A21F-0249
Operational Wind Retrieval Within the Frame of the French Weather Radar Network
The recent deployment of an innovative triple-PRT Doppler scheme within the French operational radar network, named ARAMIS, allows collecting reflectivity and radial velocity measurements simultaneously up to a range of 250 km with no ambiguity. This achievement brings new perspectives in terms of exploitation of operational radar measurements such as the long-anticipated capability to perform multiple-Doppler wind retrieval in a fully operational framework. Accordingly, and for the first time ever, a method allowing to consistently retrieve complete wind vector fields (u, v, w) in real-time from operational radar systems is being tested by the French national weather service since early 2007. This study proposes to describe the experimental setup relied upon to operationally retrieve multiple-Doppler winds in the frame of ARAMIS, as well as to investigate the potential of this new product for weather forecast applications. Using high resolution numerical wind forecasts in a variety of weather situations, we also show that these radar-derived wind fields compose unprecedented datasets to evaluate and further improve high-resolution numerical weather prediction systems being currently deployed by many national weather services.
A21F-0250
Climatology of Vertical Air Motion During Rainfall in Niamey, Niger and Black Forest, Germany using an Innovative Cloud Radar Retrieval Technique
In recent years, the DOE Atmospheric Radiation Measurement (ARM) program has deployed its ARM Mobile Facility (AMF) to collect continuous measurements in several climatologically distinct locations, including a year-long stay in Niamey, Niger and eight months in Germany's Black Forest. The AMF includes a vertically pointing 95 GHz cloud radar, a tool of choice for profiling non-precipitating clouds at high spatial and temporal resolutions, but commonly considered poorly suited to the quantitative study of precipitation, due in large part to attenuation. However, an innovative technique first explored by Lhermitte in the late 1980s, and subsequently by others, sidesteps much of the quantitative uncertainty imposed by attenuation by exploiting non-Rayleigh resonance effects of scattering from raindrops at 95 GHz. Given a modest range of suitable drop sizes, non-Rayleigh resonances appear as distinct peaks and valleys in Doppler spectra, which once identified, can be directly mapped to known drop sizes by Mie theory. Although attenuation in rain at 95 GHz is substantial, key to the technique is that all non-Rayleigh peaks and valleys in a given Doppler spectrum are affected equally, preserving their relative positions and magnitudes (barring feature extinction). Vertical air motion is retrieved very accurately by taking the difference between the measured Doppler velocity of a resonance feature (usually the first valley) and the known terminal velocity of its associated drop size. We have achieved promising retrieval accuracies at spatial and temporal resolutions of 30 meters and 2 seconds. Here we present lessons learned when the retrieval technique is automated and applied to measurements taken in rain over the full durations of the Niamey and Black Forest AMF deployments, comparing vertical air velocity patterns of monsoonal precipitation over the African desert with those of the orographically influenced precipitation in Germany's mountains.
A21F-0251
Potential of Future Hurricane Imaging Radiometer (HIRAD) Ocean Surface Wind Observations for Determining Tropical Storm Vortex Intensity and Structure
The Hurricane Imaging Radiometer (HIRAD) is an innovative technology development, which offers the potential of new and unique remotely sensed observations of both extreme oceanic wind events and strong precipitation from either UAS or satellite platforms. It is based on the airborne Stepped Frequency Microwave Radiometer (SFMR), which is a proven aircraft remote sensing technique for observing tropical cyclone ocean surface wind speeds and rain rates, including those of major hurricane intensity. The proposed HIRAD instrument advances beyond the current nadir viewing SFMR to an equivalent wide-swath SFMR imager using passive microwave synthetic thinned aperture radiometer technology. This sensor will operate over 4-7 GHz (C-band frequencies) where the required tropical cyclone remote sensing physics has been validated by both SFMR and WindSat radiometers. HIRAD incorporates a unique, technologically advanced array antenna and several other technologies successfully demonstrated by the NASA's Instrument Incubator Program. A brassboard version of the instrument is complete and has been successfully tested in an anechoic chamber, and development of the aircraft instrument is well underway. HIRAD will be a compact, lightweight, low-power instrument with no moving parts that will produce wide-swath imagery of ocean vector winds and rain during hurricane conditions when existing microwave sensors (radiometers or scatterometers) are hindered. Preliminary studies show that HIRAD will have a significant positive impact on analyses as either a new aircraft or satellite sensor.
