scholarly journals Investigation and amelioration of long-term instrumental drifts in water vapor and nitrous oxide measurements from the Aura Microwave Limb Sounder (MLS) and their implications for studies of variability and trends

2021 ◽  
Author(s):  
Nathaniel J. Livesey ◽  
William G. Read ◽  
Lucien Froidevaux ◽  
Alyn Lambert ◽  
Michelle L. Santee ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
Relative Sensitivity ◽  
Atmospheric Species ◽  
Long Term Stability ◽  
Frost Point ◽  
Global Coverage ◽  
Chemistry Experiment ◽  
Made In

Abstract. The Microwave Limb Sounder (MLS), launched on NASA's Aura spacecraft in 2004, measures vertical profiles of the abundances of key atmospheric species from the upper troposphere to the mesosphere with daily near-global coverage. We review the first 15 years of the record of H2O and N2O measurements from the MLS 190-GHz subsystem (along with other 190-GHz information), with a focus on their long-term stability, largely based on comparisons with measurements from other sensors. These comparisons generally show signs of an increasing drift in the MLS version 4 (v4) H2O record starting around 2010. Specifically, comparisons with v4.1 measurements from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) indicate a ~2–3 %/decade drift over much of the stratosphere, increasing to as much as ~7 %/decade around 46 hPa. Larger drifts, of around 7–11 %/decade, are seen in comparisons to balloon-borne frost point hygrometer measurements in the lower stratosphere. In contrast, the MLS v4 N2O product is shown to be generally decreasing over the same period (when an increase in stratospheric N2O is expected, reflecting a secular growth in emissions), with a more pronounced drift in the lower stratosphere than that found for H2O. Detailed investigations of the behavior of the MLS 190-GHz subsystem reveal a drift in its sideband fraction (the relative sensitivity of the 190-GHz receiver to the two different parts of the microwave spectrum it observes). Our studies indicate that sideband fraction drift accounts for much of the observed changes in the MLS H2O product and some portion of the changes seen in N2O. The 190-GHz sideband fraction drift has been corrected in the new version 5 MLS algorithms, which have now been used to reprocess the entire MLS record. As a result of this correction, the MLS v5 H2O record shows no statistically significant drifts compared to ACE-FTS. However, statistically significant drifts remain between MLS v5 and frost point measurements, though they are reduced. Drifts in v5 N2O are about half the size of those in v4 but remain statistically significant. Scientists are advised to use MLS v5 data in all future studies. Quantification of inter-regional and seasonal-to-annual changes in MLS H2O and N2O will not be affected by the drift. However, caution is advised in studies using the MLS record to examine long-term (multi-year) variability and trends in either of these species, especially N2O; such studies should only be undertaken in consultation with the MLS team. Importantly, this drift does not affect any of the MLS observations made in other spectral regions such as O3, HCl, CO, ClO, or temperature.

scholarly journals Investigation and amelioration of long-term instrumental drifts in water vapor and nitrous oxide measurements from the Aura Microwave Limb Sounder (MLS) and their implications for studies of variability and trends

2021 ◽  
Vol 21 (20) ◽  
pp. 15409-15430
Author(s):  
Nathaniel J. Livesey ◽  
William G. Read ◽  
Lucien Froidevaux ◽  
Alyn Lambert ◽  
Michelle L. Santee ◽  
...  
Keyword(s):  
Water Vapor ◽  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
Relative Sensitivity ◽  
Atmospheric Species ◽  
Long Term Stability ◽  
Frost Point ◽  
Broadband Emission ◽  
Stratospheric Clouds

