Greg Bodeker

Assessment of SAGE Version 6.1 Ozone Data Quality

[1]xa0The Stratospheric Aerosol and Gas Experiment (SAGE) II V6.1 ozone retrievals are shown to be of better precision at all levels and to be much more accurate than previous retrievals in the lower stratosphere below 20 km altitude. A filtering procedure for removing anomalous ozone profiles associated with volcanic aerosol/cloud effects and other identified artifacts in V6.1 ozone is described. The agreement between SAGE and ozonesondes in the mean is shown to be approximately 10% down to the tropopause. Relative to the sondes, SAGE tends to slightly overestimate ozone (less than 5%) between 15 and 20 km altitude and systematically underestimates ozone in the troposphere by approximately 30% in the regions between 8 km altitude and 2 km below the tropopause. The precisions (random errors) of SAGE ozone retrievals above 25 km altitude are estimated to be 4% or better; they are a factor of 10 worse below 16 km altitude. Linear trends in the differences between coincident SAGE and ozonesondes measurement are generally less than 0.3%/yr and not significantly different from zero in 95% confidence intervals. Compared to V5.96 retrievals, ozone trend differences between 20 and 50 km altitude are approximately 0.1%/yr; below 20 km altitude the SAGE II trends are more positive by approximately 0.2%/yr. For the 1984–1999 period, the SAGE II shows a localized ozone loss of −0.4 ± 0.25%/yr (2σ) in the tropics at 20 km altitude. In the lower stratosphere, between 16 and 22 km altitudes, the SAGE shows significant ozone losses in the midlatitudes in both hemispheres during the 1979–1999 periods. The ozone trends range from −0.24 ± 0.18%/yr to −0.77 ± 0.46%/yr (2σ). However, in the 1984–1999 period, the downward trends are smaller (−0.07%/yr to −0.25%/yr) in this altitude range, and the trends in the integrated column from 12 to 17 km altitude in midlatitudes (35°–60°) are not significantly different from zero (0.1 ± 0.6%/yr (2σ)). Averaged over the tropics (20°S–20°N), the ozone column above 15 km altitude exhibit a trend of −0.12 ± 0.08%/yr (2σ).

An Algorithm for Inferring Surface UV Irradiance Including Cloud Effects

Abstract Recent extratropical ozone depletion and the concomitant increase in surface ultraviolet (UV) radiation may be expected to adversely influence the biosphere. Since few long-term, high quality datasets of surface UV are available for assessing these effects, there is a need to develop techniques for estimating past levels of biologically harmful UV at a particular location and thus derive long-term trends. This paper presents a semiempirical algorithm, making use of readily available meteorological variables and total column ozone, for inferring historical UV levels at a particular location, including cloud cover effects. Where input data are available for a network of locations, the technique can be used to generate geographical distributions of surface UV. Measurements made at Lauder (45.04°S, 169.68°E), from November 1993 to October 1994, were used to establish the relationship between cloud-induced reductions of erythemal UV and broadband irradiance, as a function of solar zenith anglex97termed ...

Dynamically Forced Increase of Tropical Upwelling in the Lower Stratosphere

Drivers of upwelling in the tropical lower stratosphere are investigated using the E39C-A chemistry‐ climate model. The climatological annual cycle in upwelling and its wave forcing are compared to the interim ECMWF Re-Analysis (ERA-Interim). The strength in tropical upwelling and its annual cycle can be largely explainedby local resolvedwave forcing. The climatological meanforcing is due to both stationaryplanetaryscale waves that originate in the tropics and extratropical transient synoptic-scale waves that are refracted equatorward. Increases in atmospheric greenhouse gas (GHG) concentrations to 2050 force a year-round positive trend in tropical upwelling, which maximizes in the lowermost stratosphere. Tropical ascent is balanced by downwelling between 208 and 408. Strengthening of tropical upwelling can be explained by stronger local forcing by resolved wave flux convergence, which is driven in turn by processes initiated by increases in tropical sea surface temperatures (SSTs). Higher tropical SSTs cause a strengthening of the subtropical jets and modification of deep convection affecting latent heat release. While the former can modify wave propagation and dissipation, the latter affects tropical wave generation. The dominant mechanism leading to enhanced vertical wave propagation into the lower stratosphere is an upward shift of the easterly shear zone due to the strengthening and upward shift of the subtropical jets.

Effects of ozone cooling in the tropical lower stratosphere and upper troposphere

[1]xa0In this paper, we examine the tropical lower stratosphere and upper troposphere and elucidate the key role of ozone changes in driving temperature trends in this region. We use a radiative fixed dynamical heating model to show that the effects of tropical ozone decreases at 70 hPa and lower pressures can lead to significant cooling not only at stratospheric levels, but also in the “sub-stratosphere/upper tropospheric” region around 150–70 hPa. The impact of stratospheric ozone depletion on upper tropospheric temperatures stems from reduced longwave emission from above. The results provide a possible explanation for the long-standing discrepancy between modeled and measured temperature trends in the uppermost tropical troposphere and can explain the latitudinal near-homogeneity of recent stratospheric temperature trends.