A21F-0252
Enabling Characteristics Of Optical Autocovariance Lidar For Global Wind And Aerosol Profiling
Systematic global wind measurements with 70 km horizontal resolution and, depending on altitude from the PBL to stratosphere, 250m-2km vertical resolution and 0.5m/s - 2 m/s velocity precision are recognized as key to the understanding and monitoring of complex climate modulations, validation of models, and improved precision and range for weather forecasts. Optical Autocovariance Wind Lidar (OAWL) is a relatively new interferometric direct detection Doppler lidar approach that promises to meet the required wind profile resolution at substantial mass, cost, and power savings, and at reduced technical risk for a space-based system meeting the most demanding velocity precision and spatial and temporal resolution requirements. A proof of concept Optical Autocovariance Wind Lidar (OAWL) has been demonstrated, and a robust multi- wavelength, field-widened (more than 100 microR) lidar system suitable for high altitude (over 16km) aircraft demonstration is under construction. Other advantages of the OAWL technique include insensitivity to aerosol/molecular backscatter mixing ratio, freedom from complex receiver/transmitter optical frequency lock loops, prospects for practical continuous large-area coverage wind profiling from GEO, and the availability of simultaneous multiple wavelength High Spectral Resolution Lidar (OA-HSRL) for aerosol identification and optical property measurements. We will discuss theory, development and demonstration status, advantages, limitations, and space-based performance of OAWL and OA-HSRL, as well as the potential for combined mission synergies.
A21F-0253
Recent US Activities Toward Development of a Global Tropospheric 3D Wind Profiling System
The wind field plays a unique dynamical role in forcing the mass field to adjust to it at all scales in the tropics, and at small scales in the extra-tropics. Because of this unique role, knowledge of the wind field is required to accurately specify the global initial conditions for numerical weather forecasting. In addition to improving numerical weather prediction, there is also a need for improved accuracy of wind fields to assess long term sensitivity of the general circulation to climate change and to improve horizontal and vertical transport estimates of important atmospheric constituents. In spite of the significance, the 3-D structure of the wind field remains largely unobserved on a global scale. A new satellite mission to accurately measure the global wind field would fill this important gap in the Global Observing System. Space-based Doppler wind lidar has been identified as the key technology necessary to meet the global wind profiling requirement. The 2007 NRC Decadal Survey for Earth Science lists a Global Tropospheric 3-D Wind mission as one of the 15 priority missions recommended for NASA in the next decade. The NRC survey recommended a two phase approach to achieving an operational global wind measurement capability. The first recommended step is for NASA to develop the technology and fly a pre-operational mission to demonstrate the technology and measurement concept and establish the performance standards for an operational wind mission. Phase two would be to develop and fly an operational wind system in the 2025 timeframe. The technology approach recommended is a hybrid Doppler wind lidar (HDWL). The HDWL takes advantage of the complementary capabilities of two Doppler lidar technologies, a coherent Doppler lidar sensing winds from the aerosol backscattered laser signal at a wavelength of 2 microns and a direct detection Doppler lidar sensing winds from the molecular backscattered laser signal at 355 nm. The direct detection Doppler system targets the clear air regions of the free troposphere and lower stratosphere while the coherent aerosol system would be sized to measure winds in regions of moderate to high aerosol concentration or from clouds. Recently, a multi-agency team of scientists and engineers participated in two mission concept studies performed in the Mission Design Center at NASA's Goddard Space Flight Center to address the recommendations of the NRC Panel. In 2006, NASA Headquarters sponsored HDWL instrument and mission concept studies of a Global Wind Observing Sounder (GWOS) flying in a 400 km polar orbit that will meet the objectives of the pre-operational NASA demonstration mission. In 2008, the NPOESS Program Executive Office sponsored a follow on notional concept study of an operational Next Generation NPOESS Wind Observing Sounder (NWOS) flying at 828 km. In this paper, we will present an overview of the results of the GWOS and NWOS studies in the context of a roadmap to a future operational Global 3D Wind measurement system.
