84 research outputs found
SAGE 3: A visible wavelength limb sounder
A brief description is presented for the SAGE 3 (Stratospheric Aerosol and Gas Experiment 3) instrument that has been selected to fly onboard the National Polar Platform 1 (NPOP 1) for the Earth Observational System (Eos) in 1996. The SAGE 3 instrument will perform earth limb sounding with the solar occultation technique measuring the ultraviolet (UV), the visible, and the near infrared (IR) wavelength solar radiation. The instrument will produce atmospheric data for the vertical distribution of aerosol, ozone, nitrogen dioxide, water vapor, and oxygen. The details of the instrument design, data flow, and processing requirements are discussed
A Comparative Study of a 1/4-Scale Gulfstream G550 Aircraft Nose Gear Model
A series of fluid dynamic and aeroacoustic wind tunnel experiments are performed at the University of Florida Aeroacoustic Flow Facility and the NASA-Langley Basic Aerodynamic Research Tunnel Facility on a high-fidelity -scale model of Gulfstream G550 aircraft nose gear. The primary objectives of this study are to obtain a comprehensive aeroacoustic dataset for a nose landing gear and to provide a clearer understanding of landing gear contributions to overall airframe noise of commercial aircraft during landing configurations. Data measurement and analysis consist of mean and fluctuating model surface pressure, noise source localization maps using a large-aperture microphone directional array, and the determination of far field noise level spectra using a linear array of free field microphones. A total of 24 test runs are performed, consisting of four model assembly configurations, each of which is subjected to three test section speeds, in two different test section orientations. The different model assembly configurations vary in complexity from a fully-dressed to a partially-dressed geometry. The two model orientations provide flyover and sideline views from the perspective of a phased acoustic array for noise source localization via beamforming. Results show that the torque arm section of the model exhibits the highest rms pressures for all model configurations, which is also evidenced in the sideline view noise source maps for the partially-dressed model geometries. Analysis of acoustic spectra data from the linear array microphones shows a slight decrease in sound pressure levels at mid to high frequencies for the partially-dressed cavity open model configuration. In addition, far field sound pressure level spectra scale approximately with the 6th power of velocity and do not exhibit traditional Strouhal number scaling behavior
SAGE Version 7.0 Algorithm: Application to SAGE II
This paper details the Stratospheric Aerosol and Gas Experiments (SAGE) version 7.0 algorithm and how it is applied to SAGE II. Changes made between the previous (v6.2) and current (v7.0) versions are described and their impacts on the data products explained for both coincident event comparisons and time-series analysis. Users of the data will notice a general improvement in all of the SAGE II data products, which are now in better agreement with more modern data sets (e.g. SAGE III) and more robust for use with trend studies
An Analysis of Tropical Transport: Influence of the Quasi-biennial Oscillation
An analysis of over 4 years of Upper Atmosphere Research Satellite (UARS) measurements of CH4, HF, O3, and zonal wind are used to study the influence of the quasi-biennial oscillation (QBO) on constituent transport in the tropics. At the equator, spectral analysis of the Halogen Occultation Experiment (HALOE) and Microwave Limb Sounder (MLS) observations reveals QBO signals in constituent and temperature fields at altitudes between 20 and 45 km. Between these altitudes, the location of the maximum QBO amplitude roughly corresponds with the location of the largest vertical gradient in the constituent field. Thus, at 40 km where CH4 and HF have strong vertical gradients, QBO signals are correspondingly large, while at lower altitudes where the vertical gradients are weak, so are the QBO variations. Similarly, ozone, which is largely under dynamical control below 30 km in the tropics, has a strong QBO signal in the region of sharp vertical gradients (∼28 km) below the ozone peak. Above 35 km, annual and semi-annual variations are also found to be important components of the variability of long-lived tracers. Therefore, above 30 km, the variability in CH4 and HF at the equator is represented by a combination of semiannual, annual, and QBO timescales. A one-dimensional vertical transport model is used to further investigate the influence of annual and QBO variations on tropical constituent fields. QBO-induced vertical motions are calculated from observed high resolution Doppler imager (HRDI) zonal winds at the equator, while the mean annually varying tropical ascent rate is obtained from the Goddard two-dimensional model. Model simulations of tropical CH4 confirm the importance of both the annual cycle and the QBO in describing the HALOE CH4 observations above 30 km. Estimates of the tropical ascent rate and the variation due to the annual cycle and QBO are also discussed
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Aerosol microphysics simulations of the Mt.~Pinatubo eruption with the UM-UKCA composition-climate model
