Papers by Gerald Nedoluha
A 1D Var assimilation study of simulated radio occultation measure- ments is presented. High reso... more A 1D Var assimilation study of simulated radio occultation measure- ments is presented. High resolution European Center for Medium Range Weather Forecasts global atmospheric fields are read by a state-of-the-art radio occultation simulator. The simulator provides quasi-realistic bending angle and refractivity profiles. Both profiles have been used in the assimilation process to assess the advantages and disadvantages of one over the other when retrieving temperature and water vapor profiles. Also, 2 different a priori (background) fields are used to assess possible impacts of the a priori quality. An optimization with respect to the convergence was performed first, where initialization of the Levenberg-Marquardt method closer to a Newtonian iteration was generally found to be advantageous, although lower tropospheric retrieval might benefit from a steepest descent ap- proach. Retrievals using quasi-realistic measurements showed on average errors of below 0.2 K (0.5 K) for an altitud...
The top edge (20-22 km) of the Antarctic ozone hole has been identified as a good place to detect... more The top edge (20-22 km) of the Antarctic ozone hole has been identified as a good place to detect ozone recovery [Hofmann et al., 1997; WMO 2003]. During the first six POAM observation years (1994-1996, 1998-2000), the early October ozone mixing ratio at the top edge of the ozone hole was nearly constant, while during the next four years (2001-2004) it was noticeably greater. The estimated ozone photochemical loss for air sampled at 20-22 km in 2001-2004 was likewise smaller. During 2001-2004, there were fewer PSCs and generally higher temperatures during August and September at 20-22 km than prior years. The increased ozone was due to both reduced photochemical ozone loss (2001, 2003, and 2004) and enhanced vertical advection of the ozone profile (2002). Because of the changing meteorological conditions, the ozone changes at the top edge of the hole cannot be easily attributed to changes in chlorine abundance. This analysis will be updated to include the 2005 ozone hole.
We present Upper Troposphere/Lower Stratosphere (UT/LS) observations from the Polar Ozone and Aer... more We present Upper Troposphere/Lower Stratosphere (UT/LS) observations from the Polar Ozone and Aerosol Measurement (POAM) III instrument. POAM is a remote sensing instrument that uses the solar occultation technique to measure trace gas species and aerosol extinction at high latitudes. POAM began measurements in April 1998 and is still operational. Ozone and water vapor observations on potential temperature and potential vorticity surfaces will be presented, in order to study seasonal and interannual variability in the abundance of these species in the UT/LS. Isentropic stratosphere-troposphere exchange is examined by means of ozone/water vapor correlations. We find evidence of isentropic exchange from the upper troposphere at lower latitudes to the lower stratosphere at high latitudes during summer and fall. We also use POAM observations in conjunction with isentropic advection calculations of ozone, water vapor, and tracer-derived equivalent length to study seasonal variability in ...
Polar Mesospheric Clouds (PMC) form in the upper mesosphere (~ 80 to 86 km) at latitudes greater ... more Polar Mesospheric Clouds (PMC) form in the upper mesosphere (~ 80 to 86 km) at latitudes greater than 50° during the summer season in each hemisphere. These clouds are formed of water ice particles, and thus can form only in regions where the temperatures are cold enough for water vapor to be saturated relative to ice. We can verify this assumption by comparing observations of PMCs made by the Ozone Monitoring Instrument (OMI) with coincident measurements of atmospheric temperature and water vapor made by the Microwave Limb Sounder (MLS) instrument, both of which fly on the Aura satellite. The large cross-track swath of the OMI measurements with sampling every 13 km along track ensures that there will be several OMI pixels (~13 km x 48 km) overlapping with the footprint of each MLS measurement (200 km x 12 km for temperature and 300 km x 6 km for water vapor). We calculate the saturation ratio with respect to ice from the MLS measurements of temperature and water vapor at a nominal ...
