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Donna F. Tucker and Kristine S. Zentmire

Abstract

Evidence is presented to support the hypothesis that mesoscale convective complexes (MCCs) near the Rocky Mountains are more likely to form when the middle-tropospheric relative humidity is greater than average and the lower-tropospheric relative humidity is less than average. Radiosonde data for MCC events are chosen at the nearest place to first storm development and at the nearest time before first storms occurred. A sounding representing an average seasonally adjusted climatological location of orogenic MCC first storms was used to represent non-MCC days. The 500-hPa relative humidities were significantly higher for MCC events than for non-MCC days. The 700-hPa relative humidity was significantly lower for MCC events than for non-MCC days. MCC days also have somewhat less stability than non-MCC days but this factor appears to be related to higher temperatures at 500 hPa on days when the 500-hPa relative humidity is low. The values of various quantities used to assess the utility of this information for weather forecasting indicate that this method needs to be combined with other MCC forecasting methods to be useful.

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S. Baidar, S. C. Tucker, M. Beaubien, and R. M. Hardesty

Abstract

A two-look airborne Doppler wind lidar operating at the 532-nm laser wavelength, the Green Optical Autocovariance Wind Lidar (GrOAWL), was built and flown aboard the NASA WB-57 research aircraft. Flight campaign goals were to validate the instrument wind measurements and to demonstrate the two-look measurement concept proposed for spaceborne mission concepts such as the Atmospheric Transport, Hurricanes, and Extratropical Numerical Weather Prediction with the Optical Autocovariance Wind Lidar (ATHENA-OAWL) mission. The GrOAWL-measured winds were compared with collocated dropsonde measurements. Line-of-sight velocity (LOSV) measurements for the individual GrOAWL looks showed excellent agreement with dropsondes (R 2 > 0.9). The LOSV biases were very small and not statistically different from 0 m s−1 at the 95% confidence interval (−0.07 ± 0.07 m s−1 and 0.01 ± 0.07 m s−1 for look 1 and look 2, respectively). The wind speed and direction profiles retrieved by combining the two GrOAWL looks were also in very good agreement (R 2 > 0.85). An instrument performance model indicated the instrument wind measurement precision was likely lowered (uncertainty was increased) by a factor of ~3.3 during the flights relative to predicted “as built” instrument performance. The reduced performance was not observed during ground-based atmospheric testing and thus has been attributed to impacts of the harsh operating conditions of the WB-57 aircraft (high vibration, thermal gradients, and high humidity). The exercise of scaling the GrOAWL instrument performance and grid scale to space showed space-based OAWL wind measurements would yield products with precision at least as good as the GrOAWL instrument.

Open access
Tyler Tucker, Donata Giglio, Megan Scanderbeg, and Samuel S. P. Shen

Abstract

Since the mid-2000s, the Argo oceanographic observational network has provided near-real-time four-dimensional data for the global ocean for the first time in history. Internet (i.e., the “web”) applications that handle the more than two million Argo profiles of ocean temperature, salinity, and pressure are an active area of development. This paper introduces a new and efficient interactive Argo data visualization and delivery web application named Argovis that is built on a classic three-tier design consisting of a front end, back end, and database. Together these components allow users to navigate 4D data on a world map of Argo floats, with the option to select a custom region, depth range, and time period. Argovis’s back end sends data to users in a simple format, and the front end quickly renders web-quality figures. More advanced applications query Argovis from other programming environments, such as Python, R, and MATLAB. Our Argovis architecture allows expert data users to build their own functionality for specific applications, such as the creation of spatially gridded data for a given time and advanced time–frequency analysis for a space–time selection. Argovis is aimed to both scientists and the public, with tutorials and examples available on the website, describing how to use the Argovis data delivery system—for example, how to plot profiles in a region over time or to monitor profile metadata.

Open access
S. E. Nicholson, C. J. Tucker, and M. B. Ba

Many assumptions have been made about the nature and character of desertification in West Africa. This paper examines the history of this issue, reviews the current state of our knowledge concerning the meteorological aspects of desertification, and presents the results of a select group of analyses related to this question. The common notion of desertification is of an advancing “desert,” a generally irreversible anthropogenic process. This process has been linked to increased surface albedo, increased dust generation, and reduced productivity of the land. This study demonstrates that there has been no progressive change of either the Saharan boundary or vegetation cover in the Sahel during the last 16 years, nor has there been a systematic reduction of “productivity” as assessed by the water-use efficiency of the vegetation cover. While it also showed little change in surface albedo during the years analyzed, this study suggests that a change in albedo of up to 0.10% since the 1950s is conceivable.

