Southeast Australia experienced intensive and geographically extensive wildfires during the 2019-2020 summer season. The fires released substantial amounts of carbon dioxide into the atmosphere. ...However, existing emission estimates based on fire inventories are uncertain, and vary by up to a factor of four for this event. Here we constrain emission estimates with the help of satellite observations of carbon monoxide, an analytical Bayesian inversion and observed ratios between emitted carbon dioxide and carbon monoxide. We estimate emissions of carbon dioxide to be 715 teragrams (range 517-867) from November 2019 to January 2020. This is more than twice the estimate derived by five different fire inventories, and broadly consistent with estimates based on a bottom-up bootstrap analysis ofthis fire episode. Although fires occur regularly in the savannas in northern Australia, the recent episodes were extremely large in scale and intensity, burning unusually large areas of eucalyptus forest in the southeast. The fires were driven partly by climate change, making better-constrained emission estimates particularly important. This is because the build-up of atmospheric carbon dioxide may become increasingly dependent on fire-driven climate-carbon feedbacks, as highlighted by this event.
A Major Asymmetric Dust Trap in a Transition Disk van der Marel, Nienke; van Dishoeck, Ewine F.; Bruderer, Simon ...
Science (American Association for the Advancement of Science),
06/2013, Volume:
340, Issue:
6137
Journal Article
Peer reviewed
Open access
The statistics of discovered exoplanets suggest that planets form effidently. However, there are fundamental unsolved problems, such as excessive inward drift of particles in protoplanetary disks ...during planet formation. Recent theories invoke dust traps to overcome this problem. We report the detection of a dust trap in the disk around the star Oph IRS 48 using observations from the Atacama Large Millimeter/submillimeter Array (ALMA). The 0.44-millimeter-wavelength continuum map shows high-contrast crescent-shaped emission on one side of the star, originating from millimeter-sized grains, whereas both the mid-infrared image (micrometer-sized dust) and the gas traced by the carbon monoxide 6-5 rotational line suggest rings centered on the star. The difference in distribution of big grains versus small grains/gas can be modeled with a vortex-shaped dust trap triggered by a companion.
Context. Transition disks are recognized by the absence of emission of small dust grains inside a radius of up to several 10s of AUs. Owing to the lack of angular resolution and sensitivity, the gas ...content of these dust holes has not yet been determined, but is of importance for constraining the mechanism leading to the dust holes. It is thought that transition disks are currently undergoing the process of dispersal, setting an end to the giant planet formation process. Aims. We present new high-resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of gas lines towards the transition disk Oph IRS 48 previously shown to host a large dust trap. The ALMA telescope has detected the J = 6−5 line of 12CO and C17O around 690 GHz (434 μm) at a resolution of ~0.25′′ corresponding to ~30 AU (FWHM). The observed gas lines are used to set constraints on the gas surface density profile. Methods. New models of the physical-chemical structure of gas and dust in Oph IRS 48 are developed to reproduce the CO line emission together with the spectral energy distribution and the VLT-VISIR 18.7 μm dust continuum images. Integrated intensity cuts and the total spectrum from models having different trial gas surface density profiles are compared to observations. The main parameters varied are the drop in gas surface density inside the dust-free cavity with a radius of 60 AU and inside the gas-depleted innermost 20 AU. Using the derived surface density profiles, predictions for other CO isotopologues are made, which can be tested by future ALMA observations of the object. Results. From the ALMA data we find a total gas mass of the disk of 1.4 × 10-4 M⊙. This gas mass yields a gas-to-dust ratio of ~10, but with considerable uncertainty. Inside 60 AU, the gas surface density drops by a factor of ~12 for an assumed surface density slope of γ = 1 (Σ ∝ r−γ). Inside 20 AU, the gas surface density drops by a factor of at least 110. The drops are measured relative to the extrapolation to small radii of the surface density law at radii >60 AU. The inner radius of the gas disk at 20 AU can be constrained to better than ±5 AU. Conclusions. The derived gas surface density profile points to the clearing of the cavity by one or more massive planets/companions rather than just photoevaporation or grain-growth.
Since its launch in 2017, Tropospheric Monitoring Instrument (TROPOMI) on S-5P has provided very high quality data using daily global coverage for a number of key atmospheric trace gases. Over its ...first 1000 d in operation, the short-wave infrared (SWIR) module has been very stable, and the continuously monitored calibration has remained of high quality. This calibration relies on a combination of extensive pre-launch and post-launch measurements, complemented by regular monitoring of internal light sources and background measurements.
In this paper we present a method and results for independent validation of the SWIR module calibration and instrument stability by examining the signal stability of a sample of 23 pseudo-invariant calibration desert sites. The data covers over 2 years of operational data.
With a Lambertian surface assumption, the results show that the SWIR module has little to no instrument degradation down to an accuracy of about 0.3 % yr−1, validating results obtained from the internal calibration suite. The method presented here will be used as ongoing validation of the SWIR calibration.