Geographical differences in erythemally-weighted UV measured at mid-latitude USDA sites

UV measurements from instruments maintained by USDA at 16 mid-latitude sites were analysed to investigate geographic differences. Fifteen of the sites are in North America, and one is in New Zealand. The instruments measure erythemally weighted UV radiation, and the results are presented in terms of UV Index (UVI). The focus of this work is on data from 2003, but the main results are also shown for years 2002 and 2004. In the North American sites, the peak UVI values increase by approximately 15% between latitudes 47 degrees N and 40 degrees N, and they show an increase with altitude of approximately 15% in the first kilometer, but much smaller rates of increase above that level. Peak UV intensities in the New Zealand site (45 degrees S, alt. 0.37 km) exceed those at comparable latitudes and altitudes in North America by 41 +/- 5%, and are more comparable with those over 1 km higher and 5 degrees closer to the equator. The number of observations on these days that exceeded various thresholds of UVI showed similar patterns. Furthermore, the number of days in which the peak values exceeded various thresholds also showed similar patterns, with the number of extreme values in New Zealand being anomalously high. For example, the only sites in North America where UVI exceeded 12 were at the high altitude sites in Colorado and Utah, for which there were 53 days, 6 days and 2 days respectively at the 3.2 km, 1.6 and 1.4 km sites. By contrast, the peak UVI at Lauder (0.37 km) exceeded 12 on 17 days. Lauder was the only site under 1 km altitude where the UVI exceeded 11 on a regular basis (48 days). The optical depths at Lauder were significantly lower than at all North American sites. These, together with the lower ozone amounts and the closer Earth-Sun separation in summer all contribute to the relatively high UV intensities at the New Zealand site. Other sites in New Zealand show similar increases compared with corresponding sites in North America, and the differences persist from year to year. The contrast in UV between New Zealand and North America is similar to that observed previously between New Zealand and Europe. During winter months, the UVI in New Zealand is not particularly high, giving a larger summer/winter contrast in UVI, which may be important from a health perspective.

Uncertainties of global warming metrics: CO2 and CH4

[1]xa0We present a comprehensive evaluation of uncertainties in the Global Warming Potential (GWP) and Global Temperature Change Potential (GTP) of CH4, using a simple climate model calibrated to AOGCMs and coupled climate-carbon cycle models assessed in the IPCC Fourth Assessment Report (AR4). In addition, we estimate uncertainties in these metrics probabilistically by using a method that does not rely on AOGCMs but instead builds on historical constraints and uncertainty estimates of current radiative forcings. While our mean and median GWPs and GTPs estimates are consistent with previous studies, our analysis suggests that uncertainty ranges for GWPs are almost twice as large as estimated in the AR4. Relative uncertainties for GTPs are larger than for GWPs, nearly twice as high for a time horizon of 100 years. Given this uncertainty, our results imply the possibility for substantial future adjustments in best-estimate values of GWPs and in particular GTPs.

An assessment of ECC ozonesondes operated using 1% and 0.5% KI cathode solutions at Lauder, New Zealand

The effects of reducing the concentration of the potassium iodide (KI) cathode electrolyte from 1% to 0.5% in electrochemical concentration cell (ECC) ozonesondes flown at Lauder, New Zealand (45° S, 170° E) have been investigated. Four studies were made to assess these effects: 1% and 0.5% KI ozonesonde performance was compared directly in three dual flights, one year of 1% KI and one year of 0.5% KI ozonesonde profiles were compared with near-simultaneous lidar profiles, integrated ozonesonde profiles were compared with Dobson spectrophotometer measurements over the same period, and ascent and descent profiles were compared for both KI concentrations. Ozonesondes flown with a 1% KI solution showed positive differences of 3% to 8% in the ozone profile and ∼5% in the ozone column compared with the 0.5% KI ozonesondes, which also showed better agreement in profiles and ozone column compared with the lidar and Dobson spectrophotometer measurements respectively.

Reference Upper-Air Observations for Climate: From Concept to Reality

AbstractThe three main objectives of the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) are to provide long-term high-quality climate records of vertical profiles of selected essential climate variables (ECVs), to constrain and calibrate data from more spatially comprehensive global networks, and to provide measurements for process studies that permit an in-depth understanding of the properties of the atmospheric column. In the five years since the first GRUAN implementation and coordination meeting and the printing of an article (Seidel et al.) in this publication, GRUAN has matured to become a functioning network that provides reference-quality observations to a community of users.This article describes the achievements within GRUAN over the past five years toward making reference-quality observations of upper-air ECVs. Milestones in the evolution of GRUAN are emphasized, including development of rigorous criteria for site certification and assessment, the formal certificatio...

The effectiveness of N2O in depleting stratospheric ozone

Recently, it was shown that of the ozone-depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. To investigate the links between N2O and NOx concentrations, and the effects of NOx on ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA-SOCOL chemistry-climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer-Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOx cycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine-catalyzed ozone loss cycles around 2000 and enhanced rates of HOx-induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2-induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx-induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles.

Ozone profile differences between Europe and New Zealand: Effects on surface UV irradiance and its estimation from satellite sensors

[1]xa0Substantial differences in summertime surface UV irradiance between New Zealand and Europe have been reported previously. The main contributors to these differences are differences in total column ozone, differences in Sun-Earth separation between the Southern Hemisphere summer (December/January) and the Northern Hemisphere summer (June/July), and differences in tropospheric pollution. Differences due to higher Northern Hemisphere aerosol extinction have been well documented. Here we present a climatology of ozone profiles measured by balloon-borne sensors launched from Lauder, New Zealand, and from Hohenpeissenberg, Germany, to show that there are also substantial differences in the shapes of ozone profiles, especially during the summer months. A radiative transfer model is then used to investigate the extent to which these profile shape differences contribute to observed UV differences. It is found that the differences in the vertical distribution of ozone amplify existing Northern and Southern Hemisphere differences in UV. Effects can be significant in the UV-B region, but the sign of the effect depends on the solar zenith angle. Consequently, the effect on daily doses of biologically harmful UV radiation is suppressed somewhat, and the differences are responsible for differences in erythemally weighted UV of only a percent or two, which is small compared with other effects. While these effects are relatively small, differences in the vertical profile of ozone can affect the accuracy of satellite retrievals of total column ozone. This analysis shows that the lower tropospheric ozone amounts at Lauder may lead to underestimations of summertime UV from satellite by ∼4% at that site.