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Search Results: 1 - 10 of 189899 matches for " G. Nedoluha "
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Retrieval of temperature and water vapor profiles from radio occultation refractivity and bending angle measurements using an Optimal Estimation approach: a simulation study
A. von Engeln,G. Nedoluha
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2005,
Abstract: The Optimal Estimation Method is used to retrieve temperature and water vapor profiles from simulated radio occultation measurements in order to assess how different retrieval schemes may affect the assimilation of this data. High resolution ECMWF global fields are used by a state-of-the-art radio occultation simulator to provide quasi-realistic bending angle and refractivity profiles. Both types of profiles are used in the retrieval process to assess their advantages and disadvantages. The impact of the GPS measurement is expressed as an improvement over the a priori knowledge (taken from a 24h old analysis). Large improvements are found for temperature in the upper troposphere and lower stratosphere. Only very small improvements are found in the lower troposphere, where water vapor is present. Water vapor improvements are only significant between about 1 km to 7 km. No pronounced difference is found between retrievals based upon bending angles or refractivity. Results are compared to idealized retrievals, where the atmosphere is spherically symmetric and instrument noise is not included. Comparing idealized to quasi-realistic calculations shows that the main impact of a ray tracing algorithm can be expected for low latitude water vapor, where the horizontal variability is high. We also address the effect of altitude correlations in the temperature and water vapor. Overall, we find that water vapor and temperature retrievals using bending angle profiles are more CPU intensive than refractivity profiles, but that they do not provide significantly better results.
Retrieval of temperature and water vapor profiles from radio occultation refractivity and bending angle measurements using an optimal estimation approach: a simulation study
A. von Engeln,G. Nedoluha
Atmospheric Chemistry and Physics Discussions , 2005,
Abstract: The Optimal Estimation Method is used to retrieve temperature and water vapor profiles from simulated radio occultation measurements in order to assess possible assimilation impacts of this data. High resolution ECMWF global fields are used by 5 a state-of-the-art radio occultation simulator to provide quasi-realistic bending angle and refractivity profiles. Both types of profiles are used in the retrieval process to assess their advantages and disadvantages. The impact of the GPS measurement is expressed as an improvement over the a priori knowledge (taken from a 24 h old analysis). Large improvements are found for temperature in the upper troposphere and 10 lower stratosphere. Only very small improvements are found in the lower troposphere, where water vapor is present. Water vapor improvements are only significant between about 1 km to 7 km. No pronounced difference is found between retrievals based upon bending angles or refractivity. Results are compared to idealized retrievals, where the atmosphere is spherically symmetric and instrument noise is not included. Comparing 15 idealized to quasi-realistic calculations shows that the main impact of a ray tracing algorithm can be expected for low latitude water vapor, where the horizontal variability is high. We also address the effect of altitude correlations in the temperature and water vapor. Overall, we find that water vapor and temperature retrievals using bending angle profiles are significantly more CPU intensive than refractivity profiles, but that they do 20 not provide significantly better results.
Classification of Northern Hemisphere stratospheric ozone and water vapor profiles by meteorological regime
M. B. Follette,R. D. Hudson,G. E. Nedoluha
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: The subtropical and polar upper troposphere fronts serve as the boundaries to divide the Northern Hemisphere into four meteorological regimes. These regimes are defined as (1) the arctic regime – within the polar vortex, (2) the polar regime – between the polar front and the polar vortex, or when the latter is not present, the pole, (3) the midlatitude regime – between the subtropical and polar fronts, and (4) the tropical regime – between the equator and the subtropical front. Data from the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiment II (SAGE II) were used to show that within each meteorological regime, ozone and water profiles are characterized by unique ozonepause and hygropause heights. In addition, both constituents exhibited distinct profile shapes up to approximately 25 km. This distinction was most pronounced in the winter and spring months, and less in the summer and fall. Both daily measurements and seven-year (1997–2003) monthly climatologies were analyzed. Daily measurements and seven-year (1997–2003) monthly climatologies showed that, within each meteorological regime, both constituents exhibited distinct profile shapes from the tropopause up to approximately 25 km. This distinction was most pronounced in the winter and spring months, and less in the summer and fall. Despite differences in retrieval techniques and sampling between the SAGE and HALOE instruments, the seven-year monthly climatologies calculated for each regime agreed well for both species below ~25 km. Above this altitude ozone and water vapor profiles were more clearly distinct when binned by latitude rather than by regime. Given that profiles of ozone and water vapor exhibit unique profiles shapes within each regime in the UTLS, trends in this region will therefore be the result of both changes within each meteorological regime, and changes in the relative contribution of each regime to a given zonal band over time.
