LAB Announcements

Spotlight

Bhagirath Addepalli

Bhagirath Addepalli

Hometown: Hyderabad, India

Program: PhD (Graduated May 2012)

Current Position: Microsoft Program Manager

Research Interests: Fundamental and applied research in fluid dynamics, inverse and optimization techniques, and statistical modeling and analysis of data. Specifically, interests include: laboratory experiments, computational fluid dynamics, Lagrangian random-walk modeling, development of novel case-specific objective functionals (metrics) for inverse problems, development of efficient and robust optimization and inversion techniques spanning deterministic, stochastic (frequentist), and Bayesian methods, multiple criteria decision making (MCDM - Pareto optimality), linear and nonlinear regression techniques for stochastic modeling, statistical modeling of time series data, model selection in inverse problems.

Publications:
A) Journal Publications / Pre-prints:
a) Addepalli, B., K. Sikorski, E.R. Pardyjak and M.S. Zhdanov. Source characterization of atmospheric releases using stochastic search and regularized gradient optimization. Inverse Problems in Science and Engineering, 2011. 19(8): p. 1097-1124.
b) Addepalli, B. and E.R. Pardyjak. A pseudo-metric to handle zero measurements and predictions in atmospheric inverse-source problems. Under review. Submitted to Inverse Problems in Science and Engineering.
c) Addepalli, B. and E.R. Pardyjak. Investigation of flow structure in step-up street canyons. Ready to be submitted to Boundary Layer Meteorology. Pre-print available upon request.
d) Addepalli, B. and E.R. Pardyjak. Study of flow fields in asymmetric step-down street canyons. Ready to be submitted to Boundary Layer Meteorology. Pre-print available upon request.
e) Addepalli, B., E.R. Pardyjak, P. Willemsen and D.E. Johnson. Urban form optimization for air quality applications using simulated annealing and genetic algorithms. Ready to be submitted to Atmospheric Environment. Pre-print available upon request.
f) Addepalli, B. Markov Chain Monte Carlo annealing for atmospheric inverse-source problems. To be submitted to Inverse Problems in Science and Engineering. Pre-print available upon request.

B) Peer-reviewed Conference Publications:
a) Addepalli, B., K. Sikorski, E.R. Pardyjak and M.S. Zhdanov. Quasi-Monte Carlo, Monte Carlo, and regularized gradient optimization methods for source characterization of atmospheric releases. in Dagstuhl Seminar Proceedings 09391, Algorithms and Complexity for Continuous Problems. 2009. Dagstuhl, Germany: Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, Germany.
b) Addepalli, B. and E.R. Pardyjak. Study of flow fields in asymmetric step-down street canyons. in The International Workshop on Physical Modelling of Flow and Dispersion Phenomena (PHYSMOD). 2007. University of Orleans, France.

C) Conference Publications:
a) Pardyjak, E.R., Addepalli, B., et al., Impact of green infrastructure on urban microclimate and air quality, in the 8th International Conference on Urban Climate - ICUC 8. 2012: Dublin, Ireland.
b) Addepalli, B. and C. Sikorski, A note on objective functions for atmospheric inverse-source problems, in second National Conference in Advancing Tools and Solutions for Nuclear Material Detection. 2011: Salt Lake City, UT.
c) Addepalli, B. and C. Sikorski, Efficient adaption of simulated annealing and genetic algorithms to atmospheric inverse-source problems, in AIChE Annual Meeting. 2010: Salt Lake City, UT.
d) Addepalli, B. and C. Sikorski, Tools to characterize the source of hazardous releases, in 1st National Conference on Advancing Tools and Solutions for Nuclear Material Detection. 2010: Salt Lake City, UT.
e) Addepalli, B., M.J. Brown, E.R. Pardyjak and I. Senocak. Evaluation of the QUIC-URB wind model using wind-tunnel data for step-up street canyons, in Seventh Symposium on the Urban Environment. 2007: San Diego, CA.
f) Addepalli, B. and E.R. Pardyjak. 2D PIV Measurements of street canyon flow for buildings with varying angles and separation distances. in American Meteorological Society Sixth Symposium on the Urban Environment. 2006: Atlanta, GA.

