Research Applications Laboratory

Boulder City, CO, United States

Research Applications Laboratory

Boulder City, CO, United States
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Arnal L.,University of Reading | Arnal L.,European Center for Medium Range Weather Forecasts | Wood A.W.,Research Applications Laboratory | Stephens E.,University of Reading | And 3 more authors.
Journal of Hydrometeorology | Year: 2017

Seasonal streamflow prediction skill can derive from catchment initial hydrological conditions (IHCs) and from the future seasonal climate forecasts (SCFs) used to produce the hydrological forecasts. Although much effort has gone into producing state-of-the-art seasonal streamflow forecasts from improving IHCs and SCFs, these developments are expensive and time consuming and the forecasting skill is still limited in most parts of the world. Hence, sensitivity analyses are crucial to funnel the resources into useful modeling and forecasting developments. It is in this context that a sensitivity analysis technique, the variational ensemble streamflow prediction assessment (VESPA) approach, was recently introduced. VESPA can be used to quantify the expected improvements in seasonal streamflow forecast skill as a result of realistic improvements in its predictability sources (i.e., the IHCs and the SCFs)-termed "skill elasticity"-and to indicate where efforts should be targeted. The VESPA approach is, however, computationally expensive, relying on multiple hindcasts having varying levels of skill in IHCs and SCFs. This paper presents two approximations of the approach that are computationally inexpensive alternatives. These new methods were tested against the original VESPA results using 30 years of ensemble hindcasts for 18 catchments of the contiguous United States. The results suggest that one of the methods, end point blending, is an effective alternative for estimating the forecast skill elasticities yielded by the VESPA approach. The results also highlight the importance of the choice of verification score for a goal-oriented sensitivity analysis. © 2017 American Meteorological Society.

Morris G.A.,Valparaiso University | Thompson A.M.,Pennsylvania State University | Pickering K.E.,NASA | Chen S.,Pennsylvania State University | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2010

From 13 July-9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00-17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NO x. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5-5.1 km five times (15:12-17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of ∼1.6-4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of ∼(2.1-2.5) × 106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (∼1.2, ∼1.0, and ∼1.7 × 106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70-97% of the O3 change occurred in 2.5-5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry. © Author(s) 2010.

Lee J.,Yonsei University | Shin H.H.,NCAR | Hong S.-Y.,Prediction Institute | Jimenez P.A.,NCAR | And 4 more authors.
Journal of Geophysical Research D: Atmospheres | Year: 2015

This paper reports on the first attempt to investigate whether excessive precipitation over mountainous areas, which is a common problem in model simulations, could be remedied by the implementation of a more realistic surface wind field in the high-resolution Weather Research and Forecasting (WRF) model. A series of 48 h short-range forecasts was conducted for the month of July 2006 within the triple-nested WRF configuration, for which the highest resolution of 3km was focused on areas with complex orography over East Asian monsoonal regions. For accurate surface wind simulations, the subgrid-scale (SGS) orography parameterization scheme was employed. It was found that the simulated surface wind showed negative (positive) bias over mountainous (flat) regions when the SGS orography parameterization was excluded. After inclusion of the SGS orography parameterization, wind speed over mountainous (flat) regions increased (decreased), implying that the bias was mitigated. Moisture divergence (convergence) over the mountains (on the leeward side of the mountains) was induced, and surface latent heat flux increased along the mountain ranges following the improvement in the representation of the surface wind by the inclusion of the SGS orography parameterization. Eventually, excessive precipitation simulated over mountainous areas of East Asia, which is a feature commonly observed in numerical model studies, was alleviated because of the moisture divergence and increased surface latent heat flux. ©2014. American Geophysical Union. All Rights Reserved.

