Steven Lloyd - Academia.edu (original) (raw)
Papers by Steven Lloyd
Journal of Geophysical Research, 2002
In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement (POAM) III da... more In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement (POAM) III data for providing semiglobal three-dimensional ozone fields during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) winter. As a solar occultation instrument, POAM III measurements were limited to latitudes of 63°N to 68°N during the SOLVE campaign but covered a wide range of potential vorticity. Using established mapping techniques, we have used the relation between potential vorticity and ozone measured by POAM III to calculate threedimensional ozone mixing ratio fields throughout the Northern Hemisphere on a daily basis during the 1999/2000 winter. To validate the results, we have extensively compared profiles obtained from ozonesondes and the Halogen Occultation Experiment to the proxy O 3 interpolated horizontally and vertically to the correlative measurement locations. On average, the proxy O 3 agrees with the correlative observations to better than $5%, at potential temperatures below about 900 K and latitudes above about 30°N, demonstrating the reliability of the reconstructed O 3 fields in these regions. We discuss the application of the POAM proxy ozone profiles for calculating photolysis rates along the ER-2 and DC-8 flight tracks during the SOLVE campaign, and we present a qualitative picture of the evolution of polar stratospheric ozone throughout the winter.
Journal of Geophysical Research, 1997
Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO ... more Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + C1ONO2 + 2N20 5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO 2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NOy reservoir are well understood in the lower stratosphere. Introduction Stratospheric ozone (03) is destroyed in catalytic cycles involving oxides of hydrogen (HO x = OH + HO2), nitrogen (NO x = NO + NO2), chlorine (C10 x = C1 + C10 + 2C1OOC1), and bromine (BrO x = Br + BrO). Our understanding of 03 destruction cycles changed significantly with the recognition of the role of heterogeneous reactions in the stratosphere
Journal of Geophysical Research, 1999
The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of... more The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) campaign in the spring and summer of 1997 is defined. Five independent data sets of total ozone observations at Fairbanks are presented, from the Earth Probe and ADEOS Total Ozone Mapping Spectrometer (TOMS) satellite instruments, balloon-borne electrochemical concentration cell ozonesondes, and ground-based (Brewer spectroradiometer, Dobson spectrophotometer, and the Jet Propulsion Laboratory MklV infrared interferometer) instruments. The excellent agreement between different observational techniques lends confidence to the observed rate of summertime loss of total ozone at high latitudes. In addition, the small offsets between the data sets are well understood. ER-2 aircraft enabled the determination of the relative rates
Geophysical Research Letters, 2000
In situ measurements of radical and long-lived species were made in the lower Arctic stratosphere... more In situ measurements of radical and long-lived species were made in the lower Arctic stratosphere (18 to 20 km) between spring and early autumn in 1997. The measurements include 0 3, C10, OH, HO2, NO, NO2, N20, CO, and overhead 03. A photochemical box model constrained by these and other observations is used to compute the diurnally averaged destruction and production rates of 03 in this region. The rates show a strong dependence on solar exposure and ambient 03. Total destruction rates, which reach 19%/month in summer, reveal the predominant role of NOx and HOx catalytic cycles throughout the period. Production of 03 is significant only in midsummer air parcels. A comparison of observed 03 changes with destruction rates and transport effects indicates the predominant role of destruction in spring and an increased role of transport by early autumn.
Geophysical Research Letters, 1990
A:bstrac•. Simultaneous, in situ measurements of OH, :HOa, HaO, and O, from 37-23 km are reported... more A:bstrac•. Simultaneous, in situ measurements of OH, :HOa, HaO, and O, from 37-23 km are reported, The par-6fioning between OH and HOa and the total HO• concentm•:io.n are compared w•th expected steady-state values. The ratio of HOa to OH varies from less than 2 at 3õ km to .more than 3 at 25 km; in the lower stratosphere this ratio [s nearly a factor of two less than predicted. The data are used to calculate HO• production and loss rates. The measured HOx mixing ratio is consistent with production dominated by the reaction of O(•D) with HaO, and loss controlled by NOy below 28 km and HOx above 30 km. T/he steady-state concentration of H20• is inferred from t,he •me•ured HOa concentration and calculated photolym rate. The maximum H=Oa mixing ratio (at 33 km) is p•icted to be less than 0.2 ppb.
