pinecone/core-2020-05-10-deduplication huggingface dataset:
Remote sensing of bubble clouds in seawater

We report on the influence of submerged bubble clouds on the remote sensing
properties of water. We show that the optical effect of bubbles on radiative
transfer and on the estimate of the ocean color is significant. We present a
global map of the volume fraction of air in water derived from daily wind speed
data. This map, together with the parameterization of the microphysical
properties, shows the possible significance of bubble clouds on the albedo of
incoming solar energyComment: 17 pages, 6 Postscript figures, see also
  http://atol.ucsd.edu/~pflatau publications for related papers. Q. J. Roy.
  Met. Soc. in press 200
On the impact of high-resolution, high-frequency meteorological forcing on Denmark Strait ocean circulation

This paper quantifies and discusses the impact of high-resolution, high-frequency atmospheric forcing on the ocean circulation in the vicinity of the Denmark Strait. The approach is to force a 2 km resolution regional ocean circulation model with atmospheric states from reanalysis products that have different spatial and temporal resolutions. We use the National Center for Environmental Prediction global reanalysis data (2.5° resolution, 6-hourly output) and a specially configured regional atmospheric model (12 km resolution, hourly output). The focus is on the month-long period in winter 2007 during the Greenland Flow Distortion Experiment. Diagnostics of upper-ocean currents and mixing are sensitive to the small-scale variability in the high-resolution regional atmospheric model. The hydrographic state of the ocean model is insensitive over the month-long experiments, however. Both sea ice and the fluxes of volume, heat, and freshwater across the east Greenland shelf break and through the Denmark Strait show a moderate response to the high-resolution atmospheric forcing. The synoptic-scale atmospheric state has a large role in controlling sea ice too, while internal ocean dynamics is the dominant factor controlling the flux diagnostics. It is the high spatial resolution, not the temporal resolution, that causes these effects, with O(10 km)-scale features being most important. The sea-level wind field is responsible, with the other atmospheric fields playing relatively minor roles
An easterly tip jet off Cape Farewell, Greenland. I: Aircraft observations

An easterly tip jet event off Cape Farewell, Greenland, is described and analysed in considerable detail. In Part I of this study (this paper) comprehensive aircraft-based observations are described, while in Part II of this study numerical simulations and a dynamical analysis are presented. The easterly tip jet of 21 February 2007 took place during the Greenland Flow Distortion experiment. It resulted through the interaction of a barotropic synoptic-scale low pressure system in the central North Atlantic and the high topography of southern Greenland. In situ observations reveal a jet core at the coast with peak winds of almost 50 m s-1, about 600–800 m above the sea surface, and of 30 m s-1 at 10 m. The depth of the jet increased with wind speed from ~1500 m to ~2500 m as the peak winds increased from 30 to 50 m s-1. The jet accelerated and curved anticyclonically as it reached Cape Farewell and the end of the barrier. The easterly tip jet was associated with a tongue of cold and dry air along the coast of southeast Greenland, general cloud cover to the east, and cloud streets to the south of Cape Farewell. Precipitation was observed during the low-level components of the flight. The very high wind speeds generated a highly turbulent atmospheric boundary layer and resulted in some of the highest surface wind stresses ever observed over the ocean
Sensitivity experiments for ensemble forecasts of the extratropical transition of typhoon Tokage (2004)

