T. J. McGee

Validation of Aura Microwave Limb Sounder stratospheric ozone measurements

[1] 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.

Validation of UARS Microwave Limb Sounder temperature and pressure measurements

The accuracy and precision of the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) atmospheric temperature and tangent-point pressure measurements are described. Temperatures and tangent-point pressure (atmospheric pressure at the tangent height of the field of view boresight) are retrieved from a 15-channel 63-GHz radiometer measuring O2 microwave emissions from the stratosphere and mesosphere. The Version 3 data (first public release) contains scientifically useful temperatures from 22 to 0.46 hPa. Accuracy estimates are based on instrument performance, spectroscopic uncertainty and retrieval numerics, and range from 2.1 K at 22 hPa to 4.8 K at 0.46 hPa for temperature and from 200 m (equivalent log pressure) at 10 hPa to 300 m at 0.1 hPa. Temperature accuracy is limited mainly by uncertainty in instrument characterization, and tangent-point pressure accuracy is limited mainly by the accuracy of spectroscopic parameters. Precisions are around 1 K and 100 m. Comparisons are presented among temperatures from MLS, the National Meteorological Center (NMC) stratospheric analysis and lidar stations at Table Mountain, California, Observatory of Haute Provence (OHP), France, and Goddard Spaceflight Center, Maryland. MLS temperatures tend to be 1–2 K lower than NMC and lidar, but MLS is often 5 – 10 K lower than NMC in the winter at high latitudes, especially within the northern hemisphere vortex. Winter MLS and OHP (44°N) lidar temperatures generally agree and tend to be lower than NMC. Problems with Version 3 MLS temperatures and tangent-point pressures are identified, but the high precision of MLS radiances will allow improvements with better algorithms planned for the future.

Stratospheric Ozone Intercomparison Campaign (STOIC) 1989: Overview

The NASA Upper Atmosphere Research Program organized a Stratospheric Ozone Intercomparison Campaign (STOIC) held in July–August 1989 at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL). The primary instruments participating in this campaign were several that had been developed by NASA for the Network for the Detection of Stratospheric Change: the JPL ozone lidar at TMF, the Goddard Space Flight Center trailer-mounted ozone lidar which was moved to TMF for this comparison, and the Millitech/LaRC microwave radiometer. To assess the performance of these new instruments, a validation/intercomparison campaign was undertaken using established techniques: balloon ozonesondes launched by personnel from the Wallops Flight Facility and from NOAA Geophysical Monitoring for Climate Change (GMCC) (now Climate Monitoring and Diagnostics Laboratory), a NOAA GMCC Dobson spectrophotometer, and a Brewer spectrometer from the Atmospheric Environment Service of Canada, both being used for column as well as Umkehr profile retrievals. All of these instruments were located at TMF and measurements were made as close together in time as possible to minimize atmospheric variability as a factor in the comparisons. Daytime rocket measurements of ozone were made by Wallops Flight Facility personnel using ROCOZ-A instruments launched from San Nicholas Island. The entire campaign was conducted as a blind intercomparison, with the investigators not seeing each others data until all data had been submitted to a referee and archived at the end of the 2-week period (July 20 to August 2, 1989). Satellite data were also obtained from the Stratospheric Aerosol and Gas Experiment (SAGE II) aboard the Earth Radiation Budget Satellite and the total ozone mapping spectrometer (TOMS) aboard Nimbus 7. An examination of the data has found excellent agreement among the techniques, especially in the 20- to 40-km range. As expected, there was little atmospheric variability during the intercomparison, allowing for detailed statistical comparisons at a high level of precision. This overview paper will summarize the campaign and provide a “road map” to subsequent papers in this issue by the individual instrument teams which will present more detailed analysis of the data and conclusions.

