Aircraft measurements are analysed from the “First Lagrangian” of the Atlantic Stratocumulus Transition Experiment (ASTEX) from south east of the Azores Islands. In this experiment, Lagrangian strategy was used and the marine air mass, that advected southward, was followed during 12 to 14 June 1992. During the experiment, the stratocumulus clouds transitioned into thin and broken stratocumulus with cumulus cloud penetrating from below. To characterise the vertical structure in the marine boundary layer the buoyancy fluxes, the variances, the turbulent kinetic energy, the momentum fluxes and humidity fluxes were examined. The buoyancy flux profiles were used to discover the decoupling of the stratocumulus and the sub-cloud layer. Turbulence analysis for all five flights shows that the cloud layer were decoupled from the underlying layer. In the cloud layer the buoyancy production due to longwave radiative cooling at cloud top, was the main source for driving the turbulence. In the sub-cloud layer, the variances indicate wind shear to be the main generator of turbulence for the first two days. Then, as sea surface temperature increases, buoyancy produced turbulence was more pronounced. The u-, v- and w-spectra and cospectra of wθ and uw give insight into the typical eddy sizes, and how the peak wavelengths vary with height. The peak wavelengths in sub-cloud and cloud layer were larger than layer depth and u- and v-spectral peak wavelengths often larger than the peak wavelength from w-spectra. While peak wavelengths in the sub-cloud layer vary with the height above the surface, they are approximately invariant with height in the cloud layer.

Spatial variability of precipitation is examined over the state of Kentucky and surrounding areas. The study focuses on the analysis of monthly precipitation totals from the period of 1961-2000. The purpose of the study is to develop a set of indices to represent the spatial variability of the study area for a given month. Various exploratory data analysis methods such as variography, kriging, and cluster analysis were used. The study attempts to quantify the second order (local) effects of the spatial variation of precipitation as a means to provide insight into the prediction of precipitation randomness. This task can be a difficult one due to the distinction between first and second order effects being somewhat arbitrary. The study proposes that a qualitative map of mean monthly precipitation can be classified through the use of a quantitative measure. This approach allowed for the unique classification of numerous months of precipitation through the use of a standard methodology. The researcher found that trying to capture the spatial variation of precipitation with two indices is an arduous task. Months were classified based on percentiles of the variogram cloud. The data were condensed into distance bins for analysis and used for calculation of the indices. A Short Range Index (SRI) and Long Range Index (LRI) were calculated for each month. The indices were then analyzed through the use of cluster analysis. The Partioning Around Medoids (PAM) method was used for the analysis providing an average silhouette value of .32. The study found that the methods applied did not efficiently capture the spatial variability of precipitation across the study area. However, this study has provided insight into the methodologies that can be applied to investigate spatial patterns of precipitation.

This paper seeks to understand the role that the agriculture sector can play in romoting China's climate change mitigation efforts. In order to understand the history of agricultural and climate change policies in China, the beginning sections are devoted to these topics. In the following chapter,the impact of climate change on agricultural production is explored. Using research data that determine the primary sources of emissions within agriculture, and mitigation practices that have proved effective, potential GHG mitigation measures are proposed in the fourth chapter.Based on recommendations made by economists, the final chapter delineates agricultural policies that would incentive farmers to implement the GHG mitigation strategies outlined in the preceding chapter.

Thesis (M.S.)--Lehigh University, 2009. / Advisers: Stephen C. Peters; Donald P. Morris.

The aim of this study has been to derive quantitative sediment information on Amazonian rivers from photographic transparencies of Landsat multispectral scanner data covering the spectral range 0.5 to 1.1 rm. Various factors such as scattering and absorption, determining the volume reflectance of a water body are discussed with particular emphasis on the significance of particle size to Mie scattering by suspended particles. The changes in signal due to atmo~pheric conditions are.exRDined. Ratios of signals in selected spectral bands are shown to be effective in measurinG suspended sediment in individual North American water bodies suppressing atmospheric and solar elevation effects. The question of extrapolation of this technique between areas and the constraints involved are analysed. The errors involved in extracting signal values from NASA transparencies are estimated by comparing computer compatible tape and transparency derived values. Suspended sediment values are estimated for Amazonia using a calibration from North American water bodies. Comparisons with field measurements show the broad validity of this technique. Seasonal and downstream variations are investigated for some of the princip~l tributaries as are the problems of vertical and horizontal variations in the river cross sections. The Amazonian sediment values are used as part of a broad classification of Amazonian rivers including a discussion of their morphologies. Concentrations of suspended sediment estimated for the tributaries rising in the Andes and its foothills are found to be much higher than those for tributaries originating in the Brazil and Guiana Shields.

