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Robert L. Haney, Robert A. Hale, and Curtis A. Collins

Abstract

A method for extending upper ocean density observations to the deep ocean is tested using a large number of deep CTD (conductivity-temperature-depth) stations in the California Current. The specific problem considered is that of constructing the best estimate for the density profile below a certain depth D given an observed profile above that depth. For this purpose, the estimated disturbance profile is modeled as a weighted sum of empirical vertical modes (E0Fs). The EOFs are computed from the surface to 2000 m, using 126 largely independent CTP stations off Point Sur, California. Separate computations are made for the summer half-year (mid-April to mid-October) and the winter half-year (mid-October to mid-April). For each observed density profile. the EOF weights that determine the estimated profile are obtained by performing a successive least-squares fit of the disturbance density profile above D to the first N EOFs. In this study, N is taken to be 7, which is the number of EOFs that account for the “signal” in the profiles as determined by the methods of Preisendorfer et al. and Smith et al. The estimated profiles are then verified against the observed profiles to 2000 m, and the results are presented as a function of the depth D.

In general, the vertical extension method is moderately successful at estimating density fluctuations at and below 500 m from data entirely above 500 m. Observed density profiles to depths shallower than 500 m can he extended to 500 m, with a correlation that depends on the time of year as well as on the depth of the observed profile. For example, a minimum of 200 m of data is needed to perform a useful extension to 500 m, and in all cases extensions are more successful in winter than in summer. As might be expected, correlations between the estimated profiles and a seven-mode reconstruction of the observed profiles, representing the “signal” part of the observed profiles, are somewhat higher. The dynamic height of the sea surface relative to 500 m, an important integral quantity, can be estimated quite well with only 300 m of data. A practical result of this study is that data down to only 200 or 300 m, as might be acquired by a SeaSoar CTD survey, can be extended to 500 m or more using the EOF-based method with a known and useful level of skill. Tests with a small sample of independent data confirm the above results. The success of the method is attributed to the fact that in this part of the ocean the dominant EOFs represent variability in the upper ocean that is also reflected at deeper depths.

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Kevin Gallo, Robert Hale, Dan Tarpley, and Yunyue Yu

Abstract

Clear and cloudy daytime comparisons of land surface temperature (LST) and air temperature (Tair) were made for 14 stations included in the U.S. Climate Reference Network (USCRN) of stations from observations made from 2003 through 2008. Generally, LST was greater than Tair for both the clear and cloudy conditions; however, the differences between LST and Tair were significantly less for the cloudy-sky conditions. In addition, the relationships between LST and Tair displayed less variability under the cloudy-sky conditions than under clear-sky conditions. Wind speed, time of the observation of Tair and LST, season, the occurrence of precipitation at the time of observation, and normalized difference vegetation index values were all considered in the evaluation of the relationship between Tair and LST. Mean differences between LST and Tair of less than 2°C were observed under cloudy conditions for the stations, as compared with a minimum difference of greater than 2°C (and as great as 7+°C) for the clear-sky conditions. Under cloudy conditions, Tair alone explained over 94%—and as great as 98%—of the variance observed in LST for the stations included in this analysis, as compared with a range of 81%–93% for clear-sky conditions. Because of the relatively homogeneous land surface characteristics encouraged in the immediate vicinity of USCRN stations, and potential regional differences in surface features that might influence the observed relationships, additional analyses of the relationships between LST and Tair for additional regions and land surface conditions are recommended.

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Katherine L. Horgan, David M. Schultz, John E. Hales Jr., Stephen F. Corfidi, and Robert H. Johns