A21F-0254
MRI: A MOBILE FE-RESONANCE/RAYLEIGH/MIE DOPPLER LIDAR FOR GLOBAL WIND AND TEMPERATURE PROFILING
Global wind, temperature, and aerosol profiling through the middle and upper atmosphere with high accuracy, precision, and resolution is crucial in atmosphere and climate study. Funded by the National Science Foundation we are developing a Major Research Instrumentation mobile Fe-resonance/Rayleigh/Mie Doppler lidar that has compelling reasons to be attractive for these purposes. This lidar will provide simultaneous measurements of temperature (30-110 km), wind (75-110 km), Fe density (75-115 km), and aerosol (10-100 km) in both day and night through an entire year with high accuracy, high precision, and high spatial and temporal resolutions. We present the lidar design concept with a revolutionary lidar frequency-locking scheme. We also present the first Fe Doppler-free saturation-absorption spectroscopy at 372 nm achieved with our MRI lidar system. Such Fe spectroscopy provides absolute frequency reference and calibration for the entire MRI lidar system, marking a significant advancement in the Fe Doppler lidar technology. Potential measurements enabled by this lidar will be discussed in the context of atmospheric science needs. A very attractive while very challenging measurement of vertical drift associated with meridional circulation now looks very possible (requiring better than 1 cm/s accuracy) due to this lidar's capability of bias-free wind measurements.
A21F-0255
Measuring cloud motion wind vectors from ground based stereo cameras
Calibrated ground based stereo cameras are used to derive the position of cloud features in space and time. The motion of these cloud features is then used to derive vector wind fields from sequential stereo camera images. Comparison of wind speeds derived from calibrated ground-based stereo cameras is in reasonable agreement with wind fields derived from radiosonde measurements.
A21F-0256
Observations of Height Resolved Tropospheric Winds from MISR Using Cloud Motion Vectors: Data and Model Intercomparisons and Applications
The Multi-angle Imaging SpectroRadiometer (MISR) instrument on the NASA EOS Terra satellite obtains cloud motion vector winds using images from nine cameras over a time period of seven minutes from a single, polar orbiting platform. These winds represent mesoscale domains of 70 km, and are obtained with a vertical resolution of a few hundred meters based on a stereo pattern matching approach. To assess the performance of the MISR retrievals, a number of comparisons have been made between MISR and other wind data sources including QuikSCAT near surface ocean wind vectors, GOES and MODIS cloud motion vectors, and nearly coincident rawinsonde observations in the arctic. In addition, comparisons have been made with global forecast and reanalysis models for both coincident and seasonal winds. We will describe some of the results of comparisons with the NCEP reanalysis, ECMWF and GEOS-5 model wind vectors, showing similarities and highlighting interesting differences. Finally, we will present examples of applications of the MISR cloud motion vector winds to assess surface- atmosphere coupling and improve estimates of atmospheric water vapor transport.
A21F-0257
Evaluation of MISR and MODIS IR arctic wind retrievals relative to rawinsondes
The Multi-angle Imaging SpectroRadiometer (MISR) provides a unique source of purely geometric arctic wind observations insensitive to temperature inversions. From aboard the Terra satellite, MISR wind retrievals are height resolved to within a few hunded meters and provide accuracy to within a few meters per second. Here, the performance of MISR wind retrievals is evaluated relative to a number of collocated arctic rawinsonde sites, and relative to collocated MODIS IR wind retrievals. Attention is paid not only to bias and root-mean-square error relative to RAOB, but also to wind variability, cloud regimes observed, and cloud height accuracy relative to RAOB indicated cloud presence. Initial findings show enhanced wind retrieval accuracy relative to MODIS, as a likely result of more accurate wind height registration. Assimilation of MISR data into arctic weather forecasting is the ultimate goal.