Molecular velocity distributions and generalized scale invariance in the turbulent atmosphere
Faraday Discussions, 2005
Airborne observations of ozone, temperature and the spectral actinic photon flux for ozone in the... more Airborne observations of ozone, temperature and the spectral actinic photon flux for ozone in the Arctic lower stratosphere April-September 1997 and January-March 2000 allow a connection to be made between the rate of production of translationally hot atoms and molecules via ozone photodissociation and the intermittency of temperature. Seen in the context of non-equilibrium statistical mechanics literature results from molecular dynamics simulations, the observed correlation between the molecular scale production of translationally hot atoms and molecules and the macroscopic fluid mechanical intermittency of temperature may imply a departure from Maxwell-Boltzmann distributions of molecular velocities, with consequences for chemistry, radiative line shapes and turbulence in the atmosphere, arising from overpopulated high velocity tails of the probability distribution functions (PDFs).
Journal of Geophysical Research: Atmospheres, 1999
Stratospheric measurements of NO, NO2, 03, C10, and HO2 were made during spring, early summer, an... more Stratospheric measurements of NO, NO2, 03, C10, and HO2 were made during spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO2 and NO are in steady state through NO2 photolysis and reactions involving 03, C10, BrO, and HO2. By combining observations of 03, C10, and HO2, observed and modeled values of the NO2 photolysis rate coefficient (JNO2), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO2 and JNO2. An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (+50 to 70%). These results suggest that photochemistry controlling the NO2/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + 03-• NO2 + 02 would aid future analyses of these or similar atmospheric observations. 1. Introduction With mixing ratios in the parts per trillion (pptv) to parts per billion (ppbv) range in the lower stratosphere, hydrogen, nitrogen, and halogen radicals (HO x = OH + HO2; NOx = NO + NO2; C1Ox = C1 + C10; BrO x = Br + BrO) play important roles in the destruction of stratospheric ozone
Journal for the History of Astronomy
Optical remote sensing of ozone, clouds, and surface effects from the ER-2 platform during the NASA ASHOE/MAESA campaign
During the ASHOE/MAESA campaign a series of observations of the UV-visible radiation field were o... more During the ASHOE/MAESA campaign a series of observations of the UV-visible radiation field were obtained from the ER-2 aircraft with the composition and photodissociative flux measurement (CPFM) instrument. Observations were made at the limb and in the zenith and nadir directions over the spectral range 300 - 775 nm at 1 nm spectral resolution. Analysis of these data yield surface
Timepieces. (Book Reviews: Ivory Diptych Sundials, 1570-1750.)
Science
Issues in Stratospheric Ozone Depletion
ABSTRACT
Journal for the History of Astronomy
Validation of MSX/UVISI-Derived Ozone and Temperature Profiles Through Intercomparison With SAGE II, POAM III, HALOE, TOMS, and Ground-based Data
ABSTRACT
Comparison of a 27-yr Composite TOMS/SBUV(/2)/OMI Dataset of UV Lambertian Equivalent Reflectivity With the Shortwave Albedo From ERBE and CERES
This study uses eight NASA and NOAA satellite datasets of ultraviolet Lambertian Equivalent Refle... more This study uses eight NASA and NOAA satellite datasets of ultraviolet Lambertian Equivalent Reflectivity (LER), all processed with the common TOMS/SBUV/OMI version 8 retrieval algorithm, to build a 27-yr composite dataset of reflectivity (albedo) with a reliable, geophysically validated, long-term calibration. The composite LER dataset has been compared with shortwave (0.2--5.0~mum) albedo observations from the three ERBE satellite instruments (on
The Citizens And Remote Sensing Observational Network (CARSON) Guide: Merging NASA Remote-Sensing Data with Local Environmental Awareness
ABSTRACT
A 27Year Composite Dataset of Global UV Effective Reflectivity From the TOMS and SBUV(/2) Satellite Instruments
ABSTRACT
Analysis of Trends and Solar Cycle Effects in the TOMS and SBUV(/2) UV Effective Reflectivity Datasets
ABSTRACT
Journal of Geophysical Research, 2002
In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement (POAM) III da... more In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement (POAM) III data for providing semiglobal three-dimensional ozone fields during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) winter. As a solar occultation instrument, POAM III measurements were limited to latitudes of 63°N to 68°N during the SOLVE campaign but covered a wide range of potential vorticity. Using established mapping techniques, we have used the relation between potential vorticity and ozone measured by POAM III to calculate threedimensional ozone mixing ratio fields throughout the Northern Hemisphere on a daily basis during the 1999/2000 winter. To validate the results, we have extensively compared profiles obtained from ozonesondes and the Halogen Occultation Experiment to the proxy O 3 interpolated horizontally and vertically to the correlative measurement locations. On average, the proxy O 3 agrees with the correlative observations to better than $5%, at potential temperatures below about 900 K and latitudes above about 30°N, demonstrating the reliability of the reconstructed O 3 fields in these regions. We discuss the application of the POAM proxy ozone profiles for calculating photolysis rates along the ER-2 and DC-8 flight tracks during the SOLVE campaign, and we present a qualitative picture of the evolution of polar stratospheric ozone throughout the winter.
