bluuebunny/crossref_metadata_2025 huggingface dataset:
Radar Rain-Rate Estimators and Their Variability due to Rainfall Type: An Assessment Based on Hydrometeorology Testbed Data from the Southeastern United States
Authors: Matrosov Sergey Y. , Cifelli Robert , Neiman Paul J. , White Allen B.
Published: March 2016

S-band profiling (S-PROF) radar measurements from different southeastern U.S. Hydrometeorology Testbed sites indicated a frequent occurrence of rain that did not exhibit radar bright band (BB) and was observed outside the periods of deep-convective precipitation. This common nonbrightband (NBB) rain contributes ~15%–20% of total accumulation and is not considered as a separate rain type by current precipitation-segregation operational radar-based schemes, which separate rain into stratiform, convective, and, sometimes, tropical types. Collocated with S-PROF, disdrometer measurements showed that drop size distributions (DSDs) of NBB rain have much larger relative fractions of smaller drops when compared with those of BB and convective rains. Data from a year of combined DSD and rain-type observations were used to derive S-band-radar estimators of rain rate R, including those based on traditional reflectivity Ze and ones that also use differential reflectivity ZDR and specific differential phase KDP. Differences among same-type estimators for mostly stratiform BB and deep-convective rain were relatively minor, but estimators derived for the common NBB rain type were distinct. Underestimations in NBB rain-rate retrievals derived using other rain-type estimators (e.g., those for BB or convective rain or default operational radar estimators) for the same values of radar variables can be on average about 40%, although the differential phase-based estimators are somewhat less susceptible to DSD details. No significant differences among the estimators for the same rain type derived using DSDs from different observational sites were present despite significant separation and differing terrain. Identifying areas of common NBB rain could be possible from Ze and ZDR measurements.
On the Dynamics of the Formation of the Kelvin Cat’s-Eye in Tropical Cyclogenesis. Part I: Climatological Investigation
Authors: Asaadi Ali , Brunet Gilbert , Yau M. K.
Published: March 2016

Motivated by Dunkerton et al., a climatological study of 54 developing easterly waves in 1998–2001 was performed. Time-lagged composites in a translating reference frame following the disturbances indicate a weak meridional potential vorticity (PV) gradient of the easterly jet and a cyclonic critical layer located slightly to the south of the weak PV gradient, consistent with previous findings in the marsupial paradigm. Using a closed PV contour as a criterion for the formation of the cat’s-eye, it was shown that on average it takes ~2.6 days for open PV contours to transform to a closed coherent structure. Bootstrap analysis was then applied to determine the reliability of the easterly wave–like pattern in the composite perturbation PV analysis. It is suggested that the coexistence of a nonlinear critical layer and a region of weak meridional PV gradient over several days, found to occur in only ~25% of the easterly waves, might be a major factor to distinguish developing and nondeveloping disturbances. This finding may explain why only a small fraction of easterly waves contribute to tropical cyclogenesis. Additionally, an analytic time scale of the form was obtained, where Q is the mass sink, ε is the amplitude of the initial disturbance, and τ is the cat’s-eye formation time that governs the onset of nonlinearity for forced disturbances on a parabolic jet critical layer. This time scale is consistent with that found in 54 cases of easterly waves that developed into named storms, highlighting the importance of nonlinear and diabatic processes in cat’s-eye formation.
On the Relationship between Inertial Instability, Poleward Momentum Surges, and Jet Intensifications near Midlatitude Cyclones
Authors: Rowe Shellie M. , Hitchman Matthew H.
Published: March 2016

