| 1. |
- Strong, K., et al.
(författare)
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Validation of ACE-FTS N2O measurements
- 2008
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 8, s. 4759-4786
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Tidskriftsartikel (refereegranskat)abstract
- The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar occultation technique. One of these instruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volume mixing ratio (VMR) profiles of nitrous oxide (N2O) from the upper troposphere to the lower mesosphere at a vertical resolution of about 3–4 km. In this study, the quality of the ACE-FTS version 2.2 N2O data is assessed through comparisons with coincident measurements made by other satellite, balloon-borne, aircraft, and ground-based instruments. These consist of vertical profile comparisons with the SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR, and single balloon flights of SPIRALE and FIRS-2, and partial column comparisons with a network of ground-based Fourier Transform InfraRed spectrometers (FTIRs). Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between −42 ppbv and +17 ppbv, with most within ±20 ppbv. This corresponds to relative deviations from the mean that are within ±15%, except for comparisons with MIPAS near 30 km, for which they are as large as 22.5%. Between 18 and 30 km, the mean absolute differences for the satellite comparisons are generally within ±10 ppbv. From 30 to 60 km, the mean absolute differences are within ±4 ppbv, and are mostly between −2 and +1 ppbv. Given the small N2O VMR in this region, the relative deviations from the mean are therefore large at these altitudes, with most suggesting a negative bias in the ACE-FTS data between 30 and 50 km. In the comparisons with the FTIRs, the mean relative differences between the ACE-FTS and FTIR partial columns (which cover a mean altitude range of 14 to 27 km) are within ±5.6% for eleven of the twelve contributing stations. This mean relative difference is negative at ten stations, suggesting a small negative bias in the ACE-FTS partial columns over the altitude regions compared. Excellent correlation (R=0.964) is observed between the ACE-FTS and FTIR partial columns, with a slope of 1.01 and an intercept of −0.20 on the line fitted to the data.
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| 2. |
- Sherratt, K., et al.
(författare)
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Predictive performance of multi-model ensemble forecasts of COVID-19 across European nations
- 2023
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Methods: We used open-source tools to develop a public European COVID-19 Forecast Hub. We invited groups globally to contribute weekly forecasts for COVID-19 cases and deaths reported by a standardised source for 32 countries over the next 1–4 weeks. Teams submitted forecasts from March 2021 using standardised quantiles of the predictive distribution. Each week we created an ensemble forecast, where each predictive quantile was calculated as the equally-weighted average (initially the mean and then from 26th July the median) of all individual models’ predictive quantiles. We measured the performance of each model using the relative Weighted Interval Score (WIS), comparing models’ forecast accuracy relative to all other models. We retrospectively explored alternative methods for ensemble forecasts, including weighted averages based on models’ past predictive performance.Results: Over 52 weeks, we collected forecasts from 48 unique models. We evaluated 29 models’ forecast scores in comparison to the ensemble model. We found a weekly ensemble had a consistently strong performance across countries over time. Across all horizons and locations, the ensemble performed better on relative WIS than 83% of participating models’ forecasts of incident cases (with a total N=886 predictions from 23 unique models), and 91% of participating models’ forecasts of deaths (N=763 predictions from 20 models). Across a 1–4 week time horizon, ensemble performance declined with longer forecast periods when forecasting cases, but remained stable over 4 weeks for incident death forecasts. In every forecast across 32 countries, the ensemble outperformed most contributing models when forecasting either cases or deaths, frequently outperforming all of its individual component models. Among several choices of ensemble methods we found that the most influential and best choice was to use a median average of models instead of using the mean, regardless of methods of weighting component forecast models.Conclusions: Our results support the use of combining forecasts from individual models into an ensemble in order to improve predictive performance across epidemiological targets and populations during infectious disease epidemics. Our findings further suggest that median ensemble methods yield better predictive performance more than ones based on means. Our findings also highlight that forecast consumers should place more weight on incident death forecasts than incident case forecasts at forecast horizons greater than 2 weeks.