Correlations among the optical properties of cirrus‐cloud particles: Implications for spaceborne remote sensing

[1] Lidar measurements of Arctic (67.9� N) cirrus clouds reveal a strong positive correlation between particle depolarization ratio and extinction-to-backscatter (lidar) ratio for ambient cloud temperatures above 45� C, and an anti-correlation for colder temperatures. Similar correlations are evident in a 2-year midlatitude (53.5� N) cirrus data set. These data suggest that robust relationships may exist between these particle optical properties that will facilitate the retrieval of cirrus extinction profiles from polarization-sensitive (spaceborne) elastic-backscatter lidars. INDEX TERMS: 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 1640 Global Change: Remote sensing; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry

Lidar measurements of stratospheric temperature during STOIC

This paper presents stratospheric temperature measurements made by ground based lidar during the Stratospheric Ozone Intercomparison Campaign experiment. These measurements are correlated with complementary measurements made from sondes, satellite platforms, and National Meteorological Center analyses. Over the altitude range 30 to 65 km, the lidar derived temperatures were within 2 to 3 K of the temperatures derived from the other measurement systems. Specific differences are discussed in the paper.

Comparison of STOIC 1989 ground‐based lidar, microwave spectrometer, and Dobson spectrophotometer Umkehr ozone profiles with ozone profiles from balloon‐borne electrochemical concentration cell ozonesondes

Ground-based measurements of stratospheric ozone using a Jet Propulsion Laboratory (JPL) lidar, a NASA Goddard Space Flight Center (GSFC) lidar, a Millitech Corporation/NASA Langley Research Center (Millitech/LaRC) microwave spectrometer, and a NOAA Dobson ozone spectrophotometer were compared with in situ measurements made quasi-simultaneously with balloon-borne electrochemical concentration cell (ECC) ozonesondes during 10 days of the Stratospheric Ozone Intercomparison Campaign (STOIC). The campaign was conducted at Table Mountain Observatory, California, during the summer of 1989. ECC ozonesondes were flown by NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) personnel as well as by personnel from the NASA Wallops Island Flight Facility (WFF). Within the altitude range of 20–32 km, ozone measurement precisions were estimated to be ±0.6 to ±1.2% for the JPL lidar, ±0.7% for the GSFC lidar, ±4% for the microwave spectrometer, and ±3% for the NOAA ECC ozonesonde instruments. These precisions decreased in the 32 to 38.6-km altitude range to ±1.3, ±1.5, and ±3% to ±10% for the JPL lidar, GSFC lidar, and the ECC sondes, respectively, but remained at ±4% for the microwave instrument. Ozone measurement accuracies in the 20 to 32 km altitude range were estimated to be ±1.2 to ±2.4% for the JPL lidar, ±1.4% for the GSFC lidar, ±6% for the microwave radiometer, and ±5% for the ECC ozonesondes. The accuracies decreased in the 32 to 38.6-km altitude range to ±2.6, ±3.0, ±7, and 1 ± 4% to −4 ± 10% for the JPL lidar, the GSFC lidar, the microwave spectrometer, and the ECC ozonesondes, respectively. While accuracy estimates for the ECC sondes were obtained by combining random and estimated bias errors, the accuracies for the lidar instruments were obtained by doubling the measurement precision figures, with the assumption that such doubling accounts for systematic errors. Within the altitude range of 20–36 km the mean ozone profiles produced by the JPL, GSFC, and the Millitech/LaRC groups did not differ from the mean ECC sonde ozone profile by more than about 2, 4, and 5%, respectively. Six morning Dobson instrument Umkehr observations yielded mean ozone amounts in layers 3 and 5–7 that agreed with comparison ECC ozonesonde data to within ±4%. In layer 4 the difference was 7.8%. (Less favorable comparison data were obtained for six afternoon Umkehr observations made in highly polluted near-surface air.) This good agreement in overall results obtained lends credence to the reliability of the ozone measurements made at Table Mountain Observatory during STOIC 1989.

