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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'The model chain: First steps towards tomorrow's technology' taking place on Thursday, 13 March 2014 at 09:00-10:30. The meet-the-authors will take place in the poster area.

José Vidal AWS Truepower, SLU, Spain
Co-authors:
José Vidal (1) F P B. Boureau (1) J. Ochoa (1) S. Vila (1) M. Brower (2) F. Habib (3) I. Lessa (3) E. Lima (3)
(1) AWS Truepower, SLU, Barcelona, Spain (2) AWS Truepower, LLC, Albany, NY, United States of America (3) Casa dos Ventos, Sao Paulo, Brazil

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Abstract

Particularities of the wind resource at low latitudes

Introduction

This work introduce the results of a study performed to explain the wind regime in a complex site where all the scales, from general circulation to mesoscale, interact and are relevant to explain the observed wind resource. It will be shown the characteristics of the flow in areas influenced by trade winds, how the particularities of the site modify the synoptic wind, and the results of a model capable of representing faithfully the measured wind distribution over the site and provide an insight about the driving mechanisms causing it.

Approach

After a first inspection of the observed wind resource and the climatic characteristics of the area, it seemed reasonable to consider the thermal forces as candidate for the origin of the site specific wind flow. Observed diurnal cycle and seasonality were the main clues for this hypothesis. For that reason, it was decided to use a mesoscale, primitive equation model in combination with a coupled microscale linear model as a suitable tool to reproduce the observed wind distribution.

Main body of abstract

The studied area is a plateau located close to the Equator and its center is at about 7.5o S latitude. The most relevant weather patterns driving the synoptic wind regime are the positions of the Intertropical Convergence Zone (ITCZ) and the subtropical high-pressure cells; both factors lead to marked southeast trade winds over the region, somewhat weakened during the wet season, when the ITCZ is closer to the area. The site under study has a lot of tall, high quality met towers installed. These measurements showed a wind resource distribution over time and space that didn’t fit well with what can be presumed from the very characteristic synoptic regime in which the site is embedded.
A study was performed over the area using a combination of mesoscale-microscale chained models, with three main goals: first, test if mesoscale, microscale or a combination of both models would capture the not yet explained effects. Second, to help in the development of a conceptual model who can explain the observed wind resource. Finally, to make compatible the modeled wind distribution with the observations, in order to produce an accurate energy estimation.
The presentation will show how high resolution mesoscale model simulations fit very well with the observed wind distribution over the area, how the very particular diurnal evolution of the thermal vertical structure of the atmosphere is the main driver of the unexplained part of the wind resource, and how the microscale model refines the mesoscale output.


Conclusion

In this study we have seen the particularities of the trade wind regime, the effect of the seasonal displacement of the ITCZ on the synoptic winds at low latitudes and how its interaction with local orography can lead to very complex spatial distributions of the resource. A correct model selection can help in the understanding of all the factors involved and in the correct representation of the wind resource over the area.


Learning objectives
The audience will learn about the specific synoptic wind regime of regions close to the Equator, to which extent thermal effects can drastically modify the wind distribution and an example on how mesoscale models can capture complex wind flows.