The Polar Stratosphere in a Changing Climate (POLSTRACC) mission employed the German High Altitude and Long Range Research Aircraft (HALO). The payload comprised an innovative combination o...

/pdf/polstracc-airborne-experiment-for-studying-the-polar-35uxcdtjhf.pdf

Polstracc: Airborne Experiment for Studying the Polar Stratosphere in a Changing Climate with the High Altitude and Long Range Research Aircraft (HALO)

Strong turbulence was encountered by the German High-Altitude Long-Range Research Aircraft (HALO) at flight level 430 (13.8 km) on 13 October 2016 above Iceland. In this event the turbulenc...

/pdf/mountain-wave-turbulence-encounter-of-the-research-aircraft-57pt1k4z5r.pdf

Mountain-Wave Turbulence Encounter of the Research Aircraft HALO above Iceland

. Some of the Aircraft Meteorological Data Relay (AMDAR)
data include a turbulence metric of the derived equivalent vertical gust
(DEVG), in addition to wind and temperature. As the cube root of the eddy
dissipation rate (EDR) is the International Civil Aviation Organization
standard turbulence reporting metric, we attempt to retrieve the EDR from
the DEVG for more reliable and consistent observations of aviation
turbulence globally. Using the DEVG in the AMDAR data archived from
October 2015 to September 2018 covering a large portion of the Southern Hemisphere
and North Pacific and North Atlantic oceans, we convert the DEVG to the EDR
using two methods, after conducting quality control procedures to remove
suspicious turbulence reports in the DEVG. The first method remaps the DEVG
to the EDR using a lognormal mapping scheme, while the second one uses the
best-fit curve between the EDR and DEVG developed in a previous study. The
DEVG-derived EDRs obtained from the two methods are evaluated against in
situ EDR data reported by US-operated carriers. For two specified
regions of the Pacific Ocean and Europe, where both the DEVG-derived
EDRs and in situ EDRs were available, the DEVG-derived EDRs obtained by the
two methods were generally consistent with in situ EDRs, with slightly better
statistics obtained by the first method than the second one. This result is
encouraging for extending the aviation turbulence data globally with the
single preferred EDR metric, which will contribute to the improvement of
global aviation turbulence forecasting as well as to the construction of the
climatology of upper-level turbulence.

/pdf/retrieval-of-eddy-dissipation-rate-from-derived-equivalent-53gzz9fr35.pdf

Retrieval of eddy dissipation rate from derived equivalent vertical gust included in Aircraft Meteorological Data Relay (AMDAR)

. We report airborne remote-sensing observations of a tropopause fold during
two crossings of the polar front jet over northern Italy on 12 January 2016.
The GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere)
observations allowed for a simultaneous mapping of temperature, water vapour,
and ozone. They revealed deep, dry, and ozone-rich intrusions into the
troposphere. The mesoscale fine structures of dry filaments at the cyclonic
shear side north of the jet and tongues of moist air entraining tropospheric
air into the stratosphere along the anticyclonic shear side south of the jet
were clearly resolved by GLORIA observations. Vertically propagating mountain
waves with recorded temperature residuals exceeding ±3  K were detected
above the Apennines. Their presence enhanced gradients of all variables
locally in the vicinity of the tropopause. The combination of
 H2O−O3 correlations with potential temperature reveals an active
mixing region and shows clear evidence of troposphere-to-stratosphere and
stratosphere-to-troposphere exchange. High-resolution short-term
deterministic forecasts of ECMWF's integrated forecast system (IFS) applying
GLORIA's observational filter reproduce location, shape, and depth of the
tropopause fold very well. The fine structure of the mixing region, however,
cannot be reproduced even with the 9 km horizontal resolution of the
IFS, used here. This case study demonstrates convincingly the capabilities of linear
limb-imaging observations to resolve mesoscale fine structures in the upper
troposphere and lower stratosphere, validates the high quality of the IFS
data, and suggests that mountain wave perturbations have the potential to
modulate exchange processes in the vicinity of tropopause folds.

/pdf/mesoscale-fine-structure-of-a-tropopause-fold-over-mountains-3pbmmoowtq.pdf

Mesoscale fine structure of a tropopause fold over mountains

. To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography.
We observe GWs along a transect through Greenland where the GW packet covers ≈ 1 / 3 of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13  km of altitude with a horizontal wavelength of 330  km , a vertical wavelength of 2  km and a large temperature amplitude of 4.5  K . Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72  m s−1 ) the GW packet has a slow vertical group velocity of 0.05–0.2  m s−1 . This causes the GW packet to propagate long distances while spreading over a large area and remaining constrained to a narrow vertical layer.
A plausible source is not only orography, but also out-of-balance winds in a jet exit region and wind shear. To identify the GW source, 3D GLORIA observations are combined with a gravity wave ray tracer, ERA5 reanalysis and high-resolution numerical experiments. In a numerical experiment with a smoothed orography, GW activity is quite weak, indicating that the GWs in the realistic orography experiment are due to orography. However, analysis shows that these GWs are not mountain waves. A favourable area for spontaneous GW emission is identified in the jet by the cross-stream ageostrophic wind, which indicates when the flow is out of geostrophic balance. Backwards ray-tracing experiments trace into the jet and regions where the Coriolis and the pressure gradient forces are out of balance. The difference between the full and a smooth-orography experiment is investigated to reveal the missing connection between orography and the out-of-balance jet. We find that this is flow over a broad area of elevated terrain which causes compression of air above Greenland. The orography modifies the wind flow over large horizontal and vertical scales, resulting in out-of-balance geostrophic components. The out-of-balance jet then excites GWs in order to bring the flow back into balance. This is the first observational evidence of GW generation by such an orography–jet mechanism.

/pdf/orographically-induced-spontaneous-imbalance-within-the-jet-3xwiy1qkoh.pdf

Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event

Stall warnings at flight level 410 (125 km) occurred unexpectedly during a research flight of the High Altitude and Long Range Research Aircraft (HALO) over Italy on 12 January 2016 The d

/pdf/vertically-propagating-mountain-waves-a-hazard-for-high-2l11ntkro1.pdf

Vertically Propagating Mountain Waves—A Hazard for High-Flying Aircraft?

The added value of a satellite-based thunderstorm detection and nowcasting system with respect to flight safety and
efficiency is shown by comparing onboard observations carried out by Deutsche Lufthansa AG and Deutsches
Zentrum fur Luft- und Raumfahrt pilots to the detection and nowcasting information in both postflight analyses and
in real time. For the first time, detection and nowcasting data could be successfully uplinked into the cockpit of aircraft
during flight in real time, thereby demonstrating that these data are in good agreement with the returns of the onboard
radar, and furthermore provide an overview of the thunderstorm situation around the aircraft and along the
aircraft’s flight track. Pilots can use the detection and nowcasting information to strategically plan their route up to
1 h ahead in time. The result is safer flight routes that avoid inadvertent flights through areas where thunderstormrelated
hazards like turbulence, icing, and hail occur. In addition, the improved strategic planning enables smarter
flight routes, resulting in fuel savings, reduced delays, and less deviations to alternates.

/pdf/satellite-based-real-time-thunderstorm-nowcasting-for-acrdqzwn5h.pdf

Steffen Gemsa

Papers

Vertically Propagating Mountain Waves—A Hazard for High-Flying Aircraft?

Satellite-Based Real-Time Thunderstorm Nowcasting for Strategic Flight Planning En Route