This study explores the role of inertial instability in poleward momentum surges and “flare ups” of the subpolar jet near midlatitude cyclones. Two cases are simulated with the University of Wisconsin Nonhydrostatic Modeling System to investigate the mechanisms involved in jet accelerations downstream of quasi-stationary “digging troughs.” Deep convection along the cold front leads to regions of inertial instability in the upper troposphere, which are intimately linked to jet accelerations. Terms in the zonal and meridional wind equations following the motion are evaluated for a selected air parcel within the inertially unstable region. A two-stage synoptic evolution is diagnosed, which is a characteristic signature of inertial instability. First, meridional flow accelerates following the motion, because of the subgeostrophic zonal flow and strong northward pressure gradient force (a statement of inertial instability). Second, supergeostrophic poleward flow leads to zonal acceleration and a jet flare-up. Inertial instability thus effectively displaces a westerly jet maximum poleward relative to inertially stable conditions. The structure of the poleward surge involves a distinctive “head” of high angular momentum, with the region of inertial instability enclosing the jet maximum and a core of strongly negative potential vorticity inside the surge. Departures from angular momentum–conserving profiles during meridional displacement are interpreted in terms of the pressure gradient force and degree of inertial stability. Inertial instability reduces the resulting zonal wind profile relative to angular momentum conservation but provides a significant poleward displacement of the resulting zonal wind maximum.
Exploring the Role of Eddy Momentum Fluxes in Determining the Characteristics of the Equinoctial Hadley Circulation: Fixed-SST Simulations
Authors: Singh Martin S. , Kuang Zhiming
Published: March 2016

The influence of eddy momentum fluxes on the equinoctial Hadley circulation is explored using idealized simulations on an equatorial beta plane in which the sea surface temperature (SST) distribution is fixed. By comparing simulations run in a wide-domain configuration, in which large-scale eddies are present, to simulations in which the model domain is too narrow to permit baroclinic instability, the role of large-scale eddies in determining the characteristics of the Hadley circulation is elucidated. The simulations also include an explicit representation of deep convection, allowing for an evaluation of the influence of convective momentum transport on the zonal-mean circulation.

The simulated eddy momentum fluxes are much weaker in the narrow-domain configuration than in the wide-domain case, and convective momentum transport is found to be of secondary importance. As a result, many characteristics of the narrow-domain Hadley circulation are well described by axisymmetric theory and differ from those of the wide-domain case. Nevertheless, the strength of the Hadley circulation is similar irrespective of the domain width. The sensitivity of this result to the strength of the eddy forcing is investigated using narrow-domain simulations forced by artificial sinks of zonal momentum. As the magnitude of the momentum sink increases, the Hadley circulation strengthens, but the increase is relatively modest except at very strong forcing magnitudes. The results suggest that the fixed-SST boundary condition places a strong thermodynamic constraint on the Hadley circulation strength and that one should consider the energy budget as well as the angular momentum budget in order to fully understand the influence of large-scale eddies on the zonal-mean circulation in the tropics.
Large-Eddy Simulations of EUCLIPSE–GASS Lagrangian Stratocumulus-to-Cumulus Transitions: Mean State, Turbulence, and Decoupling
Authors: de Roode Stephan R. , Sandu Irina , van der Dussen Johan J. , Ackerman Andrew S. , Blossey Peter , Jarecka Dorota , Lock Adrian , Siebesma A. Pier , Stevens Bjorn
Published: March 2016

Results of four Lagrangian stratocumulus-to-shallow-cumulus transition cases as obtained from six different large-eddy simulation models are presented. The model output is remarkably consistent in terms of the representation of the evolution of the mean state, which is characterized by a stratocumulus cloud layer that rises with time and that warms and dries relative to the subcloud layer. Also, the effect of the diurnal insolation on cloud-top entrainment and the moisture flux at the top of the subcloud layer are consistently captured by the models. For some cases, the models diverge in terms of the liquid water path (LWP) during nighttime, which can be explained from the difference in the sign of the buoyancy flux at cloud base. If the subcloud buoyancy fluxes are positive, turbulence sustains a vertically well-mixed layer, causing a cloud layer that is relatively cold and moist and consequently has a high LWP. After some simulation time, all cases exhibit subcloud-layer dynamics that appear to be similar to those of the dry convective boundary layer. The humidity flux from the subcloud layer toward the stratocumulus cloud layer, which is one of the major sources of stratocumulus cloud liquid water, is larger during the night than during the day. The sensible heat flux becomes constant in time, whereas the latent heat flux tends to increase during the transition. These findings are explained from a budget analysis of the subcloud layer.
On the Dynamics of the Formation of the Kelvin Cat’s-Eye in Tropical Cyclogenesis. Part II: Numerical Simulation
Authors: Asaadi Ali , Brunet Gilbert , Yau M. K.
Published: March 2016

