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L. R. JONES and W. W. GILBERT

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C. Paton-Walsh, R. L. Mittermeier, W. Bell, H. Fast, N. B. Jones, and A. Meier

Abstract

The authors report the results of an intercomparison of vertical column amounts of hydrogen chloride (HCl), hydrogen fluoride (HF), nitrous oxide (N2O), nitric acid (HNO3), methane (CH4), ozone (O3), carbon dioxide (CO2), and nitrogen (N2) derived from the spectra recorded by two ground-based Fourier transform infrared (FTIR) spectrometers operated side-by-side using the sun as a source. The procedure used to record spectra and derive vertical column amounts follows the format of previous instrument intercomparisons organized by the Network for the Detection of Atmospheric Composition Change (NDACC), formerly known as the Network for Detection of Stratospheric Change (NDSC).

For most gases the differences were typically around 3%, and in about half of the results the error bars given by the standard deviation of the measurements from each instrument did not overlap. The worst level of agreement was for HF where differences of over 5% were typical. The level of agreement achieved during this intercomparison is a little worse than that achieved in previous intercomparisons between ground-based FTIR spectrometers.

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K. L. Davidson, C. W. Fairall, P. Jones Boyle, and G. E. Schacher

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An evaluation of the ability of an integrated (slab) marine atmospheric boundary-layer (MABL) model to predict changes in the inversion and mixed-layer temperature and humidity using data from the Los Angeles-San Diego Basin is described. The model microphysics and initialization methods are evaluated separately. The Stage and Businger stratocumulus entrainment closure formulation is used. Standard radiative flux approximations (e.g., delta-Eddington) are employed with up-to-date cloud microphysical parameterizations. The assumption of well-mixed properties is relaxed to permit a constant vertical gradient that is a function of the surface flux and the entrainment rate. Initialization of the subsidence rate receives considerable attention and is analyzed using data from suitably spaced multiple stations and from a single station. Two cases, a cloud covered and a clear sky period, are examined. In both cases the island and shoreline data are from regularly reporting locations and from a research ship which moved around the region. In one case an instrumented aircraft also provided vertical temperature profiles.

Evaluation of the prediction for the cloudy sky case concentrates on the model physics. In this case, the external forcing (subsidence, surface wind and sea-surface temperature) is based on observations during the prediction period and updated every 6 h. Comparison of observations and model results illustrates the important role of both long- and shortwave radiation, and the validity of the Stage and Businger entrainment closure. The agreement is quite good for mixed-layer parameters, mixed-layer depth and the cloud base.

Evaluation of the prediction for the clear sky case emphasizes the initialization problem. Entrainment and radiative flux divergences are roughly an order of magnitude smaller in the cloud-free situation. External forcing for this case is based on data available prior to the prediction (versus updates during the prediction). Since subsidence was large during the period, the initialization was well-tested. A period when the subsidence rate was well-established from radar and acoustic remote sensing showed excellent agreement between observed and predicted values for more than 18 h of a 24 h forecast. Results during a period when subsidence was based on single-station-derived information showed reasonable agreement only during the first 12 h of a 24 h forecast. The influence of very near coastline effects is evident in the comparison of mixed-layer temperatures and humidities at the land stations.

It is concluded that existing integrated mixed-layer predictive models can, with caution, be applied to coastal prediction problems on the basis of multiple- or single-station data. Specification of the subsidence and the effects of near-coastal circulations are critical.

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Syewoon Hwang, Wendy Graham, José L. Hernández, Chris Martinez, James W. Jones, and Alison Adams

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This research quantitatively evaluated the ability of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) to reproduce observed spatiotemporal variability of precipitation in the Tampa Bay region over the 1986–2008 period. Raw MM5 model results were positively biased; therefore, the raw model precipitation outputs were bias corrected at 53 long-term precipitation stations in the region using the cumulative distribution function (CDF) mapping approach. CDF mapping effectively removed the bias in the mean daily, monthly, and annual precipitation totals and improved the RMSE of these rainfall totals. Observed daily precipitation transition probabilities were also well predicted by the bias-corrected MM5 results. Nevertheless, significant error remained in predicting specific daily, monthly, and annual total time series. After bias correction, MM5 successfully reproduced seasonal geostatistical precipitation patterns, with higher spatial variance of daily precipitation in the wet season and lower spatial variance of daily precipitation in the dry season. Bias-corrected daily precipitation fields were kriged over the study area to produce spatiotemporally distributed precipitation fields over the dense grids needed to drive hydrologic models in the Tampa Bay region. Cross validation at the 53 long-term precipitation gauges showed that kriging reproduced observed rainfall with average RMSEs lower than the RMSEs of individually bias-corrected point predictions. Results indicate that although significant error remains in predicting actual daily precipitation at rain gauges, kriging the bias-corrected MM5 predictions over a hydrologic model grid produces distributed precipitation fields with sufficient realism in the daily, seasonal, and interannual patterns to be useful for multidecadal water resource planning in the Tampa Bay region.

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Howard B. Bluestein, Eugene W. McCaul Jr., Gregory P. Byrd, Robert L. Walko, and Robert Davies-Jones

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This is a case study of deep, but narrow convective towers which split twice into right- and left-moving components in southwestern Oklahoma on 28 May 1985. Our analysis makes use of storm-intercept visual documentation, mobile soundings, surface mesonetwork data, and frequent soundings from special sites. The data show that the convective towers behaved in many respects like low-precipitation storms, having formed in an environment of large CAPE and moderately strong unidirectional shear. The observation of towers splitting even when there is no heavy precipitation at the surface implies that rain processes are not crucial to the splitting phenomenon. The tiny storms were confined to a region northeast of a surface cyclone and low-pressure area, near the intersection of the dryline and an old outflow boundary, where convective temperature was reached. Evidence is presented that the moist layer was deepened locally just prior to convective initiation, and that the deepening was related to low-level convergence associated with the westward motion of the dryline.