Results of the 1998 Ny‐Ålesund Ozone Monitoring Intercomparison

The Ny-Alesund Ozone Monitoring Intercomparison (NAOMI) took place at Ny-Alesund,Spitsbergen (78.92 degrees N, 11.95 degrees E), from January 20 to February 10, 1998.This paper focuses on comparing stratospheric ozone profiles measured by the Alfred WegenerInstitute differential absorption lidar (AWI DIAL), in routine Network for Detection ofStratospheric Change (NDSC) operation at Ny-Alesund, the mobile Goddard Space Flight CenterDIAL (GSFC DIAL), the University of Bremen microwave radiometer (mu Wave), andelectrochemical concentration cell (ECC) ozonesondes, flown routinely by AWI. Below 30 km thetwo DIALs and the ECC sondes give virtually the same results, with instrumental precision(repeatability) better than +/-5% and no detectable bias. When their coarser altitude resolution isnot accounted for, the mu Wave data show 15% low bias at 16 km and 15% high bias at 23 km,Considerably better agreement, better than +/-5% around 20 km and above 30 km, is found whenthe altitude resolution of the other data is degraded to match that of the mu Wave. During NAOMIthe mu Wave data show high bias of up to 10% in a mixing ratio plateau around 25 km. Such biashas not been seen in routine intercomparisons between mu Wave and ECC sonde data atNy-Alesund. It is likely caused by an a priori profile 40% higher than the true profile duringNAOMI, Above 30 km the mu Wave data show the best precision (repeatability), about +/-3 to+/-5%. Precision of the GSFC DIAL data decreases from better than +/-5% at 30 km to about+/-10% at 40 km, and the precision for the AWI DIAL data decreases from better than +/-5% at30 km to +/-30% at 40 km. From 34 to 38 km the AWI profile is 12% lower than the GSFCprofile. AWI DIAL measurements that are low at 35 km often end below 40 km of show highvalues at 40 or 45 km, This behavior seems related to the way in which the AWI processingalgorithm changes altitude resolution for data with poor signal-to-noise ratio.

Correlations among the optical properties of cirrus-cloud particles: Microphysical interpretation: MICROPHYSICAL INTERPRETATION OF LIDAR DATA

Cirrus measurements obtained with a ground-based polarization Raman lidar at 67.9° N in January 1997 reveal a strong positive correlation between the particle optical properties, specifically depolarization ratio apar and extinction-to-backscatter (lidar) ratio Spar, for apar ~ 40%. Over the duration of the measurements both particle properties vary systematically. This effect is particularly pronounced in the case of apar which decreases significantly with time. The analysis of lidar humidity and radiosonde temperature data shows that the measured op- tical properties stem from scattering by dry solid ice particles, while scattering by supercooled droplets, or by wetted or subliming ice particles can be excluded. For the microphysical interpretation of the lidar measurements, ray-tracing computations of par~ticle scattering properties have been used. The comparison with the theoretical data sug- gests that the observed cirrus data can be interpreted in terms of size, shape, and growth of the cirrus particles, the latter under the assumption that the lidar measurements of consecutive cloud segments can be mapped on the temporal development of a single cloud parcel moving along its trajectory: Near the cloud top in the early stage of cirrus de- velopment, light scattering by nearly isometric particles that have the optical characteristics of hexagonal columns (short, column-like particles) is dominant. Over time the ice particles grow, and as the cloud base height extends to lower altitudes characterized by warmer temperatures they become morphologically diverse. For large Spar and depolarization values of ~ 40%, the scattering contributions of column- and plate-like parti- cles are roughly the same. In the lower ranges of the cirrus clouds, light scattering is pre- dominantly by plate-like ice particles. This interpretation assumes random orientation of the cirrus particles. Simulations with a simple model suggest, however, that the positive correlation between Spar and apar, which is observed for depolarization ratios < 40% mainly at low cloud altitudes, can be alternatively explained by horizontal alignment of a fraction of the cirrus particle population.