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Abstract
Integrated Sounding Systems (ISSs), which combine surface-based, balloon-borne, and radar observation capabilities, were deployed for the first time during the Intensive Observing Period (IOP) of the recent Coupled Ocean–Atmosphere Response Experiment. This note addresses efforts to synthesize the data from these disparate platforms as well as avenues for future research that were opened in the process.
The collaborative nature of the ISSs led to the application of different processing methods to the surface winds than were used with the winds measured by 915-MHz wind profilers. A new set of ship-based surface winds that are more directly analogous to the profiler winds has been developed. The statistical properties of these “AL-processed ISS surface winds” are shown to be similar to those of the land-based ISS surface winds, to the low-level profiler winds, and to surface winds measured at nearby buoys. A method of combining the surface and profiler winds from an ISS into one coherent dataset is also presented here; it involves assuming a logarithmic wind profile over a surface layer whose depth is invariant over the course of the IOP. While there are some obvious oversimplifications to this method, it is the most sophisticated option available from currently collected ISS data, it is more physically reasonable than a simple linear interpolation between the surface and higher-altitude winds, and it yields wind profiles that are acceptable for many applications. Both of these new datasets are now available to the community.
The process of combining the two sets of measurements not only led to a reconsideration of the postprocessing of the shipboard surface winds but also led to renewed interest in the effects of sea clutter on profiler winds. Further work is now under way in the profiler community to address the issue of sea clutter on ship-based and near-sea profiler installations.
Abstract
Integrated Sounding Systems (ISSs), which combine surface-based, balloon-borne, and radar observation capabilities, were deployed for the first time during the Intensive Observing Period (IOP) of the recent Coupled Ocean–Atmosphere Response Experiment. This note addresses efforts to synthesize the data from these disparate platforms as well as avenues for future research that were opened in the process.
The collaborative nature of the ISSs led to the application of different processing methods to the surface winds than were used with the winds measured by 915-MHz wind profilers. A new set of ship-based surface winds that are more directly analogous to the profiler winds has been developed. The statistical properties of these “AL-processed ISS surface winds” are shown to be similar to those of the land-based ISS surface winds, to the low-level profiler winds, and to surface winds measured at nearby buoys. A method of combining the surface and profiler winds from an ISS into one coherent dataset is also presented here; it involves assuming a logarithmic wind profile over a surface layer whose depth is invariant over the course of the IOP. While there are some obvious oversimplifications to this method, it is the most sophisticated option available from currently collected ISS data, it is more physically reasonable than a simple linear interpolation between the surface and higher-altitude winds, and it yields wind profiles that are acceptable for many applications. Both of these new datasets are now available to the community.
The process of combining the two sets of measurements not only led to a reconsideration of the postprocessing of the shipboard surface winds but also led to renewed interest in the effects of sea clutter on profiler winds. Further work is now under way in the profiler community to address the issue of sea clutter on ship-based and near-sea profiler installations.
Abstract
Stratocumulus (Sc) clouds occur frequently over the cold waters of the southeastern Pacific Ocean. Data collected during two Pan American Climate Study research cruises in the tropical eastern Pacific illuminate many aspects of this Sc-topped marine boundary layer (MBL). Here the focus is on understanding gaps in detectable wind-profiler reflectivities during two boreal autumn cruises. After rigorous quality control that included applying the Riddle threshold of minimum signal-to-noise ratio (SNR) detectability, there are many instances with no measurable atmospheric signals through a depth of up to several hundred meters, often lasting for an hour or more. Rain gauge data from the autumn 2004 cruise are used to calibrate the profiler, which allows SNR to be converted to both equivalent reflectivity and the structure-function parameter of the index of refraction 
Abstract
Stratocumulus (Sc) clouds occur frequently over the cold waters of the southeastern Pacific Ocean. Data collected during two Pan American Climate Study research cruises in the tropical eastern Pacific illuminate many aspects of this Sc-topped marine boundary layer (MBL). Here the focus is on understanding gaps in detectable wind-profiler reflectivities during two boreal autumn cruises. After rigorous quality control that included applying the Riddle threshold of minimum signal-to-noise ratio (SNR) detectability, there are many instances with no measurable atmospheric signals through a depth of up to several hundred meters, often lasting for an hour or more. Rain gauge data from the autumn 2004 cruise are used to calibrate the profiler, which allows SNR to be converted to both equivalent reflectivity and the structure-function parameter of the index of refraction
Abstract
While the daily cycle of near-surface winds over the equatorial east Pacific has been studied in some detail, little is known about the daily cycle above the surface layer. Furthermore, the causes of the observed near-surface daily cycle are not well understood. A better understanding of the structure and forcing mechanisms at work on the lower-tropospheric winds over this region may increase our appreciation for the varying importance of local and remote atmospheric and oceanic processes. This study documents the daily cycle of lower-tropospheric winds over one of the Galápagos Islands during the late 1990s, as well as how it varied seasonally and interannually, using half-hourly profiler winds. The well-known zonal semidiurnal tide is evident in the data, as is a diurnal cycle that is predominantly meridional and may be driven by the results of convection over the Andes. In addition, the high vertical resolution of the wind profiles reveals a decoupling of the daily cycle of winds below ∼500 m from those aloft during periods of cold (<23°C) SSTs. This decoupling, which is not evident in long-term mean profiles that effectively filter the daily cycle, may inhibit the vertical mixing of momentum or vertical propagation of tidal or wave signatures over the region.