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| 3. |
- Jin, J.J., et al.
(författare)
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Co-located ACE-FTS and Odin/SMR stratospheric-mesospheric CO 2004 measurements and comparison with a GCM
- 2005
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Ingår i: Geophysical Research Letters. - 1944-8007 .- 0094-8276. ; 32:15
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison of co-located and near simultaneous CO measurements from January to May, 2004 and from the Arctic to southern polar regions using the ACE-FTS, in solar occultation mode, and the Odin/SMR, which measures atmospheric emission. We find that there is excellent agreement between the two instruments at the locations investigated over 4 orders of magnitude from the lower stratosphere to the lower thermosphere. There is also good agreement with the CMAM model simulation from 20 km to 90 km in sub-tropical and tropical latitudes but poorer agreement in the upper stratosphere and lower mesosphere in winter polar regions. For the Arctic in March 2004 this can be attributed, at least partly, to the unique dynamical processes in the stratosphere in the winter of 2003 - 2004. Clearly CO measurements from these instruments will provide a useful tool for testing model transport from the troposphere to the thermosphere.
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| 4. |
- Jin, J.J., et al.
(författare)
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Comparison of CMAM simulations of carbon monoxide (CO), nitrous oxide (N2O), and methane (CH4) with observations from Odin/SMR, ACE-FTS, and Aura/MLS
- 2009
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 9, s. 3233-3252
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Tidskriftsartikel (refereegranskat)abstract
- Simulations of CO, N2O and CH4 from a coupled chemistry-climate model (CMAM) are compared with satellite measurements from Odin Sub-Millimeter Radiometer (Odin/SMR), Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and Aura Microwave Limb Sounder (Aura/MLS). Pressure-latitude cross-sections and seasonal time series demonstrate that CMAM reproduces the observed global CO, N2O, and CH4 distributions quite well. Generally, excellent agreement with measurements is found between CO simulations and observations in the stratosphere and mesosphere. Differences between the simulations and the ACE-FTS observations are generally within 30%, and the differences between CMAM results and SMR and MLS observations are slightly larger. These differences are comparable with the difference between the instruments in the upper stratosphere and mesosphere. Comparisons of N2O show that CMAM results are usually within 15% of the measurements in the lower and middle stratosphere, and the observations are close to each other. However, the standard version of CMAM has a low N2O bias in the upper stratosphere. The CMAM CH4 distribution also reproduces the observations in the lower stratosphere, but has a similar but smaller negative bias in the upper stratosphere. The negative bias may be due to that the gravity drag is not fully resolved in the model. The simulated polar CO evolution in the Arctic and Antarctic agrees with the ACE and MLS observations. CO measurements from 2006 show evidence of enhanced descent of air from the mesosphere into the stratosphere in the Arctic after strong stratospheric sudden warmings (SSWs). CMAM also shows strong descent of air after SSWs. In the tropics, CMAM captures the annual oscillation in the lower stratosphere and the semiannual oscillations at the stratopause and mesopause seen in Aura/MLS CO and N2O observations and in Odin/SMR N2O observations. The Odin/SMR and Aura/MLS N2O observations also show a quasi-biennial oscillation (QBO) in the upper stratosphere, whereas, the CMAM does not have QBO included. This study confirms that CMAM is able to simulate middle atmospheric transport processes reasonably well.
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| 5. |
- Nassar, R., et al.
