Charlottesville, VA, United States

Simpson Weather Associates, Inc.
Charlottesville, VA, United States
Time filter
Source Type

Pal S.,University of Virginia | de Wekker S.F.J.,University of Virginia | Emmitt G.D.,Simpson Weather Associates, Inc.
Journal of Applied Meteorology and Climatology | Year: 2016

Spatiotemporal variability in the convective boundary layer height zi over complex terrain is governed by numerous factors such as land surface processes, topography, and synoptic conditions. Observational datasets to evaluate weather forecast models that simulate this variability are sparse. This study aims to investigate the zi spatial variability (along a total leg length of 1800 km) around and over a steep isolated mountain (Granite Mountain) of horizontal and vertical dimensions of 8 and 0.9 km, respectively. An airborne Doppler lidar was deployed on seven flights during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) campaign conducted at Dugway Proving Ground (Utah) from 25 September to 24 October 2012. During the afternoon, an east-west zi gradient over the region with zi that was approximately 200 m higher on the eastern side than on the western side of Granite Mountain was observed. This gradient illustrates the impact of two different land surface properties on zi spatial variability, with a sparsely vegetated desert steppe region on the east and a dry, bare lake-bed desert with high subsurface soil moisture to the west of Granite Mountain. Additionally, the zi spatial variability was partly attributed to the impact of Granite Mountain on the downwind zi. Differences in zi were also observed by the radiosonde measurements in the afternoon but not in the morning as the zi variability in morning were modulated by the topography. The high-resolution lidar-derived zi measurements were used to estimate the entrainment zone thickness in the afternoon, with estimates ranging from 100 to 250 m. © 2016 American Meteorological Society.

Angelini I.M.,University of Virginia | Garstang M.,University of Virginia | Davis R.E.,University of Virginia | Hayden B.,University of Virginia | And 5 more authors.
Theoretical and Applied Climatology | Year: 2011

Recent studies suggest that vegetation can drive large-scale atmospheric circulations and substantially influence the hydrologic cycle. We present observational evidence to quantify the extent of coupling between vegetation and the overlying atmosphere. Within the context of vegetation-atmospheric interactions, we reanalyze existing climatological data from springtime leaf emergence, emissivity, dew point temperatures, and historical records of precipitation and forest coverage. We construct new rainfall transects based on a robust global climatology. Using isotopic analysis of precipitation, we find that rain in Amazonia comes primarily from large-scale weather systems coupling interior regions to the ocean and is not directly driven by local evaporation. We find that changes in vegetative cover and state influence the temperature and moisture content of the surface and atmospheric boundary layer but are not reflected in observable precipitation changes. This analysis reaffirms the view that changes in precipitation over continental reaches are a product of complex processes only partly influenced but not controlled by local water sources or vegetation. © 2011 Springer-Verlag.

Godwin K.S.,University of Virginia | Godwin K.S.,Simpson Weather Associates, Inc. | De Wekker S.F.J.,University of Virginia | Emmitt G.D.,Simpson Weather Associates, Inc.
Journal of Atmospheric and Oceanic Technology | Year: 2012

Airborne Doppler wind lidars are increasingly being used to measure winds in the lower atmosphere at higher spatial resolution than ever before. However, wind retrieval in the range gates closest to the earth's surface remains problematic. When a laser beam from a nadir-pointing airborne Doppler wind lidar intercepts the ground, the return signal from the ground mixes with the windblown aerosol signal. As a result, winds in a layer adjacent to the surface are often unreliable and removed from wind profiles. This paper describes the problem in detail and discusses a two-step approach to improve near-surface wind retrievals. The two-step approach involves removing high-intensity ground returns and identifying and tracking aerosol radial velocities in the layer affected by ground interference. Using this approach, it is shown that additional range gates closer to the surface can be obtained, thereby further enhancing the potential of airborne Doppler lidar in atmospheric applications. The benefits of the two-step approach are demonstrated using measurements acquired over the Salinas Valley in central California. The additional range gates reveal details of the wind field that were previously not quantified with the original approach, such as a pronounced near-surface wind speed maximum. © 2012 American Meteorological Society.

De Wekker S.F.J.,University of Virginia | Godwin K.S.,University of Virginia | Emmitt G.D.,Simpson Weather Associates, Inc. | Greco S.,Simpson Weather Associates, Inc.
Journal of Applied Meteorology and Climatology | Year: 2012

Three-dimensional winds obtained with an airborne Doppler lidar are used to investigate the spatial structure of topographically driven flows in complex coastal terrain in Southern California. The airborne Doppler lidar collected four hours of data between the surface and 3000 mMSL along a 40-km segment of the Salinas Valley during the afternoon of 12 November 2007. The airborne lidar measurements, obtained at horizontal and vertical resolutions of approximately 1500 and 50 m, respectively, reveal a detailed spatial structure of the atmospheric flows within the valley and their associated aerosol features. Clear skies prevailed on the flight day with northwesterly synoptic flows around 10 m s21. The data document a shallow sea breeze making a transition into an upvalley flow in the Salinas Valley that accelerates in the upvalley direction. Along with the acceleration of the upvalley wind, the lidar data indicate the presence of enhanced sinking motions. No return flows associated with the sea-breeze or upvalley flows are observed. While synoptic flows are aligned along the valley axis in the upvalley direction, lidar data indicate the presence of a northerly crossvalley flow around the height of the surrounding ridges. This flow intrudes into the valley atmosphere and induces, along with thermally driven slope flows on the sunlit valley sidewall, a cross-valley circulation that causes an asymmetric distribution of the aerosols. This study demonstrates the large potential of airborne Doppler lidar data in describing flows in complex terrain. © 2012 American Meteorological Society.

