Global satellite observations of ozone and carbon monoxide from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed with emphasis on those observations in the 215–100 hPa region ...(the upper troposphere and lower stratosphere). The precision, resolution and accuracy of the data produced by the MLS “version 2.2” processing algorithms are discussed and quantified. O
3
accuracy is estimated at ∼40 ppbv +5% (∼20 ppbv +20% at 215 hPa) while the CO accuracy is estimated at ∼30 ppbv +30% for pressures of 147 hPa and less. Comparisons with expectations and other observations show good agreements for the O
3
product, generally consistent with the systematic errors quoted above. In the case of CO, a persistent factor of ∼2 high bias is seen at 215 hPa. However, the morphology is shown to be realistic, consistent with raw MLS radiance data, and useful for scientific study. The MLS CO data at higher altitudes are shown to be consistent with other observations.
Simultaneous balloon‐borne observations of ozone (O3) and nitrous oxide (N2O), a long‐lived tracer of dynamical motion, are used to quantify the chemical loss of ozone in the Arctic vortex during the ...winter of 1999/2000. Chemical loss of ozone occurred between altitudes of about 14 and 22 km (pressures from ∼120 to 30 mbar) and resulted in a 61 ± 13 Dobson unit reduction in total column ozone between late November 1999 and 5 March 2000 (the date of the last balloon‐borne measurement considered here). This loss estimate is valid for the core of the vortex during the time period covered by the observations. It is shown that the observed changes in the O3 versus N2O relation were almost entirely due to chemistry and could not have been caused by dynamics. The chemical loss of column ozone inferred from the balloon‐borne measurements using the “ozone versus tracer” technique is shown to compare well with estimates of chemical loss found using both the Match technique (as applied to independent ozonesonde data) and the “vortex‐averaged descent” technique (as applied to Polar Ozone and Aerosol Measurement (POAM) III satellite measurements of ozone). This comparison establishes the validity of each approach for estimating chemical loss of column ozone for the Arctic winter of 1999/2000.
We describe a method of evaluating systematic errors in measurements of total column dry-air mole fractions of CO2 (XCO2) from space, and we illustrate the method by applying it to the v2.8 ...Atmospheric CO2 Observations from Space retrievals of the Greenhouse Gases Observing Satellite (ACOS-GOSAT) measurements over land. The approach exploits the lack of large gradients in XCO2 south of 25° S to identify large-scale offsets and other biases in the ACOS-GOSAT data with several retrieval parameters and errors in instrument calibration. We demonstrate the effectiveness of the method by comparing the ACOS-GOSAT data in the Northern Hemisphere with ground truth provided by the Total Carbon Column Observing Network (TCCON). We use the observed correlation between free-tropospheric potential temperature and XCO2 in the Northern Hemisphere to define a dynamically informed coincidence criterion between the ground-based TCCON measurements and the ACOS-GOSAT measurements. We illustrate that this approach provides larger sample sizes, hence giving a more robust comparison than one that simply uses time, latitude and longitude criteria. Our results show that the agreement with the TCCON data improves after accounting for the systematic errors, but that extrapolation to conditions found outside the region south of 25° S may be problematic (e.g., high airmasses, large surface pressure biases, M-gain, measurements made over ocean). A preliminary evaluation of the improved v2.9 ACOS-GOSAT data is also discussed.
