Showing papers by "Climate Monitoring and Diagnostics Laboratory published in 1995"

Changes in oceanic and terrestrial carbon uptake since 1982

Abstract: CHANGES in the carbon isotope ratio (δ13C) of atmospheric CO2 can be used in global carbon-cycle models1–5 to elucidate the relative roles of oceanic and terrestrial uptake of fossil-fuel CO2. Here we present measurements of δ 13C made at several stations in the Northern and Southern hemispheres over the past decade. Focusing on the highest-quality data from Cape Grim (41° S), which also provide the longest continuous record, we observe a gradual decrease in δ13C from 1982 to 1993, but with a pronounced flattening from 1988 to 1990. There is an inverse relationship between CO2 growth rate6 and El Nino/Southern Oscillation (ENSO) events which is not reflected in the isotope record. Thus, for the ENSO events in 1982, 1986 and 1991–92, we deduce that net ocean uptake of CO2 increased, whereas during La Nina events, when equatorial sea surface temperatures are lower, upwelling of carbon-rich water increases the release of CO2 from the oceans. The flattening of the trend from 1988 to 1990 appears to involve the terrestrial carbon cycle, but we cannot yet ascribe firm causes. We find that the large and continuing decrease in CO2 growth starting in 19886 involves increases in both terrestrial and oceanic uptake, the latter persisting through 1992.

Absorption of solar radiation by clouds: observations versus models.

Abstract: There has been a long history of unexplained anomalous absorption of solar radiation by clouds. Collocated satellite and surface measurements of solar radiation at five geographically diverse locations showed significant solar absorption by clouds, resulting in about 25 watts per square meter more global-mean absorption by the cloudy atmosphere than predicted by theoretical models. It has often been suggested that tropospheric aerosols could increase cloud absorption. But these aerosols are temporally and spatially heterogeneous, whereas the observed cloud absorption is remarkably invariant with respect to season and location. Although its physical cause is unknown, enhanced cloud absorption substantially alters our understanding of the atmosphere's energy budget.

Increase in lower-stratospheric water vapour at a mid-latitude Northern Hemisphere site from 1981 to 1994

Abstract: WATER vapour in the atmosphere is the key trace gas controlling weather and climate, and plays a central role in atmospheric chemistry, influencing the heterogeneous chemical reactions that destroy stratospheric ozone. Although in the upper troposphere and lower stratosphere the radiative1 and chemical2 effects of water vapour are large, there are few measurements of water-vapour concentration3–10 and its long-term variation11–13 in this region. Here we present a set of water-vapour profiles for altitudes from 9 to 27 km, obtained at Boulder, Colorado, during 1981–94, which show a significant increase in water-vapour concentration in the lower stratosphere over this time. The increase is larger, at least below about 20–25 km, than might be expected from the stratospheric oxidation of increasing concentrations of atmospheric methane14,15. The additional increase in water vapour may be linked to other climate variations, such as the observed global temperature rise in recent decades16.

Midlatitude lidar backscatter conversions based on balloonborne aerosol measurements

Abstract: Aerosol size distributions derived from balloon-borne particle counter data from Laramie, WY, are used to calculate ratios of extinction, mass, and surface area to lidar backscatter at the widely used lidar wavelength of 532 nm. The results cover the range of the stratospheric aerosol layer from the tropopause to 30 km. These ratios may be used to infer particle extinction, mass, and surface area from midlatitude lidar backscatter data for the period late 1979 to 1993. This period includes the major volcanic eruptions of El Chichon and Pinatubo. The wavelength dependence of aerosol backscatter in the visible was calculated for the period 1991 to 1993 to allow conversions of the results to other lidar wavelengths. The wavelength dependence is similar to estimates from southern hemisphere midlatitude measurements indicating that these conversions may also be applied to southern hemisphere midlatitude lidar measurements.