<p> Low coastal stratiform clouds (stratus, stratocumulus, and fog), referred to here as coastal low cloudiness (CLC), are a persistent seasonal feature of continental west coasts, including California. The importance of CLC ranges across fields, with applications ranging from solar resource forecasting, growth of endemic species, and heat wave expression and related health impacts. This dissertation improves our understanding of California&rsquo;s summertime CLC by describing its variability and influences on a range of scales from multidecadal to daily and continental to local. A novel achievement is the development of a new 19-year satellite-derived low cloud record. Trained on airport observations, this high resolution record plays a critical role in the description of CLC at finer spatial and shorter timescales. </p><p> Observations at coastal airports from Alaska to southern California reveal coherent interannual to interdecadal variation of CLC. The leading mode of CLC variability, accounting for nearly 40% of the total variance, and the majority of individual airports, exhibit decreasing low cloudiness from 1950 to 2012. The coherent patterns of CLC variability are organized by North Pacific Sea Surface Temperature (SST) anomalies, linked to the Pacific Decadal Oscillation (PDO). </p><p> The new satellite-derived low cloud retrieval reveals, in rich spatial texture, considerable variability in CLC within May-September. The average maximum cloudiness moves northward along the coast, from northern Baja, Mexico to northern California, from May to early August. Both component parts of lower tropospheric stability (LTS), SST and free-troposphere temperature, control this seasonal movement. The peak timing of cloudiness and daytime maximum temperatures are most closely aligned in northern California. </p><p> On weather timescales, daily CLC anomalies are most strongly related to stability anomalies to the north (climatologically upwind) of the CLC region. CLC is strongly linked to stability in northern (southern) California throughout (only in early) summer. Atmospheric rather than oceanic processes are responsible for the cloud dependence on stability at daily timescales. The spatial offset of the LTS-CLC relationship reveals the roles of advective processes, subsidence, and boundary layer characteristics. Free-tropospheric moisture additionally impacts CLC, implicating the North American monsoon as a factor affecting southern California&rsquo;s coastal climate in late summer.</p>

<p> In this study, the Weather Research and Forecasting Model (WRF) is coupled with the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA), a high complexity land surface model (LSM). Although WRF is a state-of-the-art regional atmospheric model with high spatial and temporal resolutions, the land surface schemes available in WRF are simple and lack the capability to simulate carbon dioxide, for example, the popular NOAH LSM. ACASA is a complex multilayer land surface model with interactive canopy physiology and full surface hydrological processes. It allows microenvironmental variables such as air and surface temperatures, wind speed, humidity, and carbon dioxide concentration to vary vertically. </p><p> Simulations of surface conditions as well as reference and actual evapotranspiration from WRF-ACASA and WRF-NOAH are compared with surface observations for year 2005 and 2006. Results show that the increase in complexity in the WRF-ACASA model not only maintains model accuracy, it also properly accounts for the dominant biological and physical processes describing ecosystem-atmosphere interactions that are scientifically valuable. The different complexities of physical and physiological processes in the WRF-ACASA and WRF-NOAH models also highlight the impacts of different land surface and model components on atmospheric and surface conditions. </p><p> Lastly, unlike the simple big-leaf WRF-NOAH model with no carbon dioxide simulation, the high complexity WRF-ACASA model is used to quantify the carbon dioxide exchange between the biosphere and atmosphere and to examine the importance of atmospheric carbon dioxide concentration on surface processes on a regional scale. A new carbon dioxide (COCO₂) tracer is introduced into the WRF-ACASA coupled model to allow atmospheric CO₂ concentration to vary spatially and temporally according to surface plant physiological processes. The comparison between the two model simulations with and without a COCO₂ tracer shows that the impact of atmospheric COCO₂ concentration and transportation are important, and therefore these should not be neglected when simulating COCO₂ flux at regional scales. Overall, this study shows that the high complexity WRF-ACASA model is robust and able to simulate the surface conditions and COCO₂ fluxes well across the region, particularly when given accurate surface representations. </p>