The article of record as published may be located at http://dx.doi.org/10.1002/qj.527The extratropical transition (ET) of tropical cyclones often has a detrimental
impact on predictability in the vicinity of the event and downstream. Ensemble
forecasts provide an appropriatemeans by which to investigate both the uncertainty
and the dynamical development leading to the different ET scenarios. Sensitivity
experiments are presented using the European Centre for Medium-Range Weather
Forecasts (ECMWF) ensemble prediction system (EPS) to investigate different
methods of perturbing the ensemble forecast of the ET of Typhoon Tokage (2004).
During ET these perturbations have a notable impact on the ensemble spread
representing the uncertainty. Three experiments were performed: one of them
without singular vectors (SVs) targeted on the tropical cyclone, the second without
stochastic physics and the third excluding both perturbation methods.
The targeted perturbations are most important for sufficient spread in track and
intensity. Without the targeted perturbations, the analysis is not contained within
the ensemble spread. Stochastic physics leads to stronger reintensification of the
ensemble members after ET. The higher track spread leads to higher variability
in processes such as lower tropospheric latent heat release. This can be related
to a higher spread in the upper-level midlatitude flow for both perturbation
methods. A connection is drawn between the strength of ET and the modification
of the downstream midlatitude flow pattern. The uncertainty due to the targeted
perturbations propagates downstream with a Rossby wave train excited during
Tokage’s ET. For the case of stochastic physics, the uncertainty spreads to the
ridge directly downstream of the ET system but is not evident further downstream.This study was sponsored by the Office of Naval Research, Marine Meteorology Program
Reproducing cloud microphysical and irradiance measurements using three 3D cloud generators

Using three cloud generators, three-dimensional (3D) cloud fields are reproduced from microphysical cloud data measured in situ by aircraft. The generated cloud fields are used as input to a 3D radiative transfer model to calculate the corresponding fields of downward and upward irradiance, which are then compared with airborne and ground-based radiation measurements. One overcast stratocumulus scene and one broken cumulus scene were selected from the European INSPECTRO field experiment, which was held in Norwich, UK, in September 2002. With these data, the characteristics of the three different cloud reproduction techniques are assessed. Besides vertical profiles and histograms of measured and modelled liquid water content and irradiance, the horizontal structure of these quantities is examined in terms of power spectra and autocorrelation lengths. 3D radiative transfer calculations are compared with the independent pixel approximation, and their differences with respect to domain-averaged quantities and 3D fields are interpreted
An easterly tip jet off Cape Farewell, Greenland. II: Simulations and dynamics

An easterly tip jet that occurred on 21 February 2007 off Cape Farewell, Greenland, is examined. In Part I of this article aircraft observations were described. Now, in Part II, numerical simulations and an analysis of the dynamical forcing mechanisms are presented. The simulations make use of a limited-area 12 km resolution configuration of the Met Office's Unified Model. Sea-surface temperatures and sea-ice concentrations have been replaced using the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) product, addressing a boundary-layer temperature bias, while roughness lengths over sea ice have been updated, addressing a wind-speed bias. These modifications ensured a reasonably accurate simulation: generally within 1–2 K and 2–3 m s-1 when compared with dropsonde observations. A momentum-budget analysis along a curved locus through the core of the jet has been derived. Off southeast Greenland, the easterly tip jet was in cross-jet geostrophic balance, but was being accelerated downstream by an along-jet pressure gradient. Over the curved part of the locus, as the jet rounded Cape Farewell, a cross-jet residual suggests that the jet was unbalanced at the height of the jet core. This residual decreases with height so that an approximate gradient wind balance applies in the upper part of the jet. The anticyclonic curvature, characteristic of easterly tip jets, was caused by a dramatic decrease in the cross-jet pressure-gradient force at the end of the barrier, after which the jet aligned with the synoptic-scale isobars and returned to approximate geostrophic balance. The momentum budget is shown to be robust and applicable to other cases
Extension of potential predictability of Indian summer monsoon dry and wet spells in recent decades

