scholarly journals An Investigation of the Goshen County, Wyoming, Tornadic Supercell of 5 June 2009 Using EnKF Assimilation of Mobile Mesonet and Radar Observations Collected during VORTEX2. Part II: Mesocyclone-Scale Processes Affecting Tornado Formation, Maintenance, and Decay

2016 ◽  
Vol 144 (9) ◽  
pp. 3441-3463 ◽  
Author(s):  
James Marquis ◽  
Yvette Richardson ◽  
Paul Markowski ◽  
Joshua Wurman ◽  
Karen Kosiba ◽  
...  
Keyword(s):  
Life Cycle ◽  
Ensemble Kalman Filter ◽  
Vertical Structure ◽  
Spatial Scales ◽  
Near Surface ◽  
Low Level ◽  
Structure Changes ◽  
In Situ Observations ◽  
Negatively Buoyant

Storm-scale and mesocyclone-scale processes occurring contemporaneously with a tornado in the Goshen County, Wyoming, supercell observed on 5 June 2009 during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) are examined using ensemble analyses produced by assimilating mobile radar and in situ observations into a high-resolution convection-resolving model. This paper focuses on understanding the evolution of the vertical structure of the storm, the outflow buoyancy, and processes affecting the vertical vorticity and circulation within the mesocyclone that correspond to changes in observed tornado intensity. Tornadogenesis occurs when the low-level mesocyclone is least negatively buoyant relative to the environment, possesses its largest circulation, and is collocated with the largest azimuthally averaged convergence during the analysis period. The average buoyancy, circulation, and convergence within the near-surface mesocyclone (on spatial scales resolved by the model) all decrease as the tornado intensifies and matures. The tornado and its parent low-level mesocyclone both dissipate surrounded by a weakening rear-flank downdraft. The decreasing buoyancy of parcels within the low-level mesocyclone may partly be responsible for the weakening of the updraft surrounding the tornado and decoupling of the mid- and low-level circulation. Although the supply of horizontal vorticity generated in the forward flank of the storm increases throughout the life cycle of the tornado, it is presumably less easily tilted and stretched on the mesocyclone-scale during tornado maturity owing to the disruption of the low-level updraft/downdraft structure. Changes in radar-measured tornado intensity lag those of ensemble Kalman filter (EnKF) mesocyclone vorticity and circulation.

In situ observations of Akashiwo sanguinea (Dinophyceae) displaying life cycle stages during blooms in a subtropical estuary

2017 ◽  
Vol 60 (6) ◽  
Author(s):  
Susan Badylak ◽  
Edward J. Phlips ◽  
Ashley Loren Mathews ◽  
Karen Kelley
Keyword(s):  
Life Cycle ◽  
Algal Bloom ◽  
Harmful Algal Bloom ◽  
Life Cycle Stages ◽  
Subtropical Estuary ◽  
In Situ Observations ◽  
Akashiwo Sanguinea

AbstractThis study reports on the harmful algal bloom (HAB) dinoflagellate

scholarly journals On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

2019 ◽  
Author(s):  
Étienne Vignon ◽  
Olivier Traullé ◽  
Alexis Berne
Keyword(s):  
Pressure Gradient ◽  
Vertical Structure ◽  
East Antarctica ◽  
Radiosonde Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Ice Shelves ◽  
Low Level ◽  
Humidity Profiles

Abstract. Eight years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large scale characterization of the fine scale vertical structure of the low troposphere up to 3 km of altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., Mc Murdo). At Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent- ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice-shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performances. A free simulation with the regional model Polar WRF (at a 35-km resolution) over the entire continent shows too strong and too shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an understimated coastal cold air bump and associated sea-continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East-Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth and it raises the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art climate model.

scholarly journals The impact of near-surface soil moisture assimilation at subseasonal, seasonal, and inter-annual timescales

2015 ◽  
Vol 19 (12) ◽  
pp. 4831-4844 ◽  
Author(s):  
C. Draper ◽  
R. Reichle
Keyword(s):  
Soil Moisture ◽  
Data Assimilation ◽  
Surface Soil ◽  
Root Zone ◽  
Surface Model ◽  
Surface Soil Moisture ◽  
Near Surface ◽  
In Situ Observations ◽  
The Impact

Abstract. A 9 year record of Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) soil moisture retrievals are assimilated into the Catchment land surface model at four locations in the US. The assimilation is evaluated using the unbiased mean square error (ubMSE) relative to watershed-scale in situ observations, with the ubMSE separated into contributions from the subseasonal (SMshort), mean seasonal (SMseas), and inter-annual (SMlong) soil moisture dynamics. For near-surface soil moisture, the average ubMSE for Catchment without assimilation was (1.8 × 10−3 m3 m−3)2, of which 19 % was in SMlong, 26 % in SMseas, and 55 % in SMshort. The AMSR-E assimilation significantly reduced the total ubMSE at every site, with an average reduction of 33 %. Of this ubMSE reduction, 37 % occurred in SMlong, 24 % in SMseas, and 38 % in SMshort. For root-zone soil moisture, in situ observations were available at one site only, and the near-surface and root-zone results were very similar at this site. These results suggest that, in addition to the well-reported improvements in SMshort, assimilating a sufficiently long soil moisture data record can also improve the model representation of important long-term events, such as droughts. The improved agreement between the modeled and in situ SMseas is harder to interpret, given that mean seasonal cycle errors are systematic, and systematic errors are not typically targeted by (bias-blind) data assimilation. Finally, the use of 1-year subsets of the AMSR-E and Catchment soil moisture for estimating the observation-bias correction (rescaling) parameters is investigated. It is concluded that when only 1 year of data are available, the associated uncertainty in the rescaling parameters should not greatly reduce the average benefit gained from data assimilation, although locally and in extreme years there is a risk of increased errors.

