This paper gives a brief overview over the International Reference Ionosphere (IRI) project and model. IRI is recognized as the official standard for the ionosphere by the International Standardization Organization (ISO). Of great importance are the external drivers of the model that help IRI to represent ionospheric conditions as realistically as possible. The paper discusses the solar and ionospheric measurements that are used as drivers and presents recent improvements and changes.

The ionosphere varies the most over the Northern hemisphere. This is called the annual anomaly. Ionospheric models, such as the International Reference Ionosphere (IRI), underrepresent the anomaly. The ionosphere affects radio waves, so it is important to always improve these models. We show that it is considering the ionosphere's hemispheric behavior is required to improve IRI. We suggest that the annual anomaly is caused by processes which differ over each hemisphere.