Diurnal ozone cycle in the tropical and subtropical marine boundary layer

A conceptual analysis of diurnal ozone (O3 ) changes in the marine boundary layer (MBL) is presented. Such changes are most pronounced downwind of O3 sources in tropical and subtropical latitudes, and during summer at higher latitudes. Previously, it has been assumed that daytime photochemical O3 loss, and nighttime replenishment through entrainment from the relatively O3 -rich free troposphere, explains the diurnal O3 cycle. We show, however, that in a net O3 -destruction environment (low NOx ) this diurnal cycle can be explained by photochemistry and advection, which establish a horizontal O3 gradient that is typical for the MBL. We support this hypothesis firstly by calculations with a conceptual 1-D advection-diffusion model, and secondly by simulations with an interactive 3-D chemistry-transport model. The results are in good agreement with observations, for example, in the Indian Ocean Experiment (INDOEX)

Indoex : chemistry of the Indian Ocean atmosphere

NDOEX (INDian Ocean EXperiment) was large international measurement campaign focussing on measuring radiation in, and the chemical compisition of, the Indian Ocean Atmosphere during northern hemisphere winter. One of the reasons to measure in this region was the specific and unique meteorological conditions of the area, making the region a particularly good environment for the radiation measurements. Another reason was the lack of scientific knowledge about the meteorology of the Indian Ocean region. INDOEX provided detailed (chemistry) measurements which can be used to validate the (chemistry-)climate models that nowadays are being used for climate predictions. Our "trust" in the output of such models highly depends on their ability to reproduce the chemical composition of todays atmosphere. The comparison between measurements from INDOEX and numerical model simulations performed with a global chemistry-climate model form the basis of this thesis. It is shown that the model is capable of reproducing the observed spatial and temporal variations of the chemical composition of the Indian Ocean atmosphere, especially with regard to large scale patterns. However, it is also shown that more (detailed) observations are needed, as well as improvement of the models with regard to the small(er) scale processes. Since the model used for this thesis appears to be capable of reproducing the large scale atmospheric processes, it is also used to study the specific meteorology of the Indian Ocean region, providing a better understanding of what actually is happening there. INDOEX (INDische Oceaan EXperiment) was een grote internationale meetcampagne met de nadruk op het meten van straling in, en de chemische samenstelling van, de atmosfeer boven de Indische oceaan, gedurende de winter op het noordelijk halfrond. Een van de redenen om in dit gebied te meten was de specifieke en unieke meteorologische omstandigheden ervan. Dit maakte het gebied bij uitstek geschikt voor de straligsmetingen. Een andere reden was het gebrek aan wetschappelijke kennis over de meteorologie van de Indische Oceaan. INDOEX leverde gedetaileerde (chemie) metingen op die gebruikt kunnen worden voor de validatie van (chemie-)klimaatmodellen die heden ten dage worden gebruikt voor klimaatvoorspellingen. Ons vertrouwen in het voorspellend vermogen van zulke modellen hangt sterk af van het vermogen van deze modellen om de huidige toestand van de atmosfeer te reproduceren. De vergelijking tussen de INDOEX-metingen en numerieke modelsimulaties met een globaal chemie-klimaatmodel vormt de basis van dit proefschrift. Er wordt aangetoond dat het model in staat is om de waargenomen ruimtelijke en temporele variaties van de chemische atmosfeer-samenstelling boven de Indische Oceaan kan reproduceren, vooral de grootschalige patronen. Echter, het blijkt tevens dat er meer (gedetaileerde) metingen nodig zijn, en dat de modellen verbeterd moeten worden met betrekking tot kleinschalige processen. Omdat het model in staat blijkt te zijn de grootschalige atmosfeerprocessen te reproduceren, is het ook gebruikt om de specifieke meteorologie te besturderen, hetgeen een beter begrip oplevert over wat er in het gebied gebeurt

Validation of six years of SCIAMACHY carbon monoxide observations using MOZAIC CO profile measurements

This paper presents a validation study of SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) carbon monoxide (CO) total column measurements from the Iterative Maximum Likelihood Method (IMLM) algorithm using vertically integrated profile aircraft measurements obtained within the MOZAIC project for the six year time period of 2003-2008. Overall we find a good agreement between SCIAMACHY and airborne measurements for both mean values also on a year-to-year basis as well as seasonal variations. Several locations show large biases that are attributed to local effects like orography and proximity of large emission sources. Differences were detected for individual years: 2003, 2004 and 2006 have larger biases than 2005, 2007 and 2008, which appear to be related to SCIAMACHY instrumental issues but require more research. Results from this study are consistent with, and complementary to, findings from a previous validation study using ground-based measurements (de Laat et al., 2010b). According to this study, the SCIAMACHY data, if individual measurements are of sufficient quality-good signal-to-noise, can be used to determine the spatial distribution and seasonal cycles of CO total columns over clean areas. Biases found over areas with strong emissions (Africa, China) could be explained by low sensitivity of the instrument in the boundary layer and users are recommended to avoid using the SCIAMACHY data while trying to quantify CO burden and/or retrieve CO emissions in such areas. © 2012 Author(s)