Plenkovic I.O.,Meteorological and Hydrological Service | Delle Monache L.,Research Applications Laboratory | Horvath K.,Meteorological and Hydrological Service | Hrastinski M.,Meteorological and Hydrological Service | Bajic A.,Meteorological and Hydrological Service
Hrvatski Meteoroloski Casopis | Year: 2015

In this paper, different post-processing methods are described and evaluated for deterministic and probabilistic point-based 10-m wind speed forecast over Croatia. These methods are applied to forecasts of operational high-resolution dynamical adaptation model (DADA) run with 2 km horizontal resolution to address the following question: which point-based post-processing method is the best suited for wind forecasting in the operational suite at DHMZ (Meteorological and Hydrological Service of Croatia). The verification procedure includes several metrics computed considering wind speed as continuous, categorical and probabilistic predictand. Those metrics were used to optimize the configuration, and to test both the deterministic and probabilistic prediction performance. This study shows that deterministic analog-based predictions (AnEn) improve the correlation between predictions and measurements while reducing forecast error better than using Kalman filter based predictions (KF), even though KF shows better bias reduction. The best results are achieved when forecasting the mean of analog ensemble or the Kalman filter of the mean of analog ensemble. Probabilistic AnEn predictions are properly dispersive, while having better resolution, discrimination and skill than forecast generated via logistic regression. These results encourage the potential use of AnEn in an operational environment at the location of meteorological stations, as well as at wind farms.

Lopez-Burgos V.,University of Arizona | Lopez-Burgos V.,U.S. Department of Agriculture | Gupta H.V.,University of Arizona | Clark M.,Research Applications Laboratory
Hydrology and Earth System Sciences | Year: 2013

Satellite remote sensing can be used to investigate spatially distributed hydrological states for use in modeling, assessment, and management. However, in the visual wavelengths, cloud cover can often obscure significant portions of the images. This study develops a rule-based, multistep method for removing clouds from MODIS snow cover area (SCA) images. The methods used include combining images from more than one satellite, time interpolation, spatial interpolation, and estimation of the probability of snow occurrence based on topographic information. Applied over the upper Salt River basin in Arizona, the method reduced the degree of cloud obscuration by 93.8 %, while maintaining a similar degree of image accuracy to that of the original images. © Author(s) 2013.

Schumann U.,German Aerospace Center | Sharman R.,U.S. National Center for Atmospheric Research | Sharman R.,Research Applications Laboratory
Journal of Aircraft | Year: 2015

The frequency of aircraft encountering the wake of other aircraft is analyzed for given aircraft, movement, and meteorological data. The method considers the descent and decay of wake vortices for a given stratification and turbulence-kinetic-energy dissipation rate, and the advection with ambient horizontal and vertical wind. An encounter is characterized in this study by the distance between the position of a follower aircraft and the centerline of a wake vortex behind the vortex generator, and by the wake-induced lift forces or roll moments on the encountering aircraft. A linear model is used for an efficient identification of potential wake-vortex encounters for all flight segments in dense traffic regions. The method is applied to radar-observed traffic over North America in 46 days in 2010/2011, and validated against pilot-reported wake encounters and automated in situ turbulence reports. Most upper-level encounters are found for medium-size aircraft on nearly parallel flight routes during descent. En route encounters of wakes from heavy aircraft flying 1000 ft higher occur relatively rarely. The frequency of wake-vortex encounters increases with the square of air-traffic density. © 2014 by Ulrich Schumann and Robert Sharman. Published by the American Institute of Aeronautics and Astronautics, Inc.

Hamill T.M.,National Oceanic and Atmospheric Administration | Brennan M.J.,National Hurricane Center | Brown B.,Research Applications Laboratory | DeMaria M.,National Oceanic and Atmospheric Administration | And 2 more authors.
Bulletin of the American Meteorological Society | Year: 2012

Uncertainty information from ensemble prediction systems can enhance and extend the suite of tropical cyclone (TC) forecast products. This article will review progress in ensemble prediction of TCs and the scientific issues in ensemble system development for TCs. Additionally, it will discuss the needs of forecasters and other users for TC uncertainty information and describe some ensemble-based products that may be able to be disseminated in the near future. We hope these proposals will jump-start a community-wide discussion of how to leverage ensemble-based uncertainty information for TC prediction. © 2012 American Meteorological Society.

