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Lookout America! the secret Hollywood studio at the heart of the Cold War
\"The story of the Cold War era Lookout Mountain Laboratory, or the 1352nd Photographic Group of the United States Air Force, which employed hundreds of Hollywood studio veterans. Engages with issues of the Cold War state and visual culture\"-- Provided by publisher.
Book
As Regular as Clockwork: Alexander von Humboldt, Robert de Lamanon and the Beginning of the Scientific Investigation of the Tidal Barometric Oscillation
The cause of the systematic daily march of barometric pressure in the tropics, notably the late morning and late evening peaks seen almost every day at all locations, was a puzzle that persisted through the nineteenth and much of the twentieth centuries. The efforts to explain the physics of the prominent 12-h solar tidal variation helped inspire some of the earliest developments in theoretical atmospheric dynamics and ultimately led in the 1960’s to a satisfactory dynamical theory for the atmospheric tides. These important theoretical developments followed the observational discoveries, which date to the late 18th and early 19th centuries, of the surprising character of the barometric daily march and of its resolution into solar and lunar period cycles. These important, if simple, discoveries emerged primarily from the efforts of European scientists to systematically study the environment in remote areas of the globe. The two key figures in initially advancing the scientific community’s understanding of the character of barometric tides were the great German polymath Alexander von Humboldt (1769–1859) and the French naturalist Robert de Lamanon (1752–1787), who each made their discoveries on their most famous and colorful scientific expeditions of their respective careers. This paper examines the history of the early observations of the barometric tide.
Journal Article
Improved Representation of Boundary Layer Clouds over the Southeast Pacific in ARW-WRF Using a Modified Tiedtke Cumulus Parameterization Scheme
A modified Tiedtke cumulus parameterization (CP) scheme has been implemented into the Advanced Research Weather Research and Forecasting model (ARW-WRF) to improve the representation of marine boundary layer (MBL) clouds over the southeast Pacific (SEP). A full month simulation for October 2006 was performed by using the National Centers for Environmental Prediction (NCEP) final analysis (FNL) as both the initial and lateral boundary conditions and the observed sea surface temperature (SST). The model simulation was compared with satellite observations and with results from an intense ship-based campaign of balloon soundings during 16–20 October 2006 at 20°S, 85°W. The model with the modified Tiedtke scheme successfully captured the main features of the MBL structure and low clouds over the SEP, including the geographical distribution of MBL clouds, the cloud regime transition, and the vertical structure of the MBL. The model simulation was repeated with the various CP schemes currently provided as standard options in ARW-WRF. The simulations with other CP schemes failed to reproduce the geographical distribution of cloud fraction and the observed cloud regime transition, and displayed an MBL too shallow compared to observations. The improved simulation with the modified Tiedtke scheme can be attributed to a more active parameterized shallow convection with the modified Tiedtke scheme than with the other CP schemes tested, which played a critical role in lifting the inversion base and the low cloud layer. Results from additional sensitivity experiments employing different planetary boundary layer (PBL) parameterization schemes demonstrated that the basic feature of the MBL structure and low clouds over the SEP were not particularly sensitive to the choice of the PBL scheme.
Journal Article
Weakened stratospheric quasibiennial oscillation driven by increased tropical mean upwelling
In the quasibiennial oscillation, the prevailing wind direction in the tropical stratosphere switches between easterly and westerly and back with a period of about two years; now an analysis of a suite of radiosonde wind data reveals that the amplitude of this oscillation has weakened over the past six decades, most probably as a result of increased tropical upwelling in the lower stratosphere.
Equatorial upper atmospheric wind trends
The flow in the tropical atmosphere above a height of 17 km is dominated by the quasibiennial oscillation (QBO), a transition between prevailing easterly and westerly winds with a nearly two-year period. The QBO is thought to be linked to the mean tropical upwelling, which models suggest should intensify in response to global warming. Observational support for changes in either the QBO or mean upwelling has so far been scarce. Now, Yoshio Kawatani and Kevin Hamilton analyse a suite of radiosonde wind data for the period 1953–2012 and find that the amplitude of the QBO has weakened over the past six decades, probably as a result of increased tropical upwelling in the lower stratosphere. Long-term changes in this upwelling are likely to influence projected climate-related changes in stratospheric chemistry.