A shallow-water model is used to study the role of critical layers in tropical cyclogenesis. Forced and unforced problems of disturbances on a parabolic jet associated with weak basic-state meridional potential vorticity (PV) gradients, leading to Kelvin cat’s-eye formation around the jet axis, are first investigated. Numerical simulations with various initial disturbance magnitudes and structures suggest that the results of previous studies can be extended to the next level of complexity toward the more realistic atmosphere. The model is therefore initialized using an observed jet profile obtained from the reanalysis data presented in Part I of this study. For this asymmetric marginally stable basic-state profile, unforced (free) and forced linear integrations show spatial contraction of the perturbation structures in the meridional direction, similar to what occurred in experiments on the parabolic jet. Nonlinear free simulations highlight the role of nonlinear processes in redistributing PV within the critical-layer region. However, they do not yield a realistic time scale for the formation of the cat’s-eye. By including diabatic heating as a mass sink term to represent convective PV generation, the nonlinear forced simulation is found to produce a realistic time scale for cat’s-eye formation, and confirms the analytical solution of τeτQ ~ O(ε−1) obtained in Part I. These results highlight the synergic role of the dynamical mechanisms, including wave breaking and PV redistribution within the nonlinear critical layer characterized by weak PV gradients and the thermodynamical mechanisms such as convectively generated PV anomalies in the cat’s-eye formation in tropical cyclogenesis.
Evolution of the Shape of the Raindrop Size Distribution in Simulated Shallow Cumulus
Authors: Naumann Ann Kristin , Seifert Axel
Published: March 2016

In this paper, the evolution of the raindrop size distribution (RSD) is investigated for two isolated shallow cumulus clouds that are modeled with large-eddy simulations. For a two-moment bulk rain microphysics scheme that assumes the RSD to follow a gamma distribution, it is shown that the evolution of the rainwater content of an individual shallow cumulus cloud—in particular, its subcloud-layer rainwater amount and its surface precipitation rate—is highly sensitive to the choice of the shape parameter of the gamma distribution.

To further investigate the shape of the RSD, a Lagrangian drop model is used to represent warm rain microphysics without a priori assumptions on the RSD. It is found that the shape parameter is highly variable in space and time and that existing closure equations, which are established from idealized studies of more heavily precipitating cases, are not appropriate for shallow cumulus. Although a relation of the shape parameter to the mean raindrop diameter is also found for individual shallow cumulus clouds, this relation differs already for the two clouds considered. It is therefore doubtful whether a two-moment scheme with a diagnostic parameterization of the shape parameter (i.e., a local closure in space and time) can be sufficient, especially when being applied across different cloud regimes. A three-moment bulk rain microphysics scheme is able to capture the general development of the relation of the shape parameter to the mean raindrop diameter for the two simulated clouds but misses some relevant features.
Wave and Jet Maintenance in Different Flow Regimes
Authors: Lachmy Orli , Harnik Nili
Published: March 2016

The wave spectrum and zonal-mean-flow maintenance in different flow regimes of the jet stream are studied using a two-layer modified quasigeostrophic (QG) model. As the wave energy is increased by varying the model parameters, the flow transitions from a subtropical jet regime to a merged jet regime and then to an eddy-driven jet regime. The subtropical jet is maintained at the Hadley cell edge by zonal-mean advection of momentum, while eddy heat flux and eddy momentum flux convergence (EMFC) are weak and concentrated far poleward. The merged jet is narrow and persistent and is maintained by EMFC from a narrow wave spectrum, dominated by zonal wavenumber 5. The eddy-driven jet is wide and fluctuating and is maintained by EMFC from a wide wave spectrum. The wave–mean flow feedback mechanisms that maintain each regime are explained qualitatively.

