pinecone/core-2020-05-10-deduplication huggingface dataset:
Long-range memory in Earth's surface temperature on time scales from months to centuries

This paper is part of Lene Østvand's doctoral thesis which is available in Munin at <a href=http://hdl.handle.net/10037/6391>http://hdl.handle.net/10037/6391</a>The paper explores the hypothesis that the temporal global temperature response can be modeled as a long-range memory (LRM) stochastic process characterized by a Hurst exponent 0.5 < H≲1.0 on time scales from months to decades. The LRM is a mathematical representation of the multitude of response times associated with the various subsystems. By analysis of instrumental and reconstructed temperature records, we verify LRM on time scales from months to centuries. We employ well-known detrending methods to demonstrate that LRM increases when one goes from local and regional (H≈0.65) to global (H≈0.75) land temperature records, and LRM is highest in records strongly influenced by the ocean (H≈1.0). The increasing trend through the last century cannot be explained as an unforced LRM fluctuation, but the amplitude of the observed 60 year oscillation can be reconciled with the LRM process. We investigate statistical bias and error of the analysis methods employed, and conclude that, for these short record lengths, the error in estimated H is ±0.07 for the instrumental records. Analysis of a northern-hemisphere reconstruction confirms that the LRM-scaling prevails up to at least 250 years with H=0.9±0.1. We show that, if this reconstruction is correct, the temperature difference between the Medieval Warm Period and the Little Ice Age cannot be explained as an LRM fluctuation
The importance of time-varying forcing for QBO modulation of the atmospheric 11 year solar cycle signal

We present results from three multidecadal sensitivity experiments with time-varying solar cycle and quasi-biennial oscillation (QBO) forcings using National Center for Atmospheric Research's Whole Atmosphere Community Climate Model (WACCM3.1). The model experiments are unique compared to earlier studies as they use time-varying forcings for the solar cycle only and the QBO, both individually and combined. The results show that the annual mean solar response in the tropical upper stratosphere is independent of the presence of the QBO. The response in the middle to lower stratosphere differs depending on the presence of the QBO and the solar cycle but is statistically indistinguishable in the three experiments. The seasonal evolution of the solar and the combined solar-QBO signals reveals a reasonable agreement with observations only for the experiment in which both the solar cycle and the QBO forcing are present, suggesting that both forcings are important to generate the observed response. More stratospheric warmings occur during solar maximum and QBO west conditions. This appears to be the result of a QBO modulation of the background zonal mean wind climatology, which modifies the solar signal. Depending on the background wind, the small initial early winter solar signal in the subtropical upper stratosphere/lower mesosphere is enhanced during QBO east and diminished during QBO west conditions. This consequently influences the transfer of the solar-QBO signal during winter and results in the observed differences during late winte
Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study

Reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core-derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional. We test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the MAECHAM5-HAM aerosol-climate model. An ensemble of 70 simulations is analyzed, with SO2 injections ranging from 8.5 to 700 Tg, with eruptions in January and July. Modeled sulfate deposition flux to Antarctica shows excellent spatial correlation with ice core-derived estimates for Pinatubo and Tambora, although the comparison suggests the modeled flux to the ice sheets is 4–5 times too large. We find that Greenland and Antarctic deposition efficiencies (the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden) vary as a function of the magnitude and season of stratospheric sulfur injection. Changes in simulated sulfate deposition for large SO2 injections are connected to increases in aerosol particle size, which impact aerosol sedimentation velocity and radiative properties, the latter leading to strong dynamical changes including strengthening of the winter polar vortices, which inhibits the transport of stratospheric aerosols to high latitudes. The resulting relationship between Antarctic and Greenland volcanic sulfate deposition is nonlinear for very large eruptions, with significantly less sulfate deposition to Antarctica than to Greenland. These model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of Tambora-magnitude and larger
Retrieving Cirrus Microphysical Properties from Stellar Aureoles

