Johannes Orphal

Rudolph Clausius is well known as a pioneer of the mechanical theory of heat (1857) and as the creator of the concept of entropy (1865). Oftentimes, he is also called the discoverer of the second law of thermodynamics although some argue that this law was already established by Sadi Carnot in 1824 (while still based on the caloric theory). But beyond any doubt, it was Clausius who gave in 1850 the first mathematically correct formulation of the first law (in its differential form that is still valid today, dQ = dU + pdV) and a particularly stringent exposition of both the necessity and independence of the two laws, indeed a logical masterpiece. This paper focuses on his concept of mathematical physics for the development of theoretical physics, contributions that have changed physics well beyond the field of thermodynamics.

“Rudolph Clausius, Gustav Magnus, and the Emergence of the Second Law of Thermodynamics” by Johannes Orphal und Dieter Hoffmann (German language).—Johannes Orphal and Dieter Hoffmann show how closely Rudolph Clausius’s path toward the mechanical theory of heat and the second law of thermodynamics was bound up with Gustav Magnus, his Berlin milieu, and the physics colloquium held in Magnus’s house on Am Kupfergraben. The essay reconstructs Clausius’s Berlin years, from his studies at Friedrich Wilhelm University and his financially burdensome work as a private tutor and teacher candidate to his doctorate, habilitation, and teaching appointment at the United Artillery and Engineering School. At the center is Magnus’s colloquium, where, beginning in 1843, Clausius reported on current international scientific literature and in 1844 discussed Émile Clapeyron’s “On the Motive Power of Heat”—a key moment that points directly toward his groundbreaking 1850 paper. Orphal and Hoffmann bring together biographical, institutional, and historical perspectives on science, showing how Magnus’s library, his network, his experimental studies in the theory of heat, and his methodological skepticism toward speculative theory helped shape Clausius’s research style. At the same time, they make clear that before 1850 Clausius was already thinking about heat and work, the mechanical equivalent of heat, molecular theory, vapor pressure, nonideal gases, and what would later become kinetic gas theory. The essay demonstrates that the emergence of the second law of thermodynamics cannot be understood in isolation, but grew out of a dense Berlin space of communication in which theoretical physics, experimental physics, and scientific networks productively converged.

This proof‐of‐concept study demonstrates that methane (CH₄) emissions from natural gas (NG) and agriculture can be disentangled using the concept of excess column observations. A network of cost‐effective sensors measured excess column‐averaged dry‐air mole fractions for CH₄ (ΔXCH₄), ethane (ΔXC₂H₆ as NG tracer), and ammonia (ΔXNH₃ from agriculture) in the Denver‐Julesburg Basin during March 2015. ΔXCH₄ varied up to 17 ppb and was >3 times higher with winds from directions where NG is produced. The ΔXCH₄ variance is explained by variations in the C₂H₆‐NH₃ tracer pair, attributing 63 ± 17% to NG, 25 ± 10% to agriculture, and 12 ± 12% to other sources. The ratios ΔXC₂H₆/ΔXCH₄ (16 ± 2%; indicates wet NG) and ΔXNH₃/ΔXCH₄ (43 ± 12%) were compatible with in situ measured ratios. Excess columns are independent of boundary layer height, characterize gases in the open atmosphere, are inherently calibrated, average over extended spatial scales, and provide a complementary perspective to quantify and attribute CH₄ emissions on regional scales.

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 H ₂ O−O ₃ 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.

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/GW-LCYCLE/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, 80 ^∘ W–30 ^∘ E. From the GLORIA infrared limb-emission measurements, two-dimensional cross sections of temperature, HNO ₃ , O ₃ , ClONO ₂ , H ₂ O 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) 1 σ 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 HNO ₃ , -3.5ppbv±116.8 ppbv for O ₃ , -15.4pptv±102.8 pptv for ClONO ₂ , -0.13ppmv±0.63 ppmv for H ₂ O 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 HNO ₃ and O ₃ 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).

Discrepancies in ozone retrievals in MIPAS channels A (685–970 cm⁻¹) and AB (1020–1170 cm⁻¹) have been a long-standing problem in MIPAS data analysis, amounting to an interchannel bias (AB–A) of up to 8 % between ozone volume mixing ratios in the altitude range 30–40 km. We discuss various candidate explanations, among them forward model and retrieval algorithm errors, interchannel calibration inconsistencies and spectroscopic data inconsistencies. We show that forward-modelling errors as well as errors in the retrieval algorithm can be ruled out as an explanation because the bias can be reproduced with an entirely independent retrieval algorithm (GEOFIT), relying on a different forward radiative transfer model. Instrumental and calibration issues can also be refuted as an explanation because ozone retrievals based on balloon-borne measurements with a different instrument (MIPAS-B) and an independent level-1 data processing scheme produce a rather similar interchannel bias. Thus, spectroscopic inconsistencies in the MIPAS database used for ozone retrieval are practically the only reason left. To further investigate this issue, we performed retrievals using additional spectroscopic databases. Various versions of the HITRAN database generally produced rather similar channel AB–A differences. Use of a different database, namely GEISA-2015, led to similar results in channel AB, but to even higher ozone volume mixing ratios for channel A retrievals, i.e. to a reversal of the bias. We show that the differences in MIPAS channel A retrievals result from about 13 % lower air-broadening coefficients of the strongest lines in the GEISA-2015 database. Since the errors in line intensity of the major lines used in MIPAS channels A and AB are reported to be considerably lower than the observed bias, we posit that a major part of the channel AB–A differences can be attributed to inconsistent air-broadening coefficients as well. To corroborate this assumption we show some clearly inconsistent air-broadening coefficients in the HITRAN-2008 database. The interchannel bias in retrieved ozone amounts can be reduced by increasing the air-broadening coefficients of the lines in MIPAS channel AB in the HITRAN-2008 database by 6 %–8 %.

We present the retrieved volume emission rates (VERs) from the airglow of both the daytime and twilight O₂(¹Σ) band and O₂(¹Δ) band emissions in the mesosphere and lower thermosphere (MLT). The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) onboard the European Space Agency Envisat satellite observes upwelling radiances in limb-viewing geometry during its special MLT mode over the range 50–150 km. In this study we use the limb observations in the visible (595–811 nm) and near-infrared (1200–1360 nm) bands. We have investigated the daily mean latitudinal distributions and the time series of the retrieved VER in the altitude range from 53 to 149 km. The maximal observed VERs of O₂(¹Δ) during daytime are typically 1 to 2 orders of magnitude larger than those of O₂(¹Σ). The latter peaks at around 90 km, whereas the O₂(¹Δ) emissivity decreases with altitude, with the largest values at the lower edge of the observations (about 53 km). The VER values in the upper mesosphere (above 80 km) are found to depend on the position of the sun, with pronounced high values occurring during summer for O₂(¹Δ). O₂(¹Σ) emissions show additional high values at polar latitudes during winter and spring. These additional high values are presumably related to the downwelling of atomic oxygen after large sudden stratospheric warmings (SSWs). Accurate measurements of the O₂(¹Σ) and O₂(¹Δ) airglow, provided that the mechanism of their production is understood, yield valuable information about both the chemistry and dynamics in the MLT. For example, they can be used to infer the amounts and distribution of ozone, solar heating rates, and temperature in the MLT.