@article{MatzkaStolleYamazakietal.2021,
  author    = {Matzka, J{\"u}rgen and Stolle, Claudia and Yamazaki, Yosuke and Bronkalla, Oliver and Morschhauser, Achim},
  title     = {The geomagnetic Kp index and derived indices of geomagnetic activity},
  series = {Space weather : the international journal of research and applications},
  volume    = {19},
  journal   = {Space weather : the international journal of research and applications},
  number    = {5},
  publisher = {Wiley},
  address   = {New York},
  issn      = {1542-7390},
  doi       = {10.1029/2020SW002641},
  pages     = {21},
  year      = {2021},
  abstract  = {The geomagnetic Kp index is one of the most extensively used indices of geomagnetic activity, both for scientific and operational purposes. This article reviews the properties of the Kp index and provides a reference for users of the Kp index and associated data products as derived and distributed by the GFZ German Research Centre for Geosciences. The near real-time production of the nowcast Kp index is of particular interest for space weather services and here we describe and evaluate its current setup.},
  language  = {en}
}
@article{YamazakiMatzkaStolleetal.2022,
  author    = {Yamazaki, Yosuke and Matzka, J{\"u}rgen and Stolle, Claudia and Kervalishvili, Guram N. and Rauberg, Jan and Bronkalla, Oliver and Morschhauser, Achim and Bruinsma, Sean L. and Shprits, Yuri Y. and Jackson, David R.},
  title     = {Geomagnetic activity index Hpo},
  series = {Geophysical research letters},
  volume    = {49},
  journal   = {Geophysical research letters},
  number    = {10},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {0094-8276},
  doi       = {10.1029/2022GL098860},
  pages     = {9},
  year      = {2022},
  abstract  = {The geomagnetic activity index Kp is widely used but is restricted by low time resolution (3-hourly) and an upper limit. To address this, new geomagnetic activity indices, Hpo, are introduced. Similar to Kp, Hpo expresses the level of planetary geomagnetic activity in units of thirds (0o, 0+, 1-, 1o, 1+, 2-, horizontal ellipsis ) based on the magnitude of geomagnetic disturbances observed at subauroral observatories. Hpo has a higher time resolution than Kp. 30-min (Hp30) and 60-min (Hp60) indices are produced. The frequency distribution of Hpo is designed to be similar to that of Kp so that Hpo may be used as a higher time-resolution alternative to Kp. Unlike Kp, which is capped at 9o, Hpo is an open-ended index and thus can characterize severe geomagnetic storms more accurately. Hp30, Hp60 and corresponding linearly scaled ap30 and ap60 are available, in near real time, at the GFZ website (https://www.gfz-potsdam.de/en/hpo-index).},
  language  = {en}
}