The aureoles around stars caused by thin cirrus limit nighttime measurement
opportunities for ground-based astronomy but can provide information on
high-altitude ice crystals for climate research. In this paper we attempt to
demonstrate quantitatively how this works. Aureole profiles can be followed out
to ~0.2 degrees from stars and ~0.5 degrees from Jupiter. Interpretation of
diffracted starlight is similar to that for sunlight, but emphasizes larger
particles. Stellar diffraction profiles are very distinctive, typically being
approximately flat out to a critical angle followed by gradually steepening
power-law falloff with slope less steep than -3. Using the relationship between
the phase function for diffraction and the average Fourier transform of the
projected area of complex ice crystals we show that defining particle size in
terms of average projected area normal to the propagation direction of the
starlight leads to a simple, analytic approximation representing large-particle
diffraction that is nearly independent of crystal habit. A similar analytic
approximation for the diffraction aureole allows it to be separated from the
point spread function and the sky background. Multiple scattering is
deconvolved using the Hankel transform leading to the diffraction phase
function. Application of constrained numerical inversion to the phase function
then yields a solution for the particle size distribution in the range between
~50 microns and ~400 microns. Stellar aureole measurements can provide one of
the very few, as well as least expensive, methods for retrieving cirrus
microphysical properties from ground-based observations.Comment: 18 pages, 21 figures, Journal of Geophysical Research, in pres
Statistical estimations of the number of future ozone exceedances due to climate change in Europe

A statistical model to examine the potential impact of increasing future temperatures due to climate change on ozone exceedances (days with daily maximum 8 h average ≥ 60 ppb) is developed for Europe. We employ gridded observed daily maximum temperatures and hourly ozone observations from nonurban stations across Europe, together with daily maximum temperatures for 2021–2050 and 2071–2100 from three regional climate models, based on the Intergovernmental Panel on Climate Change Special Reports on Emissions Scenarios A1B scenario. A rotated principal components analysis is applied to the ozone stations yielding five principal components, which divide the study domain in five subregions. The historical ozone-temperature relationship is examined and then used to provide estimates of future ozone exceedance days under current emissions and under the assumption that this relationship will retain its main characteristics. Results suggest that increases in the upper temperature percentiles lead to statistically significant increases (95% statistical significance level) of the ozone exceedances for both future periods. The greatest average increases depending on the particular regional climate model range from 5 to 12 extra ozone days/yr for 2021–2050 and from 16 to 25 for 2071–2100, in southeast Europe. The lowest average increases range from 0 to 2 extra ozone days/yr for 2021–2050 and from 2 to 4 for 2071–2100 and are seen in northwest Europe. The simulations with the dynamical Goddard Institute of Space Studies/GEOS-CHEM climate chemistry modeling system shows decreases instead of increases in eastern Europe, higher increases in northwest Europe, whereas for the other subregions similar results to the statistical model are obtained
Modelling saltation intermittency

International audienceIn order to investigate the intermittency of the aeolian saltation, a saltation model, forced with instantaneous velocity fields, has been introduced in a Large Eddy Simulation airflow model. The coupled model is evaluated on a flat erodible surface under various wind conditions and soil particle-size distribution. It is first shown that the model is able to simulate a well-developed saltation layer in equilibrium with the turbulent flow. The main characteristics of the saltation layer and their sensitivity to wind conditions are in good agreement with previous data set. Then, the saltation intermittency is visualized through the presence of blowing sand structures near the surface, known as aeolian streamers. This is the first time that such structures are reproduced numerically. From a correlation analysis, we confirm previous thoughts that these sand structures are a visual footprint of past turbulent eddies propagating in the surface boundary layer. The streamers appear to be embedded in larger saltation structures with increasing wind conditions. The spatial scales of these streamers change with wind conditions and soil particle-size distribution. This is explained by two mechanisms: (1) the modification of eddy structures with the main characteristics of the saltation layer, and (2) the reduction of saltating particle sensitivity to the near-surface eddies with increasing wind condition and soil median particle diameter, as the eddy lifetime decreases within the saltation layer and the particle response time increases, respectively. The standard deviation of the saltation flux associated to these saltation patterns represents about 10% to 20% of the mean saltation flux
The common occurrence of highly supercooled drizzle and rain near the coastal regions of the western United States