Scanning Imaging Absorption Spectrometer for Atmospheric Chartography carbon monoxide total columns: Statistical evaluation and comparison with chemistry transport model results

This paper presents a detailed statistical analysis of one year (September 2003 to August 2004) of global Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) carbon monoxide (CO) total column retrievals from the Iterative Maximum Likelihood Method (IMLM) algorithm, version 6.3. SCIAMACHY provides the first solar reflectance measurements of CO and is uniquely sensitive down to the boundary layer. SCIAMACHY measurements and chemistry transport model (CTM) results are compared and jointly evaluated. Significant improvements in agreement occur, especially close to biomass burning emission regions, when the new Global Fire Emissions Database version 2 (GFEDv2) is used with the CTM. Globally, the seasonal variation of the model is very similar to that of the SCIAMACHY measurements. For certain locations, significant differences were found, which are likely related to modeling errors due to CO emission uncertainties. Statistical analysis shows that differences between single SCIAMACHY CO total column measurements and corresponding model results are primarily explained by random instrument noise errors. This strongly suggests that the random instrument noise errors are a good diagnostic for the precision of the measurements. The analysis also indicates that noise in single SCIAMACHY CO measurements is generally greater than actual variations in total columns. It is thus required to average SCIAMACHY data over larger temporal and spatial scales to obtain valuable information. Analyses of monthly averaged SCIAMACHY measurements over 3° × 2° geographical regions indicates that they are of sufficient accuracy to reveal valuable information about spatial and temporal variations in CO columns and provide an important tool for model validation. A large spatial and temporal variation in instrument noise errors exists which shows a close correspondence with the spatial distribution of surface albedo and cloud cover. This large spatial variability is important for the use of monthly and annual mean SCIAMACHY CO total column measurements. The smallest instrument noise errors of monthly mean 3° × 2° SCIAMACHY CO total columns measurements are 0.01 × 1018 molecules/cm2 for high surface albedo areas over the Sahara. Errors in SCIAMACHY CO total column retrievals due to errors other than instrument noise, like cloud cover, calibration, retrieval uncertainties and averaging kernels are estimated to be about 0.05–0.1 × 1018 molecules/cm2 in total. The bias found between model and observations is around 0.05–0.1 1018 molecules/cm2 (or about 5%) which also includes model errors. This thus provides a best estimate of the currently achievable measurement accuracy for SCIAMACHY CO monthly mean averages

Tropospheric O3 distribution over the Indian Ocean during spring 1995 evaluated with a chemistry-climate model

An analysis of tropospheric O 3 over the Indian Ocean during spring 1995 is presented based on O 3 soundings and results from the chemistry-general circulation model ECHAM (European Centre Hamburg Model). The ECHAM model is nudged towards actual meteorology using ECMWF analyses, to enable a direct comparison between model results and in situ observations. The model reproduces observed CO levels in different air mass categories. The model also reproduces the general tendencies and the diurnal variation in the observed surface pressure, although the amplitude of the diurnal variation in the amplitude is underestimated. The model simulates the general O 3 tendencies as seen in the sonde observations. Tropospheric O 3 profiles were characterized by low surface concentrations (< 10 ppbv), mid-tropospheric maxima (60-100 ppbv, between 700-250 hPa) and upper-tropospheric minima (< 20 ppbv, between 250-100 hPa). Large-scale upper tropospheric O 3 minima were caused by convective transport of O 3 -depleted boundary layer air in the Inter Tropical Convergence Zone (ITCZ). Similarly, an upper tropospheric O 3 minimum was caused by cyclone Marlene south of the ITCZ. The mid-tropospheric O 3 maxima were caused by transport of polluted African air. The ECHAM model appears to overestimate surface O 3 levels, and does not reproduce the diurnal variations very well This could be related to unaccounted multiphase O 3 destruction mechanisms involving low level clouds and aerosols, and missing halogen chemistr

Comparing optimized CO emission estimates using MOPITT or NOAA surface network observations

[1] This paper compares two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) or CO total columns from the Measurement of Pollution in the Troposphere (MOPITT) instrument are assimilated in a 4D-Var framework. Inferred emission estimates from the two inversions are consistent over the Northern Hemisphere (NH). For example, both inversions increase anthropogenic CO emissions over Europe (from 46 to 94 Tg CO/yr) and Asia (from 222 to 420 Tg CO/yr). In the Southern Hemisphere (SH), three important findings are reported. First, due to their different vertical sensitivity, the stations-only inversion increases SH biomass burning emissions by 108 Tg CO/yr more than the MOPITT-only inversion. Conversely, the MOPITT-only inversion results in SH natural emissions (mainly CO from oxidation of NMVOCs) that are 185 Tg CO/yr higher compared to the stations-only inversion. Second, MOPITT-only derived biomass burning emissions are reduced with respect to the prior which is in contrast to previous (inverse) modeling studies. Finally, MOPITT derived total emissions are significantly higher for South America and Africa compared to the stations-only inversion. This is likely due to a positive bias in the MOPITT V4 product. This bias is also apparent from validation with surface stations and ground-truth FTIR columns. Our results show that a combined inversion is promising in the NH. However, implementation of a satellite bias correction scheme is essential to combine both observational data sets in the SH

