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Hiroaki Kondo - One of the best experts on this subject based on the ideXlab platform.
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Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area
Journal of Applied Meteorology and Climatology, 2017Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki Kondo, Jin Katagi, Osamu Nagafuchi, Koyomi Nakazawa, Naoki Kaneyasu, Yoshihiro MiyakamiAbstract:AbstractA Foehn wind is an important factor in the occurrence of many extreme high-temperature events in geographically complex regions. In this study, the authors verified the hypothesis that a Foehnlike wind contributes to high temperatures at the end of the leeward (eastward) area using three difference approaches: field experiments, numerical experiments, and statistical analyses. According to the hypothesis, a Foehnlike wind has the features of the sum of a traditional Foehn effect with adiabatic heating, plus dry-diabatic heating from the ground surface along the fetch of the wind. Field experiments conducted at seven observational points on Nobi Plain, Japan, where a mesoscale westerly wind blew, revealed that the westerly wind clearly had the features of a traditional Foehn effect in the western part of the Nobi Plain. In addition to field experiments, a simplified estimate using a simple mixed-layer model demonstrated that the wind was further heated by dry-diabatic heating (sensible heat supply)...
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investigation of a recent extreme high temperature event in the tokyo metropolitan area using numerical simulations the potential role of a hybrid Foehn wind
Quarterly Journal of the Royal Meteorological Society, 2015Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki KondoAbstract:A record-breaking high temperature of 39.8 °C for June in Japan was observed at 1420 Japan Standard Time on 24 June 2011 60 km northwest of central Tokyo. In this extreme high-temperature (EHT) event, surface air temperatures above 37.0 °C were recorded in and around Kumagaya, an area just north of the convergence line between westerly winds from the Chubu Mountains and a southwesterly wind from the Pacific Ocean. To determine the mechanism of this EHT event, we applied various analyses using the Weather Research and Forecasting (WRF) model and observational data. According to the heat budget analysis obtained from the WRF model, during the morning most of the sensible heat supply to the mixed layer came from the net heat input, due to surface sensible heat transported by subgrid-scale turbulent diffusion. However, most of the net heat input came from advective heat transport after noon, when the westerly wind penetrated the EHT area. This westerly wind, according to backward trajectory, Lagrangian energy budget and Eulerian forward tracer analyses, arose from a combination of two kinds of Foehn flow (‘hybrid’-type Foehn wind). Specifically, the westerly wind became a Foehn wind that was caused by dry-adiabatic heating and wet-diabatic heating with water vapour condensation. This ‘hybrid’ Foehn wind was an important factor in causing the present EHT event.
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Investigation of a recent extreme high‐temperature event in the Tokyo metropolitan area using numerical simulations: the potential role of a ‘hybrid’ Foehn wind
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki KondoAbstract:A record-breaking high temperature of 39.8 °C for June in Japan was observed at 1420 Japan Standard Time on 24 June 2011 60 km northwest of central Tokyo. In this extreme high-temperature (EHT) event, surface air temperatures above 37.0 °C were recorded in and around Kumagaya, an area just north of the convergence line between westerly winds from the Chubu Mountains and a southwesterly wind from the Pacific Ocean. To determine the mechanism of this EHT event, we applied various analyses using the Weather Research and Forecasting (WRF) model and observational data. According to the heat budget analysis obtained from the WRF model, during the morning most of the sensible heat supply to the mixed layer came from the net heat input, due to surface sensible heat transported by subgrid-scale turbulent diffusion. However, most of the net heat input came from advective heat transport after noon, when the westerly wind penetrated the EHT area. This westerly wind, according to backward trajectory, Lagrangian energy budget and Eulerian forward tracer analyses, arose from a combination of two kinds of Foehn flow (‘hybrid’-type Foehn wind). Specifically, the westerly wind became a Foehn wind that was caused by dry-adiabatic heating and wet-diabatic heating with water vapour condensation. This ‘hybrid’ Foehn wind was an important factor in causing the present EHT event.
Hamish A. Mcgowan - One of the best experts on this subject based on the ideXlab platform.
