bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the relationship between complexity and performance in a land surface model using the multicriteria method
Authors: Leplastrier M. , Pitman A. J. , Gupta H. , Xia Y.
Published: November 2002

The performance of five modes of a land surface model, the Chameleon Surface Model (CHASM), was investigated after calibration via the multicriteria method to monthly totals of evaporation and runoff from the Valdai data set. The use of CHASM allows for an exploration into the relationship between surface energy balance complexity and optimal performance by isolating the impacts of different parameterizations of the surface energy balance. When compared to quantities used within the calibration process, CHASM's performance was significantly increased with calibration over default simulations regardless of calibration length or mode complexity. Within the calibration period, CHASM's performance increased with increasing complexity in the representation of the surface energy balance. Outside the calibration period there was little improvement to simulations from additional complexity in the surface energy balance representation above the simplest mode. Calibration is shown to reduce the scatter between modes suggesting that some of the differences between models in PILPS Phase 2d may be explained by the specification of parameter values. For simulations of quantities not used in calibration, performance can be reduced as a result of calibration. This implies that evaporation and runoff may not be the best quantities for calibration in order to improve model performance. It is suggested that the best quantities to calibrate may be mode and model specific.
Photochemical ozone loss in the Arctic as determined by MSX/UVISI stellar occultation observations during the 1999/2000 winter
Authors: Swartz William H. , Yee Jeng‐Hwa , Vervack Ronald J. , Lloyd Steven A. , Newman Paul A.
Published: November 2002

The combined SAGE III Ozone Loss and Validation Experiment and Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) campaign during winter 1999/2000 sought, in part, to quantify ozone loss within the Arctic polar vortex using a variety of aircraft‐, balloon‐, ground‐, and space‐based instrument platforms. The Midcourse Space Experiment/Ultraviolet and Visible Imagers and Spectrographic Imagers (MSX/UVISI) suite of instruments performed 31 stellar occultation observations from 23 January through 4 March 2000 in and near the Arctic polar vortex. Using a newly developed combined extinctive‐refractive algorithm, ozone mixing ratio profiles, along with profiles of total density, pressure, and temperature, were retrieved. Retrieved temperature and ozone profiles are shown to agree well with other measurements. Diabatic trajectory calculations are used to remove the effects of subsidence within the vortex, allowing photochemical ozone loss to be inferred from these occultation measurements. A maximum ozone loss of about 1 ppmv is found at 400–500 K (∼16–21 km) during the 41‐day period for which occultation data are available, in agreement with several other ozone loss analyses of the campaign. This corresponds to an average daily loss rate of ∼0.024 ppmv/day. The combined extinctive‐refractive stellar occultation technique is demonstrated to accurately measure stratospheric ozone loss during polar winter.
1DVAR analysis of temperature and humidity using GPS radio occultation refractivity data
Authors: Poli Paul , Joiner Joanna , Kursinski E. Robert
Published: November 2002

The constellation of Global Positioning System (GPS) satellites provides a source of continuous, phase‐stable electromagnetic signals available for radio occultation observations of our planet. The atmospheric‐induced bending of the transmitted rays observed during each occultation can be converted into a refractivity profile using an Abel transform. Since refractivity is related to temperature and humidity, it may potentially be used in global data assimilation for numerical weather prediction (NWP) and for creating climate data sets. We first compare GPS/Meteorology (GPS/MET) 1995 refractivity with various backgrounds and verify that the best expected background presents generally the best fit with the observed refractivity. We implement here an efficient one‐dimensional variational (1DVAR) analysis of GPS refractivity that enables retrieving temperature, humidity, and sea‐level pressure using the finite volume data assimilation system background. 1DVAR analyses with GPS/MET 1995 data are compared with collocated radiosondes. They show an excellent capacity of the GPS measurements to resolve the tropopause. In the Northern Hemisphere, we demonstrate a net reduction of temperature bias and standard deviation, as compared with the background. The 1DVAR humidity presents reduced standard deviation as compared to the background between 550 and 400 hPa. However, a refractivity bias between the observations and the background in the lower troposphere systematically shifts the 1DVAR humidity downward. A refractivity bias over the whole profile is transformed into a 1DVAR sea‐level pressure bias. This study represents a step toward using the GPS radio occultation data in data assimilation systems to improve NWP forecasts and representation of Earth's climate in models.
Skylight polarization spectra: Numerical simulation of the Ring effect
Authors: Stam D. M. , Aben I. , Helderman F.
Published: November 2002

Observed polarization spectra of the cloud‐free zenith sky are presented. The spectra, which cover the wavelength region from 350 to 400 nm, show spectral fine structure that coincides with Fraunhofer lines in the solar irradiance spectrum (the Ring effect). The observations show that the strength of the fine structure not only depends on the solar zenith angle but also on the atmospheric conditions, in particular the aerosol content. The spectral fine structure and its angular behavior as observed in the polarization spectra compare very well with simulations for a homogeneous, aerosol‐containing model atmosphere, using a radiative transfer algorithm in which rotational Raman scattering is taken into account in the first‐ and second‐order scattering processes. A description of the radiative transfer algorithm is given.
Assimilation of ozone profiles and total column measurements into a global general circulation model
Authors: Struthers H. , Brugge R. , Lahoz W. A. , O'Neill A. , Swinbank R.
Published: November 2002