The zonal wind in the tropical stratosphere switches between prevailing easterlies and westerlies with a period of about 28 months
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. In the lowermost stratosphere, the vertical structure of this quasibiennial oscillation (QBO) is linked to the mean upwelling
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, which itself is a key factor in determining stratospheric composition. Evidence for changes in the QBO have until now been equivocal, raising questions as to the extent of stratospheric circulation changes in a global warming context. Here we report an analysis of near-equatorial radiosonde observations for 1953–2012, and reveal a long-term trend of weakening amplitude in the zonal wind QBO in the tropical lower stratosphere. The trend is particularly notable at the 70-hectopascal pressure level (an altitude of about 19 kilometres), where the QBO amplitudes dropped by roughly one-third over the period. This trend is also apparent in the global warming simulations of the four models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that realistically simulate the QBO. The weakening is most reasonably explained as resulting from a trend of increased mean tropical upwelling in the lower stratosphere. Almost all comprehensive climate models have projected an intensifying tropical upwelling in global warming scenarios
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, but attempts to estimate changes in the upwelling by using observational data have yielded ambiguous, inconclusive or contradictory results
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. Our discovery of a weakening trend in the lower-stratosphere QBO amplitude provides strong support for the existence of a long-term trend of enhanced upwelling near the tropical tropopause.
Journal Article
An unexpected disruption of the atmospheric quasi-biennial oscillation
One of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind jets in the equatorial stratosphere (approximately 16 to 50 kilometers altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead, the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption, but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, although the possibility of more frequent occurrences of similar disruptions is projected for a warming climate.
Journal Article
Remote Sensing on Alfalfa as an Approach to Optimize Production Outcomes: A Review of Evidence and Directions for Future Assessments
Alfalfa (Medicago sativa L.) is one of the most relevant forage crops due to its importance for livestock. Timely harvesting is critical to secure adequate forage quality. However, farmers face challenges not only to decide the optimal harvesting time but to predict the optimum levels for both forage production and quality. Fortunately, remote sensing technologies can significantly contribute to obtaining production and quality insights, providing scalability, and supporting complex farming decision-making. Therefore, we aim to develop a systematic review of the current scientific literature to identify the current status of research in remote sensing for alfalfa and to evaluate new perspectives for enhancing prediction of both biomass and quality (herein defined as crude protein and fibers) for alfalfa. Twelve papers were included in the database from a total of 198 studies included in the initial screening process. The main findings were (i) more than two-thirds of the studies focused on predicting biomass; (ii) half of the studies used terrestrial platforms, with only 33% using drones and 17% using satellite for remote sensing; (iii) no studies have used satellites assessed alfalfa quality traits; (iv) improved biomass and quality estimations were obtained when remote sensing data was combined with environmental information; (v) due to a direct relationship between biomass and quality, modeling them algorithmically improves the accuracy of estimation as well; (vi) from spectral wavelengths, dry biomass was better estimated in regions near 398, 551, 670, 730, 780, 865, and 1077 nm, wet biomass in regions near 478, 631, 670, 730, 780, 834, 933, 1034, and 1538 nm, and quality traits identified with narrow and very specific wavelengths (e.g., 398, 461, 551, 667, 712, and 1077 nm). Our findings might serve as a foundation to guide further research and the development of handheld sensors for assessing alfalfa biomass and quality.