Abstract
While the daily cycle of near-surface winds over the equatorial east Pacific has been studied in some detail, little is known about the daily cycle above the surface layer. Furthermore, the causes of the observed near-surface daily cycle are not well understood. A better understanding of the structure and forcing mechanisms at work on the lower-tropospheric winds over this region may increase our appreciation for the varying importance of local and remote atmospheric and oceanic processes. This study documents the daily cycle of lower-tropospheric winds over one of the Galápagos Islands during the late 1990s, as well as how it varied seasonally and interannually, using half-hourly profiler winds. The well-known zonal semidiurnal tide is evident in the data, as is a diurnal cycle that is predominantly meridional and may be driven by the results of convection over the Andes. In addition, the high vertical resolution of the wind profiles reveals a decoupling of the daily cycle of winds below ∼500 m from those aloft during periods of cold (<23°C) SSTs. This decoupling, which is not evident in long-term mean profiles that effectively filter the daily cycle, may inhibit the vertical mixing of momentum or vertical propagation of tidal or wave signatures over the region.
Statistics regarding the fractional participation of women in meteorology/atmospheric sciences gathered by the AMS are quite similar to those based on annual National Science Foundation (NSF) surveys. The absolute numbers in the biennial AMS/UCAR survey of academic departments for the Curricula series ceased being useful by around 2005, when many departments stopped participating fully, but numbers from less-frequent direct AMS membership surveys have been increasing. Despite the limitations of the AMS data, the NSF statistics confirm conclusions from an earlier analysis of AMS data. Both numbers and percentages are required to tell the evolving story of the atmospheric sciences' “pipeline.” Furthermore, after correction of an error regarding the AMS statistics in our 2010 paper, both NSF and AMS data show the same increase in the proportion of women graduate students in the field over the last four decades, as well as an apparent leveling off at approximately one-third.
Statistics regarding the fractional participation of women in meteorology/atmospheric sciences gathered by the AMS are quite similar to those based on annual National Science Foundation (NSF) surveys. The absolute numbers in the biennial AMS/UCAR survey of academic departments for the Curricula series ceased being useful by around 2005, when many departments stopped participating fully, but numbers from less-frequent direct AMS membership surveys have been increasing. Despite the limitations of the AMS data, the NSF statistics confirm conclusions from an earlier analysis of AMS data. Both numbers and percentages are required to tell the evolving story of the atmospheric sciences' “pipeline.” Furthermore, after correction of an error regarding the AMS statistics in our 2010 paper, both NSF and AMS data show the same increase in the proportion of women graduate students in the field over the last four decades, as well as an apparent leveling off at approximately one-third.
Abstract
No Abstract available.
Abstract
No Abstract available.
Abstract
During the intensive observing period of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, a large number of collocated rawinsonde and profiler wind observations were taken at six Integrated Sounding System (ISS) sites and Biak, Indonesia. To mitigate limitations in the rawinsonde dataset due to missing and bad wind observations, a procedure was developed to combine profiler and sonde winds to produce an integrated, high-quality, upper-air sounding dataset. In addition to improving the overall quality of the winds, this procedure eliminates several data gaps in the sonde dataset. For example, below 800 hPa the amount of bad and missing wind data is reduced from about 45% to 20% at the land-based ISS sites.