An understanding of the limit on potential predictability is crucial for developing appropriate tools for extended-range prediction of active/break spells of the Indian summer monsoon (ISM). The global low-frequency changes in climate modulate the annual cycle of the ISM and can influence the intrinsic predictability limit of the ISM intraseasonal oscillations (ISOs). Using 104-year (1901-2004) long daily rainfall data, the change in potential predictability of active and break spells are estimated by an empirical method. It is found that the potential predictability of both active and break spells have undergone a rapid increase during the recent three decades. The potential predictability of active spells has shown an increase from one week to two weeks while that for break spells increased from two weeks to three weeks. This result is interesting and intriguing in the backdrop of recent finding that the potential predictability of monsoon weather has decreased substantially over the same period compared to earlier decades due to increased potential instability of the atmosphere. The possible role of internal dynamics and external forcing in producing this change has been explored. The changes in energy exchange between the synoptic and ISO scale and the different ISO modes as evidenced by energetics computations in frequency domain also support the increased potential predictability of ISO. Our finding provides optimism for improved and useful extended-range prediction of monsoon active and break spells
A dynamical ocean feedback mechanism for the Madden-Julian Oscillation

Composite analysis is applied to study the dynamical ocean response to Madden-Julian (MJ) events, measured by anomalies in sea surface height from the merged TOPEX/Poseidon-European Remote Sensing satellite altimetry dataset. In each of the tropical ocean basins, significant equatorial waves are forced, which are shown to modulate the sea surface temperature (SST) by 0.2-0.3 degC in the absence of strong surface heat fluxes. In the Indian Ocean there is a clear dynamical response which may play a significant role in generating later MJ events. Surface westerly winds, associated with the active phase of the Madden-Julian Oscillation (MJO), force an eastward-propagating oceanic downwelling equatorial Kelvin wave, which, on reaching the eastern boundary at Sumatra, forces reflected downwelling equatorial Rossby waves and coastal Kelvin waves. The coastal Kelvin waves propagate southwards towards northern Australia and northwards into the Bay of Bengal, and will be important for local physical, chemical and biological processes. The equatorial Rossby waves propagate westward across the Indian Ocean, arriving in the western Indian Ocean approximately 80-100 days after the initial Kelvin wave was generated. The arrival of these waves generates positive SST anomalies which leads to convection and may trigger the next-but-one MJ event, or amplify the low-frequency tail of the MJO. This constitutes a coupled feedback mechanism from the ocean dynamics onto the MJO, somewhat similar to the delayed oscillator mechanism for the El Nino Southern Oscillation
Parametrizing turbulent exchange over summer sea ice and the marginal ice zone

The article of record as published may be located at http://dx.doi.org/10.1002/qj.618The surface of the Arctic Ocean in summer is a mix of sea ice and water in both leads
and melt ponds. Here we use data collected at multiple sites during the year-long
experiment to study the SurfaceHeatBudget of the Arctic Ocean (SHEBA)to develop
a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and
sensible and latent heat over the Arctic Ocean during summer from readily measured
or modelled quantities. The distinctive aerodynamic feature of summer sea ice is
that the leads andmelt ponds create vertical ice faces that the wind can push against;
momentum transfer to the surface is thus enhanced through form drag. In effect,
summer sea ice behaves aerodynamically like themarginal ice zone, which is another
surface that consists of sea ice and water. In our bulk flux algorithm, we therefore
combine our SHEBA measurements of the neutral-stability drag coefficient at a
reference height of 10 m, CDN10, with similar measurements from marginal ice
zones that have been reported in the literature to create a unified parametrization
for CDN10 for summer sea ice and for anymarginal ice zone. This parametrization
predicts CDN10 from a second-order polynomial in ice concentration. Our bulk flux
algorithm also includes expressions for the roughness lengths for temperature and
humidity, introduces new profile stratification corrections for stable stratification,
and effectively eliminates the singularities that often occur initerativeflux algorithms
for very light winds. In summary, this new algorithm seems capable of estimating the
friction velocity u∗ (a surrogate for the momentum flux) over summer sea ice with
an absolute accuracy of 0.02–0.03 m s−1; the sensible heat flux, with an accuracy of
about 6Wm−2; and the latent heat flux, with an accuracy of 3.5Wm−2.Both NSF (award 06-11942) and the National Aeronautics and Space Administration (award NNX07AL77G) supported ELA at NorthWest Research Associates during the preparation of this manuscript, and NSF also supported POGP with award 06-12428
Two major modes of variability of the East Asian summer monsoon

