bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advances in Continuously Profiling the Thermodynamic State of the Boundary Layer: Integration of Measurements and Methods
Authors: Löhnert Ulrich , Crewell S. , Krasnov O. , O’Connor E. , Russchenberg H. 
Published: February 2008

Abstract
This paper describes advances in ground-based thermodynamic profiling of the lower troposphere through sensor synergy. The well-documented integrated profiling technique (IPT), which uses a microwave profiler, a cloud radar, and a ceilometer to simultaneously retrieve vertical profiles of temperature, humidity, and liquid water content (LWC) of nonprecipitating clouds, is further developed toward an enhanced performance in the boundary layer and lower troposphere. For a more accurate temperature profile, this is accomplished by including an elevation scanning measurement modus of the microwave profiler. Height-dependent RMS accuracies of temperature (humidity) ranging from ∼0.3 to 0.9 K (0.5–0.8 g m−3) in the boundary layer are derived from retrieval simulations and confirmed experimentally with measurements at distinct heights taken during the 2005 International Lindenberg Campaign for Assessment of Humidity and Cloud Profiling Systems and its Impact on High-Resolution Modeling (LAUNCH) of the German Weather Service. Temperature inversions, especially of the lower boundary layer, are captured in a very satisfactory way by using the elevation scanning mode. To improve the quality of liquid water content measurements in clouds the authors incorporate a sophisticated target classification scheme developed within the European cloud observing network CloudNet. It allows the detailed discrimination between different types of backscatterers detected by cloud radar and ceilometer. Finally, to allow IPT application also to drizzling cases, an LWC profiling method is integrated. This technique classifies the detected hydrometeors into three different size classes using certain thresholds determined by radar reflectivity and/or ceilometer extinction profiles. By inclusion into IPT, the retrieved profiles are made consistent with the measurements of the microwave profiler and an LWC a priori profile. Results of IPT application to 13 days of the LAUNCH campaign are analyzed, and the importance of integrated profiling for model evaluation is underlined.
Lidar Observations of the Vertical Aerosol Flux in the Planetary Boundary Layer
Authors: Engelmann Ronny , Wandinger Ulla , Ansmann Albert , Müller Detlef , Žeromskis Egidijus , Althausen Dietrich , Wehner Birgit 
Published: February 2008

Abstract
The vertical aerosol transport in the planetary boundary layer (PBL) is investigated with lidars. Profiles of the vertical wind velocity are measured with a 2-μm Doppler wind lidar. Aerosol parameters are derived from observations with an aerosol Raman lidar. Both instruments were operated next to each other at the Institute for Tropospheric Research (IfT) in Leipzig, Germany. The eddy correlation technique is applied to calculate turbulent particle mass fluxes on the basis of aerosol backscatter and vertical wind data obtained with a resolution of 75 m and 5 s throughout the PBL. A conversion of particle backscatter to particle mass is performed by applying the IfT inversion scheme to three-wavelength Raman lidar observations. The method, so far, is restricted to stationary and dry atmospheric conditions under which hygroscopic particle growth can be neglected. In a case study, particle mass fluxes of 0.5–2.5 μg m−2 s−1 were found in the upper part of a convective PBL on 12 September 2006.
Effects of Wind Field Inhomogeneities on Doppler Beam Swinging Revealed by an Imaging Radar
Authors: Cheong B. L. , Palmer R. D. , Yu T-Y. , Yang K-F. , Hoffman M. W. , Frasier S. J. , Lopez-Dekker F. J. 
Published: February 2008

