Breakpoint Analysis of MODIS Vegetarian Cover Change in Southern California Deserts

This study applies time series breakpoint analysis to look at Moderate Resolution Imaging Spectroradiometer (MODIS) data of southern California. Past studies have looked at this desert land using Landsat data in order to analyze any changes the environment has gone through due to renewable energy development or other factors. This study develops a method for utilizing structural change models to study the DRECP land area. Focusing on breakpoints, this study found that most positive breakpoints represented years with high rainfall. Additionally, sandy washes with little vegetation did not yield any breakpoint between 2000 and 2018. This study can be used as a model for analyzing structural change in vegetation and weather data for sensitive ecosystem

A First Look at Sublimation Rates in Toss Island Region, Antarctica

70% of Earth’s fresh water is held in Antarctica ice sheet. If the sheet melts, it has the potential to raise global sea levels by 190 feet (Klekociuk and Wiennecke, 2016). As the climate changes, it is imperative that to understand precipitation systems of Antarctica in order to measure and predict weather around the world. One aspect of precipitation events that we do not understand fully in Antarctica is sublimation. Data was collected from four Ott Pluvio Precipitation Gauges with Belfort Double Alter Shields placed in and around the Ross Ice Shelf from November of 2017 to present. An R program was created to analyze and visualize periods of sublimation. A sublimation event was defined as a period at least 6 hours long that had statistically significant monotonic decreasing trend based on the Mann-Kendall Test. The rate of sublimation was then estimated using a Sen’s Slope calculation. Sublimation was detected in 60 to 70 percent of summer months and 30 to 40 percent in winter months, with median summer sublimation rates from .006 to .014 mm/hr and median winter sublimation rates from .003 to .006 mm/hr. Monthly sublimation spiked in the months of December, January, and February. These initial findings on Sublimation in Antarctica can be used to analyze the relationship between sublimation and wind, humidity, and temperature. Additionally, these sublimation estimates can be used in combination with precipitation time series to find the percentage of snowfall returning to the atmosphere via sublimation

Streamlining Computational Methods in Industrial Hygiene

The Industrial Hygiene office is tasked with identifying health hazards and implementing programs to protect employees at NASA Armstrong as outlined in NPR 1800.1. Common health hazards at the center include noise, oxygen depletion, ionizing radiation, and non-ionizing radiation. Two methods are utilized for analyzing hazards: computation and surveying. Industrial hygienists employ computational methods to check their survey results, to analyze hazards where measurement is impossible, and to analyze future scenarios. Theoretical calculations provide hazard distances for industrial hygienists to avoid harmful radiation when surveying radio frequency (RF) instruments. The process of finding hazard distances for RF instruments is tedious and prone to simple computation mistakes due to the complex nature of near field and far field power density calculations for differing types of RF emitters,. To increase efficiency and accuracy of instrument analysis, a radio frequency hazard distance calculator was created. This calculator references the IEEE 95.3 guidelines for theoretical calculations of exposure fields from RF instruments. In order to keep Armstrong employees safe, the calculator selects for conservative estimates of RF hazards. These conservative estimates were verified by surveying instruments to measure actual power density. The RF hazard distance calculator efficiently produced reasonable and conservative estimates of power densities for a variety of RF emitters

The extraordinary March 2022 East Antarctica "heat" wave. Part I: observations and meteorological drivers

peer reviewe

The extraordinary March 2022 East Antarctica "heat" wave. Part II: impacts on the Antarctic ice sheet

peer reviewe

Synoptic Drivers of Atmospheric River Induced Precipitation Near Dronning Maud Land, Antarctica

This study&nbsp;uses a&nbsp;16-node self-organizing map (SOM) trained with MERRA-2 reanalysis sea-level pressure data (Gelaro et al., 2017) to identify atmospheric rivers that make landfall in Antarctica between&nbsp;30W and 30E. These SOM-defined environments are used to explore dynamic drivers of atmospheric river precipitation. This dataset includes the SOM environments of sea level pressure anomalies along with the atmospheric landfalling timesteps and the nodes each is assigned&nbsp;to.&nbsp; &nbsp; Gelaro, R., McCarty, W., Suarez, M.J., Todling, R., Molod, A., Takacs, L., Zhao, B. (2017). The modern-era retrospective analysis for research and application, version 2 (MERRA-2).&nbsp;Journal of Climate, 30(14). doi: 10.1175/JCLI-D-16-0758.1</div

Discriminators of Antarctic Atmospheric River Environments

This study uses MERRA-2 reanalysis&nbsp;(Gelaro et al., 2017) to identify discriminators of Antarctic atmospheric river (AR) environments and a subset of high-precipitation Antarctic AR environments. To do this, we identify a collection of analog environments (timesteps that feature the closest synoptic-scale environment to each AR, but no AR), a collection of landfalling Antarctic ARs, and a subset of high-impact ARs defined by highest attributable precipitaiton.&nbsp;This dataset includes the timestep, central longitude, and precipitation information for each of the timesteps in these three categories. Gelaro, R., McCarty, W., Suarez, M.J., Todling, R., Molod, A., Takacs, L., Zhao, B. (2017). The modern-era retrospective analysis for research and application, version 2 (MERRA-2).&nbsp;Journal of Climate, 30(14). doi: 10.1175/JCLI-D-16-0758.1</p