The regime transitions are related to transitions in the wave spectrum. An analysis of the wave energy spectrum budget and a comparison with a quasi-linear version of the model show that the balance maintaining the spectrum in the merged and subtropical jet regimes is mainly a quasi-linear balance, whereas in the eddy-driven jet regime nonlinear inverse energy cascade takes place. The amplitude and wavenumber of the dominant wave mode in the merged and subtropical jet regimes are determined by the constraint that this mode would produce the wave fluxes necessary for maintaining a mean flow that is close to neutrality. In contrast, the equilibrated mean flow in the eddy-driven jet regime is weakly unstable.
The Role of the Mean State in Meridional Mode Structure and Growth
Authors: Martinez-Villalobos Cristian , Vimont Daniel J.
Published: March 2016

This study uses a simple linear coupled model to investigate the role of the WES feedback and ITCZ mean states in meridional mode variability. Optimal structures that maximize transient growth are calculated for mean states characteristic of boreal spring and boreal fall in the tropical Atlantic. During boreal spring the leading optimal structure is a zonal mode that propagates westward and does not resemble the observed meridional mode. In contrast, the leading optimal structure during fall is a sea surface temperature (SST) monopole over the Northern Hemisphere (NH) that propagates equatorward and westward and that closely matches meridional mode variability during this season. It is found that the boreal fall optimal growth greatly exceeds growth of the corresponding optimal during boreal spring, despite the observed boreal spring peak in Atlantic meridional mode variance.

Sensitivity studies are used to explore the role of Northern or Southern Hemisphere initial conditions, ITCZ width, and ITCZ location in meridional mode growth and structure. It is found that growth is favored (i) for optimal structures that originate in the Northern Hemisphere, especially for boreal fall mean states; (ii) for symmetric mean states, equatorially symmetric structures maximize growth under narrow ITCZ configurations, and antisymmetric structures maximize growth under wider ITCZ configurations; and (iii) for antisymmetric mean states (and realistic ITCZ width), growth is maximized when the ITCZ is located off of the equator. The implications of these findings are discussed.
The Precipitation Response to an Idealized Subtropical Continent
Authors: Maroon Elizabeth A. , Frierson Dargan M. W. , Kang Sarah M. , Scheff Jacob
Published: March 2016

A subtropical continent is added to two aquaplanet atmospheric general circulation models (AGCMs) to better understand the influence of land on tropical circulation and precipitation. The first model, the gray-radiation moist (GRaM) AGCM, has simplified physics, while the second model, the GFDL Atmospheric Model version 2.1 (AM2.1), is a fully comprehensive AGCM. Both models have a continent that is 60° wide in longitude from 10° to 30°N, in an otherwise slab-ocean-covered world. The precipitation response varies with cloudy- and clear-sky feedbacks and depends on continental albedo. In GRaM simulations with a continent, precipitation in the Northern Hemisphere decreases mostly as a result of decreased evaporation. In AM2.1 simulations, precipitation also shifts southward via Hadley circulation changes due to increasing albedo, but the radiative impact of clouds and moisture creates a more complex response. Results are similar when a seasonal cycle of insolation is included in AM2.1 simulations. The impact of a large, bright subtropical continent is to shift precipitation to the opposite hemisphere. In these simulations, the hemisphere of greater tropical precipitation is better predicted by the hemisphere with greater atmospheric energy input, as has been shown in previous literature, rather than the hemisphere that has higher surface temperature.
Will a Warmer World Mean a Wetter or Drier Australian Monsoon?
Authors: Brown Josephine R. , Moise Aurel F. , Colman Robert , Zhang Huqiang
Published: March 2016

Multimodel mean projections of the Australian summer monsoon show little change in precipitation in a future warmer climate, even under the highest emission scenario. However, there is large uncertainty in this projection, with model projections ranging from around a 40% increase to a 40% decrease in summer monsoon precipitation. To understand the source of this model uncertainty, a set of 33 climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) is divided into groups based on their future precipitation projections (DRY, MID, and WET terciles). The DRY model mean has enhanced sea surface temperature (SST) warming across the equatorial Pacific, with maximum increases in precipitation in the western equatorial Pacific. The DRY model mean also has a large cold bias in present day SSTs in this region. The WET model mean has the largest warming in the central and eastern equatorial Pacific, with precipitation increases over much of Australia. These results suggest lower confidence for projections of reduced monsoon precipitation because of the influence of model SST biases on the SST warming pattern and precipitation response. The precipitation changes for the DRY and WET models are also decomposed into dynamic and thermodynamic components. The component due to spatial shifts in the location of convergence and precipitation is responsible for most of the difference between DRY and WET models. As spatial shifts in precipitation are closely associated with patterns of SST change, reducing uncertainty in model SST warming patterns will be crucial to improved projections of Australian monsoon precipitation.
Coastal Clouds at the Eastern Margin of the Southeast Pacific: Climatology and Trends
Authors: Muñoz Ricardo C. , Quintana Juan , Falvey Mark J. , Rutllant José A. , Garreaud René
Published: March 2016

