Christian Mallaun

Does Strong Tropospheric Forcing Cause Large‐Amplitude Mesospheric Gravity Waves? A DEEPWAVE Case Study

The DEEPWAVE (deep-propagating wave experiment) campaign was designed for an airborne and ground-based exploration of gravity waves from their tropospheric sources up to their dissipation at high altitudes. It was performed in and around New Zealand from 24 May till 27 July 2014, being the first comprehensive field campaign of this kind. A variety of airborne instruments was deployed onboard the research aircraft NSF/NCAR Gulfstream V (GV) and the DLR Falcon. Additionally, ground-based measurements were conducted at different sites across the southern island of New Zealand, including the DLR Rayleigh lidar located at Lauder (45.04 S, 169.68 E). We focus on the intensive observing period (IOP) 10 on the 4 July 2014, when strong WSW winds of about 40 m/s at 700 hPa provided intense forcing conditions for mountain waves. At tropopause level, the horizontal wind exceeded 50 m/s and favored the vertical propagation of gravity waves into the stratosphere. The DLR Rayleigh Lidar measured temperature fluctuations with peak-to-peak amplitudes of about 20 K in the mesosphere (60 km to 80 km MSL) over a period of more than 10 hours. Two research flights were conducted by the DLR Falcon (Falcon Flight 04 and 05) during this period with straight transects (Mt. Aspiring 2a) over New Zealand´s Alps at three different flight-levels around the tropopause (approx. 11 km MSL). These research flights were coordinated with the GV (Research Flight 16) where the largest mountain wave amplitudes at flight-level (approx. 13 km MSL) were measured during DEEPWAVE. Additionally a first analysis of Falcons in-situ flight-level data revealed amplitudes in the vertical wind larger than 4 m/s at all altitudes in the vicinity of the highest peaks of the Southern Alps. Here, we present a comprehensive picture of the gravity wave characteristics and propagation properties during this interesting gravity wave event. We use the airborne observations combined with a comprehensive set of ground-based measurements consisting of 13 radiosoundings (1.5 hourly interval) together with the DLR Rayleigh lidar. To cover the altitude range from the troposphere to the mesosphere, high-resolution (1 hourly) ECMWF analyses and forecasts are used to estimate the propagation conditions of the excited mountain waves. The goal of our investigation is to find out whether the large amplitude mesospheric gravity waves are caused by the strong tropospheric forcing.

Static Pressure from Aircraft Trailing-Cone Measurements and Numerical Weather-Prediction Analysis

Accurate static-pressure measurements are a prerequisite for safe navigation and precise air-data measurements on aircraft. Pressure is also fundamental for wind and air temperature analysis in meteorology. Static-pressure measurement by aircraft is disturbed by aerodynamics and needs to be corrected using calibration. In this paper, a comparison has been made between static pressure measured by means of a trailing cone in the atmosphere behind two different jet aircraft at flight levels up to 450 and data from numerical weather predictions. The height is derived from differential Global Navigation Satellite System measurements. The Global Navigation Satellite System height is compared to numerical-weather-prediction geopotential height. The numerical-weather-prediction data were provided by the Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts. When computing the geopotential with latitude-/height-dependent gravity, the pressure/height differences are −0.01±0.15  hPa an...

Comparison of Static Pressure from Aircraft Trailing Cone Measurements and Numerical Weather Prediction Analysis

Accurate static pressure measurements are a prerequisite for safe navigation and precise air data measurements on aircraft. Pressure is also fundamental to assess winds and air temperature and, hence, important for meteorology. The direct static pressure measurement by aircraft is disturbed by the aircraft aerodynamics and needs to be corrected using proper calibration. In this paper we compare static pressure measured by means of a trailing cone (TC) in the undisturbed atmosphere behind two different jet aircraft (Dassault FALCON 20E and Gulfstream 550 “HALO”) at flight levels (FL) from 40 to 450 during 6 flights on different days with data from numerical weather predictions (NWP). The height is derived from differential Global Navigation Satellite System (GNSS) measurements. The GNSS height is compared to NWP geopotential height. The NWP data were provided by the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The IFS model assumes constant gravity g. For constant g, the pressure differences (at same height) have mean values and standard deviations of 0.40±0.17 hPa for 159 individual measurements of 43±31 s duration each. The respective height differences (at same pressure) are -10±5 m on average over the same measurements. When computing the geopotential with latitude/height dependent gravity (which is 0.4 % smaller at FL 450 than at 0 km) the agreement becomes significantly better: -0.01±0.15 hPa for pressure, 0.6±2.8 m for height. This pressure accuracy implies NWP temperature errors <0.1 K on average below 10 km altitude. Standard deviations of random errors in the TC-NWP difference are 0.06 hPa and 1 m. The TC measurements provide a first quantification of the case-specific accuracy of NWP pressure geopotential relationships. The method of comparing operational pressure/GNSS measurements on aircraft with NWP analysis or predictions can be used to test the height keeping performance of aircraft after or during operation.