In Situ Isotopic Analysis of Uraninite Microstructures from the Oklo-Okélobondo Natural Fission Reactors, Gabon

2002 ◽  
Vol 713 ◽  
Author(s):  
Mostafa Fayek ◽  
Keld A. Jensen ◽  
Rodney C. Ewing ◽  
Lee R. Riciputi
Keyword(s):  
Spatial Resolution ◽  
Spent Nuclear Fuel ◽  
Spatial Scales ◽  
Ionization Mass ◽  
Near Surface ◽  
Chain Reactions ◽  
Isotopic Analyses ◽  
Fission Reactors

ABSTRACTUranium deposits can provide important information on the long-term performance of radioactive waste forms because uraninite (UO2+X) is similar to the UO2 in spent nuclear fuel. The Oklo-Okélobondo U-deposits, Gabon, serve as natural laboratory where the long-term (hundreds to billions of years) migration of uranium and other radionuclides can be studied over large spatial scales (nm to km). The natural fission reactors associated with the Oklo- Okélobondo U-deposits occur over a range of depths (100 to 400 m) and provide a unique opportunity to study the behavior of uraninite in near surface oxidizing environments versus more reducing conditions at depth. Previously, it has been difficult to constrain the timing of interaction between U-rich minerals and post-depositional fluids. These problems are magnified because uraninite is susceptible to alteration, it continuously self-anneals radiation damage, and because these processes are manifested at the nm to μm scale. Uranium, lead and oxygen isotopes can be used to study fluid-uraninite interaction, provided that the analyses are obtained on the micro-scale. Secondary ionization mass spectrometry (SIMS) permits in situ measurement of isotopic ratios with a spatial resolution on the scale of a few μm. Preliminary U-Pb results show that uraninite from all reactor zones are highly discordant with ages aaproaching the timing of fission chain reactions (1945±50 Ma) and resetting events at 1180±47 Ma and 898±46 Ma. Oxygen isotopic analyses show that uraninite from reactors that occur in near surface environments (δ18O= −14.4‰ to −8.5‰) have reacted more extensively with groundwater of meteoric origin relative to reactors located at greater depths (μ18O= −10.2‰ to −7.3‰). This study emphasizes the importance of using in situ high spatial resolution analysis techniques for natural analogue studies.

scholarly journals Evaluation of a Statistical Model of Cloud Vertical Structure Using Combined CloudSat and CALIPSO Cloud Layer Profiles

2010 ◽  
Vol 23 (24) ◽  
pp. 6641-6653 ◽  
Author(s):  
William B. Rossow ◽  
Yuanchong Zhang
Keyword(s):  
Statistical Model ◽  
Vertical Structure ◽  
Spatial Scales ◽  
Three Dimensional ◽  
Cloud Amount ◽  
Cloud Layer ◽  
Middle Level ◽  
Polar Regions ◽  
Total Cloud Amount ◽  
Low Level

Abstract A model of the three-dimensional distribution of clouds was developed from the statistics of cloud layer occurrence from the International Satellite Cloud Climatology Project (ISCCP) and the statistics of cloud vertical structure (CVS) from an analysis of radiosonde humidity profiles. The CVS model associates each cloud type, defined by cloud-top pressure of the topmost cloud layer and total column optical thickness, with a particular CVS. The advent of satellite cloud radar (CloudSat) and lidar [Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)] measurements (together C&C) of CVS allows for a quantitative evaluation of this statistical model. The zonal monthly-mean cloud layer distribution from the ISCCP CVS agrees with that from C&C to within 10% (when normalized to the same total cloud amount). The largest differences are an overestimate of middle-level cloudiness in winter polar regions, an overestimate of cloud-top pressures of the highest-level clouds, especially in the tropics, and an underestimate of low-level cloud amounts over southern midlatitude oceans. A more severe test of the hypothesized relationship is made by comparing CVS for individual satellite pixels. The agreement of CVS is good for isolated low-level clouds and reasonably good when the uppermost cloud layer is a high-level cloud; however, the agreement is not good when the uppermost cloud layer is a middle-level cloud, even when ISCCP correctly locates cloud top. An improved CVS model combining C&C and ISCCP may require classification at spatial scales larger than individual satellite pixels.

scholarly journals Supplementing Oscat winds with Saral Altika observations for cyclone studies

