Genesis of Atlantic Lows Experiment NASA Electra Boundary Layer Flights Data Report

The objective of this research was to obtain high resolution measurements of the height of the Marine Atmospheric Boundary Layer (MABL) during cold air outbreaks using an Airborne Lidar System. The research was coordinated with other investigators participating in the Genesis of Atlantic Lows Experiment (GALE). An objective computerized scheme was developed to obtain the Boundary Layer Height from the Lidar Data. The algorithm was used on each of the four flight days producing a high resolution data set of the MABL height over the GALE experiment area. Plots of the retrieved MABL height as well as tabular data summaries are presented

Insight into the Thermodynamic Structure of Blowing Snow Layers in Antarctica from Dropsonde and CALIPSO Measurements

Blowing snow is a frequent and ubiquitous phenomenon over most over Antarctica. The transport and sublimation of blowing snow are important for the mass balance of the Antarctic ice sheet and the latter is a major contributor to the hydrological cycle in high latitude regions. While much is known about blowing snow from surface observations, our knowledge of the thermodynamic structure of deep blowing snow layers is lacking. Here dropsonde measurements are used to investigate the temperature, moisture and wind structure of deep blowing snow layers over Antarctica. The temperature lapse rate within the blowing snow layer is found to be at times close to dry adiabatic and on average between dry and moist adiabatic. Initiation of blowing snow causes the surface temperature to increase to a degree proportional to the depth of the blowing snow layer. The relative humidity is generally largest near the surface (but less than 100%) and decreases with height reaching a minimum near the top of the layer. These findings are at odds with accepted theory which assumes blowing snow sublimation will cool and eventually saturate the layer. The observations support the conclusion that high levels of wind shear induced turbulence causes mixing and entrainment of warmer and drier air from above the blowing snow layer which suppresses humidity and produces the observed well-mixed temperature structure within the layer. The results may have important consequences for Antarctic ice sheet mass balance and the moisture budget of the atmosphere in high latitudes

New Perspectives on Blowing Snow in Antarctica and Implications for Ice Sheet Mass Balance

Blowing snow processes commonly occur over the earth’s ice sheets and snow covered regions when near surface wind speed exceeds a threshold value. These processes play a key role in the sublimation and redistribution of snow, thereby influencing the surface mass balance. Prior field studies and modeling results have shown the importance of blowing snow sublimation and transport on the surface mass budget and hydrological cycle of high latitude regions. Until recently, most of our knowledge of blowing snow was obtained from field measurements or modeling. Recent advances in satellite remote sensing have enabled a more complete understanding of the nature of blowing snow. Using 12 years of satellite lidar data, climatology of blowing snow frequency has been compiled, showing the spatial and temporal distribution of blowing snow frequency over Antarctica. Other characteristics of blowing snow such as backscatter structure and profiles of temperature, relative humidity, and winds through the layer are explored. A new technique that uses direct measurements of blowing snow backscatter combined with model meteorological reanalysis fields to compute the magnitude of blowing snow sublimation and transport is also discussed

Observations of Antarctic Polar Stratospheric Clouds by Geoscience Laser Altimeter System (GLAS)

Polar Stratospheric Clouds (PSCs) frequently occur in the polar regions during winter and are important because they play a role in the destruction of stratospheric ozone. During late September and early October 2003, GLAS frequently observed PSCs over western Antarctica. At the peak of this activity on September 29 and 30 we investigate the vertical structure and extent, horizontal coverage and backscatter characteristics of the PSCs using the GLAS data. The PSCs were found to cover an area approximately 10 to 15 % of the size of Antarctica in a region where enhanced PSC frequency has been noted by previous PSC climatology studies. The area of PSC formation was found to coincide with the coldest temperatures in the lower stratosphere. In addition, extensive cloudiness was seen within the troposphere below the PSCs indicating that tropospheric disturbances might have played a role in their formation

The Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

Recent satellite lidar measurements of cloud properties spanning a period of five years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anti-correlation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7 and 10 percent, respectively, as year average sea ice extent has decreased by 5 to 7 percent. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Since longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice

The effect of mineral and organic nutrient input on yields and nitrogen balances in western Kenya

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Agriculture, Ecosystems & Environment 214 (2015): 10-20, doi:10.1016/j.agee.2015.08.006.Soil fertility declines constrain crop productivity on smallholder farms in sub-Saharan Africa. Government and non-government organizations promote the use of mineral fertilizer and improved seed varieties to redress nutrient depletion and increase crop yields. Similarly, rotational cropping with nitrogen (N)-fixing legume cover crops or trees is promoted to improve soil fertility and crop yields. We examined maize grain yields and partial N balances on 24 smallholder maize farms in western Kenya, where interventions have increased access to agricultural inputs and rotational legume technologies. On these farms, mineral fertilizer inputs ranged from 0 to 161 kg N ha-1 (mean = 48 kg N ha-1), and maize grain yields ranged from 1-7 tons ha-1 (mean = 3.4 t ha-1). Partial N balances ranged from large losses (-112 kg N ha-1) to large gains (93 kg N ha-1)with a mean of -3 kg N ha-1. Maize grain yields increased significantly with N inputs (from fertilizer and legumes) in 2012 but not in 2013 when rainfall was lower. Nitrogen inputs of 40 kg N ha-1 were required to produce 3 tons of maize ha-1. N balances varied both among farms and between years, highlighting the importance of tracking inputs and outputs on multiple farms over multiple years before drawing conclusions about nutrient management, soil fertility outcomes and food security. The addition of N from legume rotations was a strong predictor of grain yields and positive N balances in lower-yielding farms in both years. This suggested that legume rotations may be particularly important for buffering yields from climate variability and maintaining N balances in low rainfall years.This research was funded by an Earth Institute at Columbia University Cross-Cutting Initiative Grant, a National Science Foundation PIRE grant (IIA-0968211), and by the Bill and Melinda Gates Foundation (Gates Special Initiative Grant)