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Austral summer Foehn winds over the McMurdo dry valleys of Antarctica from Polar WRF
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Daniel F. Steinhoff, Johanna C. Speirs, Hamish A. Mcgowan, David H. Bromwich, Andrew J. MonaghanAbstract:Foehn winds are a prominent feature of the McMurdo Dry Valleys (MDVs) climate, and are responsible for periods of strong winds and warming. The Foehn mechanism determined from a case study presented in earlier work is shown here to be robust for a set of the MDVs summer Foehn events over the 1994-2009 period using output from the Polar Weather Research and Forecasting Model (Polar WRF). Gap flow south of the MDVs is evidenced by the positive relationship between the pressure gradient and near-surface wind speed along the gap. Subsequently, mountain waves are generated and result in adiabatic warming and the downward transport of warm air into the MDVs, and differences in mountain wave characteristics depend on the ambient wind direction and the degree of flow nonlinearity. Pressure-driven channelling then brings warm Foehn air downvalley. Although a large range of synoptic-scale circulation patterns can drive Foehn events, the warmest Foehn events are typically associated with blocking highs over the Australian sector of the Southern Ocean, leading to warm air advection over continental Antarctica. The episodic nature of Foehn events, and the tenuous connections between such events and interannual modes of climate variability, suggests that intraseasonal variability may be more important for determining their frequency and magnitude. The extraordinarily warm austral summer of 2001/2002 across Antarctica shows that advection of warm maritime air into the continental interior and strong flow aloft result in warm Foehn conditions and significant melt for the MDVs.
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Regional climate variability driven by Foehn winds in the McMurdo Dry Valleys, Antarctica
International Journal of Climatology, 2012Co-Authors: Johanna C. Speirs, Daniel F. Steinhoff, Hamish A. Mcgowan, David H. BromwichAbstract:Warm, dry and gusty Foehn winds are frequently experienced in the McMurdo Dry Valleys (MDVs), Antarctica; however, their significance in the region’s climate is unknown. Foehn events in the MDVs are caused by topographic modification of southwesterly airflow which is related to the occurrence of synoptic-scale cyclones in the Amundsen/Ross Sea region. The intra- and interannual frequency and intensity of Foehn events therefore varies in response to the position and frequency of cyclones in this region that are believed to be strongly influenced by the El Ni˜no Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Here, we present a 20-year climatology of Foehn winds from observational records in the MDVs. The SAM is found to significantly influence Foehn wind frequency during the Antarctic summer and autumn months, whereas ENSO only holds significant correlations with winter air temperatures in the MDVs. The positive relationship between the SAM and the Foehn wind regime in summer is particularly significant as Foehn winds frequently cause summer temperatures to rise above 0 °C leading to extensive melt and thaw in MDVs. Foehn winds are a major climatological feature of the MDVs with their frequency and duration affecting the region’s temperature records and their trends. Accordingly, analysis of the region’s weather and climate records and predictions of future impacts of climate change on the MDVs is incomplete without consideration of Foehn winds and their influence.
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Foehn Winds in the McMurdo Dry Valleys, Antarctica: The Origin of Extreme Warming Events*
Journal of Climate, 2010Co-Authors: Johanna C. Speirs, Daniel F. Steinhoff, Hamish A. Mcgowan, David H. Bromwich, Andrew J. MonaghanAbstract:Abstract Foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the McMurdo Dry Valleys (MDVs) of Antarctica. Strong Foehn winds in the MDVs cause dramatic warming at onset and have significant effects on landscape forming processes; however, no detailed scientific investigation of Foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau. Herein observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during Foehn events in the MDVs are presented. Results show that Foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow, which is channeled into the valleys from higher levels. Modeling of a winter Foehn event identifies mountain wave activity similar to that associated with midlatitude Foehn winds. These events are found to be caused by str...