Journal of Geophysical Research, 1997
Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO ... more Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + C1ONO2 + 2N20 5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO 2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NOy reservoir are well understood in the lower stratosphere. Introduction Stratospheric ozone (03) is destroyed in catalytic cycles involving oxides of hydrogen (HO x = OH + HO2), nitrogen (NO x = NO + NO2), chlorine (C10 x = C1 + C10 + 2C1OOC1), and bromine (BrO x = Br + BrO). Our understanding of 03 destruction cycles changed significantly with the recognition of the role of heterogeneous reactions in the stratosphere
Journal of Geophysical Research, 1999
The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of... more The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) campaign in the spring and summer of 1997 is defined. Five independent data sets of total ozone observations at Fairbanks are presented, from the Earth Probe and ADEOS Total Ozone Mapping Spectrometer (TOMS) satellite instruments, balloon-borne electrochemical concentration cell ozonesondes, and ground-based (Brewer spectroradiometer, Dobson spectrophotometer, and the Jet Propulsion Laboratory MklV infrared interferometer) instruments. The excellent agreement between different observational techniques lends confidence to the observed rate of summertime loss of total ozone at high latitudes. In addition, the small offsets between the data sets are well understood. ER-2 aircraft enabled the determination of the relative rates
Geophysical Research Letters, 2000
In situ measurements of radical and long-lived species were made in the lower Arctic stratosphere... more In situ measurements of radical and long-lived species were made in the lower Arctic stratosphere (18 to 20 km) between spring and early autumn in 1997. The measurements include 0 3, C10, OH, HO2, NO, NO2, N20, CO, and overhead 03. A photochemical box model constrained by these and other observations is used to compute the diurnally averaged destruction and production rates of 03 in this region. The rates show a strong dependence on solar exposure and ambient 03. Total destruction rates, which reach 19%/month in summer, reveal the predominant role of NOx and HOx catalytic cycles throughout the period. Production of 03 is significant only in midsummer air parcels. A comparison of observed 03 changes with destruction rates and transport effects indicates the predominant role of destruction in spring and an increased role of transport by early autumn.
Geophysical Research Letters, 1990
A:bstrac•. Simultaneous, in situ measurements of OH, :HOa, HaO, and O, from 37-23 km are reported... more A:bstrac•. Simultaneous, in situ measurements of OH, :HOa, HaO, and O, from 37-23 km are reported, The par-6fioning between OH and HOa and the total HO• concentm•:io.n are compared w•th expected steady-state values. The ratio of HOa to OH varies from less than 2 at 3õ km to .more than 3 at 25 km; in the lower stratosphere this ratio [s nearly a factor of two less than predicted. The data are used to calculate HO• production and loss rates. The measured HOx mixing ratio is consistent with production dominated by the reaction of O(•D) with HaO, and loss controlled by NOy below 28 km and HOx above 30 km. T/he steady-state concentration of H20• is inferred from t,he •me•ured HOa concentration and calculated photolym rate. The maximum H=Oa mixing ratio (at 33 km) is p•icted to be less than 0.2 ppb.