We study the two primary modes of variability associated with the East Asian summer monsoon, as identified using a multivariate Empirical Orthogonal Function (EOF) analysis. The second mode is shown to be related to changes in intensity of the South Asian High at 100 hPa while, consistent with previous work, the first mode is associated with an index for the shear vorticity of the 850 hPa zonal wind over the monsoon region. We show that a linear, dry dynamical model, when driven by the diabatic heating anomalies associated with each mode, can reproduce many of the anomalous circulation features, especially for the first EOF and in the lower troposphere. The model results indicate the importance of diabatic heating anomalies over the tropical Indian Ocean in the dynamics of both modes, especially EOF-1, and illustrate the role of local diabatic feedback for intensifying the circulation anomalies; in particular, the subtropical anticyclonic anomalies that are found in the positive phase of both modes, and the circulation anomaly associated with the Meiyu/Changma/Baiu rain band. A running cross-correlation analysis shows that the second EOF is consistently linked to both the decaying and the onset phase of El Niño/Southern Oscillation (ENSO) events throughout the study period (1958-2001). We attribute the connection in the onset phase to zonal wind anomalies along the Equator in the west Pacific associated with this mode. On the other hand, a link between the first EOF and ENSO is found only in the post-1979 period. We note also the role of sea-surface temperature anomalies in the tropical Indian Ocean in the dynamics of EOF-1, and a link to the variability of the Indian summer monsoon in the case of EOF-2. Copyright © 2010 Royal Meteorological Societ
Gap flows: Results from the Mesoscale Alpine Programme

An overview of advances in the observation, modelling, forecasting, and understanding of flows through gaps achieved in the Mesoscale Alpine Programme is given. Gaps are lateral constrictions of topography (level gaps) often combined with vertical terrain changes (passes). Of the possible flow configurations, only an asymmetric one (relatively deep and slow upstream, accelerating and thinning downstream), which connects two different reservoirs on each side of the gap, is examined. The flow is strongly nonlinear, making hydraulics (reduced-gravity shallow-water theory) rather than linear theory the simplest conceptual model to describe gap flow. Results from idealized topographical and flow conditions are presented, together with gap flows through a pass in the central Alpine Wipp Valley. For a given depth of the upstream reservoir, the gap controls the mass flux through it and marks the transition from a subcritical flow state upstream to a supercritical one downstream, which eventually adjusts to the downstream reservoir in a hydraulic jump. Three gap flow prototypes were found: a classical layer one with neutral stratification and a capping inversion and two with a continuous stratification, for which a special analytical self-similar hydraulic solution exists. In all three cases, a deepening wedge of nearly mixed and stagnant air forms on top of the gap flow plunging down from the pass. The descent causes a warming and (relative) drying of the air, making gap flows a special case of föhn. Topographical variations smaller than the gap scale cause additional hydraulic jumps, flow separation, vorticity banners, gravity waves, and interactions with cold pools. Turbulent friction cannot be neglected. The climatological frequency of gap flows depends on the establishment of two different reservoirs and reaches 20% for the Wip
A mollified Ensemble Kalman filter

It is well recognized that discontinuous analysis increments of sequential
data assimilation systems, such as ensemble Kalman filters, might lead to
spurious high frequency adjustment processes in the model dynamics. Various
methods have been devised to continuously spread out the analysis increments
over a fixed time interval centered about analysis time. Among these techniques
are nudging and incremental analysis updates (IAU). Here we propose another
alternative, which may be viewed as a hybrid of nudging and IAU and which
arises naturally from a recently proposed continuous formulation of the
ensemble Kalman analysis step. A new slow-fast extension of the popular
Lorenz-96 model is introduced to demonstrate the properties of the proposed
mollified ensemble Kalman filter.Comment: 16 pages, 6 figures. Minor revisions, added algorithmic summary and
  extended appendi
Southern Hemisphere atmospheric circulation response to the El Chichon and Pinatubo eruptions in coupled climate models