Abstract
We present full spectral scans from 200 to 670
μ
m of 26 Class 0+I protostellar sources obtained with
Herschel
-SPIRE as part of the “COPS-SPIRE” Open Time program, complementary to the ...DIGIT and WISH Key Programs. Based on our nearly continuous, line-free spectra from 200 to 670
μ
m, the calculated bolometric luminosities (
L
bol
) increase by 50% on average, and the bolometric temperatures (
T
bol
) decrease by 10% on average, in comparison with the measurements without
Herschel
. Fifteen protostars have the same class using
T
bol
and
L
bol
/
L
smm
. We identify rotational transitions of CO lines from
to
, along with emission lines of
13
CO, HCO
+
, H
2
O, and C
i
. The ratios of
12
CO to
13
CO indicate that
12
CO emission remains optically thick for
J
up
< 13. We fit up to four components of temperature from the rotational diagram with flexible break points to separate the components. The distribution of rotational temperatures shows a primary population around 100 K with a secondary population at ∼350 K. We quantify the correlations of each line pair found in our data set and find that the strength of the correlation of CO lines decreases as the difference between
J
levels between two CO lines increases. The multiple origins of CO emission previously revealed by velocity-resolved profiles are consistent with this smooth distribution if each physical component contributes to a wide range of CO lines with significant overlap in the CO ladder. We investigate the spatial extent of CO emission and find that the morphology is more centrally peaked and less bipolar at high-
J
lines. We find the CO emission observed with SPIRE related to outflows, which consists of two components, the entrained gas and shocked gas, as revealed by our rotational diagram analysis, as well as the studies with velocity-resolved CO emission.
The short-wave infrared (SWIR) module of the Tropospheric Monitoring Instrument (TROPOMI) on board the ESA's Sentinel-5 precursor (S5p) satellite has been very stable during its 5 years in orbit. ...Calibration was
performed on the ground, complemented by measurements during in-flight instrument commissioning. The radiometric response and general performance of the SWIR module are monitored by on-board calibration sources. We show that after 5 years in orbit, TROPOMI-SWIR has continued to show excellent
performance with degradation of at most 0.1 % in transmission and having lost less than 0.3 % of the detector pixels. Independent validation of the instrument calibration, via vicarious calibration, can be done through comparisons with ground-based reflectance data. In this work, ground measurements at the Railroad Valley Playa, a valley in central Nevada that is often used as a reference for satellite measurements, are used to perform vicarious calibration of the TROPOMI-SWIR measurements. This is done using dedicated measurement campaigns as well as automated reflectance measurements within the RADCALNET programme. As such, TROPOMI-SWIR is an excellent test case to explore the methodology of vicarious calibration applied to infrared spectroscopy. Using methodology developed for the vicarious calibration of the OCO-2 and GOSAT missions, the absolute radiometry of TROPOMI-SWIR performance is independently verified to be stable down to ∼ 6 %–10 % using the Railroad Valley when both the absolute and relative radiometric calibrations are applied. Differences with the on-board calibration originate from the bidirectional reflection distribution function (BRDF) effects of the desert surface, the large variety in viewing angles, and the different sizes of footprints of the TROPOMI pixels. Vicarious calibration is shown to be an additional valuable tool in validating radiance-level performances of infrared instruments such as TROPOMI-SWIR in the field of atmospheric composition. It remains clear that for instruments of similar design and resolution to TROPOMI-SWIR, on-board calibration sources will continue to provide superior results due to the limitations of the vicarious calibration method.
As atmospheric methane concentrations increase at record pace, it is critical to identify individual emission sources with high potential for mitigation. Here, we leverage the synergy between ...satellite instruments with different spatiotemporal coverage and resolution to detect and quantify emissions from individual landfills. We use the global surveying Tropospheric Monitoring Instrument (TROPOMI) to identify large emission hot spots and then zoom in with high-resolution target-mode observations from the GHGSat instrument suite to identify the responsible facilities and characterize their emissions. Using this approach, we detect and analyze strongly emitting landfills (3 to 29 t hour
−1
) in Buenos Aires, Delhi, Lahore, and Mumbai. Using TROPOMI data in an inversion, we find that city-level emissions are 1.4 to 2.6 times larger than reported in commonly used emission inventories and that the landfills contribute 6 to 50% of those emissions. Our work demonstrates how complementary satellites enable global detection, identification, and monitoring of methane superemitters at the facility level.
Landfill methane emissions with high potential for mitigation can be detected and quantified using a combination of satellites.
During its first year in operation the short-wave infrared (SWIR) Tropospheric Monitoring Instrument
(TROPOMI) was
calibrated in-flight and its performance was monitored.
In this paper we present the ...results of the in-flight calibration and the ongoing instrument monitoring. This includes the determination of the background signals, noise performance, instrument spectral response function (ISRF) stability, and stray-light stability. From these results, the number of incurred dead and bad
pixels due to cosmic-ray impacts is determined. The light-path transmission is checked by monitoring internal lamp and diffuser stabilities.
Due to its high sensitivity to Earth radiation on the eclipse side, the calibration strategy for the background (i.e. dark current and offset) monitoring was adjusted.
Trends over the first full year of nominal operations reveal a very stable SWIR module. The number of newly incurred dead and bad pixels
is less than 0.1 % over nearly a full year since the start of operations. Assuming linear degradation of various components, the SWIR module is expected to keep performing within expected parameters for the full operational lifetime.
The Tropospheric Monitoring Instrument (TROPOMI) is the single instrument on board the ESA Copernicus Sentinel-5 Precursor satellite. TROPOMI is a nadir-viewing imaging spectrometer with bands in the ...ultraviolet and visible, the near infrared and the shortwave infrared (SWIR). An accurate instrument spectral response function (ISRF) is required in the SWIR band where absorption lines of CO, methane and water vapor overlap. In this paper, we report on the determination of the TROPOMI-SWIR ISRF during an extensive on-ground calibration campaign. Measurements are taken with a monochromatic light source scanning the whole detector, using the spectrometer itself to determine the light intensity and wavelength. The accuracy of the resulting ISRF calibration key data is well within the requirement for trace-gas retrievals. Long-term in-flight monitoring of SWIR ISRF is achieved using five on-board diode lasers.
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