<p> Uncertainty of predicted change in precipitation frequency and intensity motivates the scientific community to better understand, quantify, and model the possible outcome of dryland ecosystems. In pulse dependent ecosystems (i.e. monsoon driven) soil moisture is tightly linked to atmospheric processes. Here, I analyze three overarching questions; Q1) <i>How does soil moisture presence or absence in a shallow or deep layer influence the surface energy budget and planetary boundary layer characteristics?,</i> Q2) <i> What is the role of vegetation on ecosystem albedo in the presence or absence of deep soil moisture?,</i> Q3) <i>Can we develop empirical relationships between soil moisture and the planetary boundary layer height to help evaluate the role of future precipitation changes in land surface atmosphere interactions? </i>. To address these questions I use a conceptual framework based on the presence or absence of soil moisture in a shallow or deep layer. I define these layers by using root profiles and establish soil moisture thresholds for each layer using four years of observations from the Santa Rita Creosote Ameriflux site. Soil moisture drydown curves were used to establish the shallow layer threshold in the shallow layer, while <i>NEE</i> (Net Ecosystem Exchange of carbon dioxide) was used to define the deep soil moisture threshold. Four cases were generated using these thresholds: Case 1, dry shallow layer and dry deep layer; Case 2, wet shallow layer and dry deep layer; Case 3, wet shallow layer and wet deep layer, and Case 4 dry shallow and wet deep layer. Using this framework, I related data from the Ameriflux site SRC (Santa Rita Creosote) from 2008 to 2012 and from atmospheric soundings from the nearby Tucson Airport; conducted field campaigns during 2011 and 2012 to measure albedo from individual bare and canopy patches that were then evaluated in a grid to estimate the influence of deep moisture on albedo via vegetation cover change; and evaluated the potential of using a two-layer bucket model and empirical relationships to evaluate the link between deep soil moisture and the planetary boundary layer height under changing precipitation regime. My results indicate that (1) the presence or absence of water in two layers plays a role in surface energy dynamics, (2) soil moisture presence in the deep layer is linked with decreased ecosystem albedo and planetary boundary layer height, (3) deep moisture sustains vegetation greenness and decreases albedo, and (4) empirical relationships are useful in modeling planetary boundary layer height from dryland ecosystems. Based on these results we argue that deep soil moisture plays an important role in land surface-atmosphere interactions. </p>

Surface observations, lake evaporation data and upper-air soundings were collected in a special data-collection effort during the months of August and September of 2004 and 2005 on an island in the middle of Great Bear Lake, Northwest Territories. For this period of the year, the late summer, when increasing variability in surface pressure starts occurring, the effect of different synoptic-scale regimes on the lake-atmosphere interface is investigated to understand the regional specificities, with comparisons to nearby stations and a high spatial and temporal resolution reanalysis model (North American Regional Reanalysis). The planetary boundary layer over the lake systematically shows typical surface and mixed layer structures but with varying depths depending on the mean lower tropospheric temperature. Inversions in the surface layer, linked with warm regimes, support deep mixed layers. Within the surface layer, during warm regimes, a superadiabatic lapse rate can support (or not) a higher-stability sublayer on top of it, in which case the mixed layer happens to be much deeper. The first mechanism for lake evaporation includes the occasional passage of synoptic-scale storm systems with both warm and cold frontal features creating strong, short-lived latent heat interactions between the lake and the atmosphere, but relatively low total amounts of evaporation. The main mechanism for extensive evaporation is a cold anticyclone allowing for significant daytime insolation. A lake-breeze circulation can then develop and provide strong-enough mesoscale winds for diurnal upward latent heat exchanges, with wind channelling into Keith Arm of the lake for strong lake-breeze onshore winds.

No description available.