Baker W.E.,National Oceanic and Atmospheric Administration | Atlas R.,National Oceanic and Atmospheric Administration | Cardinali C.,European Center for Medium Range Weather Forecasts | Clement A.,University of Miami | And 16 more authors.
Bulletin of the American Meteorological Society | Year: 2014

Measurement of the three-dimensional global wind field is the final frontier that must be crossed to significantly improve the initial conditions for numerical weather forecasts. Accurate measurements of the global wind field will also support major advances in the understanding of several key climate change issues. Several studies have suggested that the general circulation of the atmosphere varies considerably on decadal time scales and that some of this variation may be due to greenhouse gas forcing. Large areas of the tropical atmosphere are devoid of measured wind profiles. This suggests the potential for a large improvement in forecast skill for a variety of tropical phenomena, including tropical cyclones, monsoonal circulations, and the African easterly jet, especially given the dominance of the wind field in the mass motion balance relationship.

Pu Z.,University of Utah | Zhang L.,University of Utah | Emmitt G.D.,Simpson Weather Associates, Inc.
Geophysical Research Letters | Year: 2010

During the THORPEX Pacific Asian Regional Campaign (TPARC) field experiment in 2008, an airborne Doppler wind lidar (DWL) was onboard the U.S. Naval Research Laboratory's P-3 research flight. It was the first time the DWL was used for a tropical cyclone mission. This paper presents the first results demonstrating the impact of airborne DWL measurements on the numerical simulation of Typhoon Nuri (2008) in its formation phase. With an advanced research version of the weather research and forecasting (WRF) model and its data assimilation systems, numerical results show the DWL data have a positive impact on numerical simulations of Typhoon Nuri in terms of its formation, track and intensity. Dropsondes released in the areas where the DWL was operating show good agreement for measured winds. Compared with the three-dimensional variational method, a four-dimensional variational data assimilation system is deemed to be more promising for assimilating the DWL data. Copyright © 2010 by the American Geophysical Union.

Emmitt G.D.,Simpson Weather Associates, Inc. | Godwin K.,Simpson Weather Associates, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

An airborne Doppler Wind Lidar has been used in several atmospheric boundary layer field experiments over the past decade. These experiments have taken place in California (Salinas Valley and the Monterey Peninsula), Arizona (Yuma Proving Grounds), and Utah (Dugway Proving Grounds). A primary objective of these field experiments was to compare model predicted winds in mountainous areas with wind observations obtained from the lidar measurements. To accomplish this, there is a basic challenge to determine when a comparison is valid in space and time. Here we have introduced the case for combining 12 pint step stare scans (conical) with near nadir stares to better represent the vertical air motions in complex terrain. We have also described a new scanning pattern that allows for LOS intersections for desired altitudes such as a ridge line or a valley floor. © 2014 SPIE.

Emmitt G.D.,Simpson Weather Associates, Inc.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2010

The first ever extensive study of tropical cyclones using Doppler Wind Lidars (DWL) was conducted in 2008 within the THORPEX Pacific Asian Regional Campaign. More than 100 hours of DWL profiles were obtained with an average spacing of 3km. These wind profiles along with dropsonde temperature, moisture and wind profiles are being used to study the genesis and evolution of tropical cyclones. Initial investigations are focused upon the impact the DWL profiles have on numerical weather prediction. © 2010 IEEE.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase I | Award Amount: 143.99K | Year: 2012

The overall objective of the proposed Phase I effort is to thoroughly document the technical feasibility of a platform independent hardware/software system that combines the real-time acquisition of atmospheric data by a small light-weight airborne Doppler Wind Lidar (DWL) with a numerical model and additional atmospheric sensors to provide autonomous in-flight guidance and flight path planning for small manned aircraft or UAVs. The feasibility and advantages will be determined through analysis and computer simulations. The optimum or reasonable mixes of hardware, lidar, additional sensors and aircraft twill be identified and along with consequential impacts to the core feature detection and flight path planning and software. This information will be further used to guide us in the complete lidar-centric system design during Phase II. Through analysis of archived DWL data, we will also certify the use of airborne DWL data for atmospheric energy feature detection, as well quantifying, through simulation, the advantages of having a DWL onboard compared to using only in-situ sensors and probabilistic energy harvesting strategies.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase II | Award Amount: 493.20K | Year: 2013

During Phase I, we documented the feasibility of the AEORA hardware/software system that combines the real-time acquisition of atmospheric data by a small light-weight airborne DWL and potential sensors TBD with a SOTA numerical weather model on-board a small manned aircraft or UAV. The purpose of such a software package is to reduce mission (either military or civilian) dependence upon preflight assumptions, extend flight duration and endurance, and allow for the optimum routing of the aircraft through evolving beneficial conditions and, just as importantly, avoiding detrimental ones. In Phase II, we will continue the design, development, simulation and testing of such a system. The main focus in the Phase II effort will be in the development of robust algorithms for DWL data processing, energy feature detection and ranking, cost function analysis, flight to target guidance, energy utilization and total system management. The AEORA software/hardware system will be tested through numerous simulations and, if possible, on either a small manned aircraft or, perhaps, a UAV such as the Shadow 200.

Loading Simpson Weather Associates, Inc. collaborators
Loading Simpson Weather Associates, Inc. collaborators