We determine the degree of denitrification that occurred during the 1996–1997 Arctic winter using a technique that is based on balloon and aircraft borne measurements of NOy, N2O, and CH4. The ...NOy/N2O relation can undergo significant change due to isentropic mixing of subsided vortex air masses with extravortex air due to the high nonlinearity of the relation. These transport related reductions in NOy can be difficult to distinguish from the effects of denitrification caused by sedimentation of condensed HNO3. In this study, high‐altitude balloon measurements are used to define the properties of air masses that later descend in the polar vortex to altitudes sampled by the ER‐2 aircraft (i.e., ∼20 km) and mix isentropically with extravortex air. Observed correlations of CH4 and N2O are used to quantify the degree of subsidence and mixing for individual air masses. On the basis of these results the expected mixing ratio of NOy resulting from subsidence and mixing, defined here as NOy**, is calculated and compared with the measured mixing ratio of NOy. Values of NOy and NOy** agree well during most parts of the flights. A slight deficit of NOy versus NOy** is found only for a limited region during the ER‐2 flight on April 26, 1997. This deficit is interpreted as indication for weak denitrification (∼2–3 ppbv) in that air mass. The small degree of denitrification is consistent with the general synoptic‐scale temperature history of the sampled air masses, which did not encounter temperatures below the frostpoint and had relatively brief encounters with temperatures below the nitric acid trihydrate equilibrium temperature. Much larger degrees of denitrification would have been inferred if mixing effects had been ignored, which is the traditional approach to diagnose denitrification. Our analysis emphasizes the importance of using other correlations of conserved species to be able to accurately interpret changes in the NOy/N2O relation with respect to denitrification.
Measurements of hydrogen, nitrogen and chlorine radicals from a balloon flight on 25 September 1993 from Ft. Sumner, NM provide an opportunity to quantify photochemical production and loss of ...stratospheric ozone. Ozone loss rates determined using measured radical concentrations agree fairly well with loss rates calculated using a photochemical model. Catalytic cycles involving OH and HO2 are shown to dominate photochemical loss of ozone for altitudes between 44 and 50 km. Reactions involving NO and NO2 are the dominant sink for ozone between 25 and 38 km. The total ozone loss rate determined from the measurements balances calculated production rates for altitudes between 30 and 40 km. However, loss of ozone exceeds production by ∼35% between 42 and 50 km. The imbalance between production and loss of ozone above 42 km is larger than the uncertainty of any one of the critical kinetic parameters or species concentrations. No single adjustment to any of these parameters can simultaneously resolve the imbalance and satisfy constraints imposed by measured OH, HO2, NO2 and ClO. Our results are consistent with an additional mechanism for ozone production above 40 km other than photolysis of ground state O2.
To evaluate the risk of spinal cord revascularization and ascertain the relationship between preoperative spinal arteriography and the frequency of postoperative neurologic injury and overall ...morbidity and mortality in patients who require surgical repair of thoracoabdominal aortic aneurysms.
Fifty patients scheduled for surgical repair of a thoracoabdominal aortic aneurysm underwent spinal arteriography. All patients were divided into a positive spinal artery group (in which the spinal artery was identified) or negative spinal artery group (in which the spinal artery was not identified) and further divided based on extent of disease.
The complication rate of spinal arteriography was 4.6%; no patient had a permanent neurologic injury. No significant difference existed between the positive and negative spinal artery groups in occurrence of neurologic injury (P = .88) or combined morbidity and mortality (P = 51).
Patients who require spinal cord revascularization do not have greater frequency of neurologic injury or overall morbidity and mortality than those without this requirement. Spinal arteriography enables definitive spinal cord revascularization and thereby reduces the risk of neurologic injury.