We use a stratosphere–troposphere composition–climate model with interactive sulfur chemistry and aerosol microphysics, to investigate the effect of the 1991 Mount Pinatubo eruption on stratospheric aerosol properties. Satellite measurements indicate that shortly after the eruption, between 14 and 23 Tg of SO2 (7 to 11.5 Tg of sulfur) was present in the tropical stratosphere. Best estimates of the peak global stratospheric aerosol burden are in the range 19 to 26 Tg, or 3.7 to 6.7 Tg of sulfur assuming a composition of between 59 and 77 % H2SO4. In light of this large uncertainty range, we performed two main simulations with 10 and 20 Tg of SO2 injected into the tropical lower stratosphere. Simulated stratospheric aerosol properties through the 1991 to 1995 period are compared against a range of available satellite and in situ measurements. Stratospheric aerosol optical depth (sAOD) and effective radius from both simulations show good qualitative agreement with the observations, with the timing of peak sAOD and decay timescale matching well with the observations in the tropics and mid-latitudes. However, injecting 20 Tg gives a factor of 2 too high stratospheric aerosol mass burden compared to the satellite data, with consequent strong high biases in simulated sAOD and surface area density, with the 10 Tg injection in much better agreement. Our model cannot explain the large fraction of the injected sulfur that the satellite-derived SO2 and aerosol burdens indicate was removed within the first few months after the eruption. We suggest that either there is an additional alternative loss pathway for the SO2 not included in our model (e.g. via accommodation into ash or ice in the volcanic cloud) or that a larger proportion of the injected sulfur was removed via cross-tropopause transport than in our simulations.
We also critically evaluate the simulated evolution of the particle size distribution, comparing in detail to balloon-borne optical particle counter (OPC) measurements from Laramie, Wyoming, USA (41° N). Overall, the model captures remarkably well the complex variations in particle concentration profiles across the different OPC size channels. However, for the 19 to 27 km injection height-range used here, both runs have a modest high bias in the lowermost stratosphere for the finest particles (radii less than 250 nm), and the decay timescale is longer in the model for these particles, with a much later return to background conditions. Also, whereas the 10 Tg run compared best to the satellite measurements, a significant low bias is apparent in the coarser size channels in the volcanically perturbed lower stratosphere. Overall, our results suggest that, with appropriate calibration, aerosol microphysics models are capable of capturing the observed variation in particle size distribution in the stratosphere across both volcanically perturbed and quiescent conditions. Furthermore, additional sensitivity simulations suggest that predictions with the models are robust to uncertainties in sub-grid particle formation and nucleation rates in the stratosphere
Merged SAGEÂ II, Ozone_cci and OMPS ozone profile dataset and evaluation of ozone trends in the stratosphere
In this paper, we present a merged dataset of ozone profiles from
several satellite instruments: SAGEÂ II on ERBS, GOMOS, SCIAMACHY and
MIPAS on Envisat, OSIRIS on Odin, ACE-FTS on SCISAT, and OMPS on
Suomi-NPP. The merged dataset is created in the framework of the
European Space Agency Climate Change Initiative (Ozone_cci) with
the aim of analyzing stratospheric ozone trends. For the merged
dataset, we used the latest versions of the original ozone
datasets. The datasets from the individual instruments have been
extensively validated and intercompared; only those datasets which
are in good agreement, and do not exhibit significant drifts with
respect to collocated ground-based observations and with respect to
each other, are used for merging. The long-term SAGE–CCI–OMPS
dataset is created by computation and merging of deseasonalized
anomalies from individual instruments.
The merged SAGE–CCI–OMPS dataset consists of deseasonalized
anomalies of ozone in 10° latitude bands from 90° S
to 90° N and from 10 to 50 km in steps of
1 km covering the period from October 1984 to
July 2016. This newly created dataset is used for evaluating ozone
trends in the stratosphere through multiple linear
regression. Negative ozone trends in the upper stratosphere are
observed before 1997 and positive trends are found after 1997. The
upper stratospheric trends are statistically significant at
midlatitudes and indicate ozone recovery, as expected from the
decrease of stratospheric halogens that started in the middle of the
1990s and stratospheric cooling
Solar Occultation Satellite Data and Derived Meteorological Products: Sampling Issues and Comparisons with Aura MLS
Derived Meteorological Products (DMPs, including potential temperature (theta), potential vorticity, equivalent latitude (EqL), horizontal winds and tropopause locations) have been produced for the locations and times of measurements by several solar occultation (SO) instruments and the Aura Microwave Limb Sounder (MLS). DMPs are calculated from several meteorological analyses for the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer, Stratospheric Aerosol and Gas Experiment II and III, Halogen Occultation Experiment, and Polar Ozone and Aerosol Measurement II and III SO instruments and MLS. Time-series comparisons of MLS version 1.5 and SO data using DMPs show good qualitative agreement in time evolution of O3, N2O, H20, CO, HNO3, HCl and temperature; quantitative agreement is good in most cases. EqL-coordinate comparisons of MLS version 2.2 and SO data show good quantitative agreement throughout the stratosphere for most of these species, with significant biases for a few species in localized regions. Comparisons in EqL coordinates of MLS and SO data, and of SO data with geographically coincident MLS data provide insight into where and how sampling effects are important in interpretation of the sparse SO data, thus assisting in fully utilizing the SO data in scientific studies and comparisons with other sparse datasets. The DMPs are valuable for scientific studies and to facilitate validation of non-coincident measurements
Past changes in the vertical distribution of ozone - Part 3: Analysis and interpretation of trends
This is the final version of the article. It first appeared from Copernicus Publications via http://dx.doi.org/10.5194/acp-15-9965-2015Abstract. Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine – EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.