2014 ◽  
Vol XL-8 ◽  
pp. 1059-1064 ◽  
Author(s):  
K. Niharika ◽  
H. S. V. Usha Sundari ◽  
A. V. V. Prasad ◽  
E. V. S. Sita Kumari ◽  
V. K. Dadhwal ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Life Cycle ◽  
Wind Speed ◽  
Storm Surge ◽  
Disaster Management ◽  
Management Practices ◽  
In Situ Observations ◽  
Remote Sensing Techniques ◽  
Microwave Sensors

Accurate prediction of life cycle of cyclone is very critical to the disaster management practices. Since the cyclones originate over the oceans where in situ observations are limited, we have to resort to the remote sensing techniques. Both optical and microwave sensors help studying the cyclones. While scatterometer provide wind vectors, altimeters can give only wind speed. In this paper we present how altimeter measurements can supplement the scatterometer observations in determining the radius of maximum winds (RMW). Sustained maximum winds, indicator for the intensity of the cyclone, are within the eye wall of a cyclone at a distance of RMW. This parameter is also useful in predicting right time of the storm surge. In this paper we used the wind speed estimations from AltiKa, an altimeter operating at Ka band.

scholarly journals Terrain Trapped Airflows and Precipitation Variability during an Atmospheric River Event

2020 ◽  
Vol 21 (2) ◽  
pp. 355-375 ◽  
Author(s):  
Ju-Mee Ryoo ◽  
Sen Chiao ◽  
J. Ryan Spackman ◽  
Laura T. Iraci ◽  
F. Martin Ralph ◽  
...  
Keyword(s):  
Wrf Model ◽  
Wind Fields ◽  
Low Level ◽  
Atmospheric River ◽  
Gap Flow ◽  
Period 2 ◽  
Modeling Systems ◽  
In Situ Observations ◽  
Aircraft Data

AbstractWe examine thermodynamic and kinematic structures of terrain trapped airflows (TTAs) during an atmospheric river (AR) event impacting Northern California 10–11 March 2016 using Alpha Jet Atmospheric eXperiment (AJAX) aircraft data, in situ observations, and Weather and Research Forecasting (WRF) Model simulations. TTAs are identified by locally intensified low-level winds flowing parallel to the coastal ranges and having maxima over the near-coastal waters. Multiple mechanisms can produce TTAs, including terrain blocking and gap flows. The changes in winds can significantly alter the distribution, timing, and intensity of precipitation. We show here how different mechanisms producing TTAs evolve during this event and influence local precipitation variations. Three different periods are identified from the time-varying wind fields. During period 1 (P1), a TTA develops during synoptic-scale onshore flow that backs to southerly flow near the coast. This TTA occurs when the Froude number (Fr) is less than 1, suggesting low-level terrain blocking is the primary mechanism. During period 2 (P2), a Petaluma offshore gap flow develops, with flows turning parallel to the coast offshore and with Fr > 1. Periods P1 and P2 are associated with slightly more coastal than mountain precipitation. In period 3 (P3), the gap flow initiated during P2 merges with a pre-cold-frontal low-level jet (LLJ) and enhanced precipitation shifts to higher mountain regions. Dynamical mixing also becomes more important as the TTA becomes confluent with the approaching LLJ. The different mechanisms producing TTAs and their effects on precipitation pose challenges to observational and modeling systems needed to improve forecasts and early warnings of AR events.

Global In-Situ Observations of Essential Climate and Ocean Variables by the Global Drifter Program. Applications and Impacts

2020 ◽  
Author(s):  
Luca Centurioni ◽  
Verena Hormann
Keyword(s):  
North Atlantic Ocean ◽  
Spatial Scales ◽  
Data Access ◽  
Ocean Climate ◽  
The North ◽  
Free Data ◽  
Forecast Models ◽  
In Situ Observations ◽  
The Impact

<p>Accurate estimates and forecasts of physical and biogeochemical processes at the air-sea interface must rely on integrated in-situ and satellite surface observations of essential Ocean/Climate Variables (EOVs /ECVs). Such observations, when sustained over appropriate temporal and spatial scales, are particularly powerful in constraining and improving the skills, impact and value of weather, ocean and climate forecast models. The calibration and validation of satellite ocean products also rely on in-situ observations, thus creating further positive high-impact applications of observing systems designed for global sustained observations of EOV and ECVs.</p><p>The Global Drifter Program has operated uninterrupted for several decades and constitutes a particular successful example of a network of multiparametric platforms providing observations of climate, weather and oceanographic relevance (e.g. air-pressure, sea surface temperature, ocean currents). This presentation will review the requirements of sustainability of an observing system such as the GDP (i.e. cost effectiveness, peer-review of the observing methodology and of the technology, free data access and international cooperation), will present some key metrics recently used to quantify the impact of drifter observations, and will discuss two prominent examples of GDP regional observations and the transition to operations of novel platforms, such us wind and directional wave spectra drifters, in sparsely sampled regions of the Arabian Sea and of the North Atlantic Ocean.</p>

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