Thermal infrared radiances from the Tropospheric Emission Spectrometer (TES) between 10 and 15 μm contain significant carbon dioxide (CO2) information, however the CO2 signal must be separated from ...radiative interference from temperature, surface and cloud parameters, water, and other trace gases. Validation requires data sources spanning the range of TES CO2 sensitivity, which is approximately 2.5 to 12 km with peak sensitivity at about 5 km and the range of TES observations in latitude (40° S to 40° N) and time (2005–2011). We therefore characterize Tropospheric Emission Spectrometer (TES) CO2 version 5 biases and errors through comparisons to ocean and land-based aircraft profiles and to the CarbonTracker assimilation system. We compare to ocean profiles from the first three Hiaper Pole-to-Pole Observations (HIPPO) campaigns between 40° S and 40° N with measurements between the surface and 14 km and find that TES CO2 estimates capture the seasonal and latitudinal gradients observed by HIPPO CO2 measurements. Actual errors range from 0.8–1.8 ppm, depending on the campaign and pressure level, and are approximately 1.6–2 times larger than the predicted errors. The bias of TES versus HIPPO is within 1 ppm for all pressures and datasets; however, several of the sub-tropical TES CO2 estimates are lower than expected based on the calculated errors. Comparisons to land aircraft profiles from the United States Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) between 2005 and 2011 measured from the surface to 5 km to TES CO2 show good agreement with an overall bias of −0.3 ppm to 0.1 ppm and standard deviations of 0.8 to 1.0 ppm at different pressure levels. Extending the SGP aircraft profiles above 5 km using AIRS or CONTRAIL measurements improves comparisons with TES. Comparisons to CarbonTracker (version CT2011) show a persistent spatially dependent bias pattern and comparisons to SGP show a time-dependent bias of −0.2 ppm yr−1. We also find that the predicted sensitivity of the TES CO2 estimates is too high, which results from using a multi-step retrieval for CO2 and temperature. We find that the averaging kernel in the TES product corrected by a pressure-dependent factor accurately reflects the sensitivity of the TES CO2 product.
Volume mixing ratio profiles of the quantitatively significant NOy species NO, NO2, HNO3, HNO4, ClNO3 and N2O5 were measured remotely from 8 to 38 km by the JPL MkIV FTIR solar absorption ...spectrometer during balloon flights from Fairbanks, Alaska (64.8°N, 147.6°W) on May 8 and July 8, 1997. The observed ratio of NOx (NO + NO2) to NOy (total reactive nitrogen) is 10 to 30% greater than calculated by a steady state model using standard photochemistry constrained by MkIV measurements of long lived precursors (e.g., H2O, CH4, CO and N2O) and SAGE II aerosol surface area. The persistence of this discrepancy to 38 km altitude suggests that processes involving aerosols, such as the reduction of HNO3 on the surface of soot particles, cannot be the sole explanation. The most likely resolution to this discrepancy is that the rate of NO2 + OH + M → HNO3 + M (the dominant sink of NOx in the Arctic stratosphere during times of near continuous solar illumination) is significantly slower than the currently recommended rate.
Global satellite observations of ozone and carbon monoxide from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed with emphasis on those observations in the 2 15 - 100 hPa ...region (the upper troposphere and lower stratosphere). The precision, resolution and accuracy of the data produced by the MLS "version 2.2" processing algorithms are discussed and quantified. O3 accuracy is estimated at approx.40 ppbv +5% (approx.20 ppbv +20% at 215 hPa) while the CO accuracy is estimated at approx.30 ppbv +30% for pressures of 147 hPa and less. Comparisons with expectations and other observations show good agreements for the O3 product, generally consistent with the systematic errors quoted above. In the case of COY a persistent factor of approx.2 high bias is seen at 215 hPa. However, the morphology is shown to be realistic, consistent with raw MLS radiance data, and useful for scientific study. The MLS CO data at higher altitudes are shown to be consistent with other observations.
Radiologic studies and interventional procedures were performed in a series of 13 patients with biliary complications following laparoscopic cholecystectomy, and the results were evaluated. Two ...categories of ductal complication--minor and major--were found. Minor complications (n = 6) included bile leaks and bilomas; these were managed with percutaneous techniques or simple surgical repair. Major complications (n = 8), consisting primarily of common hepatic duct injuries or strictures, were markedly resistant to percutaneous therapy, requiring major surgical repair (hepaticojejunostomy). Percutaneous treatment of recurrent strictures after primary repair was undertaken in three patients. Diagnostically, radionuclide imaging appeared most helpful in screening for biliary complications of laparoscopic cholecystectomy, supplemented by endoscopic retrograde cholangiopancreatography and/or percutaneous transhepatic cholangiography for definitive diagnosis.
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