The support of SPARC, IO3C, IGACO-O3 and NDACC was essential to the success of
the initiative. Neil Harris thanks the UK Natural Environment Research Council for an Advanced
Research Fellowship. Work at the Jet Propulsion Laboratory was performed under contract
with the National Aeronautics and Space Administration. Measurements at Lauder are core funded through New Zealand’s
Ministry of Business, Innovation and Employment, while those at Woolongong are supported
by the Australian Research Council
Long-term evolution of upper stratospheric ozone at selected stations of the Network for the Detection of Stratospheric Change (NDSC)
The long-term evolution of upper stratospheric ozone has been recorded by lidars and
microwave radiometers within the ground-based Network for the Detection of
Stratospheric Change (NDSC), and by the space-borne Solar Backscatter Ultra-Violet
instruments (SBUV), Stratospheric Aerosol and Gas Experiment (SAGE), and Halogen
Occultation Experiment (HALOE). Climatological mean differences between these
instruments are typically smaller than 5% between 25 and 50 km. Ozone anomaly time
series from all instruments, averaged from 35 to 45 km altitude, track each other very
well and typically agree within 3 to 5%. SBUV seems to have a slight positive drift against
the other instruments. The corresponding 1979 to 1999 period from a transient simulation
by the fully coupled MAECHAM4-CHEM chemistry climate model reproduces many
features of the observed anomalies. However, in the upper stratosphere the model shows
too low ozone values and too negative ozone trends, probably due to an underestimation of
methane and a consequent overestimation of ClO. The combination of all observational
data sets provides a very consistent picture, with a long-term stability of 2% or better.
Upper stratospheric ozone shows three main features: (1) a decline by 10 to 15% since
1980, due to chemical destruction by chlorine; (2) two to three year fluctuations by 5 to
10%, due to the Quasi-Biennial Oscillation (QBO); (3) an 11-year oscillation by about
5%, due to the 11-year solar cycle. The 1979 to 1997 ozone trends are larger at the southern
mid-latitude station Lauder (45 S), reaching 8%/decade, compared to only about
6%/decade at Table Mountain (35 N), Haute Provence/Bordeaux ( 45 N), and
Hohenpeissenberg/Bern( 47 N). At Lauder, Hawaii (20 N), Table Mountain, and Haute
Provence, ozone residuals after subtraction of QBO- and solar cycle effects have levelled
off in recent years, or are even increasing. Assuming a turning point in January 1997,
the change of trend is largest at southern mid-latitude Lauder, +11%/decade, compared to
+7%/decade at northern mid-latitudes. This points to a beginning recovery of upper
stratospheric ozone. However, chlorine levels are still very high and ozone will remain
vulnerable. At this point the most northerly mid-latitude station, Hohenpeissenberg/Bern
differs from the other stations, and shows much less clear evidence for a beginning
recovery, with a change of trend in 1997 by only +3%/decade. In fact, record low upper
stratospheric ozone values were observed at Hohenpeissenberg/Bern, and to a lesser degree
at Table Mountain and Haute Provence, in the winters 2003/2004 and 2004/2005
Optimizing topological cascade resilience based on the structure of terrorist networks
Complex socioeconomic networks such as information, finance and even
terrorist networks need resilience to cascades - to prevent the failure of a
single node from causing a far-reaching domino effect. We show that terrorist
and guerrilla networks are uniquely cascade-resilient while maintaining high
efficiency, but they become more vulnerable beyond a certain threshold. We also
introduce an optimization method for constructing networks with high passive
cascade resilience. The optimal networks are found to be based on cells, where
each cell has a star topology. Counterintuitively, we find that there are
conditions where networks should not be modified to stop cascades because doing
so would come at a disproportionate loss of efficiency. Implementation of these
findings can lead to more cascade-resilient networks in many diverse areas.Comment: 26 pages. v2: In review at Public Library of Science ON
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