NCAR Technical Notes

The NCAR Technical Notes Collection comprises over 500 scientific and technical reports, issued by NCAR divisions and programs, and consists of data compilations, theoretical and numerical investigations, and experimental results.


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Accelerating 'fields' by revamping the Cholesky Decomposition
Accelerating 'fields' by revamping the Cholesky Decomposition
The Geophysical Statistics project group within the Institute for Mathematics Applied to Geosciences (IMAGe) has been making use of Matrix Algebra on GPU and Multicore Architectures (MAGMA) to accelerate the Cholesky decomposition. The acceleration is motivated by a) Its frequent use in key computations in the spatial statistics R ‘fields’ package, b) Major bottleneck in ‘fields’ package execution and c) Operations involving big matrices make it suitable for parallelization. The Cholesky Decomposition was accelerated last summer using the MAGMA library. However, the performance of the accelerated version on multiple GPUs was observed to be unconventional - a) Execution time on multiple GPUs was higher in comparison to single GPU execution and b) Deep copy and in-place algorithms had opposite impacts on performance when executed on one and multiple GPUs. Our CPU and GPU profiling, conducted this summer, explains the unconventional behavior observed in the multi-GPU executions. The profiling provided insight to further accelerate the Cholesky Decomposition hierarchically– a) accelerating the underlying C function, b) reducing the function call overhead in R and c) optimizing the R environment. We were able to optimize the code and the environment to get a speedup greater than 75x (single precision) and 65x (double precision) for large matrices. We also found a potential way to improve the MAGMA functions by replacing the communications with direct device-to-device calls.
Accelerating CMIP data analysis with parallel computing in R
Accelerating CMIP data analysis with parallel computing in R
In this Technical Note we examine eight schemes for parallelizing Extreme Value Analysis (EVA) on Coupled Model Intercomparison Project data via R foreach, doParallel, and doMPI packages. We perform strong scaling studies to delineate the performance impacts of factors such as R cluster type (TCP/IP sockets and MPI), communication protocol (Ethernet, IP over InfiniBand, and MPI), loop parallelization (outer or inner loop), and approaches to reading data from the NCAR GLADE parallel filesystem. We elucidate peculiarities of R memory management and overhead associated with interprocess communication and discuss broadcast limitations of Rmpi. The best performing scheme parallelizes the outer EVA loop across latitude and reads only the subset of the data operated on in the inner loop over longitude; the different cluster types and communication protocols all perform about equally for this scheme. This configuration represents a parallel speedup of 50 with 96 R workers, and is scalable for EVA on larger problem sizes than those presented here.
Actinides in the Environment and Their Uptake by Man
Actinides in the Environment and Their Uptake by Man
The preparation of this report was carried out in the summer of 1973 as a contribution to a study entitled "Public Health Implications of a Plutonium Energy Economy," sponsored by the Energy Policy Project of the Ford Foundation. While a final report was never published, it discusses consideration of cancer risks of actinides in the environment and their uptake by man.
Aerostatic Lift of Helium and Hydrogen in the Atmosphere
Aerostatic Lift of Helium and Hydrogen in the Atmosphere
The purpose of this report is to provide a simple and accurate method of making buoyancy calculations of lift gases. A table is included which gives pertinent model atmospheric data when the use of real atmospheric data is unnecessary. The relationships among pressure, temperature, density, and height are also discussed.
Air Motions in a Rotating Spheroidal Shell
Air Motions in a Rotating Spheroidal Shell
This report comprises translations of three papers by Max Margules on atmospheric oscillations, namely "Luftbewegungen in einer rotierenden Spharoidschale bei zonaler Druckverteilung," Sitz.-Ber. kaiserl. Akad. Wissensch. Wien, Math.-Nat. C1., Abt. IIa, vol. 101, 597-626; 1892. "Luftbewegungen in einer rotierenden Spharoidschale (II. Theil), Ibid., vol. 102, 11-56, 1893 (Mit 6 Tafeln). "Luftbewegungen in einer rotierenden Spharoidschale (III. Theil)," Ibid., vol. 102, 1369-1421; 1893 (Mit 2 Tafeln). An English translation of Margules' somewhat earlier paper, "Uber die Schwingungen periodisch erwarmter Luft," Ibid., vol. 99, 205-227; 1890, which also deals with large-scale atmospheric oscillations, especially with the diurnal and semidiurnal barometric variations, has been given in "The Mechanics of the Earth's Atmosphere" by Cleveland Abbe (Smithsonian Miscell. Coll. no. 843, 1893).
Airborne Condensation Nucleus Counter User's Guide
Airborne Condensation Nucleus Counter User's Guide
This report describes the basic operating principles of the TSI Inc. Model 3760 condensation nucleus counter, the modifications necessary for high altitude, reduced pressure operation, and data reduction procedures. It is intended both as a technical guide for RAF staff and as an aid to users in understanding and interpreting the acquired data.
Aircraft and Instrumentation in Atmospheric Research
Aircraft and Instrumentation in Atmospheric Research
This catalog provides convenient and reasonably comprehensive information on aircraft and associated instrumentation used for atmospheric research in the United States. The catalog covers university, private, U.S. Government, and other aircraft and instrumentation facilities.
Airflow and Hail Growth in Supercell Storms and Some Implications for Hail Suppression
Airflow and Hail Growth in Supercell Storms and Some Implications for Hail Suppression
This paper presents evidence that the competing embryo concept is not valid for what we have termed the archetypal supercell. Multiple radar and aircraft observations of a damaging supercell hailstorm in northeastern Colorado are synthesized to show that the airflow and hail growth conformed in many respects to earlier models derived by the lead author. Some features that before had to be inferred indirectly are now substantiated and elaborated upon by direct observation. As a result of increased confidence in certain aspects of the model, implications can be made regarding the feasibility of suppressing hail by different means.
An Airplane-Mounted System for Sensing and Recording Radio Noise in Clouds
An Airplane-Mounted System for Sensing and Recording Radio Noise in Clouds
This document reports an instrumental development which solved certain problems in field research for NCAR staff scientists concerning the detection of electrification in clouds. The instrumentation and procedures described in this report were designed to detect and record radio noise from clouds during a field study in Key West, Florida, in the summer of 1964.
An Atlas of Variations in the Solar Constant Caused by Sunspot Blocking and Facular Emissions From 1874 to 1981
An Atlas of Variations in the Solar Constant Caused by Sunspot Blocking and Facular Emissions From 1874 to 1981
The purpose of this atlas is to present such a reconstruction for a period of slightly more than a century, for the use of atmospheric and solar physicists for whom a reconstruction may be of value. As stressed in later sections of this report, the atlas reconstructs only the short-term variations in S that have now been demonstrated to follow from day-to-day changes in surface solar activity. Moreover the reconstruction is based on the physically-improbable approximation of an infinite storage time within the sun: i.e., that the solar radiant flux blocked by sunspots is never released. As we point out in Section 3 and Appendix 3, however, the best observations now available fit this assumption rather well, suggesting that the storage time within the sun must be of the time scale of months or more. In time, after longer and better measurements of S from space have been accumulated the real storage time for blocked solar flux may be better defined. It is also possible that other, longer-term drifts or modulations in S., due perhaps to other solar mechanisms, will be established. In the interim, however, an atlas of the sort given here represents the best approximations that can now be given.

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