The article of record as published may be found at http://dx.doi.org/10.1002/jgrd.50529.Highly supercooled rain and drizzle from cloud tops at  12 to  21 C down to the 0  isotherm was documented by aircraft observations in clouds over a wide range of meteorological situations under relatively pristine marine aerosol conditions. The Gulfstream-1 aircraft during the CalWater campaign in February and early March 2011 measured clouds over the coastal waters of northern California, orographically triggered convective clouds over the foothills of the Sierra Nevada, and orographic layer clouds over Yosemite National Park. Supercooled drizzle in layer clouds near Juneau, Alaska, was measured by the Wyoming King Air as part of a FAA project to study aircraft icing in this region. Low concentrations of cloud condensation nuclei (CCN) were commonly observed in all of these clouds, allowing for the formation of clouds with small concentrations of mostly large drops that coalesced into supercooled drizzle and raindrops. Another common
observation was the absence of ice nuclei (IN) and/or ice crystals in measurable concentrations, associated with persistent supercooled drizzle and rain. Average ice crystal concentrations were 0.007 l 1 at the top of convective clouds at  12 C and 0.03 l 1 in the case of layer clouds at  21 C. In combination, these two conditions of low concentrations of CCN and very few IN provide ideal conditions for the formation of highly supercooled drizzle and rain. These results help explain the anomalously high incidences of aircraft icing
at cold temperatures in U.S. west coast clouds and highlight the need to include aerosol effects when simulating aircraft icing with cloud models.California Energy CommissionU.S. Department of Energy, Office of Science, Atmospheric System Research programGrant 500-09-03
Simulated Arctic atmospheric feedbacks associated with late\ud
summer sea ice anomalies

The coupled regional climate model HIRHAM-NAOSIM is used to investigate\ud
feedbacks between September sea ice anomalies in the Arctic and atmospheric conditions in\ud
autumn and the subsequent winter. A six-member ensemble of simulations spanning the\ud
period 1949–2008 is analyzed. The results show that negative Arctic sea ice anomalies are\ud
associated with increased heat and moisture fluxes, decreased static stability, increased\ud
lower tropospheric moisture, and modified baroclinicity, synoptic activity, and atmospheric\ud
large-scale circulation. The circulation changes in the following winter display\ud
meridionalized flow but are not fully characteristic of a negative Arctic Oscillation pattern,\ud
though they do support cold winter temperatures in northern Eurasia. Internally generated\ud
climate variability causes significant uncertainty in the simulated circulation changes due to\ud
sea ice-atmosphere interactions. The simulated atmospheric feedback patterns depend\ud
strongly on the position and strength of the regional sea ice anomalies and on the analyzed\ud
time period. The strongest atmospheric feedbacks are related to sea ice anomalies in the\ud
Beaufort Sea. This work suggests that there are complex feedback mechanisms that support\ud
a statistical link between reduced September sea ice and Arctic winter circulation. However,\ud
the feedbacks depend on regional and decadal variations in the coupled\ud
atmosphere-ocean-sea ice system
An evaluation of WRF's ability to reproduce the surface wind over complex terrain based on typical circulation patterns

