An observational study of a shallow gravity current triggered by katabatic flow

Adachi, Ahoro; Clark, W. L.; Hartten, Leslie M.; Gage, K. S.; Kobayashi, Toshiharu

doi:10.5194/angeo-22-3937-2004

Cited by 10 publications

(17 citation statements)

References 35 publications

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“…The most commonly documented scenario for gravity wave formation involves a gravity current propagating into a region of strong static stability, such as a nocturnal inversion (e.g., Kingsmill and Crook 2003;Adachi et al 2004b). Recall that the second thin-line echo was generated ahead of outer rainband 2, where the first thin-line echo propagated (Figs.…”

Section: The Second Thin-line Echomentioning

confidence: 99%

“…On the other hand, their results also show that positive N 2 less than 10 À3 s À2 with a depth of more than 1000 m cannot act as a duct. Recently, Adachi et al (2004b) showed that a negative layer of N 2 with a depth of about 50 m can act as a duct for a weak solitary wave with vertical velocities within or equal to G0.3 m s À1 that propagates for at least 15 min.…”

Section: The Second Thin-line Echomentioning

confidence: 99%

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A Nonclassical Gust Front and a Solitary Wave Embedded within a Typhoon as Observed with Doppler Radar and Wind Profiler

Adachi¹,

Kobayashi²

2009

Journal of the Meteorological Society of Japan

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Observations from a Doppler radar, a wind profiler, and a meteorological tower were used to study the evolution of two thin-line echoes that were observed in the radar reflectivity field over the Kanto Plain of Japan as Typhoon Higos (0221) passed in October 2002. Both thin-line echoes were accompanied by gusty winds and followed by cold airflows, and both passed the field site of the Meteorological Research Institute (MRI) in Tsukuba, Japan. Data from the MRI instrument array and from a surface observation network revealed that the first thinline echo was caused by a gust front, and the second thin-line echo was caused by a solitary wave.Although it was demonstrated that the first thin-line echo was due to a gust front, this gust front could not be categorized as a so-called thunderstorm gust front because it had no parent thunderstorm; rather, Doppler radar and wind profiler observations suggested that both relatively strong (@4 m s À1 ) downdrafts and large momentum transported by the downdrafts from aloft (@4 km) to lower levels produced and enhanced near-surface winds behind the gust front. In contrast, the solitary wave associated with the second thin-line echo likely developed as another gust front that generated from an outer rainband to the south of the typhoon center met a stable layer formed by the cold outflow behind the gust front associated with the first thin-line echo. The ducting mechanism that enabled the solitary wave to propagate was also revealed from the wind profiler and radiosonde measurements.

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Section: The Second Thin-line Echomentioning

confidence: 99%

Section: The Second Thin-line Echomentioning

confidence: 99%

A Nonclassical Gust Front and a Solitary Wave Embedded within a Typhoon as Observed with Doppler Radar and Wind Profiler

Adachi¹,

Kobayashi²

2009

Journal of the Meteorological Society of Japan

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“…FIG. The MVD method determines the vertical velocity that minimizes the variance between the four horizontal velocity components calculated from four oblique radial velocities (see Adachi et al 2004 for details). Scatterplots of the three-beam method profiler wind speed vs the tower wind speed measured at about 200 m, for conditions classified as clear air using the vertical beam of the profiler.…”

Section: B Representativeness Of the Vertical Velocity Measurement Umentioning

confidence: 99%

Evaluation of Three-Beam and Four-Beam Profiler Wind Measurement Techniques Using a Five-Beam Wind Profiler and Collocated Meteorological Tower