(författare)
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A global inventory of stratospheric chlorine in 2004
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:22
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Tidskriftsartikel (refereegranskat)abstract
- Total chlorine (CITOT) in the stratosphere has been determined using the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measurements of HCl, ClONO2, CH3Cl, CCl4, CCl3F (CFC-11), CCl2F2 (CFC-12), CHClF2 (HCFC-22), CCl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), COClF, and ClO supplemented by data from several other sources, including both measurements and models. Separate chlorine inventories were carried out in five latitude zones (60°-82°N, 30°-60°N, 30°S-30°N, 30°-60°S, and 60°-82°S), averaging the period of February 2004 to January 2005 inclusive, when possible, to deal with seasonal variations. The effect of diurnal variation was avoided by only using measurements taken at local sunset. Mean stratospheric ClTOT values of 3.65 ppbv were determined for both the northern and southern midlatitudes (with an estimated 1σ, accuracy of ±0.13 ppbv and a precision of ±.09 ppbv), accompanied by a slightly lower value in the tropics and slightly higher values at high latitudes. Stratospheric ClTOT profiles in all five latitude zones are nearly linear with a slight positive slope in ppbv /km. Both the observed slopes and pattern of latitudinal variation can be interpreted as evidence of the beginning of a decline in global stratospheric chlorine, which is qualitatively consistent with the mean stratospheric circulation pattern and time lag necessary for transport.
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| 6. |
- Fomichev, V. I., et al.
(författare)
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Response of the middle atmosphere to CO2 doubling : Results from the Canadian Middle Atmosphere Model
- 2007
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 20:7
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Tidskriftsartikel (refereegranskat)abstract
- The Canadian Middle Atmosphere Model (CMAM) has been used to examine the middle atmosphere response to CO2 doubling. The radiative-photochemical response induced by doubling CO2 alone and the response produced by changes in prescribed SSTs are found to be approximately additive, with the former effect dominating throughout the middle atmosphere. The paper discusses the overall response, with emphasis on the effects of SST changes, which allow a tropospheric response to the CO2 forcing. The overall response is a cooling of the middle atmosphere accompanied by significant increases in the ozone and water vapor abundances. The ozone radiative feedback occurs through both an increase in solar heating and a decrease in infrared cooling, with the latter accounting for up to 15% of the total effect. Changes in global mean water vapor cooling are negligible above 30 hPa. Near the polar summer mesopause, the temperature response is weak and not statistically significant. The main effects of SST changes are a warmer troposphere, a warmer and higher tropopause, cell-like structures of heating and cooling at low and middlelatitudes in the middle atmosphere, warming in the summer mesosphere, water vapor increase throughout the domain, and O3 decrease in the lower tropical stratosphere. No noticeable change in upward-propagating planetary wave activity in the extratropical winter–spring stratosphere and no significant temperature response in the polar winter–spring stratosphere have been detected. Increased upwelling in the tropical stratosphere has been found to be linked to changed wave driving at low latitudes.
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| 7. |
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| 8. |
- Semeniuk, M., et al.
(författare)
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Design and fabrication of low-cost renewable carbon electrode materials and their thermo-kinetics for sustainable energy storage applications
- 2022
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Ingår i: Materials Today Sustainability. - : Elsevier. - 2589-2347. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- To date, there have been few studies performed on the kinetics of thermal decomposition of renewable carbon and its use in energy storage devices. Novel renewable graphitic carbon from Acer saccharum, sugar maple (SM) heartwood, and Arachis hypogaea, peanut outer shell (PS), are used as anodes in lithium-ion coin cell batteries, with steady specific capacities of 180 mAh/g and 220 mAh/g, respectively, and both retain 100% columbic efficiency for over 350 cycles. Cyclic voltammetry reveals the different charge storage kinetic mechanisms of the two. The voltammogram of SM contains an oxidation peak indicating Li ion intercalation suitable for battery application, while PS lacks a peak; thus, showing potential for function as a supercapacitor. A kinetic study is undertaken on six carbon sources to improve the understanding of the thermal degradation process leading to renewable graphitic carbon. Consistent results are shown across the various model-free methods, indicating that they can accurately describe the devolatilization process. The renewable graphitic carbons morphological features were studied by SEM, XRD, Raman and nitrogen adsorption isotherms. As SM and PS compare favorably to the electrodes they replace, renewable graphitic carbon has the potential for use in a wide variety of novel applications, such as organic thin film transistors, fuel cells, organic batteries, supercapacitors, and other bioelectronics.
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