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The meteorology and environmental implications of Foehn winds in a polar landscape: McMurdo Dry Valleys, Antarctica
2010Co-Authors: Hamish A. Mcgowan, Johanna C. SpeirsAbstract:Foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the McMurdo Dry Valleys (MDVs) of Antarctica. Strong Foehn winds in the MDVs cause dramatic warming at onset and have significant effects on landscape forming processes, however, no detailed scientific investigation of Foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau. Here we present observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during Foehn events in the MDVs. Results show that Foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow which is channeled into the valleys from higher levels. Modeling of a winter Foehn event identifies mountain wave activity similar to that associated with mid-latitude Foehn winds. These events are found to be caused by strong pressure gradients over the mountain ranges of the MDVs related to synoptic-scale cyclones positioned off the coast of Marie Byrd Land. Foehn winds in the MDVs provide an important heat source and using stream data and satellite imagery we show these winds are intimately linked to meltwater generation and snow persistence. The intra- and inter-annual frequency and intensity of Foehn events in the MDVs varies in response to the position and frequency of cyclones in the Ross Sea region. Accordingly, ENSO and other known drivers of climate variability such as the Southern Annular Mode that are known to affect cyclonic activity in the Ross Sea region may transfer a signal into the MDVs via the Foehn wind regime.
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Observations of Foehn onset in the Southern Alps, New Zealand
Meteorology and Atmospheric Physics, 2002Co-Authors: Hamish A. Mcgowan, Andrew Sturman, M. Kossmann, Peyman Zawar-rezaAbstract:Local scale windfield and air mass characteristics during the onset of two Foehn wind events in an alpine hydro-catchment are presented. Grounding of the topographically modified Foehn was found to be dependent on daytime surface heating and topographic channelling of flow. The Foehn front was observed to advance down-valley until the valley widened significantly. The Foehn wind appeared to decouple from the surface downstream of the accelerated flow associated with the valley constriction, and to be lifted above local thermally generated circulations including a lake breeze. Towards evening, the Foehn front retreated up valley in response to reduced surface heating and the intrusion into the study area of a deep and cool air mass associated with a regional scale mountain-plain circulation. Differences in the local windfield observed during both case study events reflect the importance of different thermal and dynamic forcings on airflow in complex terrain. These are the result of variation in surface energy exchanges, channelling and blocking of airflow. Observations presented here have both theoretical and applied implications with regard to forecasting Foehn onset, wind hazard management, recreational activities and air quality management in alpine settings.
Yuya Takane - One of the best experts on this subject based on the ideXlab platform.
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Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area
Journal of Applied Meteorology and Climatology, 2017Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki Kondo, Jin Katagi, Osamu Nagafuchi, Koyomi Nakazawa, Naoki Kaneyasu, Yoshihiro MiyakamiAbstract:AbstractA Foehn wind is an important factor in the occurrence of many extreme high-temperature events in geographically complex regions. In this study, the authors verified the hypothesis that a Foehnlike wind contributes to high temperatures at the end of the leeward (eastward) area using three difference approaches: field experiments, numerical experiments, and statistical analyses. According to the hypothesis, a Foehnlike wind has the features of the sum of a traditional Foehn effect with adiabatic heating, plus dry-diabatic heating from the ground surface along the fetch of the wind. Field experiments conducted at seven observational points on Nobi Plain, Japan, where a mesoscale westerly wind blew, revealed that the westerly wind clearly had the features of a traditional Foehn effect in the western part of the Nobi Plain. In addition to field experiments, a simplified estimate using a simple mixed-layer model demonstrated that the wind was further heated by dry-diabatic heating (sensible heat supply)...
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investigation of a recent extreme high temperature event in the tokyo metropolitan area using numerical simulations the potential role of a hybrid Foehn wind
Quarterly Journal of the Royal Meteorological Society, 2015Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki KondoAbstract:A record-breaking high temperature of 39.8 °C for June in Japan was observed at 1420 Japan Standard Time on 24 June 2011 60 km northwest of central Tokyo. In this extreme high-temperature (EHT) event, surface air temperatures above 37.0 °C were recorded in and around Kumagaya, an area just north of the convergence line between westerly winds from the Chubu Mountains and a southwesterly wind from the Pacific Ocean. To determine the mechanism of this EHT event, we applied various analyses using the Weather Research and Forecasting (WRF) model and observational data. According to the heat budget analysis obtained from the WRF model, during the morning most of the sensible heat supply to the mixed layer came from the net heat input, due to surface sensible heat transported by subgrid-scale turbulent diffusion. However, most of the net heat input came from advective heat transport after noon, when the westerly wind penetrated the EHT area. This westerly wind, according to backward trajectory, Lagrangian energy budget and Eulerian forward tracer analyses, arose from a combination of two kinds of Foehn flow (‘hybrid’-type Foehn wind). Specifically, the westerly wind became a Foehn wind that was caused by dry-adiabatic heating and wet-diabatic heating with water vapour condensation. This ‘hybrid’ Foehn wind was an important factor in causing the present EHT event.