Abstract
In this work, the accuracy of the Doppler beam-swinging (DBS) technique for wind measurements is studied using an imaging radar—the turbulent eddy profiler (TEP) developed by the University of Massachusetts, with data collected in summer 2003. With up to 64 independent receivers, and using coherent radar imaging (CRI), several hundred partially independent beams can be formed simultaneously within the volume defined by the transmit beam. By selecting a subset of these beams, an unprecedented number of DBS configurations with varying zenith angle, azimuth angle, and number of beams can be investigated. The angular distributions of echo power and radial velocity obtained by CRI provide a unique opportunity to validate the inherent assumption in the DBS method of homogeneity across the region defined by the beam directions. Through comparison with a reference wind field, calculated as the optimal uniform wind field derived from all CRI beams with sufficient signal-to-noise ratio (SNR), the accuracy of the wind estimates for various DBS configurations is statistically analyzed. It is shown that for a three-beam DBS configuration, although the validity of the homogeneity assumption is enhanced at smaller zenith angles, the root-mean-square (RMS) error increases because of the ill-conditioned matrix in the DBS algorithm. As expected, inhomogeneities in the wind field produce large bias for the three-beam DBS configuration for large zenith angles. An optimal zenith angle, in terms of RMS error, of approximately 9°–10° was estimated. It is further shown that RMS error can be significantly reduced by increasing the number of off-vertical beams used for the DBS processing.
Evaluation of an LES-Based Wind Profiler Simulator for Observations of a Daytime Atmospheric Convective Boundary Layer
Authors: Scipión Danny E. , Chilson Phillip B. , Fedorovich Evgeni , Palmer Robert D. 
Published: February 2008

Abstract
The daytime atmospheric convective boundary layer (CBL) is characterized by strong turbulence that is primarily caused by buoyancy forced from the heated underlying surface. The present study considers a combination of a virtual radar and large eddy simulation (LES) techniques to characterize the CBL. Data representative of a daytime CBL with wind shear were generated by LES and used in the virtual boundary layer radar (BLR) with both vertical and multiple off-vertical beams and frequencies. To evaluate the virtual radar, a multiple radar experiment (MRE) was conducted using five virtual radars with common resolution volumes at two different altitudes. Three-dimensional wind fields were retrieved from the virtual radar data and compared with the LES output. It is shown that data produced from the virtual BLR are representative of what one expects to retrieve using a real BLR and the measured wind fields match those of the LES. Additionally, results from a frequency domain interferometry (FDI) comparison are presented, with the ultimate goal of enhancing the resolution of conventional radar measurements. The virtual BLR produces measurements consistent with the LES data fields and provides a suitable platform for validating radar signal processing algorithms.
Platform-Motion Correction of Velocity Measured by Doppler Lidar
Authors: Hill Reginald J. , Brewer W. Alan , Tucker Sara C. 
Published: February 2008

Abstract
The NOAA/Earth System Research Laboratory (ESRL) has two coherent Doppler lidar systems that have been deployed on board research vessels to obtain data during several experiments. The instruments measure the wind velocity relative to the motion of the lidar; therefore, correction for the motion of the platform is required. This article gives a thorough analysis of the correction for lidar velocity measurements. The analysis is general enough to be applied to Doppler velocity measurements from all monostatic ship- and aircraftborne lidars and radars, and generalization to bistatic systems is achievable. The correction is demonstrated using miniature master-oscillator power-amplifier (mini-MOPA) Doppler velocity data obtained during the Rain in Cumulus over the Ocean (RICO) experiment.
First-Year Operation of a New Water Vapor Raman Lidar at the JPL Table Mountain Facility, California
Authors: Leblanc Thierry , McDermid I. Stuart , Aspey Robin A. 
Published: February 2008

Abstract
A new water vapor Raman lidar was recently built at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL) in California and more than a year of routine 2-h-long nighttime measurements 4–5 times per week have been completed. The lidar was designed to reach accuracies better than 5% anywhere up to 12-km altitude, and with the capability to measure water vapor mixing ratios as low as 1 to 10 ppmv near the tropopause and in the lower stratosphere. The current system is not yet fully optimized but has already shown promising results as water vapor profiles have been retrieved up to 18-km altitude. Comparisons with Vaisala RS92K radiosondes exhibit very good agreement up to at least 10 km. They also revealed a wet bias in the lidar profiles (or a dry bias in the radiosonde profiles), increasing with altitude and becoming significant near 10 km and large when approaching the tropopause. This bias cannot be explained solely by well-known too-dry measurements of the RS92K in the upper troposphere and therefore must partly originate in the lidar measurements. Excess signal due to residual fluorescence in the lidar receiver components is among the most likely candidates and is subject to ongoing investigation.
High-Resolution Radio Acoustic Sounding System Observations and Analysis up to 20 km
Authors: Alexander Simon P. , Tsuda Toshitaka 
Published: February 2008

