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T. Cherubini and S. Businger

Abstract

This paper discusses the derivation of the refractive index structure function. It shows that the traditional formulation, which is based on the hydrostatic assumption, leads to increasing errors with height when compared with a formulation that is based on the potential temperature. The paper corrects a long-standing problem of extrapolating the traditional boundary layer approximation beyond its region of validity (i.e., to the upper troposphere and lower stratosphere). The new derivation may have applications in observational work to measure and seeing and in numerical modeling efforts. A preliminary analysis of the influence of the new formulation in numerical modeling of seeing suggests that impact on seeing will be small in general, because the largest contribution to seeing generally comes from the lower troposphere. However, an accurate profile is needed because other astroclimatic parameters, such as the isoplanatic angle, can suffer from the lack of accuracy at high altitude. This work may also have application in radar meteorology, since clear-air radar sensitivity depends on accurate estimation of .

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K. Squires and S. Businger

Abstract

Data from the Long-Range Lightning Detection Network (LLDN), the Tropical Rainfall Measuring Mission (TRMM) satellite, and reconnaissance aircraft are used to analyze the morphology of lightning outbreaks in the eyewalls of Hurricanes Rita and Katrina, two of the strongest storms in the Atlantic hurricane record. Each hurricane produced eyewall lightning outbreaks during the period of most rapid intensification, during eyewall replacement cycles, and during the time period that encompassed the maximum intensity for each storm.

Within the effective range of the aircraft radar, maxima in eyewall strike density were collocated with maxima in radar reflectivity. High lightning strike rates were also consistently associated with TRMM low brightness temperatures and large precipitation ice concentration (PIC) values. The strike density ratio between the eyewall region and the outer rainband region was 6:1 for Hurricane Rita and 1:1 for Hurricane Katrina. This result is in contrast to those of previous remote lightning studies, which found that outer rainbands dominated the lightning distribution. The differences are shown to be at least in part the result of the more limited range of the National Lightning Detection Network (NLDN) data used in the earlier studies. Finally, implications of the results for the use of LLDN lightning data to remotely examine changes in hurricane intensity and structural evolution are discussed.

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T. Cherubini, S. Businger, and R. Lyman

Abstract

An optical turbulence algorithm has been running operationally since April 2005 at the Mauna Kea Weather Center. The algorithm makes use of information on turbulence kinetic energy provided by a planetary boundary layer scheme available in the Pennsylvania State University–NCAR Mesoscale Model and estimates the turbulent fluctuations of the atmospheric refractive index and seeing over the summit area of Mauna Kea. To investigate the potential and limitations of the optical turbulence algorithm, one year of observed seeing data from four observatories is compared with the model forecast seeing and a statistical analysis is carried out. Sensitivity tests regarding the accuracy of the underlying numerical weather forecasts and the model’s eddy diffusivity scheme are performed. Results from a simple calibration of the optical turbulence algorithm are presented.

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Jason K. S. Ching and J. A. Businger

Abstract

The equations for horizontally homogeneous planetary boundary layer flow with constant eddy viscosity are integrated in time and height. The special case for which the direction of the pressure gradient force is a periodic function of time is studied in detail. The nondimensional number F=z(4Kt)−½ is seen to be the proper scale which describes the flow response to the boundary layer.

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S. Businger, R. Johnson, and R. Talbot

This paper provides an overview of the trials and successes in the development of an autonomous balloon instrument platform (smart balloon) and reviews scientific insights gained through its employment as a marker in a Lagrangian strategy during recent field experiments. The smart balloons are designed and constructed at the National Oceanic and Atmospheric Administration Air Resources Laboratory Field Research Division in collaboration with the University of Hawaii. In a 2004 field deployment a smart balloon carrying a miniature ozone sensor successfully crossed the Atlantic Ocean from Long Island, New York, to the African coast of Morocco. Significant progress has been made through field experiments such as this in our understanding of the relationships between the evolution of marine boundary layers and the chemistry of aerosol and gaseous constituents in clean and polluted air masses. Innovation in design and advances in instrument and communication technology have opened a dramatic new range of applications for the smart balloon in atmospheric research, including, for example, the interesting prospect of making observations very near the ocean surface in hurricanes and typhoons, which are not possible with research aircraft.

