# Ionospheric Science: An Example of the Importance of Diversity in Approaches to Scientific Research
## 1 Introduction  
Ionospheric science has a long history of achievement going back almost a century. It has its practical roots in the 1920s when the first wave of great developments in electronics, in particular the triode valve, enabled radio measurements of conditions in Earth's upper atmosphere. Its evolution in the following decades was often linked to astronomy and space science as the exploration of the upper atmosphere was then considered part of astronomy, for example being discussed in popular astronomy textbooks published in Mid-20 th Century, e.g., see [1].  
However, in the later decades of the 20 th Century, those links became more diffuse as ionospheric science matured and became more inter-disciplinary. For example, the polar ionosphere became a major focus from the 1970s onwards, reflecting both (a) the growing scientific interest in the coupling between the ionosphere and the magnetosphere and (b) the improvements in Arctic and Antarctic transport, communications, and energy infrastructures that facilitated the deployment of advanced instruments in those regions, e.g., the European Incoherent Scatter (EISCAT) radars first deployed in Northern Scandinavia [2] and later in Svalbard [3]. Another, very different, example was the application of ionospheric science to study radio propagation through the ionosphere. Originally focused on high-frequency (HF) radio communications, this expanded greatly from the 1960s onwards with the development of radio-frequency systems for a wide range of satellite and ground-based applications [4; 5]. A further example, becoming more significant towards the end of the 20 th Century, was the scientific interest in coupling between the lower atmosphereand the ionosphere. This \"vertical coupling\" is now recognised as an important source of day-to-day variability in the ionosphere and is a major research topic that links ionospheric science to atmospheric science. Its importance to modern science may be summed up in a phrase from the late [PERSON] [6], who, at a 2008 workshop, emphasised to us all that \"The atmosphere is one system\".  
This evolution of ionospheric studies into an interdisciplinary science, with strong links both to other science disciplines and to radio system engineering, has led to a wealth of excellence, both in research and in the application of that research to the benefit of societies around the world. However, it has also led to misunderstandings in other parts of the scientific community where it has been considered that it is now time for ionospheric, and other space weather studies to be focused on applications, e.g., see the recent discussion by [PERSON] et al. [7]. This paper addresses that misunderstanding. The paper has three main sections. Section 2 sets the scene by outlining how ionospheric science developed in the early 20 th Century and also developed links with both the applications community and the astronomy community. This is followed in Section 3 by a short review of some current key issues in ionospheric science showing how it has matured into a highly interdisciplinary topic that is best considered as a branch of the environmental sciences. Section 4 then shows how, as with other environment sciences, ionospheric science needs to be positioned in a scientific culture that supports a diversity of approaches to research, a mix of curiosity-driven studies to address the fundamental understanding of a complex natural system, targeted research to develop a deep understanding of environmental conditions that have profound impacts on human societies, and effective mechanisms to support the transition of research outputs into operational services that help to manage our responses to those conditions. These three sections are followed by a summary that highlights the key conclusions of the paper.