Ozone profiles from the Microwave Limb Sounder (MLS) instrument flown on board the Upper Atmosphere Research Satellite (UARS) and total ozone columns measured by the Global Ozone Monitoring Experiment (GOME) on board the Second European Remote Sensing Satellite (ERS‐2) have been assimilated using a troposphere‐stratosphere data assimilation system. The analysis system is based on the global analysis system used for operational analysis of the stratosphere at the Meteorological Office from 1991 to 2000. Three assimilation runs have been completed for a three‐week period in April 1997 to test the advantage of using a combination of MLS and GOME observations, compared with the assimilation of each observation data set separately. The statistical information produced by the assimilation system shows that the combination of MLS and GOME observations via the assimilation process produces ozone fields that show improvement compared with analysis fields produced by the assimilation of either MLS or GOME separately. Comparison of the analyzed ozone fields with independent observations (ozonesondes, Halogen Occultation Experiment (HALOE) profiles and Total Ozone Mapping Spectrometer (TOMS) total ozone column measurements) corroborates these results and shows that the combined MLS and GOME ozone analyses provide a realistic representation of the atmospheric ozone distribution. The global root‐mean‐square residual (difference between the analyses and independent observations) against HALOE and TOMS observations is comparable to the quoted errors in the HALOE and TOMS instruments (5% in each case).
Microphysical mesoscale simulations of polar stratospheric cloud formation constrained by in situ measurements of chemical and optical cloud properties
Authors: Larsen N. , Svendsen S. Høyer , Knudsen B. M. , Voigt C. , Weisser C. , Kohlmann A. , Schreiner J. , Mauersberger K. , Deshler T. , Kröger C. , Rosen J. M. , Kjome N. T. , Adriani A. , Cairo F. , Di Donfrancesco G. , Ovarlez J. , Ovarlez H. , Dörnbrack A. , Birner T.
Published: November 2002

A detailed microphysical model has been used to simulate polar stratospheric clouds (PSC) formed in mountain leewaves over northern Scandinavia and observed in a balloonborne multi‐instrument flight on 25 January 2000. The measurements show cloud layers of large solid particles with nitric acid trihydrate (NAT) compositions at relatively high temperatures and layers containing liquid particles with supercooled ternary solution compositions at very low temperatures. The same PSC particle layers have been observed several times during the 2 1/2 h flight, offering a nearly Lagrangian picture of the particle evolution. The applied PSC model describes homogeneous freezing of ice below the ice frost point and diffusion‐limited nonequilibrium and size‐dependent growth and composition of liquid and solid‐phase particles. The microphysical box model calculations are performed on two isentropic surfaces, corresponding to different observed particle layers, using temperature histories from combined high‐resolution nonhydrostatic mesoscale and synoptic‐scale model analyses of the meteorological conditions characterized by strong mountain leewaves. The calculated particle composition, physical phase, and particle size distributions are compared with the in situ measurements of the same particle properties. It appears that homogeneous freezing of ice in liquid solutions a few degrees below the ice frost point and subsequent release of NAT at higher temperatures might explain the characteristics of the observed solid PSC particles.
Polarization observations of lightning‐produced VHF emissions by the FORTE satellite
Authors: Shao Xuan‐Min , Jacobson Abram R.
Published: November 2002

Following an earlier polarization study for a well‐defined man‐made very high frequency (VHF) signal by using the two orthogonally oriented, linear polarization antennas aboard the FORTE satellite, we report in this paper similar polarization observations for lightning‐produced radiation. A selected group of 313 transionospheric pulse pairs (TIPPs) that were geolocated by the National Lightning Detection Network (NLDN) has been analyzed. The TIPPs have been examined with high time resolution so that the magnetoionic modes can be resolved. Most of the TIPPs have been found highly polarized, with 40% of them far above the background polarization level. The polarization ellipticity and the orientation of the ellipse of the split modes have been examined as a function of the nadir and the azimuthal angles as referenced to satellite coordinates, and they are found in agreement with the predictions based on the antenna beam pattern. The original and the reflected pulses in a TIPP show nearly the same properties of polarization, except the latter appears less polarized. However, no recognizable polarization has been observed for the VHF signals accompanying more common discharge processes of initial ground strokes, dart leaders, and K streamers that usually produce continuous VHF radiation. Observations of a sequence of impulsive radiation bursts that is apparently associated with a normal negative cloud‐to‐ground flash indicate they are somewhat polarized, though not as much as the TIPPs. On the basis of the polarization observations, the possible breakdown mechanisms that are responsible for the VHF radiation have been discussed. For the highly polarized TIPP events, if they follow a cone‐shaped discharge geometry, the half‐angle of the cone is estimated to be less than 22°.
In situ observations of gravity waves and comparisons with numerical simulations during the SOLVE/THESEO 2000 campaign
Authors: Hertzog A. , Vial F. , Dörnbrack A. , Eckermann S. D. , Knudsen B. M. , Pommereau J.‐P.
Published: November 2002