Abstract
The first campaign-based measurements of virtual temperature in the upper-troposphere and lower-stratosphere (UTLS) region were made with the middle- and upper-atmosphere (MU) radar radio acoustic sounding system (RASS) during 4 days in August 1995. This dataset was examined in order to study high-frequency changes in the stability below 20 km, but especially in the UTLS region. Calculations of the WMO tropopause and cold-point tropopause heights showed the latter to be (1.0 ± 0.6) km higher, where 0.6 km is the standard deviation. A diurnal cycle of temperature and wind dominated the spectra, which was identified as the diurnal solar tide. Its phase maximum occurred in the afternoon between 5 and 15 km and showed upward energy propagation above this height. Changes in the UTLS kinetic energy dissipation rate ε showed significant high-frequency fluctuations embedded within layers that persisted for at least 1 day. Relative to the WMO tropopause height, the median ε increased from (0.5 ± 0.1) × 10−3 m2 s−3 in the upper troposphere to (0.7 ± 0.1) × 10−3 m2 s−3 in the lower stratosphere.
A Four-Year Lidar–Sun Photometer Aerosol Study at São Paulo, Brazil
Authors: Landulfo Eduardo , Papayannis Alexandros , Torres Ani Sobral , Uehara Sandro Toshio , Pozzetti Lucila Maria Viola , Alencar de Matos Caio , Sawamura Patricia , Morinobu Nakaema Walter , de Jesus Wellington 
Published: February 2008

Abstract
A backscattering lidar system, the first of this kind in Brazil, has been used to provide the vertical profile of the aerosol backscatter coefficient at 532 nm up to an altitude of 4–6 km above sea level (ASL), in a suburban area in the city of São Paulo. The lidar system has been operational since September 2001. The lidar data products were obtained in a 4-yr period (2001–04) and concerned the aerosol optical thickness (AOT), the aerosol backscattering and extinction coefficients at 532 nm, cloud properties (cloud base, thickness), planetary boundary layer (PBL) heights, aerosol layering, and the structure and dynamics of the lower troposphere. The lidar data are presented and analyzed in synergy with AOT measurements obtained by a Cimel sun-tracking photometer in the visible spectral region, not only to validate the lidar data but also to provide an input value of the so-called extinction-to-backscatter ratio [lidar ratio (LR)]. A correlation between the lidar data and the data obtained by a Cimel sun-tracking photometer [belonging to the Aerosol Robotic Network (AERONET)] is being made to set a temporal database of those data that were collected concomitantly and to cross correlate the information gathered by each instrument. The sun photometer data are used to provide AOT values at selected wavelengths and thus to derive the Ångström exponent (AE) values, single scattering albedo (SSA) and phase function values, and LR values. The analysis of these data showed an important trend in the seasonal signature of the LR indicating a change of the predominant type of aerosol between the dry and wet seasons. Thus, during the wet season the LR lidar values are greater (50–60 sr), which indicates that larger absorption by the aerosols takes place during this period. The corresponding AE values range between 1.3 and 2 for both periods.
Mobile Lidar Profiling of Tropical Aerosols and Clouds
Authors: Devara P. C. S. , Raj P. E. , Dani K. K. , Pandithurai G. , Kalapureddy M. C. R. , Sonbawne S. M. , Rao Y. J. , Saha S. K. 
Published: February 2008

Abstract
Lidar profiling of atmospheric aerosols and clouds in the lower atmosphere has been in progress at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32′N, 73°52′E, 559 m MSL), India, for more than two decades. To enlarge the scope of these studies, an eye-safe new portable dual polarization micropulse lidar (DPMPL) has been developed and installed at this station. The system utilizes a diode-pumped solid-state (DPSS) neodymium–yttrium–aluminum–garnet (Nd:YAG) laser second harmonic, with either parallel polarization or alternate parallel and perpendicular polarization, as a transmitter and a Schmidt–Cassegrain telescope, with a high-speed detection and data acquisition and processing system, as a receiver. This online system in real-time mode provides backscatter intensity profiles up to about 75 km at every minute in both parallel and perpendicular polarization channels, corresponding to each state of polarization of the transmitted laser radiation. Thus, this versatile lidar system is expected to play a vital role not only in atmospheric aerosol and cloud physics research and environmental monitoring but also in weather and climate modeling studies of the impact of radiative forcing on the earth–atmosphere radiation balance and hydrological cycle. This paper provides a detailed description of Asia’s only lidar facility and presents initial observations of space–time variations of boundary layer structure from experiments carried out during winter 2005/06.
Deriving Atmospheric Temperature of the Tropopause Region–Upper Troposphere by Combining Information from GPS Radio Occultation Refractivity and High-Spectral-Resolution Infrared Radiance Measurements
Authors: Borbas Eva E. , Menzel W. Paul , Weisz Elisabeth , Devenyi Dezso 
Published: February 2008