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Sara C. Tucker, Carl S. Weimer, Sunil Baidar, and R. Michael Hardesty

Abstract

We present the motivation, instrument concept, hardware descriptions, and initial validation testing for a Doppler wind lidar (DWL) system that uses optical autocovariance (OA) in a field-widened quadrature Mach–Zehnder interferometer lidar to measure Doppler shifts from atmospheric-aerosol-backscattered laser light. We describe system architectures for three different generations of the direct-detection aerosol Optical Autocovariance Wind Lidar (OAWL) system, including the current two-line-of-sight, dual-wavelength (355 and 532 nm) airborne configuration, designed to be an airborne demonstrator for potential space-based global wind measurement applications. We provide meter-per-second-precision results from a ground-based 355-nm OAWL aerosol winds measurement validation study alongside another DWL, results from an autumn 2011 airborne validation testing performed with radar wind profiler data, and wind measurement results from airborne validation flight testing using the 532-nm wavelength in spring 2016.

Open access
Meaghan L. Guckian, Ezra M. Markowitz, Clay S. Tucker, Elsita Kiekebusch, Toni Klemm, Lindsey Middleton, Adrienne Wootten, and Michelle D. Staudinger

Abstract

Online science communities can serve as powerful platforms for advancing scientific knowledge, capacity, and outreach by increasing collaboration and information sharing among geographically distant peers, practitioners, and the public. Here, we examine the value and role of the Early Career Climate Forum (ECCF), a climate-focused online science community that is based in the United States and is dedicated to training and providing support to the next generation of climate scientists. In a survey of community users and contributors, we find that the ECCF played a unique role in providing users access to career resources as well as climate-related research and insights. Respondents also indicated that the ECCF provides them with a strong sense of community and a sense of hope for the future of climate science research. These findings highlight the importance of online science communities in shaping and supporting the next generation of scientists and practitioners working at the science–management interface on climate change issues.

Open access
L. Bounoua, G. J. Collatz, S. O. Los, P. J. Sellers, D. A. Dazlich, C. J. Tucker, and D. A. Randall

Abstract

The sensitivity of global and regional climate to changes in vegetation density is investigated using a coupled biosphere–atmosphere model. The magnitude of the vegetation changes and their spatial distribution are based on natural decadal variability of the normalized difference vegetation index (NDVI). Different scenarios using maximum and minimum vegetation cover were derived from satellite records spanning the period 1982–90.

Albedo decreased in the northern latitudes and increased in the Tropics with increased NDVI. The increase in vegetation density revealed that the vegetation’s physiological response was constrained by the limits of the available water resources. The difference between the maximum and minimum vegetation scenarios resulted in a 46% increase in absorbed visible solar radiation and a similar increase in gross photosynthetic CO2 uptake on a global annual basis. This increase caused the canopy transpiration and interception fluxes to increase and reduced those from the soil. The redistribution of the surface energy fluxes substantially reduced the Bowen ratio during the growing season, resulting in cooler and moister near-surface climate, except when soil moisture was limiting.

Important effects of increased vegetation on climate are

  • a cooling of about 1.8 K in the northern latitudes during the growing season and a slight warming during the winter, which is primarily due to the masking of high albedo of snow by a denser canopy; and

  • a year-round cooling of 0.8 K in the Tropics.

These results suggest that increases in vegetation density could partially compensate for parallel increases in greenhouse warming. Increasing vegetation density globally caused both evapotranspiration and precipitation to increase. Evapotranspiration, however, increased more than precipitation, resulting in a global soil-water deficit of about 15%. A spectral analysis on the simulated results showed that changes in the state of vegetation could affect the low-frequency modes of the precipitation distribution and might reduce its low-frequency variability in the Tropics while increasing it in northern latitudes.