This article presents observational and numerical results on gravity waves in the Arctic polar vortex during the SAGE III—Ozone Loss and Validation Experiment and Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO) campaign. Long‐duration balloons that were launched from Kiruna, Sweden, on 18 February 2000 provided in situ meteorological measurements for several weeks in the lower stratosphere. A strong gravity wave event was observed above southern Scandinavia on 2 March 2000. The main characteristics (amplitude of disturbances, frequency, and wavelengths) are reported, and it is shown that the wave induced mesoscale temperature fluctuations were large (18 K peak to peak). Furthermore, it is found that the gravity wave was most likely generated by flow across the Norwegian mountains. The observations are compared with results of numerical simulations. In particular, the mesoscale and ray‐tracing simulations reproduced some features of the observed wave packet. However, the fluctuations induced by the wave were significantly underestimated in the general circulation model of the European Center for Medium‐Range Weather Forecasting. Finally, the overall gravity wave activity during the flight is analyzed and is found to be relatively small.
UV‐visible observations of atmospheric O4 absorptions using direct moonlight and zenith‐scattered sunlight for clear‐sky and cloudy sky conditions
Authors: Wagner T. , von Friedeburg C. , Wenig M. , Otten C. , Platt U.
Published: November 2002

Atmospheric observations of the O4 absorption bands at 360.5, 380.2, 477.3, 532.2, 577.2 and 630.0 nm are presented for different atmospheric conditions (clear and cloudy skies) and viewing geometries (direct and zenith‐scattered light observations). From the observations of direct moonlight it was possible to derive absolute O4 absorption cross sections for atmospheric conditions. We found that the relative shape of the observed absorption bands is similar to those of the O4 spectrum measured by Greenblatt et al. [1990] in the laboratory. However, in general (except for the absorption band at 380.2 nm), the O4 absorption cross sections derived in this study are larger by several percent compared to those of the other (mainly laboratory) observations. Using the observations of zenith‐scattered light, we investigated the radiative transport through the atmosphere. Our observations under cloudy sky conditions confirmed that the light path enhancement due to multiple Mie scattering on cloud droplets is independent of wavelength. From the observations under clear‐sky conditions we studied the influence of Mie scattering on aerosol. It was not possible to describe the selected clear‐sky measurements by taking into account only Rayleigh scattering. We found that the comparison of the O4 measurements with model results for different sets of assumed aerosol extinctions provides a new, very sensitive tool to derive aerosol parameters from zenith sky ground‐based measurements.
An improved retrieval of tropospheric nitrogen dioxide from GOME
Authors: Martin Randall V. , Chance Kelly , Jacob Daniel J. , Kurosu Thomas P. , Spurr Robert J. D. , Bucsela Eric , Gleason James F. , Palmer Paul I. , Bey Isabelle , Fiore Arlene M. , Li Qinbin , Yantosca Robert M. , Koelemeijer Robert B. A.
Published: November 2002

We present a retrieval of tropospheric nitrogen dioxide (NO2) columns from the Global Ozone Monitoring Experiment (GOME) satellite instrument that improves in several ways over previous retrievals, especially in the accounting of Rayleigh and cloud scattering. Slant columns, which are directly fitted without low‐pass filtering or spectral smoothing, are corrected for an artificial offset likely induced by spectral structure on the diffuser plate of the GOME instrument. The stratospheric column is determined from NO2 columns over the remote Pacific Ocean to minimize contamination from tropospheric NO2. The air mass factor (AMF) used to convert slant columns to vertical columns is calculated from the integral of the relative vertical NO2 distribution from a global 3‐D model of tropospheric chemistry driven by assimilated meteorological data (Global Earth Observing System (GEOS)‐CHEM), weighted by altitude‐dependent scattering weights computed with a radiative transfer model (Linearized Discrete Ordinate Radiative Transfer), using local surface albedos determined from GOME observations at NO2 wavelengths. The AMF calculation accounts for cloud scattering using cloud fraction, cloud top pressure, and cloud optical thickness from a cloud retrieval algorithm (GOME Cloud Retrieval Algorithm). Over continental regions with high surface emissions, clouds decrease the AMF by 20–30% relative to clear sky. GOME is almost twice as sensitive to tropospheric NO2 columns over ocean than over land. Comparison of the retrieved tropospheric NO2 columns for July 1996 with GEOS‐CHEM values tests both the retrieval and the nitrogen oxide radical (NOx) emissions inventories used in GEOS‐CHEM. Retrieved tropospheric NO2 columns over the United States, where NOx emissions are particularly well known, are within 18% of GEOS‐CHEM columns and are strongly spatially correlated (r = 0.78, n = 288, p < 0.005). Retrieved columns show more NO2 than GEOS‐CHEM columns over the Transvaal region of South Africa and industrial regions of the northeast United States and Europe. They are lower over Houston, India, eastern Asia, and the biomass burning region of central Africa, possibly because of biases from absorbing aerosols.
Lidar temperature measurements during the SOLVE campaign and the absence of polar stratospheric clouds from regions of very cold air
Authors: Burris John , McGee Thomas , Hoegy Walt , Newman Paul , Lait Leslie , Twigg Laurence , Sumnicht Grant , Heaps William , Hostetler Chris , Neuber Roland , Künzi Klaus F.
Published: November 2002