Abstract
Global positioning system radio occultation (GPS/RO) measurements from the Challenging Minisatellite Payload (CHAMP) and Satelite de Aplicaciones Cientificas-C (SAC-C) satellites are used to improve tropospheric profile retrievals derived from the Aqua platform high-spectral-resolution Atmospheric Infrared Sounder (AIRS) and broadband Advanced Microwave Sounding Unit (AMSU) measurements under clear-sky conditions. This paper compares temperature retrievals from combined AIRS, AMSU, and CHAMP/SAC-C measurements using different techniques: 1) a principal component statistical regression using coefficients established between real (and in a few cases calculated) measurements and radiosonde atmospheric profiles; and 2) a Bayesian estimation method applied to AIRS plus AMSU temperature retrievals and GPS/RO temperature profiles. The Bayesian estimation method was also applied to GPS/RO data and the AIRS Science Team operational level-2 (version 4.0) temperature products for comparison. In this study, including GPS/RO data in the tropopause region produces the largest improvement in AIRS–AMSU temperature retrievals—about 0.5 K between 100 and 300 hPa. GPS/RO data are found to provide valuable upper-tropospheric information that improves the profile retrievals from AIRS and AMSU.
Application of an Adaptive Nudging Scheme in Air Quality Forecasting in China
Authors: Xu Xiangde , Xie Lian , Cheng Xinghong , Xu Jianming , Zhou Xiuji , Ding Guoan 
Published: February 2008

Abstract
A major challenge for air quality forecasters is to reduce the uncertainty of air pollution emission inventory. Error in the emission data is a primary source of error in air quality forecasts, much like the effect of error in the initial conditions on the accuracy of weather forecasting. Data assimilation has been widely used to improve weather forecasting by correcting the initial conditions with weather observations. In a similar way, observed concentrations of air pollutants can be used to correct the errors in the emission data. In this study, a new method is developed for estimating air pollution emissions based on a Newtonian relaxation and nudging technique. Case studies for the period of 1–25 August 2006 in 47 cities in China indicate that the nudging technique resulted in improved estimations of sulfur dioxide (SO2) and nitrogen dioxide (NO2) emissions in the majority of these cities. Predictions of SO2 and NO2 concentrations in January, April, August, and October using the emission estimations derived from the nudging technique showed remarkable improvements over those based on the original emission data.
The Storm-Track Response to Idealized SST Perturbations in an Aquaplanet GCM
Authors: Brayshaw David James , Hoskins Brian , Blackburn Michael 
Published: February 2008

Abstract
The tropospheric response to midlatitude SST anomalies has been investigated through a series of aquaplanet simulations using a high-resolution version of the Hadley Centre atmosphere model (HadAM3) under perpetual equinox conditions.
Model integrations show that increases in the midlatitude SST gradient generally lead to stronger storm tracks that are shifted slightly poleward, consistent with changes in the lower-tropospheric baroclinicity. The large-scale atmospheric response is, however, highly sensitive to the position of the SST gradient anomaly relative to that of the subtropical jet in the unperturbed atmosphere. In particular, when SST gradients are increased very close to the subtropical jet, then the Hadley cell and subtropical jet is strengthened while the storm track and eddy-driven jet are shifted equatorward. Conversely, if the subtropical SST gradients are reduced and the midlatitude gradients increased, then the storm track shows a strong poleward shift and a well-separated eddy-driven jet is produced. The sign of the SST anomaly is shown to play a secondary role in determining the overall tropospheric response.
These findings are used to provide a new and consistent interpretation of some previous GCM studies concerning the atmospheric response to midlatitude SST anomalies.
Low-Frequency Variability and Remote Forcing of Gap Winds over the East Pacific Warm Pool
Authors: Karnauskas Kristopher B. , Busalacchi Antonio J. , Murtugudde Raghu 
Published: February 2008

