A Lagrangian Study of Helical Circulations in the Planetary Boundary Layer

Angell, J. K.; Pack, Donald H.; Dickson, C. R.

doi:10.1175/1520-0469(1968)025<0707:alsohc>2.0.co;2

Cited by 45 publications

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“…Of these, 12 of the aspect ratios were distributed between 1 and 5, and 16 of the wavelengths were distributed in ranges lower than 8,000 m. Two of the results were obtained in dry environments. Angell et al (1968) reported that the aspect ratios were around 2 and the wavelengths were 4 or 5; and Hanna (1969) reported only wavelengths that were less than 5 km. In the present study, the aspect ratios were distributed between 0.97 and 3.78; the wavelengths were distributed between 4,250 m and 7,256 m. Our results agree well with those attained in the former studies, and gained deeper insights into the relation of the aspect ratio to the weather condition.…”

Section: Relationship Of Development Of the Mixedmentioning

confidence: 93%

Vertical Profiles of Aeolian Dust in a Desert Atmosphere Observed using Lidar in Shapotou, China

Yasui

Zhou

Liu

et al. 2005

Journal of the Meteorological Society of Japan

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We analyzed the time series data of dust vertical profiles, observed using polarization elastic lidar, from April 8 th -21 st , 2002, during the first intensive observation period of the Aeolian Dust Experiment on Climate impact (ADEC), in Shapotou, Ninxia Province in China. We conducted the analysis with consideration to the upper atmospheric soundings and surface weather data. The results are summarized as follows. 1) A well-mixed dust layer dominated in the boundary layer sampled from around 11 a.m. until around 1 or 2 a.m. local time (Beijing time). Under well-mixed conditions, the mixed layers grew well with dry convections in the boundary layer, especially during the day and in the early evening. 2) Dry convections developed deeper during synoptic low-pressure conditions because of the systematic upward motions prevalent in the low-pressure systems. Vertical wind shear affected growth of the mixed layer as well, that is, weak vertical wind shear condition was favorable for the growth of the mixed layer. The deepest mixed layer was observed on April 13 th at a thickness of about 6-km above ground, when the pressure was the lowest, the vertical wind shear was very weak, and the atmosphere was dry. The aspect ratios (horizontal/vertical scale ratios) of the convections decreased under low-pressure and weak-shear conditions. On the other hand, the aspect ratios of the convections increased dramatically under highpressure and strong-shear conditions, because convection growth was suppressed by systematic downdrafts of the high-pressure system and by strong vertical wind shears.

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Section: Relationship Of Development Of the Mixedmentioning

confidence: 93%

Vertical Profiles of Aeolian Dust in a Desert Atmosphere Observed using Lidar in Shapotou, China

Yasui

Zhou

Liu

et al. 2005

Journal of the Meteorological Society of Japan

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“…The seif dunes are characterized by tuning-fork junctions opening into the prevailing wind direction (Folk, 1971). Large vortices have been observed in the atmosphere (Angell et al, 1968), and they may be responsible for banded cloud patterns often observed in the atmosphere (Kuettner, 1959;. Helical circulations, present in the surface layers of the ocean, form windows or wind slicks on the sea surface (Langmuir, 1938) .…”