Observations and analysis of polar stratospheric clouds detected by POAM III and SAGE III during the SOLVE II/VINTERSOL campaign in the 2002/2003 Northern Hemisphere winter
J. Alfred,M. Fromm,R. Bevilacqua,G. Nedoluha
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: 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 observations were primarily constrained to potential temperatures below 500 K. The PSC observation frequency as a function of ambient temperature relative to the NAT saturation point was used to infer irreversible denitrification. By late December 38% denitrification was inferred at both the 400–475 K and 475–550 K potential temperature ranges. By early January extensive levels of denitrification near 80% were inferred at both potential temperature ranges, and the air remained denitrified at least through early March.
Classification of Northern Hemisphere stratospheric ozone and water vapor profiles by meteorological regime
M. B. Follette-Cook, R. D. Hudson,G. E. Nedoluha
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: The subtropical and polar upper troposphere fronts and the polar vortex serve as the boundaries to divide the Northern Hemisphere into four meteorological regimes. These regimes are defined as (1) the arctic regime – within the polar vortex, (2) the polar regime – between the polar front and the polar vortex, or when the latter is not present, the pole, (3) the midlatitude regime – between the subtropical and polar fronts, and (4) the tropical regime – between the equator and the subtropical front. Data from the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiment II (SAGE II) were used to show that within each meteorological regime, ozone and water profiles are characterized by unique ozonepause and hygropause heights. Daily measurements and seven-year (1997–2003) monthly climatologies showed that, within each meteorological regime, both constituents exhibited distinct profile shapes from the tropopause up to approximately 20 km. This distinction was most pronounced in the winter and spring months, and weak in the summer and fall. Despite differences in retrieval techniques and sampling between the SAGE and HALOE instruments, the seven-year monthly climatologies calculated for each regime agreed well for both species below ~22 km. Given that profiles of ozone and water vapor exhibit unique profiles shapes within each regime in the UTLS, trends in this region will therefore be the result of both changes within each meteorological regime, and changes in the relative contribution of each regime to a given zonal band over time.
Observations and analysis of polar stratospheric clouds detected by POAM III and SAGE III during the SOLVE II/VINTERSOL campaign in the 2002/2003 Northern Hemisphere winter
J. Alfred, M. Fromm, R. Bevilacqua, G. Nedoluha, A. Strawa, L. Poole,J. Wickert
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: 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 (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 from 15 January until 4 February, and from then only 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 observations were primarily constrained to potential temperatures below 500 K. The PSC observation frequency as a function of ambient temperature relative to the nitric acid-trihydrate saturation point (using a nitric acid profile prior to denitrification) was used to infer irreversible denitrification. By late December 38% denitrification was inferred at both the 400–475 K and 475–550 K potential temperature ranges. By early January extensive levels of denitrification near 80% were inferred at both potential temperature ranges, and the air remained denitrified at least through early March.
Re-analysis of ground-based microwave ClO measurements from Mauna Kea, 1992 to early 2012
B. J. Connor,T. Mooney,G. E Nedoluha,J. W. Barrett
Atmospheric Chemistry and Physics Discussions , 2012, DOI: 10.5194/acpd-12-30571-2012
Abstract: We present a re-analysis of upper stratospheric ClO measurements from the ground-based millimeter-wave instrument from January 1992 to February 2012. These measurements are made as part of the Network for the Detection of Atmospheric Composition Change (NDACC) from Mauna Kea, Hawaii, (19.8° N, 204.5° E). Here, we use daytime and nighttime measurements together to form a day-night spectrum, from which the difference in the day and night profiles is retrieved. These results are then compared to the day-night difference profiles from the UARS and Aura Microwave Limb Sounder (MLS) instruments. We also compare them to our previous analyses of the same data, in which we retrieved the daytime ClO profile. The major focus will be on comparing the year-to-year and long-term changes in ClO derived by the two analysis methods. We conclude that the re-analyzed data set has less short-term variability and exhibits a more constant long-term trend. Data from 1995–2012 indicate a linear decline of mid-stratospheric ClO of 0.64 ± 0.08% yr 1.