This paper describes the procedure for combining sonde and profiler winds into a single, coherent merged dataset. Examining the impact of this merger upon various atmospheric analyses, the authors find that inclusion of profiler winds results in some substantial changes in the analyses, particularly on daily to weekly timescales. To assess whether these changes are an improvement, budget-derived rainfall estimates from analyses with and without profiler winds are compared to Special Sensor Microwave/Imager satellite-based estimates. Overall, this comparison shows that inclusion of profiler winds into the sonde dataset has a beneficial impact upon the analyses.
Information for accessing the merged datasets for the seven sites considered in this paper via the Internet is described.
Abstract
During the intensive observing period of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, a large number of collocated rawinsonde and profiler wind observations were taken at six Integrated Sounding System (ISS) sites and Biak, Indonesia. To mitigate limitations in the rawinsonde dataset due to missing and bad wind observations, a procedure was developed to combine profiler and sonde winds to produce an integrated, high-quality, upper-air sounding dataset. In addition to improving the overall quality of the winds, this procedure eliminates several data gaps in the sonde dataset. For example, below 800 hPa the amount of bad and missing wind data is reduced from about 45% to 20% at the land-based ISS sites.
This paper describes the procedure for combining sonde and profiler winds into a single, coherent merged dataset. Examining the impact of this merger upon various atmospheric analyses, the authors find that inclusion of profiler winds results in some substantial changes in the analyses, particularly on daily to weekly timescales. To assess whether these changes are an improvement, budget-derived rainfall estimates from analyses with and without profiler winds are compared to Special Sensor Microwave/Imager satellite-based estimates. Overall, this comparison shows that inclusion of profiler winds into the sonde dataset has a beneficial impact upon the analyses.
Information for accessing the merged datasets for the seven sites considered in this paper via the Internet is described.
Postdeployment Calibration of a Tropical UHF Profiling Radar via Surface- and Satellite-Based MethodsAbstract
Wind profiling radars are usually not calibrated with respect to reflectivity because such calibrations are both unnecessary for good wind measurements and costly. However, reflectivity from calibrated profilers can reveal many atmospheric attributes beyond winds. Establishing ways to calibrate these radars even after they have been taken out of service would expand the utility of archived profiler data. We have calibrated one operating mode of a 915-MHz profiler deployed at Manus, Papua New Guinea (1992–2001), using two methods. The first method adjusts a radar parameter until the profiler’s estimate of rainfall during stratiform events closely matches surface observations. The second adjusts the parameter so that mean brightband heights observed by the profiler (July 1992–August 1994) match the mean brightband reflectivities over the profiler as observed by the TRMM Precipitation Radar (January 1998–July 2001). The results differ by about 5% and yield very similar precipitation errors during tested stratiform events. One or both of these methods could be used on many other wind profilers, whether they have been decommissioned or are currently operational. Data from such calibrated profilers will enable research employing the equivalent reflectivity factor observed by profilers to be compared with that from other radars, and will also enable turbulent studies with C n 2.
Abstract
Wind profiling radars are usually not calibrated with respect to reflectivity because such calibrations are both unnecessary for good wind measurements and costly. However, reflectivity from calibrated profilers can reveal many atmospheric attributes beyond winds. Establishing ways to calibrate these radars even after they have been taken out of service would expand the utility of archived profiler data. We have calibrated one operating mode of a 915-MHz profiler deployed at Manus, Papua New Guinea (1992–2001), using two methods. The first method adjusts a radar parameter until the profiler’s estimate of rainfall during stratiform events closely matches surface observations. The second adjusts the parameter so that mean brightband heights observed by the profiler (July 1992–August 1994) match the mean brightband reflectivities over the profiler as observed by the TRMM Precipitation Radar (January 1998–July 2001). The results differ by about 5% and yield very similar precipitation errors during tested stratiform events. One or both of these methods could be used on many other wind profilers, whether they have been decommissioned or are currently operational. Data from such calibrated profilers will enable research employing the equivalent reflectivity factor observed by profilers to be compared with that from other radars, and will also enable turbulent studies with C n 2.
