Diurnal Winds in the Himalayan Kali Gandaki Valley. Part III: Remotely Piloted Aircraft Soundings

Joseph Egger Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Joseph Egger in
Current site
Google Scholar
PubMed
Close
,
Sapta Bajrachaya Department of Hydrology and Meteorology, Ministry of Science and Technology, Kathmandu, Nepal

Search for other papers by Sapta Bajrachaya in
Current site
Google Scholar
PubMed
Close
,
Richard Heinrich Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Richard Heinrich in
Current site
Google Scholar
PubMed
Close
,
Philip Kolb Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Philip Kolb in
Current site
Google Scholar
PubMed
Close
,
Stephan Lämmlein Fachbereich Maschinenbau, Fachhochschule Regensburg, Regensburg, Germany

Search for other papers by Stephan Lämmlein in
Current site
Google Scholar
PubMed
Close
,
Mario Mech Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Mario Mech in
Current site
Google Scholar
PubMed
Close
,
Joachim Reuder Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Joachim Reuder in
Current site
Google Scholar
PubMed
Close
,
Wolfgang Schäper Astrium, Friedrichshafen, Germany

Search for other papers by Wolfgang Schäper in
Current site
Google Scholar
PubMed
Close
,
Pancha Shakya Department of Hydrology and Meteorology, Ministry of Science and Technology, Kathmandu, Nepal

Search for other papers by Pancha Shakya in
Current site
Google Scholar
PubMed
Close
,
Jan Schween Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Jan Schween in
Current site
Google Scholar
PubMed
Close
, and
Hilbert Wendt Meteorologisches Institut, Universität München, Munich, Germany

Search for other papers by Hilbert Wendt in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

In 1998 a field campaign has been conducted in the north–south-oriented Kali Gandaki valley in Nepal to explore the structure of its extreme valley wind system. Piloted ballon (pibal) observations were made to map the strong upvalley winds as well as the weak nocturnal flows (Part I). The stratification of the valley atmosphere was not explored. In Part II of this multipart paper, numerical simulations are presented that successfully simulate most of the wind observations. Moreover, the model results suggest that the vigorous upvalley winds can be seen as supercritical flow induced by contractions of the valley. Here, the results of a further campaign are reported where remotely piloted airplanes were used to obtain vertical profiles of temperature and humidity up to heights of ∼2000 m above the ground. Such profiles are needed for an understanding of the flow dynamics in the valley and for a validation of the model results. This technique is novel in some respects and turned out to be highly reliable even under extreme conditions. In addition four automatic stations were installed along the valley's axis. Winds were observed via pibal ascents. These data complement the wind data of 1998 so that the diurnal wind system of the Kali Gandaki valley is now documented reasonably well.

It is found that the fully developed upvalley flow is confined to a turbulent layer that tends to be neutrally stratified throughout the domain of observations. The stratification above this layer is stable. A capping inversion is encountered occasionally. This finding excludes explanations of the strong winds in terms of hydraulic theories that rely on the presence of strong inversions. Pairs of simultaneous ascents separated by 5–10 km along the valley axis reveal a remarkable variability induced by the topography and, perhaps, by an instability of the flow. The analysis of the surface data as well as that of the soundings shows that the flow above the neutral layer affects the surface pressure distribution and, therefore, the acceleration of the extreme upvalley winds.

Corresponding author address: Joseph Egger, Meteorologisches Institut der Universität München, Theresienstr. 37, 80333 München, Germany. Email: j.egger@lrz.uni-muenchen.de

Abstract

In 1998 a field campaign has been conducted in the north–south-oriented Kali Gandaki valley in Nepal to explore the structure of its extreme valley wind system. Piloted ballon (pibal) observations were made to map the strong upvalley winds as well as the weak nocturnal flows (Part I). The stratification of the valley atmosphere was not explored. In Part II of this multipart paper, numerical simulations are presented that successfully simulate most of the wind observations. Moreover, the model results suggest that the vigorous upvalley winds can be seen as supercritical flow induced by contractions of the valley. Here, the results of a further campaign are reported where remotely piloted airplanes were used to obtain vertical profiles of temperature and humidity up to heights of ∼2000 m above the ground. Such profiles are needed for an understanding of the flow dynamics in the valley and for a validation of the model results. This technique is novel in some respects and turned out to be highly reliable even under extreme conditions. In addition four automatic stations were installed along the valley's axis. Winds were observed via pibal ascents. These data complement the wind data of 1998 so that the diurnal wind system of the Kali Gandaki valley is now documented reasonably well.

It is found that the fully developed upvalley flow is confined to a turbulent layer that tends to be neutrally stratified throughout the domain of observations. The stratification above this layer is stable. A capping inversion is encountered occasionally. This finding excludes explanations of the strong winds in terms of hydraulic theories that rely on the presence of strong inversions. Pairs of simultaneous ascents separated by 5–10 km along the valley axis reveal a remarkable variability induced by the topography and, perhaps, by an instability of the flow. The analysis of the surface data as well as that of the soundings shows that the flow above the neutral layer affects the surface pressure distribution and, therefore, the acceleration of the extreme upvalley winds.