The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent with the subtropical location, cloud types are dominated by stratocumuli having greatest coverage (>7 oktas) and smaller heights (600–750 m) during the nighttime of austral winter and spring. Meridionally, nighttime cloud fraction and cloud-base heights increase from south to north. Long-term trends in mean cloud cover are observed at all sites albeit with a seasonal modulation, with increasing (decreasing) coverage in the spring (fall). Consistent trend patterns are also observed in independent sunshine hour measurements at the same sites. Cloud heights show negative trends of about 100 m decade−1 (1995–2010), although the onset time of this tendency differs between sites. The positive cloud fraction trends during the cloudy season reported here disagree with previous studies, with discrepancies attributed to differences in datasets used or to methodological differences in data analysis. The cloud-base height tendency, together with a less rapid lowering of the subsidence inversion base height, suggests a deepening of the coastal cloud layer. While consistent with the tendency toward greater low-level cloud cover and the known cooling of the marine boundary layer in this region, these tendencies are at odds with a drying trend of the near-surface air documented here as well. Assessing whether this intriguing result is caused by physical factors or by limitations of the data demands more detailed observations, some of which are currently under way.
An Equatorial–Extratropical Dipole Structure of the Atlantic Niño
Authors: Nnamchi Hyacinth C. , Li Jianping , Kucharski Fred , Kang In-Sik , Keenlyside Noel S. , Chang Ping , Farneti Riccardo
Published: March 2016

Equatorial Atlantic variability is dominated by the Atlantic Niño peaking during the boreal summer. Studies have shown robust links of the Atlantic Niño to fluctuations of the St. Helena subtropical anticyclone and Benguela Niño events. Furthermore, the occurrence of opposite sea surface temperature (SST) anomalies in the eastern equatorial and southwestern extratropical South Atlantic Ocean (SAO), also peaking in boreal summer, has recently been identified and termed the SAO dipole (SAOD). However, the extent to which and how the Atlantic Niño and SAOD are related remain unclear. Here, an analysis of historical observations reveals the Atlantic Niño as a possible intrinsic equatorial arm of the SAOD. Specifically, the observed sporadic equatorial warming characteristic of the Atlantic Niño (~0.4 K) is consistently linked to southwestern cooling (~−0.4 K) of the Atlantic Ocean during the boreal summer. Heat budget calculations show that the SAOD is largely driven by the surface net heat flux anomalies while ocean dynamics may be of secondary importance. Perturbations of the St. Helena anticyclone appear to be the dominant mechanism triggering the surface heat flux anomalies. A weakening of the anticyclone will tend to weaken the prevailing northeasterlies and enhance evaporative cooling over the southwestern Atlantic Ocean. In the equatorial region, the southeast trade winds weaken, thereby suppressing evaporation and leading to net surface warming. Thus, it is hypothesized that the wind–evaporation–SST feedback may be responsible for the growth of the SAOD events linking southern extratropics and equatorial Atlantic variability via surface net heat flux anomalies.
Effects of Spatial Aggregation on the Accuracy of Statistically Downscaled Precipitation Predictions
Authors: Chardon Jérémy , Favre Anne-Catherine , Hingray Benoît
Published: March 2016