Abstract. The Microwave Limb Sounder (MLS), launched on NASA's Aura spacecraft in 2004, measures vertical profiles of the abundances of key atmospheric species from the upper troposphere to the mesosphere with daily near-global coverage. We review the first 15 years of the record of H2O and N2O measurements from the MLS 190 GHz subsystem (along with other 190 GHz information), with a focus on their long-term stability, largely based on comparisons with measurements from other sensors. These comparisons generally show signs of an increasing drift in the MLS “version 4” (v4) H2O record starting around 2010. Specifically, comparisons with v4.1 measurements from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) indicate a ∼ 2 %–3 % per decade drift over much of the stratosphere, increasing to as much as ∼ 7 % per decade around 46 hPa. Larger drifts, of around 7 %–11 % per decade, are seen in comparisons to balloon-borne frost point hygrometer measurements in the lower stratosphere. Microphysical calculations considering the formation of polar stratospheric clouds in the Antarctic winter stratosphere corroborate a drift in MLS v4 water vapor measurements in that region and season. In contrast, comparisons with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission, and with ground-based Water Vapor Millimeter-wave Spectrometer (WVMS) instruments, do not show statistically significant drifts. However, the uncertainty in these comparisons is large enough to encompass most of the drifts identified in other comparisons. In parallel, the MLS v4 N2O product is shown to be generally decreasing over the same period (when an increase in stratospheric N2O is expected, reflecting a secular growth in emissions), with a more pronounced drift in the lower stratosphere than that found for H2O. Comparisons to ACE-FTS and to MLS N2O observations in a different spectral region, with the latter available from 2004 to 2013, indicate an altitude-dependent drift, growing from 5 % per decade or less in the mid-stratosphere to as much as 15 % per decade in the lower stratosphere. Detailed investigations of the behavior of the MLS 190 GHz subsystem reveal a drift in its “sideband fraction” (the relative sensitivity of the 190 GHz receiver to the two different parts of the microwave spectrum that it observes). Our studies indicate that sideband fraction drift accounts for much of the observed changes in the MLS H2O product and some portion of the changes seen in N2O. The 190 GHz sideband fraction drift has been corrected in the new “version 5” (v5) MLS algorithms, which have now been used to reprocess the entire MLS record. As a result of this correction, the MLS v5 H2O record shows no statistically significant drifts compared to ACE-FTS. However, statistically significant drifts remain between MLS v5 and frost point measurements, although they are reduced. Drifts in v5 N2O are about half the size of those in v4 but remain statistically significant. Scientists are advised to use MLS v5 data in all future studies. Quantification of interregional and seasonal to annual changes in MLS H2O and N2O will not be affected by the drift. However, caution is advised in studies using the MLS record to examine long-term (multiyear) variability and trends in either of these species, especially N2O; such studies should only be undertaken in consultation with the MLS team. Importantly, this drift does not affect any of the MLS observations made in other spectral regions such as O3, HCl, CO, ClO, or temperature.

No Justice Without Peace, But What Peace Is on Offer?

2020 ◽  
Author(s):  
Mark Kersten
Keyword(s):  
Middle East ◽  
International Criminal Court ◽  
International Criminal ◽  
Criminal Court ◽  
Term Stability ◽  
Long Term Stability ◽  
Peace Processes ◽  
Lasting Peace ◽  
Made In

Abstract Does the potential investigation into Palestine by the International Criminal Court (ICC) threaten the chances of a lasting ‘peace’ between Israel and Palestine? This article endeavours to answer that question and critically assesses claims that the Court could undermine peace in the Middle East. I first examine the key claims made in the so-called ‘peace versus justice’ debate. I then outline some of the specific arguments made in the context of a possible ICC investigation in Palestine that touch upon concerns over the Court’s impacts on peace processes and negotiations. Following this, I try to assess critically the validity of these claims, arguing that while it would be wrong to conclude that the ICC will invariably have positive impacts on efforts to establish peace, there is no evidence that the Court will undermine whatever ‘peace’ is currently on offer for Palestinians and Israelis. On the contrary, this ‘peace’ may itself be a threat to resolving the conflict peaceably and to long-term stability in the region. Finally, I conclude the article with some reflections on the peace-justice debate and its applicability to the Israel–Palestine situation.

scholarly journals The high Arctic in extreme winters: vortex, temperature, and MLS and ACE-FTS trace gas evolution