NASA Goddard Space Flight Center's Airborne Raman Ozone, Temperature, and Aerosol Lidar (AROTEL) measured extremely cold temperatures during all three deployments (1–16 December 1999, 14–29 January 2000, and 27 February to 15 March 2000) of the SAGE III Ozone Loss and Validation Experiment (SOLVE). Temperatures were significantly below values observed in previous years with large regions regularly below 191 K and frequent temperature retrievals yielding values at or below 187 K. Temperatures well below the saturation point of type I polar stratospheric clouds (PSCs) were regularly encountered, but their presence was not well correlated with PSC observations made by NASA Langley Research Center's aerosol lidar colocated with AROTEL. Temperature measurements by meteorological sondes launched within areas traversed by the DC‐8 showed minimum temperatures consistent in time and vertical extent with those derived from AROTEL data. Calculations to establish whether PSCs could exist at measured AROTEL temperatures and observed mixing ratios of nitric acid and water vapor showed large areas favorable to PSC formation but that were lacking PSCs. The flight on 12 December 1999 encountered large regions having temperatures up to 10 K below the NAT saturation temperature but only small, localized regions that might be identified as PSCs.
Direct radiative forcing and regional climatic effects of anthropogenic aerosols over East Asia: A regional coupled climate‐chemistry/aerosol model study
Authors: Giorgi Filippo , Bi Xunqiang , Qian Yun
Published: November 2002

We present a series of simulations aimed at assessing the radiative forcing and surface climatic effects of anthropogenic sulfate and fossil fuel soot over east Asia. The simulations are carried out with a coupled regional climate‐chemistry/aerosol model for the 5‐year period of 1993–1997 using published estimates of sulfur emissions. Anthropogenic sulfate induces a negative top‐of‐the‐atmosphere (TOA) radiative forcing which varies spatially from −1 to −8 W m−2 in the winter to −1 to −15 W m−2 in the summer. The aerosol radiative forcing is maximum over the Sichuan Basin of southwest China and over some areas of east and northeast China. This forcing induces a surface cooling in the range of −0.1 to −0.7 K that is also maximum over the Sichuan Basin. Fossil fuel soot exerts a positive TOA radiative forcing of 0.5 to 2 W m−2 and enhances the surface cooling by a few tenths of Kelvins due to increased surface shielding from solar radiation. Doubling of the sulfur emission induces a substantial increase in negative radiative forcing (up to −7 to −8 W m−2) and associated surface cooling. With doubled sulfur emission, the surface cooling exceeds −1 K and is statistically significant at the 90% confidence level over various areas of China. The aerosol‐induced radiative forcing and surface cooling tend to inhibit precipitation over the region, although this effect is relatively small in the simulations. Some features of the simulated aerosol‐induced surface cooling are consistent with temperature trends observed in recent decades over different regions of China.
An analysis of large HNO3‐containing particles sampled in the Arctic stratosphere during the winter of 1999/2000
Authors: Northway M. J. , Gao R. S. , Popp P. J. , Holecek J. C. , Fahey D. W. , Carslaw K. S. , Tolbert M. A. , Lait L. R. , Dhaniyala S. , Flagan R. C. , Wennberg P. O. , Mahoney M. J. , Herman R. L. , Toon G. C. , Bui T. P.
Published: November 2002

Large (>2 μm diameter) HNO3‐containing polar stratospheric cloud (PSC) particles were measured in situ by the NOAA NOyinstrument on board the NASA ER‐2 aircraft during seven flights in the 1999/2000 Arctic winter vortex. Here we discuss the detection of these large PSC particles, their spatial distribution, the ambient conditions under which they were detected, and our methods for interpreting NOytime series with respect to particle sizes and number concentrations. The particles were observed through the use of two NOyinlets on a particle separator extending below the ER‐2 aircraft. The particle phase is assumed to be nitric acid trihydrate (NAT) or nitric acid dihydrate (NAD). Over a 48‐day period, particles were sampled in the Arctic vortex over a broad range of latitudes (60–85°N) and altitudes (15–21 km). Typically, regions of the atmosphere up to 4 km above the observed large particle clouds were saturated with respect to NAT. Occasionally, large particles were measured in air subsaturated with respect to NAT, suggesting ongoing particle evaporation. Vortex minimum temperatures in the observation period suggest that synoptic‐scale ice saturation conditions are not required for the formation of this type of particle. Three analytical methods are used to estimate size and number concentrations from the NOytime series. Results indicate particle sizes between 5 and 20 μm diameter and concentrations from 10−5to 10−3cm−3. These low number concentrations imply a selective nucleation mechanism. Particle sizes and number concentrations were greater during the midwinter flights than the late winter flights. Knowledge of the geographical extent of large particles, actual sampling conditions, and particle size distributions offers multiple constraints for atmospheric models of PSC formation, which will lead to a better understanding of the process of denitrification and improvements in modeling future ozone loss.
Chemical indicators of sulfate sensitivity to nitrogen oxides and volatile organic compounds
Authors: Stein Ariel F. , Lamb Dennis
Published: November 2002