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José L. Hernández, Syewoon Hwang, Francisco Escobedo, April H. Davis, and James W. Jones

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This paper explored recent land use and land cover change in western central Florida, examining both socioeconomic and biophysical influences on land transformation and the impacts of that change. Between 1995 and 2006, a growth in population resulted in the conversion of agricultural areas, grasslands, and upland forests to urban areas. Additionally, the amount of extractive land uses (e.g., mining) increased by 21.8%, water reservoirs by 19.9%, and recreation areas by 13.3%. Regional climate modeling experiments suggest that the overall effects of land use change (LUC) on mesocale climates in summer days resulted in modified temperatures that were modulated by the new LU characteristics, local and synoptic atmospheric circulations, and the distance of rural and urban land uses from the shoreline. The difference between the extreme and actual LU simulations for temperature, wind speed, wind direction, and precipitation presented higher variability in the inland urbanized and rural zones. Results can be used to better understand the basic influences of LUC and urbanization on key climate parameters, and urban heat island effects in peninsular Florida under typical weather conditions.

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Roland J. Viger, Lauren E. Hay, Steven L. Markstrom, John W. Jones, and Gary R. Buell

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The potential effects of long-term urbanization and climate change on the freshwater resources of the Flint River basin were examined by using the Precipitation-Runoff Modeling System (PRMS). PRMS is a deterministic, distributed-parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land cover on streamflow and multiple intermediate hydrologic states. Precipitation and temperature output from five general circulation models (GCMs) using one current and three future climate-change scenarios were statistically downscaled for input into PRMS. Projections of urbanization through 2050 derived for the Flint River basin by the Forecasting Scenarios of Future Land-Cover (FORE-SCE) land-cover change model were also used as input to PRMS. Comparison of the central tendency of streamflow simulated based on the three climate-change scenarios showed a slight decrease in overall streamflow relative to simulations under current conditions, mostly caused by decreases in the surface-runoff and groundwater components. The addition of information about forecasted urbanization of land surfaces to the hydrologic simulation mitigated the decreases in streamflow, mainly by increasing surface runoff.

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Cynthia E. Bluteau, Rolf G. Lueck, Gregory N. Ivey, Nicole L. Jones, Jeffrey W. Book, and Ana E. Rice

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Ocean mixing has historically been estimated using Osborn’s model by measuring the rate of dissipation of turbulent kinetic energy ϵ and the background density stratification N while assuming a value of the flux Richardson number . A constant is typically assumed, despite mounting field, laboratory, and modeling evidence that varies. This challenge can be overcome by estimating the turbulent diffusivity of heat using the Osborn–Cox model. This model, however, requires measuring the rate of dissipation of thermal variance χ, which has historically been challenging, particularly in energetic flows because the high wavenumbers of the temperature gradient spectra are unresolved with current technology. To overcome this difficulty, a method is described that determines χ by spectral fitting to the inertial-convective (IC) subrange of the temperature gradient spectra. While this concept has been exploited for moored time series, particularly near the bottom boundary, it has yet to be adapted to vertical microstructure profilers such as gliders, and autonomous and ship-based vertical profilers from which there are the most measurements. By using the IC subrange, χ, and hence , can be estimated even in very energetic events—precisely the conditions requiring more field observations. During less energetic periods, the temperature gradient spectra can also be integrated to obtain χ. By combining these two techniques, microstrucure profiles at a field site known for its very energetic internal waves are analyzed. This study demonstrates that the spectral fitting approach resolves intense mixing events with . By equating the Osborn and Osborn–Cox models, indirect estimates for can also be obtained.

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D. E. Weissman, B. W. Stiles, S. M. Hristova-Veleva, D. G. Long, D. K. Smith, K. A. Hilburn, and W. L. Jones

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Measurements of global ocean surface winds made by orbiting satellite radars have provided valuable information to the oceanographic and meteorological communities since the launch of the Seasat in 1978, by the National Aeronautics and Space Administration (NASA). When Quick Scatterometer (QuikSCAT) was launched in 1999, it ushered in a new era of dual-polarized, pencil-beam, higher-resolution scatterometers for measuring the global ocean surface winds from space. A constant limitation on the full utilization of scatterometer-derived winds is the presence of isolated rain events, which affect about 7% of the observations. The vector wind sensors, the Ku-band scatterometers [NASA’s SeaWinds on the QuikSCAT and Midori-II platforms and Indian Space Research Organisation’s (ISRO’s) Ocean Satellite (Oceansat)-2], and the current C-band scatterometer [Advanced Wind Scatterometer (ASCAT), on the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)’s Meteorological Operation (MetOp) platform] all experience rain interference, but with different characteristics. Over this past decade, broad-based research studies have sought to better understand the physics of the rain interference problem, to search for methods to bypass the problem (using rain detection, flagging, and avoidance of affected areas), and to develop techniques to improve the quality of the derived wind vectors that are adversely affected by rain. This paper reviews the state of the art in rain flagging and rain correction and describes many of these approaches, methodologies, and summarizes the results.

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Hunter M. Jones, E. L. Mecray, S. D. Birkel, K. C. Conlon, P. L. Kinney, V. B. S. Silva, W. Solecki, and T. M. Surgeon Rogers
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