2008 ◽  
Vol 8 (3) ◽  
pp. 505-522 ◽  
Author(s):  
G. L. Manney ◽  
W. H. Daffer ◽  
K. B. Strawbridge ◽  
K. A. Walker ◽  
C. D. Boone ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
High Arctic ◽  
Trace Gas ◽  
Satellite Measurements ◽  
Broadband Emission ◽  
Gas Measurements ◽  
Chemistry Experiment ◽  
Very High ◽  
Good Agreement

Abstract. The first three Arctic winters of the ACE mission represented two extremes of winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns were conducted at Eureka (80° N, 86° W) during each of these winters. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), and Aura Microwave Limb Sounder (MLS), along with meteorological analyses and Eureka lidar temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport, and to provide a context for interpretation of ACE-FTS and validation campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, near 75 km. ACE measurements covered both vortex and extra-vortex conditions in each winter, except in late-February through mid-March 2004 and 2006, when the strong, pole-centered vortex that reformed after the SSWs resulted in ACE sampling only inside the vortex in the middle through upper stratosphere. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with lidar data up to 50–60 km, and ACE-FTS, MLS and SABER show good agreement in high-latitude temperatures throughout the winters. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex in late January through March 2006 compared to that in 2005.

scholarly journals The SPARC water vapour assessment II: Profile-to-profile and climatological comparisons of stratospheric <i>δ</i>D(H<sub>2</sub>O) observations from satellite

2018 ◽  
Author(s):  
Charlotta Högberg ◽  
Stefan Lossow ◽  
Ralf Bauer ◽  
Kaley A. Walker ◽  
Patrick Eriksson ◽  
...  
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
Isotopic Ratio ◽  
Michelson Interferometer ◽  
Data Sets ◽  
Data Set ◽  
Spectroscopic Database ◽  
Temporal And Spatial ◽  
Chemistry Experiment

Abstract. Within the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), we have evaluated five data sets of δD(H2O) obtained from observations of Odin/SMR (Sub-Millimetre Radiometer), Envisat/MIPAS (Environmental Satellite/Michelson Interferometer for Passive Atmospheric Sounding) and SCISAT/ACE-FTS (Science Satellite/Atmospheric Chemistry Experiment-Fourier Transform Spectrometer) using profile-to-profile and climatological comparisons. Our focus is on stratospheric altitudes, but results from the upper troposphere to the lower mesosphere are provided. There are clear quantitative differences in the measurements of the isotopic ratio, which primarily concerns the comparisons to the SMR data set. In the lower stratosphere, this data set shows a higher depletion than the MIPAS and ACE-FTS data sets. The differences maximise close to 50 hPa and exceed 200 per mille. With increasing altitude, the biases typically decrease. Above 4 hPa, the SMR data set shows a lower depletion than the MIPAS data sets, on occasion exceeding 100 per mille. Overall, the δD biases of the SMR data set are driven by HDO biases in the lower stratosphere and by H2O biases in the upper stratosphere and lower mesosphere. In between, in the middle stratosphere, the biases in δD are a combination of deviations in both HDO and H2O. These biases are attributed to issues with the calibration, in particular in terms of the sideband filtering for H2O, and uncertainties in spectroscopic parameters. The MIPAS and ACE-FTS data sets agree rather well between about 100 hPa and 10 hPa. The MIPAS data sets show less depletion below about 15 hPa (up to about 30 per mille), due to differences in both HDO and H2O. Higher up the picture is reversed, and towards the upper stratosphere the biases typically increase. This is driven by increasing biases in H2O and on occasion the differences in δD exceed 80 per mille. Below 100 hPa, the differences between the MIPAS and ACE-FTS data sets are even larger. In the climatological comparisons, the MIPAS data sets continue to show less depletion than the ACE-FTS data sets below 15 hPa during all seasons, with some variations in magnitude. The differences between the MIPAS and ACE-FTS data come from different aspects, such as differences in the temporal and spatial sampling (except for the profile-to-profile comparisons), cloud influence, vertical resolution, and the microwindows and spectroscopic database chosen. Differences between data sets from the same instrument are typically small in the stratosphere.