Limitations of wind extraction from 4-D-Var assimilation of trace gases
D. R. Allen,K. W. Hoppel,G. E. Nedoluha,D. D. Kuhl
Atmospheric Chemistry and Physics Discussions , 2012, DOI: 10.5194/acpd-12-32985-2012
Abstract: Time-dependent variational data assimilation allows the possibility of extracting wind information from observations of long-lived trace gases. Since trace gas observations are not available at sufficient resolution for deriving feature-track winds, they must be combined with model background information to produce an analysis. If done with time-dependent variational assimilation, wind information may be extracted via the adjoint of the linearized tracer continuity equation. This paper presents idealized experiments that illustrate the mechanics of tracer-wind extraction and demonstrate some of the limitations of this procedure. We first examine tracer-wind extraction using a simple one-dimensional advection equation. The analytic solution for a single trace gas observation is discussed along with numerical solutions for multiple observations. The limitations of tracer-wind extraction are then explored using highly idealized ozone experiments performed with a development version of the Navy Global Environmental Model (NAVGEM) in which stratospheric globally-distributed hourly stratospheric ozone profiles are assimilated in a single 6-h update cycle in January 2009. Starting with perfect background ozone conditions, but imperfect dynamical conditions, ozone errors develop over the 6-h background window. Wind increments are introduced in the analysis in order to reduce the differences between background ozone and ozone observations. For "perfect" observations (unbiased and no random error), this results in root mean square (RMS) vector wind error reductions of up to ~ 3 m s 1 in the winter hemisphere and tropics. Wind extraction is more difficult in the summer hemisphere due to weak ozone gradients and smaller background wind errors. The limitations of wind extraction are also explored for observations with imposed random errors and for limited sampling patterns. As expected, the amount of wind information extracted degrades as observation errors or data voids increase. In the case of poorly specified observation error covariances, assimilation of ozone data with imposed errors may result in erroneous wind increments, since the assimilation is constrained too tightly to the noisy observations.
Limitations of wind extraction from 4D-Var assimilation of ozone
D. R. Allen,K. W. Hoppel,G. E. Nedoluha,D. D. Kuhl
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2013, DOI: 10.5194/acp-13-3501-2013
Abstract: Time-dependent variational data assimilation allows the possibility of extracting wind information from observations of ozone or other trace gases. Since trace gas observations are not available at sufficient resolution for deriving feature-track winds, they must be combined with model background information to produce an analysis. If done with time-dependent variational assimilation, wind information may be extracted via the adjoint of the linearized tracer continuity equation. This paper presents idealized experiments that illustrate the mechanics of tracer–wind extraction and demonstrate some of the limitations of this procedure. We first examine tracer–wind extraction using a simple one-dimensional advection equation. The analytic solution for a single trace gas observation is discussed along with numerical solutions for multiple observations. The limitations of tracer–wind extraction are then explored using highly idealized ozone experiments performed with a development version of the Navy Global Environmental Model (NAVGEM) in which globally distributed hourly stratospheric ozone profiles are assimilated in a single 6 h update cycle in January 2009. Starting with perfect background ozone conditions, but imperfect dynamical conditions, ozone errors develop over the 6 h background window. Wind increments are introduced in the analysis in order to reduce the differences between background ozone and ozone observations. For "perfect" observations (unbiased and no random error), this results in root-mean-square (RMS) vector wind error reductions of up to ~4 m s 1 in the winter hemisphere and tropics. Wind extraction is more difficult in the summer hemisphere due to weak ozone gradients and smaller background wind errors. The limitations of wind extraction are also explored for observations with imposed random errors and for limited sampling patterns. As expected, the amount of wind information extracted degrades as observation errors or data voids increase. In the case of poorly specified observation error covariances, assimilation of ozone data with imposed errors may result in increased RMS wind error, since the assimilation is constrained too tightly to the noisy observations.
Limitations of wind extraction from 4D-Var assimilation of ozone
D. R. Allen, K. W. Hoppel, G. E. Nedoluha, D. D. Kuhl, N. L. Baker, L. Xu,T. E. Rosmond
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2013,
Abstract: Time-dependent variational data assimilation allows the possibility of extracting wind information from observations of ozone or other trace gases. Since trace gas observations are not available at sufficient resolution for deriving feature-track winds, they must be combined with model background information to produce an analysis. If done with time-dependent variational assimilation, wind information may be extracted via the adjoint of the linearized tracer continuity equation. This paper presents idealized experiments that illustrate the mechanics of tracer–wind extraction and demonstrate some of the limitations of this procedure. We first examine tracer–wind extraction using a simple one-dimensional advection equation. The analytic solution for a single trace gas observation is discussed along with numerical solutions for multiple observations. The limitations of tracer–wind extraction are then explored using highly idealized ozone experiments performed with a development version of the Navy Global Environmental Model (NAVGEM) in which globally distributed hourly stratospheric ozone profiles are assimilated in a single 6 h update cycle in January 2009. Starting with perfect background ozone conditions, but imperfect dynamical conditions, ozone errors develop over the 6 h background window. Wind increments are introduced in the analysis in order to reduce the differences between background ozone and ozone observations. For "perfect" observations (unbiased and no random error), this results in root-mean-square (RMS) vector wind error reductions of up to ~4 m s 1 in the winter hemisphere and tropics. Wind extraction is more difficult in the summer hemisphere due to weak ozone gradients and smaller background wind errors. The limitations of wind extraction are also explored for observations with imposed random errors and for limited sampling patterns. As expected, the amount of wind information extracted degrades as observation errors or data voids increase. In the case of poorly specified observation error covariances, assimilation of ozone data with imposed errors may result in increased RMS wind error, since the assimilation is constrained too tightly to the noisy observations.
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