The effects of spatial aggregation on the skill of downscaled precipitation predictions obtained over an 8 × 8 km2 grid from circulation analogs for metropolitan France are explored. The Safran precipitation reanalysis and an analog approach are used to downscale the precipitation where the predictors are taken from the 40-yr ECMWF Re-Analysis (ERA-40). Prediction skill—characterized by the continuous ranked probability score (CRPS), its skill score, and its decomposition—is generally found to continuously increase with spatial aggregation. The increase is also greater when the spatial correlation of precipitation is lower. This effect is shown from an empirical experiment carried out with a fully uncorrelated dataset, generated from a space-shake experiment, where the precipitation time series of each grid cell is randomly assigned to another grid cell. The underlying mechanisms of this effect are further highlighted with synthetic predictions simulated using a stochastic spatiotemporal generator. It is shown 1) that the skill increase with spatial aggregation jointly results from the higher and lower values obtained for the resolution and uncertainty terms of the CRPS decomposition, respectively, and 2) that the lower spatial correlation of precipitation is beneficial for both terms. Results obtained for France suggest that the prediction skill indefinitely increases with aggregation. A last experiment is finally proposed to show that this is not expected to be always the case. A prediction skill optimum is, for instance, obtained when the mean areal precipitation is estimated over a region where local precipitations of different grid cells originate from different underlying meteorological processes.
The Total Energy Flux Leaving the Ocean’s Mixed Layer
Authors: Rimac Antonija , Storch Jin-Song von , Eden Carsten
Published: March 2016

The total energy flux leaving the ocean’s spatially and seasonally varying mixed layer is estimated using a global ⅝1/10° ocean general circulation model. From the total wind-power input of 3.33 TW into near-inertial waves (0.35 TW), subinertial fluctuations (0.87 TW), and the time-mean circulation (2.11 TW), 0.92 TW leave the mixed layer, with 0.04 TW (11.4%) due to near-inertial motions, 0.07 TW (8.04%) due to subinertial fluctuations, and 0.81 TW (38.4%) due to time-mean motions. Of the 0.81 TW from the time-mean motions, 0.5 TW result from the projection of the horizontal flux onto the sloped bottom of the mixed layer. This projection is negligible for the transient fluxes. The spatial structure of the vertical flux is determined principally by the wind stress curl. The mean and subinertial fluxes leaving the mixed layer are approximately 40%–50% smaller than the respective fluxes across the Ekman layer according to the method proposed by Stern. The fraction related to transient fluctuations tends to decrease with increasing depth of the mixed layer and with increasing strength of wind stress variability.
Wave-Breaking Turbulence in the Ocean Surface Layer
Authors: Thomson Jim , Schwendeman Michael S. , Zippel Seth F. , Moghimi Saeed , Gemmrich Johannes , Rogers W. Erick
Published: March 2016

Observations of winds, waves, and turbulence at the ocean surface are compared with several analytic formulations and a numerical model for the input of turbulent kinetic energy by wave breaking and the subsequent dissipation. The observations are generally consistent with all of the formulations, although some differences are notable at winds greater than 15 m s−1. The depth dependence of the turbulent dissipation rate beneath the waves is fit to a decay scale, which is sensitive to the choice of vertical reference frame. In the surface-following reference frame, the strongest turbulence is isolated within a shallow region of depths much less than one significant wave height. In a fixed reference frame, the strong turbulence penetrates to depths that are at least half of the significant wave height. This occurs because the turbulence of individual breakers persists longer than the dominant period of the waves and thus the strong surface turbulence is carried from crest to trough with the wave orbital motion.
Wind Sea behind a Cold Front and Deep Ocean Acoustics
Authors: Farrell W. E. , Berger J. , Bidlot J.-R. , Dzieciuch M. , Munk W. , Stephen R. A. , Worcester P. F.
Published: March 2016

A rapid and broadband (1 h, 1 < f < 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4- and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10–20 km h−1 (2.8–5.6 m s−1), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front’s speed, 8.5 km h−1 (2.4 m s−1). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity , where Fζ is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain.
Quality Control Program for Real-Time Hourly Temperature Observation in Taiwan
Authors: Cheng Anne Ru , Lee Tim Hau , Ku Hsin I. , Chen Yi Wen
Published: March 2016