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Investigation of a recent extreme high‐temperature event in the Tokyo metropolitan area using numerical simulations: the potential role of a ‘hybrid’ Foehn wind
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Yuya Takane, Hiroyuki Kusaka, Hiroaki KondoAbstract:A record-breaking high temperature of 39.8 °C for June in Japan was observed at 1420 Japan Standard Time on 24 June 2011 60 km northwest of central Tokyo. In this extreme high-temperature (EHT) event, surface air temperatures above 37.0 °C were recorded in and around Kumagaya, an area just north of the convergence line between westerly winds from the Chubu Mountains and a southwesterly wind from the Pacific Ocean. To determine the mechanism of this EHT event, we applied various analyses using the Weather Research and Forecasting (WRF) model and observational data. According to the heat budget analysis obtained from the WRF model, during the morning most of the sensible heat supply to the mixed layer came from the net heat input, due to surface sensible heat transported by subgrid-scale turbulent diffusion. However, most of the net heat input came from advective heat transport after noon, when the westerly wind penetrated the EHT area. This westerly wind, according to backward trajectory, Lagrangian energy budget and Eulerian forward tracer analyses, arose from a combination of two kinds of Foehn flow (‘hybrid’-type Foehn wind). Specifically, the westerly wind became a Foehn wind that was caused by dry-adiabatic heating and wet-diabatic heating with water vapour condensation. This ‘hybrid’ Foehn wind was an important factor in causing the present EHT event.
Andrew J. Monaghan - One of the best experts on this subject based on the ideXlab platform.
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Austral summer Foehn winds over the McMurdo dry valleys of Antarctica from Polar WRF
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Daniel F. Steinhoff, Johanna C. Speirs, Hamish A. Mcgowan, David H. Bromwich, Andrew J. MonaghanAbstract:Foehn winds are a prominent feature of the McMurdo Dry Valleys (MDVs) climate, and are responsible for periods of strong winds and warming. The Foehn mechanism determined from a case study presented in earlier work is shown here to be robust for a set of the MDVs summer Foehn events over the 1994-2009 period using output from the Polar Weather Research and Forecasting Model (Polar WRF). Gap flow south of the MDVs is evidenced by the positive relationship between the pressure gradient and near-surface wind speed along the gap. Subsequently, mountain waves are generated and result in adiabatic warming and the downward transport of warm air into the MDVs, and differences in mountain wave characteristics depend on the ambient wind direction and the degree of flow nonlinearity. Pressure-driven channelling then brings warm Foehn air downvalley. Although a large range of synoptic-scale circulation patterns can drive Foehn events, the warmest Foehn events are typically associated with blocking highs over the Australian sector of the Southern Ocean, leading to warm air advection over continental Antarctica. The episodic nature of Foehn events, and the tenuous connections between such events and interannual modes of climate variability, suggests that intraseasonal variability may be more important for determining their frequency and magnitude. The extraordinarily warm austral summer of 2001/2002 across Antarctica shows that advection of warm maritime air into the continental interior and strong flow aloft result in warm Foehn conditions and significant melt for the MDVs.