This article describes the 1995 and 1996 Flatland boundary layer experiments, known as Flatland95 and Flatland96. A number of scientific and instrumental objectives were organized around the central theme of characterization of the convective boundary layer, especially the boundary layer top and entrainment zone. In this article the authors describe the objectives and physical setting of the experiments, which took place in the area near the Flatland Atmospheric Observatory, near Champaign–Urbana, Illinois, in August–September 1995 and June–August 1996. The site is interesting because it is extremely flat, has uniform land use, and is in a prime agricultural area. The instruments used and their performance are also discussed. The primary instruments were a triangle of UHF wind-profiling radars. Rawinsondes and surface meteorological and flux instruments were also included. Finally, some early results in terms of statistics and several case studies are presented.
This article describes the 1995 and 1996 Flatland boundary layer experiments, known as Flatland95 and Flatland96. A number of scientific and instrumental objectives were organized around the central theme of characterization of the convective boundary layer, especially the boundary layer top and entrainment zone. In this article the authors describe the objectives and physical setting of the experiments, which took place in the area near the Flatland Atmospheric Observatory, near Champaign–Urbana, Illinois, in August–September 1995 and June–August 1996. The site is interesting because it is extremely flat, has uniform land use, and is in a prime agricultural area. The instruments used and their performance are also discussed. The primary instruments were a triangle of UHF wind-profiling radars. Rawinsondes and surface meteorological and flux instruments were also included. Finally, some early results in terms of statistics and several case studies are presented.
Abstract
Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (∼23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experiment-mean findings include a net heat input from the atmosphere into the ocean of 70 W m−2. The dominant cooling was an experiment-mean latent heat flux of 108 W m−2, equivalent to an evaporation rate of 0.16 mm h−1. Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2- and 3-km altitude associated with a land–sea breeze, and a broad moist layer at 5–6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000–700-hPa winds reached 12 m s−1, net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2–3 km and another at 5–6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5–6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States.
Abstract
Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (∼23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experiment-mean findings include a net heat input from the atmosphere into the ocean of 70 W m−2. The dominant cooling was an experiment-mean latent heat flux of 108 W m−2, equivalent to an evaporation rate of 0.16 mm h−1. Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2- and 3-km altitude associated with a land–sea breeze, and a broad moist layer at 5–6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000–700-hPa winds reached 12 m s−1, net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2–3 km and another at 5–6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5–6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States.
Abstract
Comparisons of data taken by collocated Doppler wind profilers using 100-, 500-, and 1000-m pulse lengths show that the velocity profiles obtained with the longer pulses are displaced in height from contemporaneous profiles measured with the shorter pulses. These differences are larger than can be expected from random measurement errors. In addition, there is evidence that the 500-m pulse may underestimate the wind speed when compared with the 100-m pulse.
The standard radar equation does not adequately account for the conditions under which observations are made. In particular, it assumes that atmospheric reflectivity is constant throughout the pulse volume and that observations can be assigned to the peak of the range-weighting function. However, observations from several tropical profilers show that reflectivity gradients with magnitudes greater than 10 dB km−1 are common. Here, a more general radar equation is used to simulate the radar response to the atmosphere. The simulation shows that atmospheric reflectivity gradients cause errors in the range placement. Observed reflectivity gradients can be used to calculate a correction to the range location of the observations that helps to reduce these errors.
Examples of these errors and the application of the correction to selected cases are shown. The evidence presented shows that reflectivity gradients are the main cause of the pervasive differences observed between the different radar observations.
Abstract
Comparisons of data taken by collocated Doppler wind profilers using 100-, 500-, and 1000-m pulse lengths show that the velocity profiles obtained with the longer pulses are displaced in height from contemporaneous profiles measured with the shorter pulses. These differences are larger than can be expected from random measurement errors. In addition, there is evidence that the 500-m pulse may underestimate the wind speed when compared with the 100-m pulse.
The standard radar equation does not adequately account for the conditions under which observations are made. In particular, it assumes that atmospheric reflectivity is constant throughout the pulse volume and that observations can be assigned to the peak of the range-weighting function. However, observations from several tropical profilers show that reflectivity gradients with magnitudes greater than 10 dB km−1 are common. Here, a more general radar equation is used to simulate the radar response to the atmosphere. The simulation shows that atmospheric reflectivity gradients cause errors in the range placement. Observed reflectivity gradients can be used to calculate a correction to the range location of the observations that helps to reduce these errors.
Examples of these errors and the application of the correction to selected cases are shown. The evidence presented shows that reflectivity gradients are the main cause of the pervasive differences observed between the different radar observations.