Molecular velocity distributions and generalized scale invariance in the turbulent atmosphere
Faraday Discussions, 2005
Airborne observations of ozone, temperature and the spectral actinic photon flux for ozone in the... more Airborne observations of ozone, temperature and the spectral actinic photon flux for ozone in the Arctic lower stratosphere April-September 1997 and January-March 2000 allow a connection to be made between the rate of production of translationally hot atoms and molecules via ozone photodissociation and the intermittency of temperature. Seen in the context of non-equilibrium statistical mechanics literature results from molecular dynamics simulations, the observed correlation between the molecular scale production of translationally hot atoms and molecules and the macroscopic fluid mechanical intermittency of temperature may imply a departure from Maxwell-Boltzmann distributions of molecular velocities, with consequences for chemistry, radiative line shapes and turbulence in the atmosphere, arising from overpopulated high velocity tails of the probability distribution functions (PDFs).
Journal of Geophysical Research: Atmospheres, 1999
Stratospheric measurements of NO, NO2, 03, C10, and HO2 were made during spring, early summer, an... more Stratospheric measurements of NO, NO2, 03, C10, and HO2 were made during spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO2 and NO are in steady state through NO2 photolysis and reactions involving 03, C10, BrO, and HO2. By combining observations of 03, C10, and HO2, observed and modeled values of the NO2 photolysis rate coefficient (JNO2), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO2 and JNO2. An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (+50 to 70%). These results suggest that photochemistry controlling the NO2/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + 03-• NO2 + 02 would aid future analyses of these or similar atmospheric observations. 1. Introduction With mixing ratios in the parts per trillion (pptv) to parts per billion (ppbv) range in the lower stratosphere, hydrogen, nitrogen, and halogen radicals (HO x = OH + HO2; NOx = NO + NO2; C1Ox = C1 + C10; BrO x = Br + BrO) play important roles in the destruction of stratospheric ozone
Journal for the History of Astronomy
Optical remote sensing of ozone, clouds, and surface effects from the ER-2 platform during the NASA ASHOE/MAESA campaign
During the ASHOE/MAESA campaign a series of observations of the UV-visible radiation field were o... more During the ASHOE/MAESA campaign a series of observations of the UV-visible radiation field were obtained from the ER-2 aircraft with the composition and photodissociative flux measurement (CPFM) instrument. Observations were made at the limb and in the zenith and nadir directions over the spectral range 300 - 775 nm at 1 nm spectral resolution. Analysis of these data yield surface
Timepieces. (Book Reviews: Ivory Diptych Sundials, 1570-1750.)
Science
Issues in Stratospheric Ozone Depletion
ABSTRACT
Journal for the History of Astronomy
Validation of MSX/UVISI-Derived Ozone and Temperature Profiles Through Intercomparison With SAGE II, POAM III, HALOE, TOMS, and Ground-based Data
ABSTRACT
Comparison of a 27-yr Composite TOMS/SBUV(/2)/OMI Dataset of UV Lambertian Equivalent Reflectivity With the Shortwave Albedo From ERBE and CERES
This study uses eight NASA and NOAA satellite datasets of ultraviolet Lambertian Equivalent Refle... more This study uses eight NASA and NOAA satellite datasets of ultraviolet Lambertian Equivalent Reflectivity (LER), all processed with the common TOMS/SBUV/OMI version 8 retrieval algorithm, to build a 27-yr composite dataset of reflectivity (albedo) with a reliable, geophysically validated, long-term calibration. The composite LER dataset has been compared with shortwave (0.2--5.0~mum) albedo observations from the three ERBE satellite instruments (on
The Citizens And Remote Sensing Observational Network (CARSON) Guide: Merging NASA Remote-Sensing Data with Local Environmental Awareness
ABSTRACT
A 27Year Composite Dataset of Global UV Effective Reflectivity From the TOMS and SBUV(/2) Satellite Instruments
ABSTRACT
Analysis of Trends and Solar Cycle Effects in the TOMS and SBUV(/2) UV Effective Reflectivity Datasets
ABSTRACT