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Clay S. Tucker, Jill C. Trepanier, Pamela B. Blanchard, Ed Bush, James W. Jordan, Mark J. Schafer, and John Andrew Nyman

Abstract

Environmental education is key in solving environmental problems and for producing a future workforce capable of solving issues of climate change. Over the last two decades, the Coastal Roots Program at Louisiana State University (LSU) has reached more than 26,676 K–12 students in Louisiana to teach them environmental science and has brought them to restoration sites to plant 194,336 school-grown trees and grasses. The codirectors of Coastal Roots are continually searching for opportunities to enrich the experience of teachers and students in connecting school subjects, Coastal Roots, and stewardship. In school year 2018/19, students in five local schools entered a pilot program to learn how tree-ring science informs environmental science broadly. During their scheduled restoration planting trips, students were asked to collect the following tree data: tree cores, tree height, tree diameter, tree species, and global positioning system location points. Data were given to scientists at LSU for preliminary analysis, and graphical representation of the data were shown to the students for their interpretation. Results from this program indicate that bringing students into the field and teaching them a new scientific skill improved their understanding of environmental science and their role in coastal restoration, and tree-ring data showed significant correlations to various climate parameters in Louisiana. Additionally, we find that bringing this knowledge to teachers allows the knowledge to spread for multiple generations of students. Here we present tree-ring data from this project, lessons learned during the pilot program, advantages to student-based citizen science, and recommendations for similar programs.

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Lawrence S. Jackson, Declan L. Finney, Elizabeth J. Kendon, John H. Marsham, Douglas J. Parker, Rachel A. Stratton, Lorenzo Tomassini, and Simon Tucker

Abstract

The Hadley circulation and tropical rain belt are dominant features of African climate. Moist convection provides ascent within the rain belt, but must be parameterized in climate models, limiting predictions. Here, we use a pan-African convection-permitting model (CPM), alongside a parameterized convection model (PCM), to analyze how explicit convection affects the rain belt under climate change. Regarding changes in mean climate, both models project an increase in total column water (TCW), a widespread increase in rainfall, and slowdown of subtropical descent. Regional climate changes are similar for annual mean rainfall but regional changes of ascent typically strengthen less or weaken more in the CPM. Over a land-only meridional transect of the rain belt, the CPM mean rainfall increases less than in the PCM (5% vs 14%) but mean vertical velocity at 500 hPa weakens more (17% vs 10%). These changes mask more fundamental changes in underlying distributions. The decrease in 3-hourly rain frequency and shift from lighter to heavier rainfall are more pronounced in the CPM and accompanied by a shift from weak to strong updrafts with the enhancement of heavy rainfall largely due to these dynamic changes. The CPM has stronger coupling between intense rainfall and higher TCW. This yields a greater increase in rainfall contribution from events with greater TCW, with more rainfall for a given large-scale ascent, and so favors slowing of that ascent. These findings highlight connections between the convective-scale and larger-scale flows and emphasize that limitations of parameterized convection have major implications for planning adaptation to climate change.

Open access
Declan L. Finney, John H. Marsham, David P. Rowell, Elizabeth J. Kendon, Simon O. Tucker, Rachel A. Stratton, and Lawrence S. Jackson

Abstract

Eastern Africa’s fast-growing population is vulnerable to changing rainfall and extremes. Using the first pan-African climate change simulations that explicitly model the rainfall-generating convection, we investigate both the climate change response of key mesoscale drivers of eastern African rainfall, such as sea and lake breezes, and the spatial heterogeneity of rainfall responses. The explicit model shows widespread increases at the end of the century in mean (~40%) and extreme (~50%) rain rates, whereas the sign of changes in rainfall frequency has large spatial heterogeneity (from −50% to over +90%). In comparison, an equivalent parameterized simulation has greater moisture convergence and total rainfall increase over the eastern Congo and less over eastern Africa. The parameterized model also does not capture 1) the large heterogeneity of changes in rain frequency; 2) the widespread and large increases in extreme rainfall, which result from increased rainfall per humidity change; and 3) the response of rainfall to the changing sea breeze, even though the sea-breeze change is captured. Consequently, previous rainfall projections are likely inadequate for informing many climate-sensitive decisions—for example, for infrastructure in coastal cities. We consider the physics revealed here and its implications to be relevant for many other vulnerable tropical regions, especially those with coastal convection.

Open access