The formation of aerosol sulfate (SO42−) in eastern North America is chemically linked to the emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC) through oxidation of the gaseous precursor, sulfur dioxide (SO2). The response of sulfate production to controls in NOx and VOC emissions depends, in part, on the resulting changes in oxidant levels and the competition that naturally exists between the gas‐ and aqueous‐phase pathways for SO2 oxidation. We propose the use of a combination of concentrations of nitric acid, particulate nitrate, hydrogen peroxide, and ambient sulfate as a nondimensional indicator of the effectiveness of VOC or NOx controls in decreasing SO42− abundance. The concentrations of these indicator species were calculated from a series of photochemical model simulations with varying rates of NOx and VOC emissions using a three‐dimensional Eulerian model (MODELS‐3) that covers the northeastern United States. This study shows that ambient sulfate concentrations are likely to decrease more effectively as VOC emissions are reduced, when the nondimensional indicator is less than a certain threshold. However, a higher value of the indicator identifies a regime in which NOx emissions reductions are more effective for reducing sulfate than are VOC emissions. In addition, a description of the sulfate‐formation pathways, along with a theoretical analysis of the transition between NOx‐ and VOC‐sensitive regimes, provides a strong rationale for the use of the sulfate sensitivity indicator.
Kalman filter analysis of ice core data 1. Method development and testing the statistics
Authors: Trudinger C. M. , Enting I. G. , Rayner P. J.
Published: November 2002

The Kalman filter is applied to the analysis of trace gas concentrations in ice core air bubbles. A simple model for atmospheric methane is investigated to infer information about source variability from the concentration measurements. A random walk model for source evolution is tested in the role of nonprescriptive prior. Key inputs to the model are the covariance of stochastic forcing, Q, and measurement error, R. We look at both the physics and the statistics to determine the most appropriate values for Q and R in this application. We explore the sensitivity of the calculation to the input statistics in preparation for use of the method for analyzing ice core CO2 and δ13CO2 measurements in a companion paper. The method allows a rigorous analysis of the variability of concentrations and sources from ice core measurements.
Kalman filter analysis of ice core data 2. Double deconvolution of CO2 and δ13C measurements
Authors: Trudinger C. M. , Enting I. G. , Rayner P. J. , Francey R. J.
Published: November 2002

A new method for deconvolving ice core CO2 and δ13CO2 measurements to estimate net CO2 uptake by the terrestrial biosphere and the oceans has been developed. The method, which uses the Kalman filter, incorporates statistical analysis into the calculation. This allows a more rigorous analysis of CO2 variability than the usual deconvolution method. The Kalman filter method estimates uncertainties on the deduced fluxes as part of the calculation. The deconvolution method is applied to the Law Dome CO2 and δ13C ice core record. The calculation suggests that natural variability in CO2 fluxes may be as large as 1 GtC yr−1 (GtC is gigatonnes carbon, 1 Gt = 1015 g) on the timescale of just less than a decade. The Law Dome CO2 measurements show a slight decrease in CO2 around the 1940s. Analysis with the carbon cycle model and a numerical model of firn processes suggests that about 3 GtC yr−1 uptake (mostly oceanic) is required in the 1940s to match the ice core measurements. The estimates of variation in the terrestrial biospheric flux between 1950 and 1980 from the double deconvolution calculation are in very good agreement with an independent estimate of the global terrestrial flux from a climate‐driven ecosystem model.
Microphysical properties of wave polar stratospheric clouds retrieved from lidar measurements during SOLVE/THESEO 2000
Authors: Hu Rong‐Ming , Carslaw Kenneth S. , Hostetler Chris , Poole Lamont R. , Luo Beiping , Peter Thomas , Füeglistaler Stefan , McGee Thomas J. , Burris John F.
Published: November 2002

Mountain wave induced ice clouds in the stratosphere are known to cause the formation of nitric acid hydrate particles downwind. Understanding the microphysical properties of these solid particles is important because they may contribute to a general background of solid polar stratospheric clouds (PSCs) that is observed but whose origin is not understood. Based on the limited set of observations of PSCs directly attributable to mountain waves, it has not been possible to determine their general microphysical properties. Here we analyze lidar observations from the SOLVE/THESEO 2000 campaign. Between December 1999 and March 2000, seven of the twelve flights of the DC‐8 aircraft showed clear signs of mountain wave induced clouds, with nitric acid hydrate clouds often extending many hundreds of kilometers downwind of mountains. On the basis of T‐matrix calculations, we have developed a technique to estimate the microphysical properties of spherical and nonspherical particles from multiwavelength backscatter and depolarization data from the Goddard Space Flight Center/Langley Research Center (GSFC/LaRC) aerosol lidar. The technique allows particle radius, condensed mass, and number densities of ice, nitric acid trihydrate, and liquid PSCs to be estimated. Ice clouds were found to contain approximately 1–3 ppmv of condensed water with a number density from 1 to 10 cm−3 and a narrow size distribution width with mode radii from 1 to 1.5 μm. Nitric acid hydrate particles downwind of the ice clouds were consistent with 1–5 ppbv condensed HNO3, a number density from 0.5 to 2 cm−3, and mode radius around 0.5 μm. These hydrate clouds are characterized by high aerosol backscatter and depolarization and are distinct from type 1a clouds that are observed away from mountains, which have low aerosol backscatter.
Bromide content of sea‐salt aerosol particles collected over the Indian Ocean during INDOEX 1999
Authors: Gabriel R. , von Glasow R. , Sander R. , Andreae M. O. , Crutzen P. J.
Published: November 2002

