Analysis of Gap Flow Phenomena and Machine Learning Strategies for the Prediction of Atmospheric Flows

Doctoral Dissertation

Abstract

Meteorological flows are difficult to predict due to their extreme complexity and non-linearity. Current numerical weather models are primarily equipped for prediction of less capricious meso and synoptic-scale phenomena. Modeling of microscale phenomena, particularly in complex terrain, remains a pain point for the modeling community.

This thesis attempts to shed light on multiple questions related to environmental physics and modeling. The first investigation focuses on the effects of stratification on microscale gap flow observed during the Perdig√£o campaign. Modified forms of non-dimensional mountain height G are proposed to account for real-world atmospheric variability, and the results are discussed in terms of a gap-averaged value Gc. The nature of gap flow is highly dependent on Gc, wherein a nearly neutral flow regime (Gc < 1), a transitional mountain wave regime (Gc ~ O(1)), and a gap-jetting regime (Gc > O(1)) are identified. The findings suggest that microscale gaps, while having only a minor effect on the surrounding flow field during nearly neutral time periods, are highly influential as stratification increases and buoyancy becomes a main driver of the flow.

The next investigation explores the effects of physics-informed feature engineering when utilizing an artificial neural network for vertical extrapolation of wind speeds.

Non-dimensional inputs, namely turbulence intensity, current wind speed, and previous wind speed, are the features that most reliably improve extrapolation accuracy. The developed model provides drastically improved extrapolation accuracy compared to the commonly used log law and power law extrapolation methods.

A similar question is posed in the third investigation, but for wind speed forecasting. A random forest model is used to predict the forecasting error from a bias-corrected autoregressive integrated moving average (ARIMA) model. Multiple meteorological variables are used as inputs, and variables conveying information about atmospheric stability, turbulence, and inertia are all found to be useful in dealing with non-linear error prediction. The developed model is shown to improve upon both the bias-corrected ARIMA and persistence models.

Finally, a study is performed which investigates optimal machine learning strategies for wind speed forecasting. Three sets of modeling strategies are analyzed, suggesting that target variable differencing and direct forecasting are more accurate and robust strategies for multi-step wind speed forecasting. The model is shown to improve as up to 8 equivalent years of training data is added, although such improvement may be negated by changing environmental flow patterns.

Attributes

Attribute NameValues
Author Daniel Vassallo
Contributor Kenneth Christensen, Committee Member
Contributor Harindra J. Fernando, Research Director
Contributor Raghavendra Krishnamurthy, Committee Member
Contributor Joannes Westerink, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Civil and Environmental Engineering and Earth Sciences
Degree Name Doctor of Philosophy
Banner Code
  • PHD-CEES

Defense Date
  • 2020-11-13

Submission Date 2020-12-08
Subject
  • Utilizing machine learning for wind speed forecasting and extrapolation

  • Gap flows through complex topography

  • Machine learning strategies for wind speed forecasting

  • Integrating physics into machine learning models

Record Visibility Public
Content License
  • All rights reserved

Departments and Units
Catalog Record

Files

Please Note: You may encounter a delay before a download begins. Large or infrequently accessed files can take several minutes to retrieve from our archival storage system.