Observations of a Reversal in Long-Term Average Vertical Velocities near the Jet Stream Wind Maximum

Fukao, S.; Larsen, M. F.; Yamanaka, Manabu D.; Furukawa, Hiroyuki; Tsuda, Toshitaka; Kato, S.

doi:10.1175/1520-0493(1991)119<1479:ooaril>2.0.co;2

Cited by 45 publications

(28 citation statements)

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“…Such vertical motions scale down to a few cm/s or more at the tropospheric level, which is comparable to mean vertical motions in the troposphere (e.g. Fukao et al, 1991;Nastrom and VanZandt, 1994) but less than typical instantaneous vertical motions of up to a few tens of cm/s associated with tropospheric gravity waves (Nastrom et al, 1990).…”

Section: Atmospheric Gravity Waves In the Lower Atmospherementioning

confidence: 78%

The influence of solar wind on extratropical cyclones – Part 2: A link mediated by auroral atmospheric gravity waves?

2009

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Abstract. Cases of mesoscale cloud bands in extratropical cyclones are observed a few hours after atmospheric gravity waves (AGWs) are launched from the auroral ionosphere. It is suggested that the solar-wind-generated auroral AGWs contribute to processes that release instabilities and initiate slantwise convection thus leading to cloud bands and growth of extratropical cyclones. Also, if the AGWs are ducted to low latitudes, they could influence the development of tropical cyclones. The gravity-wave-induced vertical lift may modulate the slantwise convection by releasing the moist symmetric instability at near-threshold conditions in the warm frontal zone of extratropical cyclones. Latent heat release associated with the mesoscale slantwise convection has been linked to explosive cyclogenesis and severe weather. The circumstantial and statistical evidence of the solar wind influence on extratropical cyclones is further supported by a statistical analysis of high-level clouds (<440 mb) extracted from the International Satellite Cloud Climatology Project (ISCCP) D1 dataset. A statistically significant response of the high-level cloud area index (HCAI) to fast solar wind from coronal holes is found in mid-tohigh latitudes during autumn-winter and in low latitudes during spring-summer. In the extratropics, this response of the HCAI to solar wind forcing is consistent with the effect on tropospheric vorticity found by Wilcox et al. (1974) and verified by Prikryl et al. (2009). In the tropics, the observed HCAI response, namely a decrease in HCAI at the arrival of solar wind stream followed by an increase a few days later, is similar to that in the northern and southern mid-to-high latitudes. The amplitude of the response nearly doubles for stream interfaces associated with the interplanetary magnetic field B Z component shifting southward. When the IMF B Z after the stream interface shifts northward, the autumn-winter Correspondence to: P. Prikryl (paul.prikryl@crc.ca) effect weakens or shifts to lower (mid) latitudes and no statistically significant response is found at low latitudes in springsummer. The observed effect persists through years of low and high volcanic aerosol loading. The similarity of the response in mid-to-high and low latitudes, the lack of dependence upon aerosol loading, and the enhanced amplitude of the effect when IMF B Z component shifts southward, favor the proposed AGW link over the atmospheric electric circuit (AEC) mechanism (Tinsley et al., 1994). The latter requires the presence of stratospheric aerosols for a significant effect and should produce negative and positive cloud anomalies in mid-to-high and low latitudes, respectively. However, if the requirement of aerosols for the AEC mechanism can be relaxed, the AGW and AEC mechanisms should work in synergy at least in mid-to-high latitudes.

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Section: Atmospheric Gravity Waves In the Lower Atmospherementioning

confidence: 78%

The influence of solar wind on extratropical cyclones – Part 2: A link mediated by auroral atmospheric gravity waves?

2009

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“…We used a standard observation technique (the so-called GRATMAC1 observation mode) of the MU radar, of which details have been described in Fukao et al (1990Fukao et al ( , 1991. In this technique we operate the radar to search echoes from 128 points at 150m intervals in the vertical direction within about 1min.…”

Section: The Mu Radarmentioning

confidence: 99%

“…The time and height resolutions are -60s and 150m, respectively (Fukao et al, 1985b(Fukao et al, , c, 1990(Fukao et al, , 1991, and the observed wind velocity is a mean Doppler velocity in a radar scattering volume of which the spatial scale is -102m . The MU radar observation is a single-stationed (vertical and time) observation, but we could study the three-dimensional struc-tore of atmospheric disturbances if they passed by the radar site without remarkable modifications in time.…”

Section: Introductionmentioning

confidence: 99%

Hierarchical Structures of Vertical Velocity Variations and Precipitating Clouds near the Baiu Frontal Cyclone Center Observed by the MU and Meteorological Radars

