Valley winds and slope winds ? Observations and elementary thoughts

Vergeiner, I.; Dreiseitl, E.

doi:10.1007/bf01045154

Cited by 165 publications

(149 citation statements)

References 19 publications

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“…The vertical profiles of wind from radiosonde data at lower levels (850-900 mb) in Besisahar during June 1999 reported by Barros and Lang (2003) also show the presence of northwesterly mountain wind from mid-night to morning, which transitions to up-valley wind around 09:00 LT in the morning and strengthens during daytime. These observations are consistent with the descriptive models provided by Defant (1949Defant ( , 1951, Vergeiner and Dreiseitl (1987), Rampanelli et al (2004), Mcnider et al (1984) for mountain valley circulations in narrow valleys. Therefore, mountain valley wind mechanisms can be expected to play an important role in transporting the pollutants further inwards into the inner Himalayan region from the low lying plains.…”

Section: Regional Influence On Aerosol Spectrasupporting

confidence: 79%

Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010

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Abstract. Aerosol particle number size distribution and chemical composition were measured at two low altitude sites, one urban and one relatively pristine valley, in Central Nepal during the 2009 pre-monsoon season (May-June). This is the first time that aerosol size distribution and chemical composition were measured simultaneously at lower elevations in the middle Himalayan region in Nepal. The aerosol size distribution was measured using a Scanning Mobility Particle Sizer (SMPS, 14-340 nm), and the chemical composition of the filter samples collected during the field campaign was analyzed in the laboratory. Teflon membrane filters were used for ion chromatography (IC) and watersoluble organic carbon and nitrogen analysis. Quartz fiber filters were used for organic carbon and elemental carbon analysis. Multi-lognormal fits to the measured aerosol size distribution indicated a consistent larger mode around 100 nm which is usually the oldest, most processed background aerosol. The smaller mode was located around 20 nm, which is indicative of fresh but not necessarily local aerosol. The diurnal cycle of the aerosol number concentration showed the presence of two peaks (early morning and evening), during the transitional periods of boundary layer growth and collapse. The increase in number concentration during the peak periods was observed for the entire size distribution. Although the possible contribution of local emissions in size ranges similar to the larger mode cannot be completely ruled out, another plausible explanation is the mixing of aged elevated aerosol in the residual layer during the morning period as suggested by previous studies. Similarly, the evening time concentration peaks when the boundary layer becomes shalCorrespondence to: A. P. Barros (barros@duke.edu) low concurrent with increase in local activity. A decrease in aerosol number concentration was observed during the nighttime with the development of cold (downslope) mountain winds that force the low level warmer air in the valley to rise. The mountain valley wind mechanisms induced by the topography along with the valley geometry appear to have a strong control in the diurnal cycle of the aerosol size distribution. During the sampling period, the chemical composition of PM 2.5 was dominated by organic matter at both sites. Organic carbon (OC) comprised the major fraction (64-68%) of the aerosol concentration followed by ionic species (24-26%, mainly SO 2− 4 and NH + 4 ). Elemental Carbon (EC) compromised 7-10% of the total composition and 27% of OC was found to be water soluble at both sites. The day-to-day variability observed in the time series of aerosol composition could be explained by the synoptic scale haze that extended to the sampling region from the Indian Gangetic Plain (IGP), and rainfall occurrence. In the presence of regional scale haze during dry periods, the mean volume aerosol concentration was found to increase and so did the aerosol mass concentrations.

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Section: Regional Influence On Aerosol Spectrasupporting

confidence: 79%

Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010

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“…ac.uk/data/radiosonde/radhelp.html), the data were not temporally coincident and, therefore, did not improve our interpretation of wind patterns for the satellite tracks. Although topographic features such as valleys and slope angle will undoubtedly affect local wind conditions, anabatic/katabatic wind phenomena are common in every terrestrial mountain range on earth (19)(20)(21)(22)(23)(24)(25) and operate at the scale of mountain ranges, relevant to the migratory distance traveled by the geese. The Pyramid station data describe wind speed and direction at 30-min intervals for the year and cover the period over which we tracked birds migrating.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