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T. Cherubini, S. Businger, C. Velden, and R. Ogasawara

Abstract

Tropospheric motions can be inferred from geostationary satellites by tracking clouds and water vapor in sequential imagery. These atmospheric motion vectors (AMV) have been operationally assimilated into global models for the past three decades, with positive forecast impacts. This paper presents results from a study to assess the impact of AMV derived from Geostationary Operational Environmental Satellite (GOES) imagery on mesoscale forecasts over the conventional data-poor central North Pacific region. These AMV are derived using the latest automated processing methodologies by the University of Wisconsin—Cooperative Institute for Meteorological Satellite Studies (CIMSS). For a test case, a poorly forecast subtropical cyclone (kona low) that occurred over Hawaii on 23–27 February 1997 was chosen. The Local Analysis and Prediction System (LAPS) was used to assimilate GOES-9 AMV data and to produce fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) initial conditions. The satellite wind assimilation is carried out on the 27-km-resolution domain covering the central Pacific area. The MM5 was run with three two-way nested domains (27, 9, and 3 km), with the innermost domain moving with the kona low. The AMV data are found to influence the cyclone’s development, improving the prediction of the cyclone’s central pressure and the track of the low’s center. Since September 2003, GOES-10 AMV data have been routinely accessed from CIMSS in real time and assimilated into the University of Hawaii (UH) LAPS, providing high-resolution initial conditions for twice-daily runs of MM5 at the Mauna Kea Weather Center collocated at the UH. It is found that the direct assimilation of AMV data into LAPS has a positive impact on the forecast accuracy of the UH LAPS/MM5 operational forecasting system when validated with observations in Hawaii. The implications of the results are discussed.

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S. E. Larsen, F. W. Weller, and J. A. Businger

Abstract

A continuous wave sonic anemometer-thermometer has been developed for simultaneous measurements of vertical velocity and temperature. The phase angle fluctuations are detected by means of a monolithic integrated phase-locked loop, the latter feature providing for inexpensive and accurate electronics. The principle is described and discussed.

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T. Cherubini, S. Businger, R. Lyman, and M. Chun

Abstract

Atmospheric turbulence is a primary concern for astronomers. Turbulence causes amplitude and phase fluctuations in electromagnetic waves propagating through the atmosphere, constraining the maximum telescope resolution and resulting in telescope image degradation. Astronomical parameters that quantify these effects are generically referred to as seeing. Adaptive optics (AO) is used to reduce image degradation associated with optical turbulence. However, to optimize AO, knowledge of the vertical profile of turbulence and overall (integrated) seeing is needed. In this paper, an optical turbulence algorithm is described that makes use of the information on turbulence kinetic energy provided by a planetary boundary layer scheme available in the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Optical turbulence data collected on Mauna Kea during the 2002 site monitoring campaign are used to validate the algorithm, which has been implemented in operational runs of MM5 at the Mauna Kea Weather Center.

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S. F. Zhang, J. C. Wyngaard, J. A. Businger, and S. P. Oncley

Abstract

A new sonic anemometer, called the U.W. sonic anemometer, has been designed to minimize the flow distortion due to the transducer wakes. We present a general analytical model for calculating the effect of these transducer wakes on measured velocity spectra, and show that the effects in the U.W. sonic anemometer are indeed less than in conventional arrays. We suggest a method of correcting for the errors caused by the transducer wakes.

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S. Businger, R. McLaren, R. Ogasawara, D. Simons, and R. J. Wainscoat

The summit of Mauna Kea is arguably the best site on Earth for astronomical observations and the capital investment in telescopes on Mauna Kea has exceeded $600 million. The success of astronomical observations on Mauna Kea is strongly influenced by weather conditions. During prevailing clear periods, astronomical observing quality varies substantially due to changes in the vertical profiles of temperature, wind, moisture, and turbulence. Cloud and storm systems occasionally cause adverse or even hazardous conditions. To facilitate the best possible use of good atmospheric conditions and to support operation safety on the 4200-m mountain summit, a new interdisciplinary research program has been initiated that provides custom weather forecasts/nowcasts and meteorological data to the Mauna Kea Observatories. An operational mesoscale numerical modeling effort provides crucial forecast guidance for astronomical image quality, or seeing, during prevalent fair weather and for adverse weather. Of the existing telescopes on Mauna Kea, several commonly have multiple instruments or detectors mounted simultaneously, increasing the observational choices and thereby also increasing the utility of the custom weather forecast products provided by the newly established Mauna Kea Weather Center. Summit temperature forecasts allow mirrors to be set to the ambient temperature to reduce image degradation. Precipitable water forecasts allow infrared and submillimeter observations to be prioritized according to atmospheric opacity. Forecasts of adverse weather protect the safety of personnel, mitigate the hazard to telescope facilities, and allow for scheduling of maintenance when observing is impaired by cloud. This paper provides an overview of the unique forecast requirements and challenges faced by Mauna Kea weather forecasters. Progress toward meeting these challenges and opportunities for future research are discussed.

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