Bromide can be depleted from sea‐salt aerosol particles in the marine boundary layer (MBL) and converted to reactive gas‐phase species like Br, BrO, and HOBr, which affect ozone chemistry. Air pollution can enhance the bromine release from sea‐salt aerosols and thus inject additional bromine into the MBL. During the winter monsoon the northern Indian Ocean is strongly affected by air pollution from the Indian subcontinent and Asia. As part of the Indian Ocean Experiment (INDOEX), aerosol particles were sampled with stacked filter units (SFU) on the NCAR Hercules C‐130 aircraft during February‐March 1999. We determined the vertical and latitudinal distribution of the major inorganic aerosol components (NH4+, Na+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−) and the Br− content of the coarse aerosol to examine the role of the bromine release on the gas‐phase chemistry in the marine boundary layer over the tropical Indian Ocean. The aerosol mass and composition varied significantly with air mass origin and sampling location. In the northern part of the Indian Ocean (5°–15°N, 66°–73°E), high concentrations of pollution‐derived inorganic species were found in the marine boundary layer extending from the sea surface to about 1.2 km above sea level. In this layer, the average mass concentration of all aerosol species detected by our technique was comparable to pollution levels observed in industrialized regions. In the Southern Hemisphere (1°–9°S, 66°– 73°E), the aerosol concentrations rapidly declined to remote background levels. A chloride loss from the coarse aerosol particles was observed in parallel to the latitudinal gradient of the non sea salt SO42− burden. In most of the samples, Br− was depleted from the sea‐salt aerosols. However, we found an enrichment in bromide in aerosols affected by air masses originating over strong pollution sources in India (Bombay, Calcutta). In these cases the additional pollution‐derived Br from organo‐halogen additives in petrol outweighs the release of sea‐salt bromine.
Variability of polar stratospheric water vapor observed by ILAS
Authors: Pan L. L. , Randel W. J. , Massie S. T. , Kanzawa H. , Sasano Y. , Nakajima H. , Yokota T. , Sugita T.
Published: November 2002

We present an analysis of polar stratospheric water vapor from measurements of the Improved Limb Atmospheric Spectrometer (ILAS) onboard the Advanced Earth Observing Satellite (ADEOS). The variability of water vapor is examined using contemporaneous potential vorticity fields to separate the vortex from the extravortex air. The overall water vapor distribution from the ILAS measurements agrees qualitatively with the water vapor climatology in the UARS reference atmosphere (covering 1992–1999), and the space‐time variability is consistent with the known stratospheric circulation. Quantitatively, comparisons between ILAS and Halogen Occultation Experiment (HALOE) equivalent latitude zonal means show agreement to within 5% in the lower stratosphere (400–800 K potential temperature or 15–30 km). In the upper stratosphere (800–1800 K potential temperature or 30–45 km), however, ILAS data have a 10% to 20% high bias compared to the 8‐year (1992–1999) UARS climatology and to HALOE data for the same time period. The ILAS data, covering the time period November 1996 to June 1997, were measured during a winter‐spring period when the Arctic polar stratosphere was anomalously cold. The ILAS water vapor data suggest an Arctic vortex that is more isolated and persistent in the spring than that seen in the UARS climatology. The spatial and temporal extent of the Arctic vortex this year was very similar to that of the Antarctic vortex. This feature is supported by HALOE data for the same measurement period. Using a trajectory model, we show that the NH vortex in spring 1997 was significantly more isolated compared to other years in the decade, and this explains the unusual confinement of high water vapor within the Arctic vortex observed by ILAS.
POAM III measurements of dehydration in the Antarctic and comparisons with the Arctic
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Hoppel Karl W.
Published: November 2002

We present measurements of stratospheric water vapor taken at high northern and southern latitudes by the Polar Ozone and Aerosol Measurement (POAM) III instrument. The measurements show the seasonal variations in both hemispheres, including wintertime descent in the polar vortices and dehydration in the Antarctic. While POAM is unable to measure in regions with high aerosol extinction and can therefore not measure the temporary sequestration of water in ice clouds, POAM can measure the effects of such dehydration events if they result in the permanent removal of water vapor from an air parcel. A study of POAM “matches,” where the same parcel is observed more than once by the POAM instrument, shows significant permanent dehydration in the Antarctic for nearly all cases in which the parcel is either exposed to conditions where the mixing ratio either exceeds the saturation mixing ratio by >2 ppmv or experiences temperatures that remain below the saturation temperature for >2 days. These POAM matches suggest that parcels undergo several episodes of dehydration before their water vapor mixing ratio is reduced to the 1–2 ppmv level typically observed within the vortex in the Antarctic spring. Interannual differences in Antarctic vortex temperatures are shown to be qualitatively consistent with interannual differences in dehydration observed by POAM. Although analyses of parcels observed by POAM in the Arctic indicate that a few of these parcels experience conditions which generally cause permanent dehydration in the Antarctic, no significant permanent dehydration is observed in the POAM Arctic measurements.
Further investigations of a mesospheric inversion layer observed in the ALOHA‐93 Campaign
Authors: Huang Tai‐Yin , Hickey Michael P. , Tuan Tai‐Fu , Dewan E. M. , Picard R. H.
Published: November 2002