We present mesospheric water vapor measurements from the WVMS instruments at Lauder, New Zealand ... more We present mesospheric water vapor measurements from the WVMS instruments at Lauder, New Zealand (1993-present) and Mauna Loa, Hawaii (1996-present), mesospheric and stratospheric measurements from HALOE (1991-2005), and stratospheric water vapor measurements from POAM III (1998-2005). There have been three major variations in these datasets that have persisted on timescales longer than the QBO. One of these variations is the solar cycle, which affects water vapor above ~60km, and makes the identification of secular trends particularly difficult in the upper mesosphere. There is also a well documented early 1990s increase, which persisted until ~1996 and affected water vapor throughout the middle atmosphere. In the lower mesosphere, below the altitude where solar cycle effects begin to become important, water vapor has remained nearly constant since ~1996. There was also a sudden decrease in water vapor in the lower stratosphere in 2001 which was, unlike the 1991-1996 increase, well...
Atmospheric Chemistry and Physics
The Polar Ozone and Aerosol Measurement and Stratospheric Aerosol and Gas Experiment instruments ... more The Polar Ozone and Aerosol Measurement and Stratospheric Aerosol and Gas Experiment instruments both observed high numbers of polar stratospheric clouds (PSCs) in the polar region during the second SAGE Ozone Loss and Validation Experiment (SOLVE II) and Validation of INTERnational Satellites and Study of Ozone Loss (VINTERSOL) campaign, conducted during the 2002/2003 Northern Hemisphere winter. Between 15 November 2002 (14 November 2002) and 18 March 2003 (21 March 2003) SAGE (POAM) observed 122 (151) aerosol extinction profiles containing PSCs. PSCs were observed on an almost daily basis, from early December through 15 January, in both instruments. No PSCs were observed from either instrument until 4 February, and sparingly in three periods in mid-and-late February and mid-March. In early December, PSCs were observed in the potential temperature range from roughly 375 K to 750 K. Throughout December the top of this range decreases to near 600 K. In February and March, PSC observa...
Earth Observation with CHAMP, 2005
We present an Optimal Estimation processing of simulated radio occultation data. Temperature and ... more We present an Optimal Estimation processing of simulated radio occultation data. Temperature and water vapor profiles are retrieved from either bending angle or refractivity measurements. The advantages of one over the other are assessed. A comparison with idealized calculations shows the potential of ray tracer calculations.
Occultations for Probing Atmosphere and Climate, 2004
A 1D Var sensitivity study of simulated radio occultation measurements is presented. Temperature ... more A 1D Var sensitivity study of simulated radio occultation measurements is presented. Temperature and water vapor profiles are retrieved, along with a reference pressure to generate the pressure profile by applying the hydrostatic equation. High resolution European Center for Medium Range Weather Forecasts (ECMWF) atmospheric fields are used with a ray tracing tool to calculate the exact positions of the tangent point. The atmospheric profiles following the calculated tangent points trajectory in the 3D ECMWF fields are used to simulate bending angle measurements with a 1D forward model. Assimilation of these bending angles in a 1D Var tool employing the same 1D forward model is performed. We analyze the sensitivity of the retrieval to the assumption of hydrostatic equilibrium for a non-vertical atmospheric scan. Deviations of more than 1 % from a hydrostatic pressure profile can occur for certain mid-latitude and polar conditions. The effect upon the retrieval capabilities is usually negligible except for the most extreme cases.
First, we present a detailed intercomparison of the ground based microwave radiometers for middle... more First, we present a detailed intercomparison of the ground based microwave radiometers for middle atmospheric water vapor of the Network for the Detection of Atmospheric Composition Change, NDACC. For this purpose the retrievals of all microwave systems have been adapted as much as possible using the temperatures measured by EOS MLS and using the same set of spectroscopic parameters. The EOS MLS water vapor record has then been used as reference and allowed to perform an intercomparison of the ground based radiometers. The agreement between the ground based systems is better than 5% in a pressure range between 1 and 0.03 hPa. Second, we focus on the water vapor time series at 10 hPa as measured by the Middle Atmospheric WAter vapor RAdiometer, MIAWARA, over Switzerland. A total of 6 coincident balloon soundings with a FLASH hygrometer on board are evaluated revealing good consistency between the in situ and the remote sensing measurements. We further analyze the variability of the 1...
News from and developments within the Network for the Detection of Atmospheric Composition Change... more News from and developments within the Network for the Detection of Atmospheric Composition Change (NDACC).