Detection of Vegetation Cover Change in Renewable Energy Development Zones of Southern California Using MODIS NDVI Time Series Analysis, 2000 to 2018

New solar energy facilities on public lands in the deserts of southern California are being monitored long-term to detect environmental impacts. For this purpose, we have developed a framework for detecting changes in vegetation cover region-wide using greenness index data sets from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor. This study focused on three sites, Joshua Tree National Park (JOTR), Mojave National Preserve (MOJA), and a proximal group of solar energy Development Focus Areas (DFAs). Three MODIS vegetation indices (VIs), the normalized difference (NDVI), enhanced (EVI), and soil-adjusted (SAVI), all at 250-m spatial resolution, were evaluated using the Breaks for Additive Season and Trend (BFAST) methodology to estimate significant time series shifts (&ldquo;breakpoints&rdquo;) in green vegetation cover, from February 2000 to May 2018. The sample cross-correlation function with local precipitation records and comparison with timing of wildfires near the study sites for breakpoint density (proportion of area with a breakpoint) showed that NDVI had the strongest response and hence greatest sensitivity to these major disturbances compared to EVI and SAVI, supporting its use over the other VIs for subsequent analysis. Time series of NDVI breakpoint change densities for individual solar energy DFAs did not have a consistent vegetation response following construction. Bootstrap-derived 95% confidence intervals show that the DFAs have significantly larger kurtosis and standard deviation in positive NDVI breakpoint distribution than protected National Park System (NPS) sites, but no significant difference appeared in the negative distribution among all sites. The inconsistent postconstruction NDVI signal and the large number of detected breakpoints across all three sites suggested that the largest shifts in greenness are tied to seasonal and total annual precipitation amounts. Further results indicated that existing site-specific conditions are the main control on vegetation response, mostly driven by the history of human disturbances in DFAs. Although the results do not support persistent breakpoints in solar energy DFAs, future work should seek to establish links between statistical significance and physical significance through ground-based studies to provide a more robust interpretation

Synoptic and planetary-scale dynamics modulate antarctic atmospheric river precipitation intensity

International audienceAlthough rare, atmospheric rivers substantially influence the interannual variability of Antarctic surface mass balance. Here we use MERRA-2 reanalysis to identify characteristics unique to atmospheric river environments by comparing (1) Analog (environments that feature high-low pressure couplets, similar to Atmospheric River environments, but no Atmospheric River), (2) Atmospheric River, and (3) Top Atmospheric River (highest precipitation) timesteps during 1980–2019 around Antarctica. We find significant differences between Atmospheric River and Analog environments including more intense and poleward-shifted mid-tropospheric geopotential height couplets as well as larger atmospheric moisture anomalies. We find similar significant enhancement in synoptic-scale dynamic drivers of Top Atmospheric Rivers compared to all Atmospheric River environments, but no significant difference in local integrated water vapor anomalies. Instead, our results highlight the importance of large-scale dynamic drivers during Top Atmospheric River timesteps, including amplified Rossby waves excited by tropical convection

Examining Atmospheric River Life Cycles in East Antarctica

International audienceDuring atmospheric river (AR) landfalls on the Antarctic ice sheet, the high waviness of the circumpolar polar jet stream allows for subtropical air masses to be advected toward the Antarctic coastline. These rare but high‐impact AR events are highly consequential for the Antarctic mass balance; yet little is known about the various atmospheric dynamical components determining their life cycle. By using an AR detection algorithm to retrieve AR landfalls at Dumont d'Urville and non‐AR analogs based on 700 hPa geopotential height, we examined what makes AR landfalls unique and studied the complete life cycle of ARs reaching Dumont d'Urville. ARs form in the mid‐latitudes/subtropics in areas of high surface evaporation, likely in response to tropical deep convection anomalies. These convection anomalies likely lead to Rossby wave trains that help amplify the upper‐tropospheric flow pattern. As the AR approaches Antarctica, condensation of isentropically lifted moisture causes latent heat release that—in conjunction with poleward warm air advection—induces geopotential height rises and anticyclonic upper‐level potential vorticity tendencies downstream. As evidenced by a blocking index, these tendencies lead to enhanced ridging/blocking that persist beyond the AR landfall time, sustaining warm air advection onto the ice sheet. Finally, we demonstrate a connection between tropopause polar vortices and mid‐latitude cyclogenesis in an AR case study. Overall, the non‐AR analogs reveal that the amplified jet pattern observed during AR landfalls is a result of enhanced poleward moisture transport and associated diabatic heating which is likely impossible to replicate without strong moisture transport