“…Large mountainous areas are characterized by daily slope winds that occur due to predictable changes in daily solar radiation and thermal conditions [e.g., the Alps (19,20), the Andes (21), the Himalaya (22,23), and mountainous areas in the United States (24,25)]. These winds reach an upslope "anabatic" maximum during the warmest part of the day, and a downslope, "katabatic" maximum in the evening and overnight (19,20). In the Eastern Himalaya, near Mount Everest, these winds start to blow upslope (from a southerly direction) at ∼09:00 h local time, reaching their maximum of around 22 km·h −1 by 12:45 h and reversing overnight to blow southward (Fig.…”

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confidence: 99%

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The trans-Himalayan flights of bar-headed geese ( Anser indicus )

Hawkes

Balachandran

Batbayar

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

144

125

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Birds that fly over mountain barriers must be capable of meeting the increased energetic cost of climbing in low-density air, even though less oxygen may be available to support their metabolism. This challenge is magnified by the reduction in maximum sustained climbing rates in large birds. Bar-headed geese (Anser indicus) make one of the highest and most iconic transmountain migrations in the world. We show that those populations of geese that winter at sea level in India are capable of passing over the Himalayas in 1 d, typically climbing between 4,000 and 6,000 m in 7-8 h. Surprisingly, these birds do not rely on the assistance of upslope tailwinds that usually occur during the day and can support minimum climb rates of 0.8-2.2 km·h −1 , even in the relative stillness of the night. They appear to strategically avoid higher speed winds during the afternoon, thus maximizing safety and control during flight. It would seem, therefore, that bar-headed geese are capable of sustained climbing flight over the passes of the Himalaya under their own aerobic power.exercise physiology | high altitude | satellite tracking | vertebrate migration | climbing flight M ountains and high plateaus present formidable obstacles to the migratory flights of a number of bird species. Large birds, such as cranes and geese, may find such barriers particularly challenging as the sustained climbing rates of birds scale negatively with increasing body mass (1). For example, brent geese (Branta bernicla) are unable to sustain climbing flights over the Greenland icecap (summit elevation 3,207 m, mean elevation >2,000 m) and make regular stops to recover, possibly from partly anaerobic flights (2). Nevertheless, populations of bar-headed geese (Anser indicus) that spend the winter at sea level in India and the summer in central Asia must perform the world's steepest migratory flight north over the highest mountain range on earth, the Himalaya (3). There, most passes are at altitudes greater than 5,000 m, where the air density and partial pressure of oxygen are only about half of those at sea level. As a consequence, the partial pressure of oxygen (PO 2 ) in the arterial blood may begin to limit maximum performance (4, 5), although negative effects on the rate of oxygen diffusion may be partially ameliorated by an increase in the gas diffusion coefficient (6). The thinner air at these higher altitudes will also reduce lift generation during flapping flight for any given air speed, thus increasing the energy costs of flying by around 30% (7,8).However, bar-headed geese have adapted in a variety of ways for living and flying at high altitudes (4, 5). Their skeletal and cardiac muscles are better supplied with oxygen, having greater capillary density, more homogenous capillary spacing, a higher proportion of mitochondria in a subsarcolemmal location, and a greater proportion of oxidative fibers than other waterfowl (9, 10). Bar-headed goose hemoglobin is also highly effective at oxygen loading (11), compared with many other bird species, largel...

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“…Bulk steady-state models [99] provide an alternative approach for estimating transport by slope winds. While the Prandtl model provides a continuous one-dimensional representation of the flow field over a slope, bulk models only evaluate a few integral properties of the slope wind layer.…”

Section: Pointwise Perspective On Upslope Windsmentioning

confidence: 99%

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

et al. 2018

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Abstract:The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, and turbulence. This article reviews the key challenges relevant to the understanding of exchange processes in the mountain boundary layer and outlines possible research priorities for the future. The review describes the limitations of the experimental study of turbulent exchange over complex terrain, the impact of slope and valley breezes on the structure of the convective boundary layer, and the role of intermittent mixing and wave-turbulence interaction in the stable boundary layer. The interplay between exchange processes at different spatial scales is discussed in depth, emphasizing the role of elevated and ground-based stable layers in controlling multi-scale interactions in the atmosphere over and near mountains. Implications of the current understanding of exchange processes over mountains towards the improvement of numerical weather prediction and climate models are discussed, considering in particular the representation of surface boundary conditions, the parameterization of sub-grid-scale exchange, and the development of stochastic perturbation schemes.

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Valley winds and slope winds ? Observations and elementary thoughts

Cited by 165 publications

References 19 publications

Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

The trans-Himalayan flights of bar-headed geese ( Anser indicus )

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

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