We study the response of the Southern Hemisphere circulation to the 1982 eruption of El Chichon and 1991 eruption of Pinatubo volcanoes in a suite of up-to-date coupled climate models.We find a significant response in austral spring and autumn in the years following the eruptions, which consists of a stronger stratospheric polar vortex and lowered sea-level pressure over the Antarctic, both consistent with the positive phase of the Southern Annular Mode. The seasonality of the response may be explained in terms of zonal flowÃ¢Â�Â�planetary wave interactions. This dynamical response is inconsistent with the observational reanalyses in the polar stratosphere in spring, but not in the troposphere where the internal variability is large compared to the magnitude of the response
A large-eddy model for cirrus clouds with explicit aerosol and ice microphysics and Lagrangian ice particle tracking

We introduce a novel large-eddy model for cirrus clouds with explicit aerosol and ice microphysics, and validate its central components. A combined Eulerian/Lagrangian approach is used to simulate the formation and evolution of cirrus. While gas and size-resolved aerosol phases are treated over a fixed Eulerian grid similar to the dynamical and thermodynamical variables, the ice phase is treated by tracking a large number of simulation ice particles. The macroscopic properties of the ice phase are deduced from statistically analysing large samples of simulation ice particle properties. The new model system covers non-equilibrium growth of liquid supercooled aerosol particles, their homogeneous freezing, heterogeneous ice nucleation in the deposition or immersion mode, growth of ice crystals by deposition of water vapour, sublimation of ice crystals and their gravitational sedimentation, aggregation between ice crystals due to differential sedimentation, the effect of turbulent dispersion on ice particle trajectories, diabatic latent and radiative heating or cooling, and radiative heating or cooling of ice crystals. This suite of explicitly resolved physical processes enables the detailed simulation and analysis of the dynamicalÃ¢Â�Â�microphysicalÃ¢Â�Â�radiative feedbacks characteristic of cirrus.\ud
\ud
We draw special attention to the ice aggregation process which redistributes large ice crystals vertically and changes the ice particle size distributions accordingly. We find that aggregation of ice crystals is the key process to generate precipitation-sized ice crystals in stratiform cirrus. A process-oriented algorithm is developed for ice aggregation based on the trajectories and sedimentation velocities of simulation ice particles for use in the dynamically and microphysically complex, multi-dimensional large-eddy approach. By virtue of an idealized model set-up, designed to isolate the effect of aggregation on the cirrus development, we show that aggregation and its effect on the ice crystal size distribution in the model is consistent with a theoretical scaling relation, which was found to be in good agreement with in situ measurement
Upper-Tropospheric features and the Alps: An overview

One focus of the Mesoscale Alpine Programme (MAP) was the study of upper-tropospheric potential vorticity (PV) anomalies that take the form of narrow meridionally elongated troughs termed ‘PV streamers’. A systematic\ud
effort was undertaken within the MAP framework to: establish a streamer climatology, develop appropriate instrumentation and undertake a measurement programme to better ascertain their structure, study both their intrinsic dynamics and their modification by the Alps, and perform model experiments to examine their significance for numerical weather prediction.\ud
Here an overview is given of the progress made toward achieving these objectives. In particular it is shown that PV streamers translating toward the Alpine region are dynamically distinctive and constitute an identifiable precursor of and contribute seminally to heavy precipitation events on the south side of the Alps and possess rich mesoscale sub-structures that can be examined with novel water vapour absorption lidar instrumentation. It is also shown that the\ud
accurate representation of a streamer might well be a critical prerequisite for accurate quantitative prediction of mesoscale precipitation. Copyright  2007 Royal Meteorological Societ