Temperature and wind data obtained from a Na wind/temperature lidar operated by the University of Illinois group during the Airborne Lidar and Observations of the Hawaiian Airglow (ALOHA‐93) Campaign, previously analyzed by Huang et al. [1998] using an isothermal Brunt‐Väisälä frequency, have been reexamined to include temperature gradients in the calculation of the Richardson number. In the previous analysis using the isothermal Brunt‐Väisälä frequency the existence of convective instability could not be assessed. New analysis shows that the nonisothermal Richardson number preserves some features found previously, with some striking differences noticable at times between 0900 and 1030 UT. The nonisothermal Richardson number becomes negative as early as 0930 UT, indicating conditions conducive to the development of convective instability and turbulence. The possibility that turbulence could exist at times earlier than previously thought explains more satisfactorily the large temperature increase observed before 1000 UT.
Evapotranspiration and turbulent transport in an irrigated desert orchard
Authors: Stoughton Thomas E. , Miller David R. , Huddleston Ellis W. , Ross James B.
Published: November 2002

Micrometeorological measurements were recorded in an irrigated pecan orchard for 2 weeks in the summer of 1996 near Las Cruces, NM. A vertical array of five sonic anemometers recorded three‐dimensional wind and temperature data within and above the orchard. The measured energy budget closure error was only 3.2% of net radiation, indicating freedom from local edge advection. The effects of regional (oasis) advection and unsteady winds on evapotranspiration (ET) were considered by comparing the observed latent heat flux values to estimates of ET using the Penman–Monteith and Advection–Aridity approaches. Penman–Monteith underestimated observed ET values by 82%. The Advection–Aridity modifications of potential evapotranspiration (PET) underestimated ET by 11%. Profiles of turbulence statistics demonstrated vertical heterogeneity of turbulence within the canopy. Directly above the canopy, momentum flux profiles showed little divergence. However, at a level of two times the tree heights, sensible heat flux profiles did show divergence, confirming the presence of “oasis” advection resulting from warm, dry air moving above the internal boundary layer. Upward convection from the hot soil surface between the trees diluted the oasis condition to the point where a weak upward sensible heat flux was observed during the midday periods when the soil was not shaded. Convection ratios, and exuberance ratios, generated from quadrant analyses of the heat and momentum flux events, showed that turbulent motions moved freely up and down within this canopy with little attenuation due to the open spaces between the trees.
Temperature dependence of the NO3 loss frequency: A new indicator for the contribution of NO3 to the oxidation of monoterpenes and NOx removal in the atmosphere
Authors: Geyer Andreas , Platt Ulrich
Published: November 2002

Nitrate radicals are known to act as important oxidizing agents for many volatile organic compounds (VOCs) (especially terpenes and dimethyl sulfide (DMS)) and NOx in the nighttime boundary layer. The quantification of these oxidation rates so far ideally implied the measurement of all species reacting with this radical and was therefore restricted to short‐term intensive campaigns. In this paper we present a new method to quantify the seasonal variation of the contribution of NO3 to the atmospheric oxidation capacity and the removal of nitrogen oxides. The indicator is based on the different temperature dependences of the NO3 loss processes, which arise from the temperature dependences of kinetic constants and of the monoterpene (or DMS) emission rate. The application of this indicator is simple: It is sufficient to measure ambient concentration time series of NO3, NO2, O3, and temperature (the data should cover a time period of preferably several months). The three concentrations can be readily measured, e.g., using a Differential Optical Absorption Spectroscopy system. The new indicator was applied to data of long‐term observations at a maritime (Rügen, in 1994) and a continental site (Lindenberg, in 1998) in Germany. At the latter site the seasonal variation of the VOC oxidation and NOx removal (conversion rate of NOx to HNO3) rate was studied: During August a diurnal average of the NO3‐induced monoterpene oxidation rate of 9 × 105 molecules cm−3 s−1 was determined, which is 3 times higher than during March. The production rate of HNO3/NO3− was found to have its minimum during the summer time, while it is a factor of 10 higher during March, averaging 6.3 × 105 cm−3 s−1 from March to September 1998 during a full diurnal cycle.
NOy partitioning and aerosol influences in the stratosphere
Authors: Küll V. , Riese M. , Tie X. , Wiemert T. , Eidmann G. , Offermann D. , Brasseur G. P.
Published: November 2002