The performance of the Weather Research and Forecasting (WRF) model to reproduce the surface wind circulations over complex terrain is examined. The atmospheric evolution is simulated using two versions of the WRF model during an over 13year period (1992 to 2005) over a complex terrain region located in the northeast of the Iberian Peninsula. A high horizontal resolution of 2km is used to provide an accurate representation of the terrain features. The multiyear evaluation focuses on the analysis of the accuracy displayed by the WRF simulations to reproduce the wind field of the six typical wind patterns (WPs) identified over the area in a previous observational work. Each pattern contains a high number of days which allows one to reach solid conclusions regarding the model performance. The accuracy of the simulations to reproduce the wind field under representative synoptic situations, or pressure patterns (PPs), of the Iberian Peninsula is also inspected in order to diagnose errors as a function of the large-scale situation. The evaluation is accomplished using daily averages in order to inspect the ability of WRF to reproduce the surface flow as a result of the interaction between the synoptic scale and the regional topography. Results indicate that model errors can originate from problems in the initial and lateral boundary conditions, misrepresentations at the synoptic scale, or the realism of the topographic features
Horizontal structure function and vertical correlation analysis of mesoscale water vapor variability observed by airborne lidar

Analysis is presented of airborne lidar measurements of water vapor, covering a height range from 1.5 to 10.4 km, from three field campaigns (midlatitude summer, polar\ud
winter, and subtropical summer). The lidar instrument provides two-dimensional cross sections of absolute humidity, with high accuracy (errors less than 5–7%) and high\ud
vertical (� 200 m) and horizontal (� 2 km) resolution. Structure functions, i.e., statistical moments up to the fifth-order of absolute increments over a range of scales, are\ud
investigated, and power law scaling or statistical-scale invariance was found over horizontal distances from 5 to 100 km. The scaling exponents are found to take different\ud
values, depending on whether or not the observations were taken in an air mass where convective clouds were present. The exponent of the first-order structure function in\ud
nonconvective regions, H = 0.63 +- 0.10, is large indicating a smooth series with long-range correlations, in contrast to the lower value H = 0.35 +- 0.11 found in convective air masses. Correspondingly, the moisture field in the convective regime was found to be more intermittent than for the nonconvective regime, i.e., water vapor structures in convectively influenced air mass show more jump discontinuities, which could be explained by the moistening and drying effects of updrafts and downdrafts in convective air mass. Within each regime (convective or nonconvective), the values appear to be universal, with no significant dependence on the season, latitude, or height where the observations were made. Furthermore, some evidence is found that vertical\ud
correlation lengths are longer in convective air masses
Space-time variability of the rainfall over the western Mediterranean region: A statistical analysis

International audienceThis study aims at better understanding the space-time statistical properties of rain over a Mediterranean region. To this end we analyzed temporal, spatial, and spatio-temporal spectra of rain field maps provided by an X-band radar situated in the southeast part of France. The database extends from 2009 to 2012 and has a spatial and temporal resolution of 1 km<sup>2</sup> and 5 min. The analysis highlights several scaling regimes, which are interpreted in terms of meteorological structures (convective cells, mesoscale structures, and midlatitude cyclones). The analysis of spectra per month confirms the dependency of the spectral signature to the underlying meteorological process. Nevertheless, our results also reveal that for a given range of scales (20-45 min in time and 7-20 km in space), spectral slope is monthly invariant. It means that rain behaves identically, in terms of scaling, whatever the mechanism that generated it (convection, front). Moreover, spectral analysis shows that the temporal decorrelation scale is 10 days, which can possibly be related to the longest lifetime of a meteorological phenomenon in the region (i.e., about 10 days). An approach to compute the scaling anisotropy between space and time is proposed. It reveals that, over two distinct ranges of scales (7-20 km/20-45 min and 20-70 km/45 min-3 h), the scaling anisotropic coefficient is equal to 2. It also reveals that the ratio of spectral slope of 2-D angle averaged spatial spectrum versus 1-D temporal spectrum is equal to 1 over these ranges of scales. It suggests a similarity in the second-order properties (e.g., correlation) of temporal and spatial rain field. All these results are important to better understand rainfall statistical behavior and could also be used for the development of downscaling schemes and the validation of numerical weather models
Mapping the radio sky with an interferometric network of low-frequency radio receivers