D) Conference Presentations:
a) Addepalli, B., E.R. Pardyjak, P. Willemsen and D.E. Johnson. GPU-MCDM: A new module of the Quick Urban and Industrial Complex (QUIC) dispersion modeling system for urban form optimization. in the 8th International Conference on Urban Climate - ICUC 8. 2012: Dublin, Ireland.
b) Addepalli, B., E.R. Pardyjak, P. Willemsen and D.E. Johnson. Development of a multiple criteria decision making (MCDM) tool for urban form optimization. in 92nd AMS Annual Meeting. 2012: New Orleans, LA.
c) Addepalli, B., E.R. Pardyjak, P. Willemsen and D.E. Johnson. Urban form optimization for air quality applications using simulated annealing and genetic algorithms. in Ninth Symposium on the Urban Environment. 2010: Keystone, CO.
d) Addepalli, B., M.J. Brown, E.R. Pardyjak and I. Senocak. Investigation of the flow structure around step-up, step-down, deep canyon, and isolated tall building configurations using wind-tunnel PIV measurements, in Seventh Symposium on the Urban Environment. 2007: San Diego, CA.
e) Addepalli, B., E.R. Pardyjak and M.J. Brown. The effect of geometry on the wake structure of a surface mounted obstacle. in 60th Annual Meeting of the APS Divison of Fluid Dynamics. 2007: Salt Lake City, UT.
f) Addepalli, B. and E.R. Pardyjak. Experimental investigation of the effect of Reynolds number and HΔ value on flow fields in street canyons with cubical Buildings. in American Physical Society, 59th Annual Meeting of the APS Division of Fluid Dynamics. 2006: Tampa Bay, FL.
g) Addepalli, B. and E.R. Pardyjak. 2D PIV measurements of flow between a pair of model buildings with varying geometries. in American Physical Society, 58th Annual Meeting of the Division of Fluid Dynamics. 2005: Chicago, IL.

E) Technical Reports:
a) Addepalli, B., C. Sikorski and E.R. Pardyjak. Source Characterization of atmospheric releases using quasi-random sampling and gradient optimization. Report submitted to the School of Computing, University of Utah. Report number: UUCS 09-001.
b) Nelson, M., B. Addepalli, D. Boswell and M.J. Brown. QUIC Start Guide (v 4.5). Los Alamos National Labratory. LA-UR-07-2799.

Contact: addbugs@gmail.com

MATHERHORN PRESS RELEASE - June 3, 2013

alternate textPhoto collage from the Fall MATERHORN Campaign compiled courtesy of professor Stephan DeWekker, University of Virginia.

MATERHORN Field Studies Delve into Scale Intricacies of Mountain Weather

On May 31st, 2013, investigators of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program successfully completed two unique field campaigns focusing on meteorological phenomena with time scales from a few seconds to hours, and covering spatial extents of tens of kilometers down to millimeters. Mountain weather can evolve dramatically over different scales, and the MATERHORN Program capitalized on its access to the Granite Mountain Atmospheric Sciences Test Bed (GMAST) of the US Army Dugway Proving Ground (DPG) to maximize these scale ranges in a sheltered, yet completely natural setting. A bevy of participants filled the GMAST with high-end instrumentation, making these two campaigns perhaps the most extensive mountain terrain field experiments conducted hitherto in terms of instrumentation and scope. The fall experiments (September 25 to October 31, 2012) focused on quiescent fair weather (wind speeds < 5 m/s) wherein diurnal heating/cooling provided main forcing. The spring study, begun on May 1 and only just completed on May 31st, dealt with larger, synoptic flow effects, moister surface conditions, and covered mostly moderate (5 to 10 m/s) and strong (> 10m/s) wind periods.

Field experiments are a key component of MATERHORN’s principle thrusts (Modeling, Experimental, Technology and Parameterization) that are symbiotically directed at improving weather predictions in complex terrain. A Multidisciplinary University Research Initiative (MURI) grant from the Office of Naval Research provides the main funding for MATERHORN, with University of Notre Dame (lead), University of California (Berkeley), Naval Postgraduate School, University of Utah and University of Virginia as grantees. A number of additional US and foreign institutions joined MATERHORN, leveraging alternative funding sources, mainly the Army Research Office and Air Force Weather Office (http://www.nd.edu/~dynamics/materhorn).