Abstract

A 5-yr climatology of elevated severe convective storms was constructed for 1983–87 east of the Rocky Mountains. Potential cases were selected by finding severe storm reports on the cold side of surface fronts. Of the 1826 days during the 5-yr period, 1689 (91%) had surface fronts east of the Rockies. Of the 1689 days with surface fronts, 129 (8%) were associated with elevated severe storm cases. Of the 1066 severe storm reports associated with the 129 elevated severe storm cases, 624 (59%) were hail reports, 396 (37%) were wind reports, and 46 (4%) were tornado reports. A maximum of elevated severe storm cases occurred in May with a secondary maximum in September. Elevated severe storm cases vary geographically throughout the year, with a maximum over the south-central United States in winter to a central and eastern U.S. maximum in spring and summer. A diurnal maximum of elevated severe storm cases occurred at 2100 UTC, which coincided with the diurnal maximum of hail reports. The wind reports had a broad maximum during the daytime. Because the forecasting of hail from elevated storms typically does not pose as significant a forecast challenge as severe wind for forecasters and tornadoes from elevated storms are relatively uncommon, this study focuses on the occurrence of severe wind from elevated storms. Elevated severe storm cases that produce only severe wind reports occurred roughly 5 times a year. To examine the environments associated with cases that produced severe winds only, five cases were examined in more detail. Common elements among the five cases included elevated convective available potential energy, weak surface easterlies, and shallow near-surface stable layers (less than 100 hPa thick).

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Carlyle H. Wash, Robert A. Hale, Paul H. Dobos, and Eric J. Wright

Abstract

Explosive cyclogenesis during the winter of the First Global GARP Experiment (January–February 1979) is analyzed using the revised European Centre for Medium Range Weather Forecasts (ECMWF) analyses. Explosive cyclogenesis is defined as a decrease in the sea level pressure at the rate of 1 mb h−1 for at least 12 h. Diagnostics for 23 explosively developing cases and 16 nonexplosive cases are evaluated. Parameters compared include the dry static stability, low-level relative vorticity, vorticity advection, upper-level divergence, kinematic vertical velocities, and the strength of the low-level baroclinity. These parameters are compared statistically at the initial, 12-, and 24-h time periods. Parameters for which the explosive and nonexplosive cyclone ensembles were statistically separable are the kinematic vertical velocity and the upper-level divergence and vorticity advection. The strong upper-level processes for the explosive cases at the initial time indicate the importance of upper-tropospheric features in producing the stronger vertical motions and more rapid cyclogenesis.

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Matthew S. van den Broeke, David M. Schultz, Robert H. Johns, Jeffry S. Evans, and John E. Hales

Abstract

During 9–11 November 1998 and 9–10 March 2002, two similar convective lines moved across the central and eastern United States. Both convective lines initiated over the southern plains along strong surface-based cold fronts in moderately unstable environments. Both lines were initially associated with cloud-to-ground (CG) lightning, as detected by the National Lightning Detection Network, and both events met the criteria to be classified as derechos, producing swaths of widespread damaging wind. After moving into areas of marginal, if any, instability over the upper Midwest, CG lightning production ceased or nearly ceased, although the damaging winds continued. The 9 March 2002 line experienced a second phase of frequent CG lightning farther east over the mid-Atlantic states. Analysis of these two events shows that the production of CG lightning was sensitive to the occurrence and vertical distribution of instability. Periods with frequent CG lightning were associated with sufficient instability within the lower mixed-phase region of the cloud (i.e., the temperature range approximately between −10° and −20°C), a lifting condensation level warmer than −10°C, and an equilibrium level colder than −20°C. Periods with little or no CG lightning possessed limited, if any, instability in the lower mixed-phase region. The current Storm Prediction Center guidelines for forecasting these convective lines are presented.

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Walter F. Dabberdt, Jeremy Hales, Steven Zubrick, Andrew Crook, Witold Krajewski, J. Christopher Doran, Cynthia Mueller, Clark King, Ronald N. Keener, Robert Bornstein, David Rodenhuis, Paul Kocin, Michael A. Rossetti, Fred Sharrocks, and Ellis M. Stanley Sr.

