HIWIND Instrument Description HIWIND (High altitude Interferometer WIND experiment) is the first balloon-borne Fabry Perot interferometer (FPI) for thermospheric wind observations [Wu et al., 2012; 2019a; 2019b]. Because it makes observations while flying at ~ 40 km altitude, it overcomes the high sun-light scattering during the day and is able to observe the O 630 nm dayglow emission for Doppler wind measurements without high background as it would on the ground. The sun light scattering at 40 km altitude is only 0.1 percent of that at the sea level. The HIWIND instrument has similar design as the National Center for Atmospheric Research (NCAR) FPI built for Resolute station [Wu et al., 2004]. It has a 10 cm clear aperture with 2.0 cm gap. The etalon coating has 80% reflectivity. The etalon is housed in a sealed and temperature-controlled chamber. It uses a Princeton Pixis 512B CCD camera. It has a 5-position 10 cm aperture filter wheel, while only the 630 nm emission filter was used for airglow observations. HIWIND has a single rotating mirror points its viewing direction at 40-degree elevation angle. The rotating mirror points the HIWIND field of view at four orthogonal directions. The FPI instrument and its controlling electronics are housed inside a cylindrical shape pressure vessel, which maintains 1 atm pressure and is insolated and actively controlled to maintain room temperature. A radiator with a coolant circulation system keeps the pressure vessel from overheating. There are four portholes on the upper portion of the pressure vessel to allow the FPI view the four orthogonal directions for thermospheric wind observations. HIWIND instrument is mounted inside a gondola, which also carries NASA communication and flight control system, solar panels, batteries, radiator, antenna booms, and on occasion piggyback instruments. The orientation of the gondola is controlled by a NASA Wallops Flight Facility provided rotator, which maintains the pointing towards the sun with less 1-degree jitter. HIWIND balloon flew twice from Kiruna (68 deg N, 20 deg E), Sweden in 2011 and 2018. In both cases, HIWIND balloon landed in Canada carried by westward stratospheric wind across the Atlantic Ocean. During the 2011 flight, observations were made during the first two days (June 14 and 15, 2011). The observations were cut short due to a power system issue. During its second flight, HIWIND was launched from Kiruna on June 24, 2018 and landed about 80 km west of Kugluktuk in Canada on June 30. Observations were made throughout the flight. After every flight, the HIWIND payload was recovered and is waiting to be refurbished and flown again. Since the HIWIND balloon was controlled to point at the sun, the four orthogonal viewing direction do not align with the cardinal directions. To obtain meridional zonal components, the orthogonal viewing observations were decomposed and formed meridional and zonal winds. HIWIND used 1-minute integration time for all its observations. Zero winds values are based averaged of opposite viewing directions. The balloon orientation, moving direction, and speed are measured by a Magellan ADU5 GPS compass (< 1 degree pointing RMS). The balloon speed is removed from the apparent thermospheric wind relative to the balloon. The balloon speed is about 15-20 m/s, which is typical summer northern polar region stratospheric speed and much smaller than thermospheric winds ( ~ 100 m/s). The wind errors from HIWIND are airglow intensity dependent and ranging from 10 to 40 m/s. The data provided in these files are meridional and zonal winds obtained by decomposing the orthogonal viewing observations. Data from the two flights (2011 and 2018) are listed here. The balloon latitude and longitudes are given so are the time, meridional wind, its error, and time, zonal wind, and its error. Acknowledgement HIWIND was supported by NASA grants NNX08AV35G and NNX15AK75G to NCAR High Altitude Observatory (HAO). The HIWIND instrument was built by HAO Instrument Group. PI/Provider name: Qian Wu Institute: National Center for Atmospheric Research Contact info: Qian Wu qwu@ucar.edu Mission name: HIWIND Instrument: Fabry Perot Interferometer Time resolution/cadence: 1 minute integration time Data format: ASCII Data description: HIWIND is the first balloon borne Fabry Perot interferometer for thermospheric wind observation. Filenames: hiwind_fpi_YYYYDOY.asc 4-digit year and 3-digit day of year DOI: doi:10.5065/4GER‐3779 (2011 and 2018 data, first two days) doi:10.5065/ad71-8827 (2018 day 180 data). Reference: Wu, Q., R. D. Gablehouse, S. C. Solomon, T. L. Killeen, and C.-Y. She (2004), A new Fabry-Perot interferometer for upper atmosphere research, Proc. SPIE 5660, Instruments, Sci. Methods Geosp. Planet. Remote Sensing,, 218, doi:10.1117/12.573084. Wu, Q., W. Wang, R. G. Roble, I. Häggström, and A. Strømme (2012), First daytime thermospheric wind observation from a balloon-borne Fabry-Perot interferometer over Kiruna (68N), Geophys. Res. Lett., 39(14), 1–7, doi:10.1029/2012GL052533. Wu, Q., Knipp, D., Liu, J., Wang, W., Häggström, I., Jee, G., et al. (2019a). What do the new 2018 HIWIND thermospheric wind observations tell us about high‐latitude ion‐neutral coupling during daytime? Journal of Geophysical Research: Space Physics, 124, 6173– 6181. https://doi.org/10.1029/2019JA026776 Wu, Q., Knipp, D., Liu, J., Wang, W., Varney, R., Gillies, R., et al (2019b). HIWIND Observation of Summer Season Polar Cap Thermospheric Winds. Journal of Geophysical Research: Space Physics, 124. https://doi.org/10.1029/2019JA027258