Frisius T.,University of Hamburg | Schonemann D.,University of Hamburg | Vigh J.,Research Applications Laboratory
Journal of the Atmospheric Sciences | Year: 2013

The assumption of gradient wind balance is customarily made so as to derive the theoretical upper-bound intensity of a mature tropical cyclone. Emanuel's theory of hurricane potential intensity (E-PI) makes use of this assumption, whereas more recent studies by Bryan and Rotunno demonstrate that the effect of unbalanced flow can result in maximum winds that are well in excess of E-PI (superintensity). The existence of supergradient winds has been verified in a slab boundary layer model developed by Smith. Here, the authors apply the slab boundary layer model within the framework of classical E-PI theory to investigate the sensitivity of supergradient winds to the radius of maximum gradient wind (RMGW) and four nondimensional model parameters. The authors find that the Rossby number, the drag coefficient, and the modified Rankine decay parameter all have a considerable influence on the strength of the unbalanced flow. In contrast, the ratio of surface exchange coefficients has little noticeable effect on superintensity. The inclusion of horizontal momentum diffusion leads to a weaker superintensity, but the qualitative features of the model remain similar. To further elucidate these findings, the authors use the boundary layer model to examine the modified E-PI theory proposed by Emanuel and Rotunno. They assume a constant Richardson number for the outflow. The boundary layer model driven by the modified E-PI solution depends on just three model parameters rather than the four parameters used in the classical E-PI framework. Despite this apparent advantage, the results obtained in the framework of the modified E-PI are less realistic than those computed with the classical E-PI approach. © 2013 American Meteorological Society.

Gupta H.V.,University of Arizona | Perrin C.,IRSTEA | Bloschl G.,Vienna University of Technology | Montanari A.,University of Bologna | And 3 more authors.
Hydrology and Earth System Sciences | Year: 2014

A holy grail of hydrology is to understand catchment processes well enough that models can provide detailed simulations across a variety of hydrologic settings at multiple spatiotemporal scales, and under changing environmental conditions. Clearly, this cannot be achieved only through intensive place-based investigation at a small number of heavily instrumented catchments, or by empirical methods that do not fully exploit our understanding of hydrology. In this opinion paper, we discuss the need to actively promote and pursue the use of a "large catchment sample" approach to modeling the rainfall-runoff process, thereby balancing depth with breadth. We examine the history of such investigations, discuss the benefits (improved process understanding resulting in robustness of prediction at ungauged locations and under change), examine some practical challenges to implementation and, finally, provide perspectives on issues that need to be taken into account as we move forward. Ultimately, our objective is to provoke further discussion and participation, and to promote a potentially important theme for the upcoming Scientific Decade of the International Association of Hydrological Sciences entitled Panta Rhei. © Author(s) 2014.

Prabha T.V.,Indian Institute of Tropical Meteorology | Patade S.,Indian Institute of Tropical Meteorology | Pandithurai G.,Indian Institute of Tropical Meteorology | Khain A.,Hebrew University of Jerusalem | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2012

[1] The combined effect of humidity and aerosol on cloud droplet spectral width (σ) in continental monsoon clouds is a topic of significant relevance for precipitation and radiation budgets over monsoon regions. The droplet spectral width in polluted, dry premonsoon conditions and moist monsoon conditions observed near the Himalayan Foothills region during Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) is the focus of this study. Here σ is small in premonsoon clouds developing from dry boundary layers. This is attributed to numerous aerosol particles and the absence/suppression of collision-coalescence during premonsoon. For polluted and dry premonsoon clouds, σ is constant with height. In contrast to premonsoon clouds, σ in monsoon clouds increases with height irrespective of whether they are polluted or clean. The mean radius of polluted monsoon clouds is half that of clean monsoon clouds. In monsoon clouds, both mean radius and σ decreased with total cloud droplet number concentration (CDNC). The spectral widths of premonsoon clouds were independent of total droplet number concentrations, but both σ and mean radius decreased with small droplet (diameter < 20 μm) number concentrations in the diluted part of the cloud. Observational evidence is provided for the formation of large droplets in the adiabatic regions of monsoon clouds. The number concentration of small droplets is found to decrease in the diluted cloud volumes that may be characterized by various spectral widths or mean droplet radii. © 2012. American Geophysical Union. All Rights Reserved.

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