Retrievals of thick cloud optical depth from the Geoscience Laser Altimeter System (GLAS) by calibration of solar background signal

Laser beams emitted from the Geoscience Laser Altimeter System (GLAS), as well as other spaceborne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (< about 3 for GLAS) are retrieved from the reflected lidar signal. This paper presents a comprehensive study of possible retrievals of optical depth of thick clouds using solar background light and treating GLAS as a solar radiometer. To do so one must first calibrate the reflected solar radiation received by the photon-counting detectors of the GLAS 532-nm channel, the primary channel for atmospheric products. Solar background radiation is regarded as a noise to be subtracted in the retrieval process of the lidar products. However, once calibrated, it becomes a signal that can be used in studying the properties of optically thick clouds. In this paper, three calibration methods are presented: (i) calibration with coincident airborne and GLAS observations, (ii) calibration with coincident Geostationary Opera- tional Environmental Satellite (GOES) and GLAS observations of deep convective clouds, and (iii) cali- bration from first principles using optical depth of thin water clouds over ocean retrieved by GLAS active remote sensing. Results from the three methods agree well with each other. Cloud optical depth (COD) is retrieved from the calibrated solar background signal using a one-channel retrieval. Comparison with COD retrieved from GOES during GLAS overpasses shows that the average difference between the two retriev- als is 24%. As an example, the COD values retrieved from GLAS solar background are illustrated for a marine stratocumulus cloud field that is too thick to be penetrated by the GLAS laser. Based on this study, optical depths for thick clouds will be provided as a supplementary product to the existing operational GLAS cloud products in future GLAS data releases

Assessment of Cloud Screening with Apparent Surface Reflectance in Support of the ICESat-2 Mission

The separation of cloud and clear scenes is usually one of the first steps in satellite data analysis. Before deriving a geophysical product, almost every satellite mission requires a cloud mask to label a scene as either clear or cloudy through a cloud detection procedure. For clear scenes, products such as surface properties may be retrieved; for cloudy scenes, scientist can focus on studying the cloud properties. Hence the quality of cloud detection directly affects the quality of most satellite operational and research products. This is certainly true for the Ice, Cloud, and land Elevation Satellite-2 (lCESat-2), which is the successor to the ICESat-l. As a top priority mission, ICESat-2 will continue to provide measurements of ice sheets and sea ice elevation on a global scale. Studies have shown that clouds can significantly affect the accuracy of the retrieved results. For example, some of the photons (a photon is a basic unit of light) in the laser beam will be scattered by cloud particles on its way. So instead of traveling in a straight line, these photons are scattered sideways and have traveled a longer path. This will result in biases in ice sheet elevation measurements. Hence cloud screening must be done and be done accurately before the retrievals

First Satellite-detected Perturbations of Outgoing Longwave Radiation Associated with Blowing Snow Events over Antarctica

We present the first satellite-detected perturbations of the outgoing longwave radiation (OLR) associated with blowing snow events over the Antarctic ice sheet using data from Cloud-Aerosol Lidar with Orthogonal Polarization and Clouds and the Earth's Radiant Energy System. Significant cloud-free OLR differences are observed between the clear and blowing snow sky, with the sign andmagnitude depending on season and time of the day. During nighttime, OLRs are usually larger when blowing snow is present; the average difference in OLRs between without and with blowing snow over the East Antarctic Ice Sheet is about 5.2 W/m2 for the winter months of 2009. During daytime, in contrast, the OLR perturbation is usually smaller or even has the opposite sign. The observed seasonal variations and day-night differences in the OLR perturbation are consistent with theoretical calculations of the influence of blowing snow on OLR. Detailed atmospheric profiles are needed to quantify the radiative effect of blowing snow from the satellite observations

The Algorithm Theoretical Basis Document for the GLAS Atmospheric Data Products

The purpose of this document is to present a detailed description of the algorithm theoretical basis for each of the GLAS data products. This will be the final version of this document. The algorithms were initially designed and written based on the authors prior experience with high altitude lidar data on systems such as the Cloud and Aerosol Lidar System (CALS) and the Cloud Physics Lidar (CPL), both of which fly on the NASA ER-2 high altitude aircraft. These lidar systems have been employed in many field experiments around the world and algorithms have been developed to analyze these data for a number of atmospheric parameters. CALS data have been analyzed for cloud top height, thin cloud optical depth, cirrus cloud emittance (Spinhirne and Hart, 1990) and boundary layer depth (Palm and Spinhirne, 1987, 1998). The successor to CALS, the CPL, has also been extensively deployed in field missions since 2000 including the validation of GLAS and CALIPSO. The CALS and early CPL data sets also served as the basis for the construction of simulated GLAS data sets which were then used to develop and test the GLAS analysis algorithms