Jörn Ungermann

Tomographic reconstruction of atmospheric gravity wave parameters from airglow observations

Gravity waves (GWs) play an important role in the dynamics of the mesosphere and lower thermosphere (MLT). Therefore, global observations of GWs in the MLT region are of particular interest. The small scales of GWs, however, pose a major problem for the observation of GWs from space. We propose a new observation strategy for GWs in the mesopause region by combining limb and sub-limb satellite-borne remote sensing measurements for improving the spatial resolution of temperatures that are retrieved from atmospheric soundings. In our study, we simulate satellite observations of the rotational structure of the O2 A-band nightglow. A key element of the new method is the ability of the instrument or the satellite to operate in so-called “target mode”, i.e. to point at a particular point in the atmosphere and collect radiances at different viewing angles. These multi-angle measurements of a selected region allow for tomographic 2-D reconstruction of the atmospheric state, in particular of GW structures. The feasibility of this tomographic retrieval approach is assessed using simulated measurements. It shows that one major advantage of this observation strategy is that GWs can be observed on a much smaller scale than conventional observations. We derive a GW sensitivity function, and it is shown that “target mode” observations are able to capture GWs with horizontal wavelengths as short as∼ 50 km for a large range of vertical wavelengths. This is far better than the horizontal wavelength limit of 100– 200 km obtained from conventional limb sounding.

Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

Limb sounding instruments play an important role in the monitoring of climate trends, as they provide a good vertical resolution. Traceability to the International System of Units (SI) via onboard reference or transfer standards is needed to compare trend estimates from multiple instruments. This study investigates the required uncertainty of these radiation standards to properly resolve decadal trends of climate-relevant trace species like ozone, water vapor, and temperature distribution for the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). Temperature nonuniformities of the onboard reference blackbodies, used for radiometric calibration, have an impact on the calibration uncertainty. The propagation of these nonuniformities through the retrieval is analyzed. A threshold for the maximum tolerable uncertainty of the blackbody temperature is derived, so that climate trends can be significantly identified with GLORIA.

Airborne limb-imaging measurements of temperature, HNO 3 , O 3 , ClONO 2 , H 2 O and CFC-12 during the Arctic winter 2015/16: characterization, in-situ validation and comparison to Aura/MLS

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) was operated on board the German High Altitude and Long Range Research Aircraft (HALO) during the PGS (POLSTRACC/GWLCYCLE/SALSA) aircraft campaigns in the Arctic winter 2015/2016. Research flights were conducted from 17 December 2015 until 18 March 2016 within 25–87 N, 80W–30 E. From the GLORIA infrared limb-emission measurements, two-dimensional cross sections of temperature, HNO3, O3, ClONO2, H2O and CFC-12 are retrieved. During 15 scientific flights of the PGS campaigns the GLORIA instrument measured more than 15 000 atmospheric profiles at high spectral resolution. Dependent on flight altitude and tropospheric cloud cover, the profiles retrieved from the measurements typically range between 5 and 14 km, and vertical resolutions between 400 and 1000 m are achieved. The estimated total (random and systematic) 1σ errors are in the range of 1 to 2 K for temperature and 10 % to 20 % relative error for the discussed trace gases. Comparisons to in situ instruments deployed on board HALO have been performed. Over all flights of this campaign the median differences and median absolute deviations between in situ and GLORIA observations are−0.75K±0.88 K for temperature, −0.03ppbv± 0.85 ppbv for HNO3, −3.5ppbv± 116.8 ppbv for O3,−15.4pptv±102.8 pptv for ClONO2,−0.13ppmv± 0.63 ppmv for H2O and −19.8pptv± 46.9 pptv for CFC-12. Seventy-three percent of these differences are within twice the combined estimated errors of the cross-compared instruments. Events with larger deviations are explained by atmospheric variability and different sampling characteristics of the instruments. Additionally, comparisons of GLORIA HNO3 and O3 with measurements of the Aura Microwave Limb Sounder (MLS) instrument show highly consistent structures in trace gas distributions and illustrate the potential of the high-spectral-resolution limb-imaging GLORIA observations for resolving narrow mesoscale structures in the upper troposphere and lower stratosphere (UTLS).

Towards High Resolution Infrared Limb Sounding of the Upper Troposphere / Lower Stratosphere (UTLS)

We give an overview on the role of the upper troposphere and stratosphere in the climate system and the important scientific questions that can the investigated based on previous and newly developed infrared limb-sounding technique.

Integration of Infrared Focal Plane Array Detectors in the GLORIA Imaging FTS

The five years of deployment of the GLORIA iFTS has taught us a great deal about the combination of imaging and FTS systems. The detector related effects, their impact and their mitigation are presented.

The Three-dimensional Reconstruction of Temperature and Trace Gas Distributions from Measurements of the Airborne Limb-imager GLORIA

This paper describes the tomographic processing of dynamics mode measurements of the airborne Fourier-transform spectrometer GLORIA. First trace gas results are presented including validation against in situ measurements.