Section: Origin Of Furrowsmentioning

confidence: 99%

Studies of deep-sea sedimentary microtopography in the North Atlantic Ocean

Flood¹

1978

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partial fulfillment of the requirements for the degree of Doctor of Philosophy.. ABSTRACTMany of the small-scale topographic features (dimensions of centimeters to kilometers) found on the Blake-Bahama Outer Ridge (western North Atlantic, water depth greater than 4000 m) and in the Rockall Trough (northeastern North Atlantic, water depth greater than 2000 m) have been formed as bed forms of deep currents. These bed forms, all developed in cohesive sediments, include current ripples (spacings of tens of centimeters, formed transverse to the flow), longitudinal triangular ripples (spacings of meters, formed in sandy muds and parallel to the flow), furrows (spacings of tens to 100's of meters, formed parallel to the flow and presently either erosional or depositional), and regular sediment waves (spacings of a few kilometers, now found oblique to the flow and migrating either upstream or downstream).The local distribution of any given bed form is influenced by the presence of larger features. Bed forms are often found in zones which strike parallel to the regional contours.Debris flows, affecting areas of 1000's to 10,000's of square kilometers, are also present in these areas. A debris flow studied in the Rockall Trough is erosional at its shallowest depths and depositional at greater depths. Gravitational flows strike perpendicular to the contours. Pockmarks (tens of meters in diameter, marking fluid seeps) are also found on the Blake-Bahama Outer Ridge.The larger topographic features (greater than several meters) with steep slopes (greater than about 200) can be observed on surface echo-sounding profiles either as fields of regular hyperbolic echoes (e.g., echoes from regularly spaced furrows), fields of irregularly spaced, dissimilar hyperbolae (e.g., echoes from blocks, ridges, and folds in debris flows), or as regular features whose structfre is often obscured by side echoes (e.g., echoes fro .sediment waves).Although nearbottom investigations are required to describe the features, the nature of the sea floor can often be inferred from the character of the echo-sounding profile. Similar echo-sounding records in different areas of the ocean indicate the presence of similar sea-floor features.The morphology of the bed forms studied and the current and temperature structure of the overlying water column lead to conclusions about bed form origin and present-day interactions with deep currents.Furrows form as erosional bed forms during high-velocity (>20? cm/sec) current events by large, helical secondary circulations in the bottom boundary layer. Once formed, furrows may develop into depositional features, or they may continue as erosional ones, depending on the local currents and the sediment supply.Large, regular sediment waves may be formed at current speeds of 5 to 10 cm/sec by lee waves generated by topographic irregularities on the sea floor, such as submarine canyons, or by instabilities in the flow of deep, contour-following currents. Sediment waves develop where there is an abundant supply of sediment an...

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“…Many observational and theoretical studies concerning the cloud bands have been conducted (e.g., Angell et al, 1968;Asai, 1970;Kuettner, 1971;Brown, 1970Brown, , 1972Brown, , 1980Kelly, 1982Kelly, , 1984LeMone, 1973;LeMone and Pennell, 1976;Miura, 1986). The necessary condition for the formation of cloud bands has been identified as a convectively unstable layer having significant vertical wind shear.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Radar Echo Structure of a Snow Band Formed on the Lee Side of a Mountain

Fujiyoshi

Tsuboki

Satoh

et al. 1992

Journal of the Meteorological Society of Japan

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A snow band, formed on the lee side of Mt. Akaiwa at Takashima Peninsula, Hokkaido, was observed by a three-dimensional scanning Doppler radar. The snow band was composed of meso-* scale (*20 km) radar echoes, whose interval of appearance was about 40 minutes. Inside the meso-* scale echoes, were two or three convective echoes with 10 km in size. Further, each convective echo was composed of several convective cells 1-2 km in size. The snow band elongated from west to north and convective cells existing along the southern part of the snow band always appeared the most active and the highest. The convective cells successively formed only along the northern part of the snow band. The width of the snow band was dependent on the number of convective cells which composed the convective clouds. Thus, the snow band was asymmetrical in shape in the vertical plane, perpendicular to its elongated direction.on an average, the band width increased proportional to (distance)1/3. The band thickness linearly increased with increase in band width, and the ratio between them increased, that is, the snow band flattened as distance increased. Averaged snow water content continued to increase over the ocean, for the convective clouds which continued to grow. But it decreased near the sea coast. This can be explained as follows: When a cloud approaches land, snow particles which are sustained in the air over the sea begin to fall near the sea coast because the averaged speed of updraft in a cloud decreases there. After landfall, the convective clouds regenerated, owing to horizontal wind convergence created by Mt. Asoiwa and weakened rapidly on its lee side.

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A Lagrangian Study of Helical Circulations in the Planetary Boundary Layer

Cited by 45 publications

References 0 publications

Vertical Profiles of Aeolian Dust in a Desert Atmosphere Observed using Lidar in Shapotou, China

Vertical Profiles of Aeolian Dust in a Desert Atmosphere Observed using Lidar in Shapotou, China

Studies of deep-sea sedimentary microtopography in the North Atlantic Ocean

Three-Dimensional Radar Echo Structure of a Snow Band Formed on the Lee Side of a Mountain

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