92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012
Methodology Toward a Long-Term Realistic Wind Resource Assessment Applied in Colima Valley, México
Hall E (New Orleans Convention Center )
Gilles J. M. Arfeuille, Univ. Autonoma del Estado de Mexico, Toluca, Mexico; and A. L. Quintanilla, L. Zizumbo, and F. C. Viesca González
Manuscript (464.7 kB)

Poster PDF (717.1 kB)

In the present work SODAR technology combined with a specific meteorological tower network are used to investigate characteristics and evolution of the planetary boundary layer in the valley of Colima, central western Mexico, and its wind power generation potential; relevant mesoscale phenomena such as supergeostrophic Low Level Jets are reported and characterised in Colima valley for the years 2010 and 2011. This region is typically considered to have a low wind power generation potential as many other parts of the Mexican transverse volcanic axis and other regions with complex topography. Wind resource assessment is typically conducted analysing WMO weather station network data, and in some cases rawinsonde data, to develop 40 to 50 km grided wind maps as a first approach, in general at 50 m Above Ground Level, using a logarithmic extrapolation from data at low height (usually extrapolated from10-m measurements). Once some regions are catalogued with a good wind potential, up to 80-m instrumented towers are typically installed by companies involved in wind farm development to further investigate the potential of selected sites, as observed in Oaxaca, southern Mexico, and Baja California regions. It has been shown in previous work the great importance to wind power generation of mesoscale phenomena such as Low Level Jets, as for example over the North American Great Plains and Northern Europe. Important work has been made to investigate the mechanisms of such phenomena in these specific regions. Other studies had tried to pin point regions in the world where conditions favourable for consistent Low Level Jets exist. The latter studies also use WMO weather station network data integrating rawinsonde data. As for wind maps aforementioned, for regions with complex topography such as the one of the present study, Low Level Jet phenomena don't appear in the results of such studies. It is possible that the scale of such phenomena escape to these specific approaches, and it must be considered that WMO network is designed to comply with civil aviation and other weather related important needs and not for wind resource assessment. Hub height for modern wind turbines is typically around or greater than 100 m AGL, and the data set presented here for different time periods of 2010 and 2011 shows a non-logarithmic wind profile of the lower 500 m of the Atmospheric Boundary Layer, especially at night and early morning, due to the systematic presence of supergeostrophic low level jets. It is important to mention that these phenomena had not been reported in these tropical regions before. This invalidates typical logarithmic extrapolation from lower heights as used normally for wind resource assessment; and the presence of such phenomena increases drastically the potential for wind power generation in such region. To evaluate more specifically this potential, the supergeostrophic low level jets are characterised considering criteria defined in previous studies of the Low Level Jets of the North American Great Plains and refined by others using similar monitoring tools as the ones used in the present study, such as in CASES-99, Lamar Project and ABLE studies. Almost every night shows the development of at least one Jet with nose height between 100 m and 700 m above the valley floor with categories ranging from sub-zero up to category 2 jets, with lower height zero-category jets dominating with a consistent northerly direction. The region of study being in the tropics, most of the year the horizontal pressure gradient is typically small implying a relatively weak geostrophic back ground state in the wind field making the observed jets strongly supergeostrophic. The onset of the jets is typically later than in other regions since the region of study is only at 19.23° north. Wind profiles and time evolution of wind direction at nose level are investigated to determine if inertial oscillation mechanism is dominating over baroclinicity over sloping terrain. So far it is not clear which one is the leading mechanism and more work is needed to determine that aspect and analyse the key forcing affecting the region of interest, even it is clear the ocean-land interaction and topography play an important role. Also the spatial scale of such meso β scale phenomena reaches farther than our monitoring network and this makes mesoscale modelling a fundamental complementary tool to realise a complete study. Therefore another approach than the traditional one for wind resource assessment is needed to be able to determine realistically the availability of such renewable energy in other regions than the typically known high potential regions. As the present study shows, it can be done integrating classical instrumented towers, wind profiler technology such as SODAR or LIDAR, and mesoscale modelling. This kind of methodology can also be useful at existing wind farm for managing purposes doing short range mesoscale forecast.

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