Adachi¹,

Kobayashi²,

Gage

et al. 2005

Journal of Atmospheric and Oceanic Technology

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In this paper a five-beam wind profiler and a collocated meteorological tower are used to estimate the accuracy of four-beam and three-beam wind profiler techniques in measuring horizontal components of the wind. In the traditional three-beam technique, the horizontal components of wind are derived from two orthogonal oblique beams and the vertical beam. In the less used four-beam method, the horizontal winds are found from the radial velocities measured with two orthogonal sets of opposing coplanar beams. In this paper the observations derived from the two wind profiler techniques are compared with the tower measurements using data averaged over 30 min. Results show that, while the winds measured using both methods are in overall agreement with the tower measurements, some of the horizontal components of the three-beam-derived winds are clearly spurious when compared with the tower-measured winds or the winds derived from the four oblique beams. These outliers are partially responsible for a larger 30-min, threebeam standard deviation of the profiler/tower wind speed differences (2.2 m s Ϫ1 ), as opposed to that from the four-beam method (1.2 m s Ϫ1 ). It was also found that many of these outliers were associated with periods of transition between clear air and rain, suggesting that the three-beam technique is more sensitive to small-scale variability in the vertical Doppler velocity because of its reliance on the point measurement from the vertical beam, while the four-beam method is surprisingly robust. Even after the removal of the rain data, the standard deviation of the wind speed error from the three-beam method (1.5 m s Ϫ1 ) is still much larger than that from the four-beam method. Taken together, these results suggest that the spatial variability of the vertical airflow in nonrainy periods or hydrometeor fall velocities in rainy periods makes the vertical beam velocities significantly less representative over the area across the three beams, and decreases the precision of the three-beam method. It is concluded that profilers utilizing the four-beam wind profiler technique have better reliability than wind profilers that rely on the three-beam wind profiler technique.

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“…Koch and Clark (1999) observed the development of a bore from a gravity current along a cold front, the subsequent propagation of the bore ahead of the front on a low-level inversion, and the process of a severe thunderstorm development along the front by a dense remote-sensing network with a 915-MHz profiler. Adachi et al (2004b) observed a solitary wave with a 1.3-GHz profiler that was excited by gravity currents created by katabatic flow originating on the mountain slopes in the Kanto region of Japan.…”

Section: Trapped Waves and Gravity Currentsmentioning

confidence: 99%

Recent Advances in Atmospheric Radar Study

Fukao

2007

Journal of the Meteorological Society of Japan

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With certain limitations, atmospheric radars generally called MST (mesosphere, stratosphere, and troposphere) radars or ST (stratosphere and troposphere) radars are capable of continuously monitoring three-dimensional winds, waves, turbulence, and atmospheric stability over the wide altitude range 1-100 km in the Earth's atmosphere. In particular, direct measurement of vertical wind velocity over such a wide altitude range is possible only with MST radars. Their time resolution of about 1 min and altitude resolution of 75-150 m are unequalled by conventional instruments (e.g., rawinsondes and rocketsondes), making it possible for MST radars to quantitatively investigate the small-scale atmospheric gravity waves that are considered to play important roles in the dynamics of the Earth's atmosphere. It is also noted that the vertical flux of horizontal momentum can be measured with high accuracy by MST radars. MST radars in the VHF band have the capability to discriminate echoes from clear air and precipitation particles, while microwave meteorological radars generally detect only precipitation echoes. In the last three decades, this excellent capability has been used extensively to study various dynamical disturbances in the Earth's atmosphere, developing new frontiers of atmospheric research on, primarily, mesoscale and micro-scale phenomena. In the present paper, these advances are reviewed briefly.

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An observational study of a shallow gravity current triggered by katabatic flow

Cited by 10 publications

References 35 publications

A Nonclassical Gust Front and a Solitary Wave Embedded within a Typhoon as Observed with Doppler Radar and Wind Profiler

A Nonclassical Gust Front and a Solitary Wave Embedded within a Typhoon as Observed with Doppler Radar and Wind Profiler

Evaluation of Three-Beam and Four-Beam Profiler Wind Measurement Techniques Using a Five-Beam Wind Profiler and Collocated Meteorological Tower

Recent Advances in Atmospheric Radar Study

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