Is there a trend in cirrus cloud cover due to aircraft traffic?

Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in cirrus. Still we regard the results to be indicative of an impact of aircraft on cirrus amount. The main emphasis of our study is on the area covered by the METEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic contrasts with a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm^-2 (lower limit 0.01, upper limit 0.08 Wm^-2) for the radiative forcing due to aircraft induced cirrus. The mean is close to the value given by IPCC (1999) as an upper limit

Is there a trend in cirrus cloud cover due to aircraft traffic?

International audienceTrends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus could cover due to aircraft traffic. Main emphasis has been on the area covered by the METEOSAT satellite, to avoid trends in the ISCCP data resulting from changing satellite positions. An alternative retrieval of high clouds in this region has been used to complement the analysis based on ISCCP data. In Europe, which is within the METEOSAT region, we find indications of a trend of about 2%/decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic seems to have contrasted a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a best estimate of 0.05 Wm?2 for the radiative forcing due to aircraft. This is close to the value given by IPCC (1999) as an upper limit

Large-scale distributions of tropospheric nitric, formic, and acetic acids over the western Pacific basin during wintertime

We report here measurements of the acidic gases nitric (HNO3), formic (HCOOH), and acetic (CH3COOH) over the western Pacific basin during the February-March 1994 Pacific Exploratory Mission-West (PEM-West B). These data were obtained aboard the NASA DC-8 research aircraft as it flew missions in the altitude range of 0.3–12.5 km over equatorial regions near Guam and then further westward encompassing the entire Pacific Rim arc. Aged marine air over the equatorial Pacific generally exhibited mixing ratios of acidic gases \u3c100 parts per trillion by volume (pptv). Near the Asian continent, discrete plumes encountered below 6 km altitude contained up to 8 parts per billion by volume (ppbv) HNO3 and 10 ppbv HCOOH and CH3COOH. Overall there was a general correlation between mixing ratios of acidic gases with those of CO, C2H2, and C2Cl4, indicative of emissions from combustion and industrial sources. The latitudinal distributions of HNO3 and CO showed that the largest mixing ratios were centered around 15°N, while HCOOH, CH3COOH, and C2Cl4 peaked at 25°N. The mixing ratios of HCOOH and CH3COOH were highly correlated (r2 = 0.87) below 6 km altitude, with a slope (0.89) characteristic of the nongrowing season at midlatitudes in the northern hemisphere. Above 6 km altitude, HCOOH and CH3COOH were marginally correlated (r2 = 0.50), and plumes well defined by CO, C2H2, and C2Cl4 were depleted in acidic gases, most likely due to scavenging during vertical transport of air masses through convective cloud systems over the Asian continent. In stratospheric air masses, HNO3 mixing ratios were several parts per billion by volume (ppbv), yielding relationships with O3 and N2O consistent with those previously reported for NOy

Combined Characterisation of GOME and TOMS Total Ozone Using Ground-Based Observations from the NDSC

Several years of total ozone measured from space by the ERS-2 GOME, the Earth Probe Total Ozone Mapping Spectrometer (TOMS), and the ADEOS TOMS, are compared with high-quality ground-based observations associated with the Network for the Detection of Stratospheric Change (NDSC), over an extended latitude range and a variety of geophysical conditions. The comparisons with each spaceborne sensor are combined altogether for investigating their respective solar zenith angle (SZA) dependence, dispersion, and difference of sensitivity. The space- and ground-based data are found to agree within a few percent on average. However, the analysis highlights for both Global Ozone Monitoring Experiment (GOME) and TOMS several sources of discrepancies, including a dependence on the SZA at high latitudes and internal inconsistencies

Origin of Ozone NO(x) in the Tropical Troposphere: A Photochemical Analysis of Aircraft Observations Over the South Atlantic Basin

The photochemistry of the troposphere over the South Atlantic basin is examined by modeling of aircraft observations up to 12-km altitude taken during the TRACE A expedition in September-October 1992. A close balance is found in the 0 to 12-km column between photochemical production and loss Of O3, with net production at high altitudes compensating for weak net loss at low altitudes. This balance implies that O3 concentrations in the 0-12 km column can be explained solely by in situ photochemistry; influx from the stratosphere is negligible. Simulation of H2O2, CH3OOH, and CH2O concentrations measured aboard the aircraft lends confidence in the computations of O3 production and loss rates, although there appears to be a major gap in current understanding of CH2O chemistry in the marine boundary layer. The primary sources of NO(x) over the South Atlantic Basin appear to be continental (biomass burning, lightning, soils). There is evidence that NO(x) throughout the 0 to 12-km column is recycled from its oxidation products rather than directly transported from its primary sources. There is also evidence for rapid conversion of HNO3 to NO(x) in the upper troposphere by a mechanism not included in current models. A general representation of the O3 budget in the tropical troposphere is proposed that couples the large scale Walker circulation and in situ photochemistry. Deep convection in the rising branches of the Walker circulation injects NO(x) from combustion, soils, and lightning to the upper troposphere, leading to O3 production; eventually, the air subsides and net O3 loss takes place in the lower troposphere, closing the O3 cycle. This scheme implies a great sensitivity of the oxidizing power of the atmosphere to NO(x) emissions in the tropics

Distribution of C1 - C2 Aldehydes in the Free Troposphere

A sensitive and selective measurement technique for the determination of tropospheric formaldehyde and acetaldehyde in background air is described . The method is based on the derivatization of aldehydes with 2,4 dinitrophenylhydrazine (DNPH) . The derivative aldehyde hydrazones are then separated using high performance liquid chromatography (HPLC) and detected at 355 nm using a conventional HPLC UV/VIS absorbance detector. Aldehydes were collected with Waters Sep-Pak C®18 DNPHcoated cartridges using a portable sampling system . The apparatus proved to be easy and convenient to operate, even in remote clean air locations where aldehyde mixing ratios and their natural variations are likely to be of special interest in air chemistry. The method was used for ground-based measurements of formaldehyde and acetaldehyde during an uninterupted two-week period in August 1990 in Jülich . Ground level measurements in Jülich for formaldehyde and acetaldehyde were shown to vary from 0 .5 to 7 ppb and 0 .1 to 2 .0 ppb, respectively . Diurnal mean mixing ratios of, formaldehyde and acetaldehyde were 2 .8 +/® 1 .5 ppb and 0 .7 -+/® 0 .4 ppb respectively . Significant diurnal patterns were observed with maximum mixing ratios in the early afternoons, and minimum mixing ratios shortly before sunrise . A potential interference from organic hydroperoxides is also discussed. ~n~'r cr ai6~ 9 ~ Lv~ vr.m. $ re measurements up ac .o nearly ~ 8L811 är J=s t he s.~ai ;f ei a•®rs-I an, in z vi av,=-rns, -F ver‘fw { .°174YiF.9'i ®~fl to November 1 9 4 0 showed the potential of cartridge-based methods for aldehyde measurements in the free troposphere . These test flights indicated that formaldehyde vertical profiles can be dependent on inversion height and cloud frequency . In-cloud formaldehyde measurements tended to be lower than gas-phase measurement