Investigation of inertia gravity waves observed by dropsonde and airborne Radio Occultation during an Atmosphere River event in the northeast Pacific

Jets and fronts in the mid-latitudes generate internal gravity waves that influence the circulation in the middle atmosphere and contribute to clear-air turbulence. There is an ongoing effort to study the gravity waves in the vicinity of jets and fronts using different datasets and numerical models. However, detailed vertical profile observations of gravity waves associated with jets and fronts are rare. During the Atmospheric Reconnaissance 2018 Campaign (AR Recon 2018), dense dropsondes in the region of the jet core and exit region and Airborne Radio Occultation (ARO) measurements are available in multiple transects across the frontal system. On 26-27 Jan 2018, 88 dropsondes were released from three aircraft (the National Oceanic and Atmospheric Administration (NOAA) G-IV and two Air Force C-130 jets). A Septentrio GNSS receiver was installed on NOAA G-IV to perform radio occultation measurements from which refractivity and temperature profiles to the side of aircraft were derived. Utilizing dropsonde and ARO measurements, multiple occurrences of inertia gravity waves were identified with a typical vertical wavelength near 3-4 km and inferred intrinsic periods near 6-8 hrs. Dropsonde transects provide a unique opportunity to investigate the inertia gravity waves and relate the waves to their potential excitation sources. Potential wave sources in the vicinity include a jet stream with windspeeds up to 70 m/s at about 9 km altitude, frontal system, and latent heat release due to moist convection in the lower troposphere. High resolution mesoscale simulations of the event using the Weather Research and Forecasting Model (WRF) are constrained by the dropsonde data. These simulated model fields are used to investigate inertial gravity waves at the same scale as those detected in the observations. The wave-induced fluctuations are expected to lead to conditions locally conducive to turbulence. Wave breaking and turbulence are investigated in the analysis of aircraft in-situ measurements.