The Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura satellite has provided essentially daily global measurements of ozone (O3) profiles from the upper troposphere to the ...upper mesosphere since August of 2004. This paper focuses on validation of the MLS stratospheric standard ozone product and its uncertainties, as obtained from the 240 GHz radiometer measurements, with a few results concerning mesospheric ozone. We compare average differences and scatter from matched MLS version 2.2 profiles and coincident ozone profiles from other satellite instruments, as well as from aircraft lidar measurements taken during Aura Validation Experiment (AVE) campaigns. Ozone comparisons are also made between MLS and balloon‐borne remote and in situ sensors. We provide a detailed characterization of random and systematic uncertainties for MLS ozone. We typically find better agreement in the comparisons using MLS version 2.2 ozone than the version 1.5 data. The agreement and the MLS uncertainty estimates in the stratosphere are often of the order of 5%, with values closer to 10% (and occasionally 20%) at the lowest stratospheric altitudes, where small positive MLS biases can be found. There is very good agreement in the latitudinal distributions obtained from MLS and from coincident profiles from other satellite instruments, as well as from aircraft lidar data along the MLS track.
We present results of early validation studies using retrieved atmospheric profiles from the Earth Observing System Microwave Limb Sounder (MLS) instrument on the Aura satellite. "Global" results are ...presented for MLS measurements of atmospheric temperature, ozone, water vapor, hydrogen chloride, nitrous oxide, nitric acid, and carbon monoxide, with a focus on the January-March 2005 time period. These global comparisons are made using long-standing global satellites and meteorological datasets, as well as some measurements from more recently launched satellites. Comparisons of MLS data with measurements from the Ft. Sumner, NM, September 2004 balloon flights are also presented. Overall, good agreement is obtained, often within 5% to 10%, but we point out certain issues to resolve and some larger systematic differences; some artifacts in the first publicly released MLS (version 1.5) dataset are noted. We comment briefly on future plans for validation and software improvements.
Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, ...show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere.
Vertical profiles of stratospheric HOCl calculated with a diurnal steady-state photochemical model that uses currently recommended reaction rates and photolysis cross sections underestimate observed ...profiles of HOCl obtained by two balloon-borne instruments, FIRS-2 (a far-infrared emission spectrometer) and MkIV (a mid-infrared, solar absorption spectrometer). Considerable uncertainty (a factor of two) persists in laboratory measurements of the rate constant (k(sub 1)) for the reaction ClO + HO2 yields HOCl + O2. Agreement between modeled and measured HOCl can be attained using a value of k(sub 1) from Stimpfle et al. (1979) that is about a factor-of-two faster than the currently recommended rate constant. Comparison of modeled and measured HOCl suggests that models using the currently recommended value for k(sub 1) may underestimate the role of the HOCl catalytic cycle for ozone depletion, important in the midlatitude lower stratosphere.
The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ...ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.
We present volume mixing ratio profiles of NO, NO2, HNO3, HNO4, N2O5, and ClNO3 and their composite budget (NOy), from 20 to 39 km, measured remotely in solar occultation by the Jet Propulsion ...Laboratory MkIV Interferometer during a balloon flight from Fort Sumner, New Mexico (35°N), on September 25, 1993. In general, observed profiles agree well with values calculated using a photochemical steady state model constrained by simultaneous MkIV observations of long‐lived precursors and aerosol surface area from the Stratospheric Aerosol and Gas Experiment II. The measured variation of concentrations of NOx (= NO + NO2) and N2O5 between sunrise and sunset reveals the expected ∼2:1 stoichiometry at all altitudes. Despite relatively good agreement between theory and observation for profiles of NO and HNO3 the observed concentration of NO2 becomes progressively higher than model values below 30 km, with the discrepancy reaching ∼30% at 22 km. This suggests an incomplete understanding of factors that regulate the NO/NO2 and NO2/HNO3 ratios below 30 km. Observations obtained during September 1990, prior to the June 1991 eruption of Mount Pinatubo, as well as during April 1993 and September 1993 provide a test of our understanding of the affect of aerosol surface area on the NOx/NOy ratio at midlatitudes. The observations reveal a decrease in the NOx/NOy ratio for increasing aerosol surface area that is consistent with the heterogeneous hydrolysis of N2O5 being the dominant sink of between altitudes of 18 and 24 km for the conditions encountered (e.g., surface areas as high as 14 μm2 cm−3 and temperatures from 209 to 219 K).
Measurements made in the outer ring of the northern polar vortex from October 1991 through March 1992 reveal an altitude-dependent change in ozone, with a decrease at the bottom of the vortex and a ...substantial increase at the highest altitudes accessible to measurement. The increase is the result of ozone-rich air entering the vortex, and the decrease reflects ozone loss accumulated after the descent of the air through high concentrations of reactive chlorine. The depleted air that is released out of the bottom of the vortex is sufficient to significantly reduce column ozone at mid-latitudes.
The concentrations of the hydrogen radicals OH and HO$_2$ in the middle and upper troposphere were measured simultaneously with those of NO, O$_3$, CO, H$_2$O, CH$_4$, non-methane hydrocarbons, and ...with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O$_3$ in this region of the atmosphere. Comparison of the measured concentrations of OH and HO$_2$ with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO$_x$ required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O$_3$ is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO$_2$ and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O$_3$ than expected.
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.
On May 8, 1997, vertical profiles of over 30 different gases were measured remotely in solar occultation by the Jet Propulsion Laboratory MkIV Interferometer during a balloon flight launched from ...Fairbanks, Alaska. These gases included H2O, N2O, CH4, CO, NOx, NOy, HCl, ClNO3, CCl2F2, CCl3F, CCl4, CHClF2, CClF2CCl2F, SF6, CH3Cl, and C2H6, all of which were also measured in situ by instruments on board the NASA ER‐2 aircraft, which was making flights from Fairbanks during this same early May time period as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) experiment. A comparison of the gas volume mixing ratios in the upper troposphere and lower stratosphere reveals agreement better than 5% for most gases. The three significant exceptions to this are SF6 and CCl4 for which the remote measurements exceed the in situ observations by 15–20% at all altitudes, and H2O for which the remote measurements are up to 30% smaller than the in situ observations near the hygropause.
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