Technical Notes
Practical guides to help you better understand atmospheric data, reanalysis, observations, forecasting, and the tools and formats used to work with them. These notes are designed to provide clear, accessible explanations of technical concepts and practical workflows for anyone working with atmospheric and environmental data, from research and education to professional applications.
Observations, Reanalysis, and Forecasting
Three Different Products, One Common Framework
Observations, reanalysis, and numerical weather prediction are three interconnected but distinct components of the atmospheric information system. This guide explains how observations are collected and used, how reanalysis reconstructs the past, and how numerical weather prediction projects the future, with an overview of the main observing systems, global reanalyses, and operational forecasting systems.
Understanding ERA5
ECMWF's Fifth-Generation Atmospheric Reanalysis
ERA5 is one of the world's most widely used global reanalysis datasets, providing hourly atmospheric, land-surface, and ocean-wave data from 1940 to the present. This guide provides a concise introduction to how ERA5 is produced, the main products and variables available, and its key strengths and limitations.
ERA5 vs ERA5-Land
What's the Difference, and Which One Should You Use?
ERA5-Land is a global land-surface reanalysis providing higher-resolution information on soil, snow, water, and energy conditions from 1950 to the present. This guide explains how ERA5-Land relates to ERA5, its main technical characteristics and variables, and when ERA5-Land, ERA5, or both datasets should be used.