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured a variety of trace gases globally with high spatial resolution during two Space Shuttle missions. This paper concentrates on members of the NOy family and highlights differences between CRISTA 1 (November 1994) and CRISTA 2 (August 1997). A sequential assimilation technique is used to combine the CRISTA measurements of total NOy fields with corresponding model forecasts based on the National Center for Atmospheric Research Research for Ozone in the Stratosphere and its Evolution (ROSE) model. For this study we use a model version driven by wind and temperature data provided by the UK Met Office. NO2 and N2O show large‐ and medium‐scale structures caused by dynamical processes. N2O5 shows a strong dependence on the aerosol load and solar zenith angles. N2O5 and NO2 changes from CRISTA 1 to CRISTA 2 are consistent with a reduction of aerosol concentrations in the Southern Hemisphere and minor aerosol changes in the Northern Hemisphere. For both missions the model reproduces well the measured diurnal cycles of the NOy family members. Measured diurnal variations of N2O5 and NO2 are consistent with the nighttime production of N2O5 from NO2. Compared to the effect of heterogeneous chemistry, the influence of ozone and temperature changes on the NOy partitioning is rather small. A model run based on a three‐dimensional aerosol field derived from CRISTA observations indicates that zonal asymmetries in the background aerosol have strong local effects on the N2O5 and NO2 distribution.
Effect of oceanic uptake on atmospheric lifetimes of selected trace gases
Authors: Yvon‐Lewis Shari A. , Butler James H.
Published: November 2002

We have calculated from a 2° × 2° grid of oceanic properties the contribution of oceanic loss to the overall lifetimes of a number of anthropogenic and naturally produced trace gases involved in global warming and stratospheric ozone depletion. The model, originally developed for atmospheric methyl bromide, can be used for any well‐mixed trace gas where the seawater degradation rate constants and solubilities are known. Of the gases tested, it is clear that known oceanic chemical degradation processes alone are not significant sinks for most HFCs and HCFCs. Chemical degradation in the oceans is a substantial sink for COS (28%) and COCl2 (8%) and a minor sink for CH3Cl (<2%) and CH3I (2.5%), and it should be considered when determining atmospheric lifetimes and sink strengths for these gases. Biological degradation processes are likely to increase the oceanic uptake rates of many gases.
Effects of observed horizontal inhomogeneities within cirrus clouds on solar radiative transfer
Authors: Buschmann Nicole , McFarquhar Greg M. , Heymsfield Andrew J.
Published: November 2002

In situ microphysical and combined radar and radiometer measurements of 11 cirrus clouds from Central Equatorial Pacific Experiment (CEPEX), European Cloud and Radiation Experiment (EUCREX), investigation of Clouds by Ground‐Based and Airborne Radar and Lidar (CARL), and First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) are used to investigate effects of horizontal cloud inhomogeneities on solar radiative transfer. A three‐dimensional ray‐tracing model (GRIMALDI), based on the Monte Carlo method, is used to calculate upward and downward flux densities and absorption for the spectral range from 0.38 to 4.0 μm. Radiative flux densities are calculated using the inhomogeneous clouds derived from the observations and for horizontally and vertically averaged homogeneous clouds. Horizontally averaged values of radiative flux densities and absorption for heterogeneous clouds can differ by up to 30% from those calculated for the homogeneous clouds for convectively induced tropical cirrus clouds. The midlatitude cases examined tended to be more homogeneous, and hence differences between radiative properties for the homogeneous and heterogeneous clouds did not exceed 10%. For cirrus clouds with mean optical thicknesses smaller than 5 and with relative variances of optical thickness smaller than 0.2, errors caused by the homogeneous assumption are smaller than ±10%.
A search for an anticorrelation between H2O and O3 in the lower mesosphere
Authors: Siskind David E. , Nedoluha Gerald E. , Summers Michael E. , Russell James M.
Published: November 2002

We have looked for the expected anticorrelation between H2O and O3 in the lower mesosphere using data from HALOE and a simple one‐dimensional photochemical model. We use the fractional difference between the model and the data (ΔO3/O3) as a measure of the goodness of the fit of the model to the data. The model is run for each of over 1000 days of HALOE measurements from 30° S–30° N and from 1992–1999. Despite the 10% changes in upper stratospheric H2O which were observed during this period, we detect no significant ozone change in response to this H2O variability. Indeed, in the 2.0–0.4 mb region, the model error is lower when the water vapor is arbitrarily assumed to be invariant. Further, when H2O variability is considered, (ΔO3/O3) anticorrelates with H2O but not the temperature and solar flux. From this we conclude that the temperature and solar flux dependence are fairly well modeled and that the model error is due to the representation of the ozone dependence upon H2O in the model. Our results suggest that ozone near the stratopause is surprisingly insensitive to variations in H2O. If true, this insensitivity may make easier the observation of ozone recovery in the upper stratosphere due to declining chlorine. This result should also be considered when assessing the response of upper stratospheric ozone to increases in stratospheric humidity.
A 780‐year annually resolved record of Indian Ocean monsoon precipitation from a speleothem from south Oman
Authors: Burns Stephen J. , Fleitmann Dominik , Mudelsee Manfred , Neff Ulrich , Matter Albert , Mangini Augusto
Published: November 2002

Meteorological records of monsoon rainfall in the Indian Ocean are generally less than 100 years long. The relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales, to determine what factors influence the intensity of rainfall on these timescales, or to place possible changes in the twentieth century into a broader historical context. Development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward. We have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern Arabia. Our results show that monsoon variation over the past century is not outside of the range of the past 800 years. Decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the Indian Ocean. Spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales. Decadal to interannual cycles in the record appear to originate in the tropical Pacific Ocean.