The Astrophysical Journal, 1994
The Astrophysical Journal, 1994
The Astronomical Journal, 1992
Radio Science, 2012
ABSTRACT For 20 years the Naval Research Laboratory has been making continuous water vapor profil... more ABSTRACT For 20 years the Naval Research Laboratory has been making continuous water vapor profile measurements at 22.235 GHz with the Water Vapor Millimeter-Wave Spectrometer (WVMS) instruments, with the program expanding from one to three instruments in the first 6 years. Since the initial deployments there have been gradual improvements in the instrument design which have improved data quality and reduced maintenance requirements. Recent technological developments have made it possible to entirely redesign the instrument and improve not only the quality of the measurements but also the capability of the instrument. We present the fourth-generation instrument now operating at Table Mountain, California, which incorporates the most recent advances in microwave radiometry. This instrument represents the most significant extension of our measurement capability to date, enabling us to measure middle atmospheric water vapor from ˜26-80 km.
Optical Engineering, 2002
ABSTRACT
Journal of Geophysical Research, 2007
1] We compare middle atmospheric water vapor measurements from the Halogen Occultation Experiment... more 1] We compare middle atmospheric water vapor measurements from the Halogen Occultation Experiment (HALOE), Water Vapor Mm-wave Spectrometer (WVMS), and Earth Observing System (EOS) Microwave Limb Sounder (MLS) instruments from 40 to 70 km. The ground-based WVMS measurements shown here were taken at Network for the Detection of Atmospheric Composition Change (NDACC) sites at Mauna Loa, Hawaii (19.5°N, 204.4°E), and Lauder, New Zealand (45.0°S, 169.7°E). A comparison of measurements where HALOE, MLS, and WVMS are all available shows that the average HALOE water vapor retrievals are lower than those from MLS at all altitudes from 40 to 70 km and lower than the WVMS retrievals everywhere except above 64 km at Lauder. The average difference between all coincident WVMS and MLS water vapor profiles is within 0.2 ppmv over almost the entire 40-70 km altitude range, both at Lauder and Mauna Loa. The standard deviation of the difference between weekly WVMS retrievals and coincident MLS retrievals is $0.2 ppmv at Mauna Loa and $0.3-0.4 ppmv at Lauder. The interannual correlation between water vapor observed by MLS and WVMS is slightly improved by the use of MLS temperature measurements in the WVMS retrievals. The MLS and WVMS profiles at Mauna Loa show particularly good interannual agreement, including a clear QBO signature.
Journal of Geophysical Research, 2006
1] Stratospheric dehydration and high aerosol extinctions are examined for the 1998 Antarctic win... more 1] Stratospheric dehydration and high aerosol extinctions are examined for the 1998 Antarctic winter using the Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) model and data obtained by the Polar Ozone and Aerosol Measurement (POAM) III instrument. The model is applied to individual air parcels which are advected along 3-D trajectories using the United Kingdom Meteorological Office (UKMO) global wind and temperature fields. Model results are compared to water vapor and aerosol extinction measurements obtained with the POAM instrument. Results suggest that the water vapor mixing ratio at the end of the season is predicted with reasonable accuracy. However, dehydration occurs more rapidly in the simulation than is indicated by the POAM data. In addition to dehydration results, the frequency of high aerosol extinction measurements is examined for all model runs and compared to POAM data. The aerosol extinction comparisons are consistent with the assumption that heterogeneous nitric acid trihydrate (NAT) freezing occurs in approximately 1% of all particles. Various model parameters influencing ice cloud microphysics are altered to examine their effects on both the water vapor mixing ratio and high aerosol extinction events. While a reduction in the ice accommodation coefficient and an increase in the ice nucleation barrier both improve the agreement in the water vapor mixing ratio, the agreement in aerosol extinction is worsened. Extinction comparisons suggest that the model results are consistent with either high or low NAT-ice lattice compatibility factors, although intermediate values agree poorly with POAM data. The extent of dehydration is highly dependent on temperature; therefore, an uncertainty as small as ±1 K in the UKMO temperature fields may significantly change the model results.
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Papers by Gerald Nedoluha