Abstract
The low-frequency variability of gap winds at the Isthmuses of Tehuantepec and Papagayo is investigated using a 17-yr wind stress dataset merging the remotely sensed observations of Special Sensor Microwave Imager (SSM/I) and Quick Scatterometer (QuikSCAT) satellite sensors. A decadal signal is identified in the Tehuantepec gap winds, which is shown to be related to the Atlantic tripole pattern (ATP). Using linear regression and spectral analysis, it is demonstrated that the low-frequency variability of the Tehuantepec gap winds is remotely forced by the ATP, and the Papagayo gap winds are primarily governed by El Niño–Southern Oscillation (ENSO) with the ATP being of secondary importance.
The Tehuantepec (Papagayo) time series of wind stress anomalies can be better reconstructed when the local cross-isthmus pressure difference and large-scale climate information such as the ATP (ENSO) are included, suggesting that there is important information in the large-scale flow that is not transmitted directly through the background sea level pressure gradient. The geostrophic modulation of the easterly trades in the western Caribbean also serve as a remote driver of the Papagayo gap winds, which is itself not fully independent from ENSO. Finally, it is suggested that precipitation variability in the Inter-Americas region is closely related to the same remote forcing as that of the Tehuantepec gap winds, being the ATP and associated large-scale atmospheric circulation.
Stationarity of Regression Relationships: Application to Empirical Downscaling
Authors: Schmith Torben 
Published: February 2008

AbstractThe performance of a statistical downscaling model is usually evaluated for its ability to explain a large fraction of predictand variance. In this note, it is shown that although this fraction may be high, the longest time scales, including trends, may not be explained by the model. This implies that the model is nonstationary over the training period of the model, and it questions the basic stationarity assumption of statistical downscaling. This is exemplified by using a simple regression model for downscaling European precipitation and surface temperature where appropriate Monte Carlo–based field significance tests are developed, taking into account the intercorrelation between predictand series. Based on this test, it is concluded that care is needed in selecting predictors to avoid this form of nonstationarity. Even though this is illustrated for a simple regression-type statistical downscaling model, the main conclusions may also be valid for more complicated models.
Interannual to Diurnal Variations in Tropical and Subtropical Deep Convective Clouds and Convective Overshooting from Seven Years of AMSU-B Measurements
Authors: Hong Gang , Heygster Georg , Notholt Justus , Buehler Stefan A. 
Published: February 2008

Abstract
This study surveys interannual to diurnal variations of tropical deep convective clouds and convective overshooting using the Advanced Microwave Sounding Unit B (AMSU-B) aboard the NOAA polar orbiting satellites from 1999 to 2005. The methodology used to detect tropical deep convective clouds is based on the advantage of microwave radiances to penetrate clouds. The major concentrations of tropical deep convective clouds are found over the intertropical convergence zone (ITCZ), the South Pacific convergence zone (SPCZ), tropical Africa, the Indian Ocean, the Indonesia maritime region, and tropical and South America. The geographical distributions are consistent with previous results from infrared-based measurements, but the cloud fractions present in this study are lower. Land–ocean and Northern–Southern Hemisphere (NH–SH) contrasts are found for tropical deep convective clouds. The mean tropical deep convective clouds have a slightly decreasing trend with −0.016% decade−1 in 1999−2005 while the mean convective overshooting has a distinct decreasing trend with −0.142% decade−1. The trends vary with the underlying surface (ocean or land) and with latitude. A secondary ITCZ occurring over the eastern Pacific between 2° and 8°S and only in boreal spring is predominantly found to be associated with cold sea surface temperatures in La Niña years. The seasonal cycles of deep convective cloud and convective overshooting are stronger over land than over ocean. The seasonal migration is pronounced and moves south with the sun from summer to winter and is particularly dramatic over land. The diurnal cycles of deep convective clouds and convective overshooting peak in the early evening and have their minima in the late morning over the tropical land. Over the tropical ocean the diurnal cycles peak in the morning and have their minima in the afternoon to early evening. The diurnal cycles over the NH and SH subtropical regions vary with the seasons. The local times of the maximum and minimum fractions also vary with the seasons. As the detected deep convective cloud fractions are sensitive to the algorithms and satellite sensors used and are influenced by the life cycles of deep convective clouds, the results presented in this study provide information complementary to present tropical deep convective cloud climatologies.