scholarly journals The decrease in mid-stratospheric tropical ozone since 1991

2015 ◽  
Vol 15 (8) ◽  
pp. 4215-4224 ◽  
Author(s):  
G. E. Nedoluha ◽  
D. E. Siskind ◽  
A. Lambert ◽  
C. Boone
Keyword(s):  
Atmospheric Chemistry ◽  
Concomitant Increase ◽  
Using Data ◽  
The Tropics ◽  
Chemistry Experiment ◽  
Long Term Variations ◽  
Halogen Occultation Experiment

Abstract. While global stratospheric O3 has begun to recover, there are localized regions where O3 has decreased since 1991. Specifically, we use measurements from the Halogen Occultation Experiment (HALOE) for the period 1991–2005 and the NASA Aura Microwave Limb Sounder (MLS) for the period 2004–2013 to demonstrate a significant decrease in O3 near ~ 10 hPa in the tropics. O3 in this region is very sensitive to variations in NOy, and the observed decrease can be understood as a spatially localized, yet long-term increase in NOy. In turn, using data from MLS and from the Atmospheric Chemistry Experiment (ACE), we show that the NOy variations are caused by decreases in N2O which are likely linked to long-term variations in dynamics. To illustrate how variations in dynamics can affect N2O and O3, we show that by decreasing the upwelling in the tropics, more of the N2O can photodissociate with a concomitant increase in NOy production (via N2O + O(1D) → 2NO) at 10 hPa. Ultimately, this can cause an O3 decrease of the observed magnitude.

scholarly journals Chemical isolation in the Asian monsoon anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS) data

2008 ◽  
Vol 8 (3) ◽  
pp. 757-764 ◽  
Author(s):  
M. Park ◽  
W. J. Randel ◽  
L. K. Emmons ◽  
P. F. Bernath ◽  
K. A. Walker ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Chemical Constituents ◽  
Strong Correlations ◽  
Near Surface ◽  
Upper Troposphere ◽  
Relative Age ◽  
Rapid Transport ◽  
Chemistry Experiment

Abstract. Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer instrument during summer (June–August) of 2004–2006. Carbon monoxide (CO) shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS); these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13–15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl) exhibit decreased values inside the anticyclone between ~12–20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air) suggest relatively rapid transport of fresh emissions up to the tropopause level inside the anticyclone.

scholarly journals Partitioning between the inorganic chlorine reservoirs HCl and ClONO<sub>2</sub> during the Arctic winter 2005 from the ACE-FTS

2006 ◽  
Vol 6 (8) ◽  
pp. 2355-2366 ◽  
Author(s):  
G. Dufour ◽  
R. Nassar ◽  
C. D. Boone ◽  
R. Skelton ◽  
K. A. Walker ◽  
...  
Keyword(s):  
Fourier Transform ◽  
High Resolution ◽  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
The Arctic ◽  
Fourier Transform Spectrometer ◽  
Cold Winter ◽  
Winter Conditions ◽  
Reservoir Species ◽  
Chemistry Experiment

Abstract. From January to March 2005, the Atmospheric Chemistry Experiment high resolution Fourier transform spectrometer (ACE-FTS) on SCISAT-1 measured many of the changes occurring in the Arctic (50–80° N) lower stratosphere under very cold winter conditions. Here we focus on the partitioning between the inorganic chlorine reservoirs HCl and ClONO2 and their activation into ClO. The simultaneous measurement of these species by the ACE-FTS provides the data needed to follow chlorine activation during the Arctic winter and the recovery of the Cl-reservoir species ClONO2 and HCl. The time evolution of HCl, ClONO2 and ClO as well as the partitioning between the two reservoir molecules agrees well with previous observations and with our current understanding of chlorine activation during Arctic winter. The results of a chemical box model are also compared with the ACE-FTS measurements and are generally consistent with the measurements.

scholarly journals Climate intercomparison of GPS radio occultation, RS90/92 radiosondes and GRUAN over 2002 to 2013