Evidence for long-range transport of Carbon Monoxide in the Southern Hemisphere from SCIAMACHY observations

The SCIAMACHY satellite instrument shows enhanced carbon monoxide (CO) columns in the Southern Hemisphere during the local Spring. Chemistry-transport model simulations using the new GFEDv2 biomass-burning emission database show a similar temporal and spatial CO distribution, indicating that the observed enhancements are mainly due to biomass burning (BB). Large differences between the year 2003 and 2004 are observed in both the measurements and the model for South America and Australia. This study analyzes the origin of these observed enhancements in the Southern Hemisphere. The fact that SCIAMACHY is sensitive to surface CO allows for the observation of enhanced CO columns in both emission areas and in areas that are affected by long-range transport of CO. Model results show a large contribution of South American BB CO over Australian BB regions during the 2004 BB season of up to similar to 30-35% and up to 55% further south, with smaller contributions for 2003. BB CO transported from southern Africa contributes up to similar to 40% in 2003 and similar to 30% in 2004. The results indicate that differences between SCIAMACHY CO and the model simulations over Australian BB areas are probably not only caused by uncertainties in local emissions but also in overseas emissions

Spatial regression analysis on 32 years of total column ozone data

Multiple-regression analyses have been performed on 32 years of total ozone column data that was spatially gridded with a 1 × 1.5° resolution. The total ozone data consist of the MSR (Multi Sensor Reanalysis; 1979-2008) and 2 years of assimilated SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) ozone data (2009-2010). The two-dimensionality in this data set allows us to perform the regressions locally and investigate spatial patterns of regression coefficients and their explanatory power. Seasonal dependencies of ozone on regressors are included in the analysis. A new physically oriented model is developed to parameterize stratospheric ozone. Ozone variations on nonseasonal timescales are parameterized by explanatory variables describing the solar cycle, stratospheric aerosols, the quasi-biennial oscillation (QBO), El Niño-Southern Oscillation (ENSO) and stratospheric alternative halogens which are parameterized by the effective equivalent stratospheric chlorine (EESC). For several explanatory variables, seasonally adjusted versions of these explanatory variables are constructed to account for the difference in their effect on ozone throughout the year. To account for seasonal variation in ozone, explanatory variables describing the polar vortex, geopotential height, potential vorticity and average day length are included. Results of this regression model are compared to that of a similar analysis based on a more commonly applied statistically oriented model. The physically oriented model provides spatial patterns in the regression results for each explanatory variable. The EESC has a significant depleting effect on ozone at mid-and high latitudes, the solar cycle affects ozone positively mostly in the Southern Hemisphere, stratospheric aerosols affect ozone negatively at high northern latitudes, the effect of QBO is positive and negative in the tropics and mid-to high latitudes, respectively, and ENSO affects ozone negatively between 30° N and 30° S, particularly over the Pacific. The contribution of explanatory variables describing seasonal ozone variation is generally large at mid-to high latitudes. We observe ozone increases with potential vorticity and day length and ozone decreases with geopotential height and variable ozone effects due to the polar vortex in regions to the north and south of the polar vortices. Recovery of ozone is identified globally. However, recovery rates and uncertainties strongly depend on choices that can be made in defining the explanatory variables. The application of several trend models, each with their own pros and cons, yields a large range of recovery rate estimates. Overall these results suggest that care has to be taken in determining ozone recovery rates, in particular for the Antarctic ozone hole. © 2014 Author(s)

Claim of solar influence is on thin ice:Are 11-year cycle solar minima associated with severe winters in Europe?

A recent paper in Geophysical Research Letters, 'Solar influence on winter severity in central Europe', by Sirocko et al (2012 Geophys. Res. Lett. 39 L16704) claims that 'weak solar activity is empirically related to extremely cold winter conditions in Europe' based on analyses of documentary evidence of freezing of the River Rhine in Germany and of the Reanalysis of the Twentieth Century (20C). However, our attempt to reproduce these findings failed. The documentary data appear to be selected subjectively and agree neither with instrumental observations nor with two other reconstructions based on documentary data. None of these datasets show significant connection between solar activity and winter severity in Europe beyond a common trend. The analysis of Sirocko et al of the 20C circulation and temperature is inconsistent with their time series analysis. A physically-motivated consistent methodology again fails to support the reported conclusions. We conclude that multiple lines of evidence contradict the findings of Sirocko et al