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Dynamics of the Foehn Mechanism in the McMurdo Dry Valleys of Antarctica from Polar WRF
Quarterly Journal of the Royal Meteorological Society, 2012Co-Authors: Daniel F. Steinhoff, David H. Bromwich, Andrew J. MonaghanAbstract:Foehn events over the McMurdo Dry Valleys (MDVs), the largest ice-free region of Antarctica, promote glacial melt that supports biological activity in the lakes, streams, rocks and soils. Although MDVs Foehn events are known to depend upon the synoptic-scale circulation, the physical processes responsible for Foehn events are unknown. A polar-optimized version of the Weather Research and Forecasting model (Polar WRF) is used for a case study of a representative summer Foehn event from 29 December 2006 to 1 January 2007 in order to identify and explain the MDVs Foehn mechanism. Pressure differences across an elevated mountain gap upstream of the MDVs provide forcing for southerly flow into the western, upvalley entrance of the MDVs. Complex terrain over the elevated gap and the MDVs leads to mountain wave effects such as leeside acceleration, hydraulic jumps, wave breaking and critical layers. These mountain wave effects depend on the ambient (geostrophic) wind direction. Pressure-driven channelling then brings the warm, dry Foehn air downvalley to eastern MDV sites. Brief easterly intrusions of maritime air into the eastern MDVs during Foehn events previously have been attributed to either a sea-breeze effect in summer or local cold-pooling effects in winter. In this particular case, the easterly intrusions result from blocking effects of nearby Ross Island and the adjacent Antarctic coast. Temperature variability during the summer Foehn event, which is important for meltwater production and biological activity when it exceeds 0°C, primarily depends on the source airmass rather than differences in Foehn dynamics.
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Foehn Winds in the McMurdo Dry Valleys, Antarctica: The Origin of Extreme Warming Events*
Journal of Climate, 2010Co-Authors: Johanna C. Speirs, Daniel F. Steinhoff, Hamish A. Mcgowan, David H. Bromwich, Andrew J. MonaghanAbstract:Abstract Foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the McMurdo Dry Valleys (MDVs) of Antarctica. Strong Foehn winds in the MDVs cause dramatic warming at onset and have significant effects on landscape forming processes; however, no detailed scientific investigation of Foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau. Herein observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during Foehn events in the MDVs are presented. Results show that Foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow, which is channeled into the valleys from higher levels. Modeling of a winter Foehn event identifies mountain wave activity similar to that associated with midlatitude Foehn winds. These events are found to be caused by str...
Achim Zeileis - One of the best experts on this subject based on the ideXlab platform.
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Automatic and Probabilistic Foehn Diagnosis with a Statistical Mixture Model
Journal of Applied Meteorology and Climatology, 2014Co-Authors: David Plavcan, Georg J. Mayr, Achim ZeileisAbstract:Diagnosing Foehn winds from weather station data downwind of topographic obstacles requires distinguishing them from other downslope winds, particularly nocturnal ones driven by radiative cooling. An automatic classification scheme to obtain reproducible results that include information about the (un)certainty of the diagnosis is presented. A statistical mixture model separates Foehn and no-Foehn winds in a measured time series of wind. In addition to wind speed and direction, it accommodates other physically meaningful classifiers such as the (potential)temperature difference to an upwind station (e.g., near the crest) or relative humidity. The algorithm was tested for Wipp Valley in the central Alps against human expert classificationandapreviousobjectivemethod(DrechselandMayr2008),whichthenewmethodoutperforms. Climatologically, using only wind information gives nearly identical Foehn frequencies as when using additional covariables. A data record length of at least one year is required for satisfactory results. The suitability of mixture models for objective classification of Foehn at other locations will have to be tested in further studies.
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Automatic and Probabilistic Foehn Diagnosis with a Statistical Mixture Model
2013Co-Authors: David Plavcan, Georg J. Mayr, Achim ZeileisAbstract:Diagnosing Foehn winds from weather station data downwind of topographic obstacles requires distinguishing them from other downslope winds, particularly nocturnal ones driven by radiative cooling. We present an automatic classification scheme to obtain reproducible results that include information about the (un)certainty of the diagnosis. A statistical mixture model separates Foehn and no-Foehn winds in a measured time series of wind. In addition to wind speed and direction, it accommodates other physically meaningful classifiers such as relative humidity or the (potential) temperature difference to an upwind station (e.g., near the crest). The algorithm was tested for the central Alpine Wipp Valley against human expert classification and a previous objective method (Drechsel and Mayr 2008), which the new method outperforms. Climatologically, using only wind information gives nearly identical Foehn frequencies as when using additional covariables, making the method suitable for comparable Foehn climatologies all over the world where station data are available for at least one year.