# Tutorial on Satellite Derived Wind Products

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## Chapter I: Introduction

### Table of Contents

- Chapter I: Introduction
- Introduction

### Introduction

Winds are a driving force, for small scale thunderstorms as well as for larger scale tropical cyclones. Over land numerous in-situ observations provide a good overview of the predominant wind conditions, whereas over the oceans and seas wind measurements are rare (see Figure 1).

Figure 1: Worldwide data sources for wind measurements (Source: Regis Borde).

Although no satellite instrument can measure the wind field directly, there are a number of techniques that can be used to derive wind observations indirectly. Atmospheric motion vectors (AMV) are extracted by tracking clouds or moisture patterns in satellite image sequences. Furthermore the roughness of the sea can be used to determine the wind conditions over oceans either by active radar scatterometers (e.g. ASCAT) or by passive microwave radiometers (e.g. WindSat).

Wind data thus obtained by satellites plays a major role in data assimilation. Numerical models perform better with an increased amount of wind data, especially over the oceans. In this way satellite derived winds improve weather forecasts and warnings. They are of great benefit for deducing convergence/divergence (AMVs) or have a great impact on marine nowcasting (scatterometer data). The European Centre for Medium-Range Weather Forecasts (ECMWF) has been implementing AMVs into their forecast models operationally since the 1980s, and scatterometer winds have been included since the mid-1990s. This has dramatically improved the model's ability to forecast the track of tropical cyclones and has also increased the model's ability to predict wave heights and and storm surges. Also, satellite-derived winds are routinely used by NOAA and NWS to modify NWP outputs related to severe weather.

Satellite-derived wind data and products are used for a wide range of applications in the field of oceanography, meteorology and air/sea interactions. This tutorial provides a comprehensive overview of the various types of satellite derived winds and their applications.

Figure 2: Small scale ocean waves (Source: oceanleadership.org).

In the following chapter (chapter 2) you will learn how AMV winds are derived and which satellite instruments are involved.

Finally some meteorological applications of satellite derived winds in very short range nowcasting are shown (chapter 3).