, from 30 July to 3 August 1999. A 5-day foehn is extraordinarily persistent and was not observed during the 24-year period 1975-1998, which makes the 1999 summer quite exceptional. While an anticyclone east of Japan is intensified over the 5-day period, a combination of the anticyclone with a rapidly developing cyclone over southeastern Siberia and a typhoon migrating northward into the East China Sea induces a definite intensification of southerly geostrophic winds over central Japan, a favorable condition for the occurrence of unusually prolonged foehn.Observational and model results show that on a monthly mean basis, a noticeable east-west pressure gradient around Japan is present due to the prominence of the Pacific and Japan (PJ) teleconnection pattern in response to tropical convective heating, resulting in reinforcing southerly geostrophic winds across central Japan. Once large-scale circulation anomalies are initiated and sustained as a result of such an extratropical response, the development and movement of adjacent synoptic-scale disturbances are largely regulated by those anomalies. A combined effect of the excitation of the PJ pattern and associated synoptic-scale disturbances is crucial for the extraordinary persistence of foehn along the coast of the Sea of Japan. The PJ pattern that appeared in July 1999 has an unusual geographical location and configuration because enhanced cumulus convection over the warm pool region of the western North Pacific is significantly displaced about 20 westward and 2-3 northward, compared to the typical hot summer that Japan experiences. This displacement is presumably attributed to a similar shift of distinctive warm SST anomalies over the warm pool region.

On the Warming Events over Toyama Plain by Using NHRCM

“…The moist and dry adiabatic processes are attributed to strong transmountain winds, which are caused by mountain waves. Toyama Plain is located at the base of high mountains, where several foehn studies have been conducted (e.g., Arakawa et al 1982;Inaba et al 2002). This study reveals that the warming phenomena cannot depend on only the occurrence of foehn.…”

“…It is sometimes associated with rainfall in the windward mountains, sometimes beginning during the night. Several studies explain the warming events in relation to "foehn" (Arakawa et al 1982;Inaba et al 2002). However, few statistical studies address the warming mechanism.…”

On the Role of Typhoons in Generating PJ Teleconnection Patterns over the Western North Pacific in Late Summer

“…At the same time, a salient foehn often occurs along the coast of the Japan Sea. Once large-scale circulation anomalies related to PJ are initiated and sustained as a result of the extratropical response, on the other hand, the development and movement of adjacent synopticscale disturbances such as typhoons are significantly regulated by the PJ-related anomalies (Inaba et al 2002). Actually, the typhoons tend to migrate northnorthwestward to the south of Japan under the westward extention of the North Pacific High (see Fig.…”

Role of Large-Scale Circulation in Triggering Foehns in the Hokuriku District of Japan during Midsummer

“…These criteria are similar to those proposed by Inaba et al (2002), but the first and fourth criteria were modified in this study. Although Inaba et al adopted 35 C as the daily maximum temperature threshold, we lowered the threshold somewhat because their study focused specifically on severe foehns with the potential to seriously damage a variety of crops.…”

“…In the present study, using the criteria of Inaba et al (2002), we first extracted midsummer foehn events that occurred in Hokuriku district of Japan during the past three decades. Next, we conducted composite analyses of atmospheric variables with respect to tropical cyclone-induced and extratropical cyclone-induced foehns, and examined how the large-scale circulation contributes to the occurrence of foehns and whether there is a possible interaction between synoptic-scale disturbances and large-scale circulation.…”