2014 ◽  
Vol 7 (11) ◽  
pp. 11735-11769
Author(s):  
F. Ladstädter ◽  
A. K. Steiner ◽  
M. Schwärz ◽  
G. Kirchengast
Keyword(s):  
Radio Occultation ◽  
Global Climate ◽  
Time Frame ◽  
Specific Humidity ◽  
Radiosonde Data ◽  
Gps Radio Occultation ◽  
Long Term Stability ◽  
High Vertical Resolution ◽  
Global Coverage

Abstract. Observations from the GPS radio occultation (GPSRO) satellite technique and from the newly established GCOS Reference Upper Air Network (GRUAN) are both candidates to serve as reference observations in the Global Climate Observing System (GCOS). Such reference observations are key to decrease existing uncertainties in upper-air climate research. There are now more than 12 years of data available from GPSRO, with the recognized properties high accuracy, global coverage, high vertical resolution, and long-term stability. These properties make GPSRO a suitable choice for comparison studies with other upper-air observational systems. The GRUAN network consists of reference radiosonde ground stations (16 at present), which adhere to the GCOS climate monitoring principles. In this study, we intercompare GPSRO temperature and humidity profiles and Vaisala RS90/92 data from the "standard" global radiosonde network over the whole 2002 to 2013 time frame. Additionally, we include the first years of GRUAN data (using Vaisala RS92), available since 2009. GPSRO profiles which occur within 3 h and 300 km of radiosonde launches are used. Very good agreement is found between all three datasets with temperature differences usually less than 0.2 K. In the stratosphere above 30 hPa, temperature differences are larger but still within 0.5 K. Day/night comparisons with GRUAN data reveal small deviations likely related to a warm bias of the radiosonde data at high altitudes, but also residual errors from the GPSRO retrieval process might play a role. Vaisala RS90/92 specific humidity exhibits a dry bias of up to 40% in the upper troposphere, with a smaller bias at lower altitudes within 15%. GRUAN shows a marked improvement in the bias characteristics, with less than 5% difference to GPSRO up to 300 hPa. GPSRO dry temperature and physical temperature are validated using radiosonde data as reference. We find that GPSRO provides valuable long-term stable reference observations with well-defined error characteristics for climate applications and for anchoring other upper-air measurements.

scholarly journals What drives the observed variability of HCN in the troposphere and lower stratosphere?

2009 ◽  
Vol 9 (21) ◽  
pp. 8531-8543 ◽  
Author(s):  
Q. Li ◽  
P. I. Palmer ◽  
H. C. Pumphrey ◽  
P. Bernath ◽  
E. Mahieu
Keyword(s):  
Atmospheric Chemistry ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Negative Bias ◽  
Mixing Ratio ◽  
Chemistry Transport Model ◽  
Annual Variations ◽  
Surface Emission ◽  
Chemistry Experiment

Abstract. We use the GEOS-Chem global 3-D chemistry transport model to investigate the relative importance of chemical and physical processes that determine observed variability of hydrogen cyanide (HCN) in the troposphere and lower stratosphere. Consequently, we reconcile ground-based FTIR column measurements of HCN, which show annual and semi-annual variations, with recent space-borne measurements of HCN mixing ratio in the tropical lower stratosphere, which show a large two-year variation. We find that the observed column variability over the ground-based stations is determined by a superposition of HCN from several regional burning sources, with GEOS-Chem reproducing these column data with a positive bias of 5%. GEOS-Chem reproduces the observed HCN mixing ratio from the Microwave Limb Sounder and the Atmospheric Chemistry Experiment satellite instruments with a mean negative bias of 20%, and the observed HCN variability with a mean negative bias of 7%. We show that tropical biomass burning emissions explain most of the observed HCN variations in the upper troposphere and lower stratosphere (UTLS), with the remainder due to atmospheric transport and HCN chemistry. In the mid and upper stratosphere, atmospheric dynamics progressively exerts more influence on HCN variations. The extent of temporal overlap between African and other continental burning seasons is key in establishing the apparent bienniel cycle in the UTLS. Similar analysis of other, shorter-lived trace gases have not observed the transition between annual and bienniel cycles in the UTLS probably because the signal of inter-annual variations from surface emission has been diluted before arriving at the lower stratosphere (LS), due to shorter atmospheric lifetimes.

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