The 10th Prospectus Development Team (PDT-10) of the U.S. Weather Research Program was charged with identifying research needs and opportunities related to the short-term prediction of weather and air quality in urban forecast zones. Weather has special and significant impacts on large numbers of the U.S. population who live in major urban areas. It is recognized that urban users have different weather information needs than do their rural counterparts. Further, large urban areas can impact local weather and hydrologic processes in various ways. The recommendations of the team emphasize that human life and well-being in urban areas can be protected and enjoyed to a significantly greater degree. In particular, PDT-10 supports the need for 1) improved access to real-time weather information, 2) improved tailoring of weather data to the specific needs of individual user groups, and 3) more user-specific forecasts of weather and air quality. Specific recommendations fall within nine thematic areas: 1) development of a user-oriented weather database; 2) focused research on the impacts of visibility and icing on transportation; 3) improved understanding and forecasting of winter storms; 4) improved understanding and forecasting of convective storms; 5) improved forecasting of intense/severe lightning; 6) further research into the impacts of large urban areas on the location and intensity of urban convection; 7) focused research on the application of mesoscale forecasting in support of emergency response and air quality; 8) quantification and reduction of uncertainty in hydrological, meteorological, and air quality modeling; and 9) the need for improved observing systems. An overarching recommendation of PDT-10 is that research into understanding and predicting weather impacts in urban areas should receive increased emphasis by the atmospheric science community at large, and that urban weather should be a focal point of the U.S. Weather Research Program.

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Roger Pielke Sr., John Nielsen-Gammon, Christopher Davey, Jim Angel, Odie Bliss, Nolan Doesken, Ming Cai, Souleymane Fall, Dev Niyogi, Kevin Gallo, Robert Hale, Kenneth G. Hubbard, Xiaomao Lin, Hong Li, and Sethu Raman

The objective of this research is to determine whether poorly sited long-term surface temperature monitoring sites have been adjusted in order to provide spatially representative independent data for use in regional and global surface temperature analyses. We present detailed analyses that demonstrate the lack of independence of the poorly sited data when they are adjusted using the homogenization procedures employed in past studies, as well as discuss the uncertainties associated with undocumented station moves. We use simulation and mathematics to determine the effect of trend on station adjustments and the associated effect of trend in the reference series on the trend of the adjusted station. We also compare data before and after adjustment to the reanalysis data, and we discuss the effect of land use changes on the uncertainty of measurement.

A major conclusion of our analysis is that there are large uncertainties associated with the surface temperature trends from the poorly sited stations. Moreover, rather than providing additional independent information, the use of the data from poorly sited stations provides a false sense of confidence in the robustness of the surface temperature trend assessments.

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Rezaul Mahmood, Roger A. Pielke Sr., Kenneth G. Hubbard, Dev Niyogi, Gordon Bonan, Peter Lawrence, Richard McNider, Clive McAlpine, Andres Etter, Samuel Gameda, Budong Qian, Andrew Carleton, Adriana Beltran-Przekurat, Thomas Chase, Arturo I. Quintanar, Jimmy O. Adegoke, Sajith Vezhapparambu, Glen Conner, Salvi Asefi, Elif Sertel, David R. Legates, Yuling Wu, Robert Hale, Oliver W. Frauenfeld, Anthony Watts, Marshall Shepherd, Chandana Mitra, Valentine G. Anantharaj, Souleymane Fall, Robert Lund, Anna Treviño, Peter Blanken, Jinyang Du, Hsin-I Chang, Ronnie Leeper, Udaysankar S. Nair, Scott Dobler, Ravinesh Deo, and Jozef Syktus
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Qing Wang, Denny P. Alappattu, Stephanie Billingsley, Byron Blomquist, Robert J. Burkholder, Adam J. Christman, Edward D. Creegan, Tony de Paolo, Daniel P. Eleuterio, Harindra Joseph S. Fernando, Kyle B. Franklin, Andrey A. Grachev, Tracy Haack, Thomas R. Hanley, Christopher M. Hocut, Teddy R. Holt, Kate Horgan, Haflidi H. Jonsson, Robert A. Hale, John A. Kalogiros, Djamal Khelif, Laura S. Leo, Richard J. Lind, Iossif Lozovatsky, Jesus Planella-Morato, Swagato Mukherjee, Wendell A. Nuss, Jonathan Pozderac, L. Ted Rogers, Ivan Savelyev, Dana K. Savidge, R. Kipp Shearman, Lian Shen, Eric Terrill, A. Marcela Ulate, Qi Wang, R. Travis Wendt, Russell Wiss, Roy K. Woods, Luyao Xu, Ryan T. Yamaguchi, and Caglar Yardim

Abstract

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

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