The field studies were designed using guidance from the WRF Model. Background meteorology was characterized via radiosonde launches (at 7 locations), 6 ceilometers, 3 Sodars, a Sodar/RASS, a wind profiler, two microwave radiometers, a FM/CW radar and a C-Band Doppler Radar. An array of 51 Portable Weather Instrumentation Data Systems (PWIDs), 31 Surface Atmospheric Measurement Systems (SAMS) and 51 MiniSAMS recorded the wind patterns in GMAST at kilometer and sub-kilometric scales, and two sets of tethered balloons measured the vertical profiles up to several kilometers at a meter scale resolution. Moisture was probed at km scales via two newly developed RF crosshairs (surface), microwave radiometers (vertical profiles) and infrared gas analyzers (fluxes). Three Doppler Lidars scanned dynamic regions around the mountain, each covering a hemisphere of about 1 km. At times, Lidars were coordinated to a triple Lidar mode to form virtual towers. Swaths along preferred slopes as well as a valley and canyons were instrumented with twenty sonic flux towers (10 to 32 m high), a series of 17 HOBO® weather stations and 17 Local Energy-balance Measurements Stations (LEMS). A fiber optic distributed temperature system (DTS) was deployed over a 2 km track of the most highly instrumented slope, which provided near surface measurements on meter and seconds scales. Five surface energy budget stations were deployed for evaluating land-surface schemes used for modeling. Detecting the smallest scales of turbulence that dissipates turbulent kinetic energy were two hot-wire stations, one dedicated to near surface turbulence and the other in the surface layer. High-speed IR imagery was used to characterize the effects of shadow fronts on slope flow formation and to correlate with turbulent fluxes over the desert playa. Manned Navy Twin Otter flights with Doppler Wind Lidar (TODWL) and unmanned aerial vehicles crisscrossed GMAST vertically and horizontally during selected periods. Elaborate multiple smoke releases helped visualize flow streak lines associated with the complex mountain flow physics.

Each campaign included ten Intensive Observational Periods (IOPs) where all instruments operated in coordination. The fall study included six IOPs with quiescent fair weather, the rest with moderate and strong winds. Nine IOPs of the spring experiment had either moderate or strong winds and were associated with higher moisture levels. An ensemble of numerical modeling (WRF ensembles, NAM, and GFS models) and satellite products guided the selection of IOP days via weather briefing provided by DPG forecasters.

A quick glance at data promises possible uncovering of new sub-meso phenomena triggered by flow interactions at disparate scales and even the upscale energy transfer. Although flow surrounding Granite Peak is considered nominally simple, the canonical up and down slope/valley flows existed only for short time, only to be overshadowed by those arriving from nearby mountains, basins, canyons, ravines and gullies. Overflowing cold pools from one basin to another through gaps produced expanding ‘thermal rivers’ and distorted dipolar eddies, which can be central to corridors of fog formation, turbidity and low visibility. In particular, existing meso-scale models fail to capture essentials of these interactions, as they occur in relatively thin layers, such as fronts between flows, interfaces between layers of different densities and instabilities that affect a range flow scales. Collisions of disparate katabatic flows appeared to produce enhanced shear, sporadic turbulence and even solitary waves near the ground. Katabatic currents are ‘shaved off’ by overlying skewed flows originating from nearby topographies. At times, katabatic flows were lifted above denser currents undercutting from below, and all interactions occurred on sub-kilometer scales. Thin, extremely strong, thermally forced near surface meso-scale jets developed over the west desert playa, producing intense turbulence in the lowest levels of the atmosphere. Existing flux parameterizations in models ignore such ephemeral yet energetic episodes. Synoptic flow effects may wipe out thermal flows of exposed mountains, but they cannot penetrate those in tandem, thus leaving thermal circulation in the wakes of exposed mountains relevant. As the data processing progresses, many new phenomena and parameterizations are expected to emerge, and field investigators will work synergistically with modelers to decipher mountain terrain weather intricacies and improve their predictions.

And for now, it is clear that not even simplest, loneliest mountains in nature can act alone!