New evidence for the stratospheric dehydration mechanism in the equatorial Pacific

Abstract: Water vapor profile measurements obtained in the western and central Pacific during the Central Equatorial Pacific Experiment (CEPEX) show a strong connection between the water vapor content near the tropopause and areas of deep convection. We show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume (ppmv), which is much lower than the average mixing ratio observed in the stratosphere. A sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells. A mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone, water vapor, and potential temperature. Furthermore, a local maximum was observed at 20 km, which is an indication for the seasonal cycle of the tropopause temperature.

A determination of the CH4, NO x and CO2 emissions from the Prudhoe Bay, Alaska oil development

Abstract: In this paper we quantify the CH4, CO2 and NO x emissions during routine operations at a major oil and gas production facility, Prudhoe Bay, Alaska, using the concentrations of combustion by products measured at the NOAA-CMDL observatory at Barrow, Alaska and fuel consumption data from Prudhoe Bay During the 1989 and 1990 measurement campaigns, 10 periods (called ‘events’) were unambiguously identified where surface winds carry the Prudhoe Bay emissions to Barrow (approximately 300 km) The events ranged in duration from 8–48 h and bring ambient air masses containing substantially elevated concentrations of CH4, CO2 and NO y to Barrow Using the slope of the observed CH4 vs CO2 concentrations during the events and the CO2 emissions based on reported fuel consumption data, we calculate annual CH4 emissions of (24+/−8)×103 metric tons from the facility In a similar manner, the annual NO x emissions are calculated to be (12+/−4)×103 metric tons, which is in agreement with an independently determined value The calculated CH4 emissions represent the amount released during routine operations including leakage However this quantity would not include CH4 released during non-routine operations, such as from venting or gas flaring

Recovery of ozone in the lower stratosphere at the South Pole during the spring of 1994

Abstract: During 1994, springtime Antarctic ozone measured at the south pole did not reach the record lows recorded during the 1993 ozone hole period when a value of 91±5 DU was observed. A low value of 102 DU was recorded on October 5, 1994, but such values were not sustained as in 1993. The recovery of total ozone in 1994 was mainly the result of moderation of ozone destruction in the 10–14 km region, probably related to diminishing stratospheric aerosol from the Pinatubo eruption, and may have also been partially related to disturbance of the vortex earlier than normal. As in 1993, ozone profiles at the minimum showed nearly complete destruction of ozone between 15 and 20 km in 1994. In this region, the rate of decline of ozone in September was at least as fast or somewhat faster than in 1992 and 1993 indicating continuing saturation of the ozone destroying chemistry, which is expected as stratospheric chlorine amounts continue to rise. As in 1993, ozone was again observed to be reduced in the 22–24 km region, suggesting that the ozone hole has now probably extended to a region unaffected prior to 1992.

Evidence for midwinter chemical ozone destruction over Antarctica

Abstract: Two ozone profiles on June 15 and June 19, obtained over McMurdo, Antarctica, showed a strong depletion in stratospheric ozone, and a simultaneous profile of water vapor on June 19 showed the first clear signs of dehydration. The observation of Polar Stratospheric Clouds (PSCs) beginning with the first sounding showing ozone depletion, the indication of rehydration layers, which could be a sign for recent dehydration, and trajectory calculations indicate that the observed low ozone was not the result of transport from lower latitudes. During this time the vortex was strongly distorted, transporting PSC processed air well into sunlit latitudes where photochemical ozone destruction may have occurred. The correlation of ozone depletion and dehydration indicates that water ice PSCs provided the dominant surface for chlorine activation. An analysis of the time when the observed air masses could have formed type II PSCs for the first time limits the time scale for the observed ozone destruction to about 4 days.

Mid stratospheric ozone minima in polar regions

Abstract: Recent springtime measurements of ozone vertical profiles in polar regions have revealed local ozone depressions of about 25% at altitudes near 30 km. Similar features are also identified in three-dimensional photochemical model results. The modeled ozone depressions are local and temporary, often associated with stratospheric warming events which transport air from low latitudes, altering its photochemical history. The feature may be a component of the climatology of the region, but occurs less frequently in the model, possibly because of the long-standing problem of the underprediction of upper stratospheric ozone.