The structure of the 100 kHz radio sky is determined with two interferometric networks of 10 radio receivers which are distributed over local areas of ∼1 × 1 km2 and ∼10 × 10 km2. The radio waves arrive at individual receiver pairs with small time differences which are used to determine the arrival direction of the electromagnetic waves including both the bearing and the elevation angle. The results show that the major part of the 100 kHz radio wave energy comes from the horizon at bearings which are consistent with known locations of Long Range Navigation (LORAN) transmitters. Some part of the radio wave energy arrives from the sky at elevation angles which are consistent with the first and second sky hop waves of LORAN transmissions. A minor part of the 100 kHz radio wave energy comes from lightning discharges at distances up to ∼1000 km with bearings which are consistent with lightning locations reported by the arrival time difference (ATD) lightning detection network of the UK Met Office. The angular resolution for mapping the radio sky depends on the network geometry, the instrumental timing accuracy, and on the signal-to-noise ratio of the radio waves. The resulting angular resolution of the interferometric networks used in this study is ∼1° in bearing at zero elevation and several degrees in elevation. Key Points Novel interferometric network to detect atmospheric discharges is described Radio map of the 100 kHz radio sky is measured for the first time Sky hop waves arrive at elevation angles in excellent agreement with theory
Idealized dry quasi 2-D mesoscale simulations of cold-air outbreaks\ud
over the marginal sea ice zone with fine and coarse resolution

A nonhydrostatic model (NH3D) is used for idealized dry quasi 2-D simulations of\ud
Arctic cold-air outbreaks using horizontal grid spacings between 1.25 and 60 km. Despite\ud
the idealized setup, the model results agree well with observations over Fram Strait. It is\ud
shown that an important characteristic of the flow regime during cold-air outbreaks is an\ud
ice-breeze jet (IBJ) with a maximum wind speed exceeding often the large-scale\ud
geostrophic wind speed. According to the present simulations, which agree very well with\ud
those of another nonhydrostatic mesoscale model (METRAS), the occurrence, strength,\ud
and horizontal extent L of this jet depend strongly on the external forcing and especially on\ud
the direction of the large-scale geostrophic wind relative to the orientation of the ice edge.\ud
The latter dependency is explained by the effects of the thermally induced geostrophic\ud
wind over open water and Coriolis force. It is found that coarse-resolution runs\ud
underestimate the strength of the jet. This underestimation has important consequences to\ud
the surface fluxes of heat and momentum, which are also underestimated by about\ud
10–15% on average over the region between the ice edge and 120–180 km downstream.\ud
Our results suggest that a grid spacing of about L/7 is required (about 10–30 km) to\ud
simulate the IBJ strength with an accuracy of at least 10%. Thus, the results of large-scale\ud
models as well might contain uncertainties with regard to the simulated IBJ strength which\ud
would influence the energy budget in a large region along the marginal sea ice zones
Timescale dependence of aeolian sand flux observations under atmospheric turbulence

The transport of sand in saltation is driven by the persistently unsteady stresses
exerted by turbulent winds. Based on coupled high-frequency observations of wind
velocity and sand flux on a desert dune during intermittent saltation, we show here how
observations of saltation by natural winds depend significantly on the timescale and
method used for determining shear stress and sand flux. The correlation between sand
flux and excess shear stress (stress above a threshold value) systematically improves for longer averaging timescale, T, and is better for stress determined by the law-of-the-wall versus the Reynolds stress method. Fitting parameters for the stress-flux relationship do not converge with increasing T, which may be explained by the nonstationary nature of wind velocity statistics. We show how it may be possible, based on the scale-dependent statistics of stress fluctuations, to rescale saltation flux predictions for wind observations made at different timescales. However, our observations indicate hysteresis and time lags in thresholds for initiation and cessation of saltation, which complicate threshold-based approaches to predicting sediment transport at different timescales.Ye