Shibagaki

Yamanaka

Hashiguchi

et al. 1997

Journal of the Meteorological Society of Japan

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We carried out a three-week observation campaign using the MU radar and meteorological (C-, X-, Kuband) radars during the Baiu season in 1991 (17 June-8 July). A complete data set of three-dimensional atmospheric motions with high reliability and resolution was produced after removing raindrop echoes. The Baiu front was located to the south of the radar site during 17-24 June, and to the north during 25-28 June. After 29 June, surface medium-scale (meso-a-scale) cyclone centers passed near the MU observatory, and the tropopause jet stream became strong (one or two days) after the low-level jet stream appeared near the surface cyclone center. We have investigated meso-b-scale vertical velocity fluctuations and precipitating cloud clusters with temporal scales of several hours for various locations relative to the surface cyclone centers: (i) one case in the northern side of a cyclone center on the Baiu front, (ii) four cases near developing surface cyclone centers and (iii) one case in the southern side of the Baiu front far from a cyclone center. For (i) and (ii), the vertical distributions of upward-velocity regions were strongly dependent on the level of lowest stratiform turbulence near the tropopause level (LSTT) and the frontal surface. The upward velocities in the cases (ii) were associated with the developing cloud cluster on the northern side of the surface warm front, while they were dominant over the region of meso-b scale but did not always have precipitation on the northern side of the surface cold front. For (iii) some upward-velocity regions without precipitation penetrated LSTT. Each meso-b-scale fluctuation for all the cases (i)-(iii) included a number of upward-velocity peaks corresponding to meso-r-scale disturbances. Some of them were coincident with surface rainfall (and lower-tropospheric precipitation echo) peaks. Based on all the observational evidence mentioned above, we propose a schematic picture of the 'hierarchical structure' of the vertical velocity fluctuations near the Baiu front. This is partly the same as the well-known multi-scale structure composed of meso-a-scale cyclones, meso-b-scale cloud clusters and meso-r-scale precipitating clouds, but covers more broad clear regions which cannot be observed by foregoing studies based on only meteorological radars and satellites.

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“…The MU radar of the Radio Atmospheric Science Center (RASC), Kyoto University is a VHF radar which is valuable for the observation of three-dimensional wind velocity including vertical velocity with fine time and height resolutions (-150 s and -150 m, respectively) (Fukao et al, 1985b(Fukao et al, , 1985c(Fukao et al, , 1991. The MU radar observation is a single-stationed observation (at 34.85°N, 136.10°E), but we can observe typical mesoscale atmospheric motions which appear near the Baiu (early summer rainy season) front in Japan every year.…”

Section: Introductionmentioning

confidence: 99%

Hierarchical Structures of Medium-Scale Cyclones and Cloud Clusters near the Baiu Front Observed by MU and Meteorological Radars: Outline and Preliminary Results of Three-Week Observation Campaign.

Shibagaki

Yamanaka

Uyeda

et al. 1996

J. geomagn. geoelec

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We have carried out tropospheric observations by the MU radar (VHF-band) and meteorological radars (C-, Ku-and X-bands) for three weeks during the Bain (early summer rain) season in 1991 (17 June -8 July). We produced a complete data set of three-dimensional wind velocity, turbulence parameters, cloud and precipitation with high reliability and resolution. Results of the data analysis show that a meso-a-scale cyclone on the Baiu front has an asymmetric hierarchical structure of vertical velocity fluctuation distributions, which consists of meso-/3-scale cloud clusters (with strong upward velocities and rainfalls) and meso-y-scale developing clouds (with remarkably strong events). Further, they are restricted by the lowest level of the stratiform turbulence near the tropopause and the frontal surface and are especially activated near the warm and cold fronts on the ground in the cyclone center.

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Observations of a Reversal in Long-Term Average Vertical Velocities near the Jet Stream Wind Maximum

Cited by 45 publications

References 0 publications

The influence of solar wind on extratropical cyclones – Part 2: A link mediated by auroral atmospheric gravity waves?

The influence of solar wind on extratropical cyclones – Part 2: A link mediated by auroral atmospheric gravity waves?

Hierarchical Structures of Vertical Velocity Variations and Precipitating Clouds near the Baiu Frontal Cyclone Center Observed by the MU and Meteorological Radars

Hierarchical Structures of Medium-Scale Cyclones and Cloud Clusters near the Baiu Front Observed by MU and Meteorological Radars: Outline and Preliminary Results of Three-Week Observation Campaign.

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