Corresponding author address: Joseph Egger, Meteorologisches Institut der Universität München, Theresienstr. 37, 80333 München, Germany. Email: j.egger@lrz.uni-muenchen.de

Save
  • Arakawa, S., 1969: Climatological and dynamical studies on the local strong winds, mainly in Hokkaido. Japan Geophys. Mag., 34 , 349425.

    • Search Google Scholar
    • Export Citation
  • Armi, L., 1986: The hydraulics of two flowing layers of different densities. J. Fluid Mech., 163 , 2758.

  • Armi, L., and R. Williams, 1993: The hydraulics of a stratified fluid flowing through a contraction. J. Fluid Mech., 251 , 355375.

  • Baines, P., 1995: Topographic Effects in Stratified Flows. Cambridge Monographs on Mechanics, Cambridge University Press, 482 pp.

  • Barros, A., M. Joshi, J. Putkonen, and D. Burbank, 2000: A study of the 1999 monsoon rainfall in a mountainous region in central Nepal using TRMM products and rain gauge observations. Geophys. Res. Lett., 27 , 36833686.

    • Search Google Scholar
    • Export Citation
  • Brehm, M., and C. Freytag, 1982: Erosion of the night-time thermal circulation in an Alpine valley. Arch. Meteor. Geophys. Bioklimatol., B31 , 331352.

    • Search Google Scholar
    • Export Citation
  • Chilson, Ph, P. Johansson, M. Johnsson, R. Moses, J. Stanojev, Th Hedquist, A. Niva, and R. Scheifele, 1999: Ripan: A remotely controlled aircraft project for tropospheric and stratosphere research. Proc. 14th ESA Symp. on European Rocket and Balloon Programs, Potsdam, Germany, ESA SP-437, 111–116.

    • Search Google Scholar
    • Export Citation
  • Clements, W., J. Archuleta, and P. Gudiksen, 1989: Experimental designs of the 1984 ASCOT field study. J. Appl. Meteor., 28 , 405413.

  • Dai, A., and J. Wang, 1999: Diurnal and semidiurnal tides in global surface pressure fields. J. Atmos. Sci., 56 , 38743891.

  • Drazin, Ph, and W. Reid, 1981: Hydrodynamic Stability. Cambridge Monographs on Mechanics and Applied Mathematics, Cambridge University Press, 525 pp.

    • Search Google Scholar
    • Export Citation
  • Egger, J., S. Bajrachaya, U. Egger, R. Heinrich, J. Reuder, P. Shakya, H. Wendt, and V. Wirth, 2000: Diurnal winds in the Himalayan Kali Gandaki valley. Part I: Observations. Mon. Wea. Rev., 128 , 11061122.

    • Search Google Scholar
    • Export Citation
  • Jackson, P., and D. Steyn, 1994a: Gap winds in a fjord. Part I: Observations and numerical simulation. Mon. Wea. Rev., 122 , 26452665.

    • Search Google Scholar
    • Export Citation
  • Jackson, P., . 1994b: Gap winds in a fjord. Part II. Hydraulic analog simulations. Mon. Wea. Rev., 122 , 26662676.

  • Konrad, T., M. Hill, J. Rowland, and J. Meyer, 1970: A small radio-controlled aircraft as a platform for meteorological sensors. APL Tech. Dig., 10 , 1119.

    • Search Google Scholar
    • Export Citation
  • McKee, Th, and R. O'Neil, 1989: The role of valley geometry and energy budget in the formation of valley wind. J. Appl. Meteor., 28 , 445456.

    • Search Google Scholar
    • Export Citation
  • Nickus, U., and I. Vergeiner, 1984: The thermal structure of the Inn valley atmosphere. Arch. Meteor. Geophys. Bioklimatol., A33 , 199215.

    • Search Google Scholar
    • Export Citation
  • Pan, F., and R. Smith, 1999: Gap winds and wakes: SAR observations and numerical simulations. J. Atmos. Sci., 56 , 905923.

  • Pettre, P., 1982: On the problem of violent valley winds. J. Atmos. Sci., 39 , 542554.

  • Ramage, C., 1971: Monsoon Meteorology. International Geophysics Series, Vol. 15, Academic Press, 296 pp.

  • Renno, N., and E. Williams, 1995: Quasi-Lagrangian measurements in convective boundary layer plumes and their implications for the calculation of CAPE. Mon. Wea. Rev., 123 , 27332742.

    • Search Google Scholar
    • Export Citation
  • Stephens, G., and Coauthors. . 2000: The Department of Energy's Atmospheric Radiation Measurement (ARM) unmanned aerospace vehicle (UAV) program. Bull. Amer. Meteor. Soc., 81 , 29152937.

    • Search Google Scholar
    • Export Citation
  • Whiteman, C., 1990: Observations of thermally developed wind systems in mountainous terrain. Atmospheric Processes over Complex Terrain, Meteor. Monogr., No. 45, Amer. Meteor. Soc., 5–42.

    • Search Google Scholar
    • Export Citation
  • Zängl, G., J. Egger, and V. Wirth, 2001: Diurnal winds in the Himalayan Kali Gandaki valley. Part II: Modeling. Mon. Wea. Rev., 129 , 10621078.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 318 84 24
PDF Downloads 194 39 1