A21F-0258
Remote Sensing Winds - PBL Modeling Synergism
Microwave scatterometers, radiometers, SARs and altimeters have now provided three decades of surface winds over the oceans. When compared to in situ measurements they comprise a "surface truth" base that is significantly better than other sources of winds. In fact, in many cases these products are revolutionary, changing the way we view the world. Conclusions are: * Numerical global models are often inadequate in representing surface winds for most synoptic and many climate models. * Data show that the secondary flow characteristics of the nonlinear PBL solution (Rolls or Coherent Structures) are present more often than not over the world's oceans. This has serious consequences for K-theory modeling. * The University of Washington PBL model with a nonlinear Ekman layer solution patched to a log layer provides a single parameter similarity PBL model that is sufficiently accurate to determine surface pressure fields from satellite data alone. * Capturing storm and frontal dynamics require at least 25-km resolution. New revelations are possible with potential sensor development and deployment. * Wind measurements sensors are not currently part of the NOAA or NASA Earth Science schedule (A scatterometer is planned circa 2012, a Doppler wind lidar for 2022). The conclusions from these observations are important yet have been often ignored by the modeling community.
A21F-0259
Uncertainties in the global wind analysis: implication for the minimum requirements of Doppler wind lidar measurements for seasonal climate studies
This study examines the uncertainties in the seasonal global wind analysis by comparing the wind analysis from NCEP/DOE reanalysis II and ERA-40 reanalysis data products during 1980-1999. Significant differences are found in seasonal mean wind field between the two reanalyses. Preliminary results show that the differences are mainly distributed in the tropical and Polar regions of the troposphere and in the sub- tropical areas of the upper atmosphere, which implies uncertainties in the wind analysis and a lack of wind observations in these areas. Seasonal and height variations are also found in the uncertainties of the wind analysis. More detailed studies are conducted to investigate the seasonal and year-to-year variability of these uncertainties. The implication of the analysis results on the minimum requirement of the future space- based Doppler Wind Lidar measurements for seasonal climate study is discussed.
A21F-0260
The Impact of Stratospheric Wind and Ozone Observations on Analyses and Forecasts: OSSE Description and Initial Results
An earlier observation simulation system experiment (OSSE) conducted by Lahoz et al. (2005) provided an assessment of the positive potential impact of SWIFT stratospheric wind and ozone observations on data assimilation analyses. That work has been partially repeated and also extended with a different system and a full, yet simple to implement, simulation setup for conventional observations (e.g. AMSU-A). The main motivation for embarking on this current OSSE work is to ultimately estimate the potential impact of stratospheric wind and ozone observations on the analyses and forecasts of the Canadian weather forecasting system. The current phase of the study, which supports and adds to results of the earlier work showing most notable impact in the tropics, is restricted to use of local nature runs and 3D-Var with FGAT assimilations. Individual and combined impact of SWIFT-type Doppler wind and ozone profiles and MIPAS- type ozone profiles are examined with focus of the impact on wind and temperature using the nature runs serving as truth. Results of multivariate ozone-dynamics assimilation using simple coupling operators are therefore also presented.
A21F-0261
The Role of Numerical Weather Prediction in Operational Forecasting at the Storm Prediction Center: A Case Study
The forecasting process is a complex one that is not often completely understood by the meteorological community. Evident in this process is the increasing importance of rapidly developing numerical weather prediction tools to generate accurate forecasts. An evaluation of the use of these tools by forecasters at the Storm Prediction Center is presented here. The evaluation focused on a period several days in advance of the April 17-18, 2008 severe thunderstorm event. As the event approached, forecasters relied heavily on forecast guidance provided by the National Center for Environmental Prediction, National Severe Storms Laboratory, and European Center for Medium-Range Weather Forecasts. Several parameters typically used in severe thunderstorm forecasts (e.g. thermodynamic instability, precipitation forecasts, wind, vertical shear, and lift) were comparatively examined using the guidance provided by these centers to quantify the potential for severe thunderstorm activity during the event. It was found that forecasters rarely depended on a single deterministic solution to generate a forecast. Instead, they used multiple solutions to develop a conceptual model of how the atmosphere (and resultant severe threat) would evolve during the forecast period. It was also found that their effective use of forecast guidance was heavily dependent on recognition of systematic model errors of atmospheric features that play key roles in model forecasts of atmospheric convection (e.g., dryline or frontal position, convective feedback, unrealistic moistening, etc.). Effective use of models appeared to be hampered somewhat by the rapid evolution of parameterization schemes and the inability of forecasters to 'keep up' with the changes.