Journal Article
Downscaling of Climate Change in the Hawaii Region Using CMIP5 Results
The Weather Research and Forecasting (WRF) model has been configured as a regional climate model for the Hawaii region (HRCM) to assess the uncertainties associated with the pseudo–global warming (PGW) downscaling method using different warming increments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) model experiments. Results from 15-km downscaling experiments using warming increments from 10 individual CMIP5 models for the two warming scenarios representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) are compared with experiments using multimodel mean warming increments. The results show that changes in 2-m temperatures, 10-m wind speed, rainfall, water vapor path, and trade wind inversion vary significantly among the individual model experiments. This translates into large uncertainties when picking one particular CMIP5 model to provide the warming increments for dynamical downscaling in the Hawaii region. The simulations also show that, despite the large interexperiment spread, a single downscaling experiment using multimodel mean warming increments gives very similar results to the ensemble mean of downscaling experiments using warming increments obtained from 10 individual CMIP5 models. Robust changes of the projected climate by the end of the twenty-first century in the Hawaii region shown by most downscaling experiments include increasing 2-m temperatures with stronger warming at higher elevations, a large increase in precipitable water, and an increase in the number of days with a trade wind inversion (TWI). Furthermore, most experiments agree on a reduction in TWI height and an increase in the TWI strength. Uncertainties in the projected changes in rainfall and 10-m wind speed are large and there is little consensus among the individual downscaling experiments.
Journal Article
Effect of Convective Entrainment/Detrainment on the Simulation of the Tropical Precipitation Diurnal Cycle
A regional atmospheric model (RegCM) developed at the International Pacific Research Center (IPRC) is used to investigate the effect of assumed fractional convective entrainment/detrainment rates in the Tiedtke mass flux convective parameterization scheme on the simulated diurnal cycle of precipitation over the Maritime Continent region. Results are compared with observations based on 7 yr of the Tropical Rainfall Measuring Mission (TRMM) satellite measurements. In a control experiment with the default fractional convective entrainment/detrainment rates, the model produces results typical of most other current regional and global atmospheric models, namely a diurnal cycle with precipitation rates over land that peak too early in the day and with an unrealistically large diurnal range. Two sensitivity experiments were conducted in which the fractional entrainment/detrainment rates were increased in the deep and shallow convection parameterizations, respectively. Both of these modifications slightly delay the time of the rainfall-rate peak during the day and reduce the diurnal amplitude of precipitation, thus improving the simulation of precipitation diurnal cycle to some degree, but better results are obtained when the assumed entrainment/detrainment rates for shallow convection are increased to the value consistent with the published results from a large eddy simulation (LES) study. It is shown that increasing the entrainment/detrainment rates would prolong the development and reduce the strength of deep convection, thus delaying the mature phase and reducing the amplitude of the convective precipitation diurnal cycle over the land. In addition to the improvement in the simulation of the precipitation diurnal cycle, convective entrainment/detrainment rates also affect the simulation of temporal variability of daily mean precipitation and the partitioning of stratiform and convective rainfall in the model. The simulation of the observed offshore migration of the diurnal signal is realistic in some regions but is poor in some other regions. This discrepancy seems not to be related to the convective lateral entrainment/detrainment rate but could be due to the insufficient model resolution used in this study that is too coarse to resolve the complex land–sea contrast.
Journal Article
Configuration and Evaluation of the WRF Model for the Study of Hawaiian Regional Climate
The Weather Research and Forecasting (WRF) model V3.3 has been configured for the Hawaiian Islands as a regional climate model for the region (HRCM). This paper documents the model configuration and presents a preliminary evaluation based on a continuous 1-yr simulation forced by observed boundary conditions with 3-km horizontal grid spacing in the inner nested domain. The simulated vertical structure of the temperature and humidity are compared with twice-daily radiosonde observations at two stations. Generally the trade wind inversion (TWI) height and occurrence days are well represented. The simulation over the islands is compared with observations from nine surface climatological stations and a dense network of precipitation stations. The model simulation has generally small biases in the simulated surface temperature, relative humidity, and wind speed. The model realistically simulated the magnitude and geographical distribution of the mean rainfall over the Hawaiian Islands. In addition, the model simulation reproduced reasonably well the individual heavy rainfall events as seen from the time series of pentad mean rainfall averaged over island scales. Also the model reproduced the geographical variation of the mean diurnal rainfall cycle even though the observed diurnal cycle displays quite different features over different islands. Comparison with results obtained using the land surface dataset from the official release of the WRF model confirmed that the newly implemented land surface dataset generally improved the simulation of surface variables. These results demonstrate that the WRF can be a useful tool for dynamical downscaling of regional climate over the Hawaiian Islands.
Journal Article