This paper introduces a quality control (QC) program for the real-time hourly land surface temperature observation developed by the Central Weather Bureau in Taiwan. There are three strategies involved. The first strategy is a range check scheme that inspects whether the observation falls inside the climatological limits of the station to screen out the obvious outliers. Limits are adjusted according to the station’s elevation. The second strategy is a spatial check scheme that scrutinizes whether the observation falls inside the derived confidence interval, according to the data from the reference stations and the correlations among the stations, to judge the reliability of the data. The scheme is specialized, as it employs the theorems of unbiased and minimum error estimators to determine the weights. The performance evaluation results show that the new method is in theory superior to the spatial regression test (You et al.). The third strategy is a temporal check scheme that examines whether the temperature difference of two successive observations exceeds the temperature variation threshold for judging the rationality of the data. Different thresholds are applied for the data observed in different times under different rainfall conditions. Procedurally, the observation must pass the range check first and then go through the spatial or the temporal check. The temporal check is applied only when the spatial check is unavailable. Post-examinations of the data from 2014 show that the QC program is able to filter out most of the significant errors.
Diurnal, Seasonal, and 11-yr Solar Cycle Variation Effects on the Virtual Ionosphere Reflection Height and Implications for the Met Office’s Lightning Detection System, ATDnet
Authors: Hudson T. S. , Horseman A. , Sugier J.
Published: March 2016

The virtual ionosphere reflection height variation is investigated temporally and spatially, with specific reference to the Met Office’s lightning detection network, the Arrival Time Difference Network (ATDnet). Data from this network, operating at 13.7 kHz, and a propagation model built by the Met Office based upon published theory were used to investigate this variation, specifically with regard to diurnal, seasonal, and 11-yr solar cycle variation. Variation over these temporal scales is chosen, since they correspond with variation in solar irradiance upon the earth’s atmosphere, something known to drive ionosphere height variation. The virtual ionosphere reflection height is found to vary diurnally from ~65 km for the period 1000–1600 UTC to ~80 km for the period 2200–0400 UTC, from 1 June to 31 August 2013 inclusive. A similar magnitude of variation is also observed seasonally, with the ionosphere height for daytime in August 2013 being ~64 km and for December 2013 being ~76 km. No significant variation is observed between the minimum and maximum of the last solar cycle, with a difference in ionosphere height of ~1 km at most. The potential impacts of these results upon a very low-frequency (VLF) lightning detection network such as ATDnet are discussed, with solutions such as subnetting and wave-mode dominance analysis examined.
Sensitivity of a Cumulus Parameterization Scheme to Precipitation Production Representation and Its Impact on a Heavy Rain Event over Korea
Authors: Han Ji-Young , Hong Song-You , Sunny Lim Kyo-Sun , Han Jongil
Published: March 2016

The sensitivity of a cumulus parameterization scheme (CPS) to a representation of precipitation production is examined. To do this, the parameter that determines the fraction of cloud condensate converted to precipitation in the simplified Arakawa–Schubert (SAS) convection scheme is modified following the results from a cloud-resolving simulation. While the original conversion parameter is assumed to be constant, the revised parameter includes a temperature dependency above the freezing level, which leads to less production of frozen precipitating condensate with height. The revised CPS has been evaluated for a heavy rainfall event over Korea as well as medium-range forecasts using the Global/Regional Integrated Model system (GRIMs). The inefficient conversion of cloud condensate to convective precipitation at colder temperatures generally leads to a decrease in precipitation, especially in the category of heavy rainfall. The resultant increase of detrained moisture induces moistening and cooling at the top of clouds. A statistical evaluation of the medium-range forecasts with the revised precipitation conversion parameter shows an overall improvement of the forecast skill in precipitation and large-scale fields, indicating importance of more realistic representation of microphysical processes in CPSs.
Analyzing the Grell–Freitas Convection Scheme from Hydrostatic to Nonhydrostatic Scales within a Global Model
Authors: Fowler Laura D. , Skamarock William C. , Grell Georg A. , Freitas Saulo R. , Duda Michael G.
Published: March 2016

The authors implemented the Grell–Freitas (GF) parameterization of convection in which the cloud-base mass flux varies quadratically as a function of the convective updraft fraction in the global nonhydrostatic Model for Prediction Across Scales (MPAS). They evaluated the performance of GF using quasi-uniform meshes and a variable-resolution mesh centered over South America, the resolution of which varied between hydrostatic (50 km) and nonhydrostatic (3 km) scales. Four-day forecasts using a 50-km and a 15-km quasi-uniform mesh, initialized with GFS data for 0000 UTC 10 January 2014, reveal that MPAS overestimates precipitation in the tropics relative to the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis data. Results of 4-day forecasts using the variable-resolution mesh reveal that over the refined region of the mesh, GF performs as a precipitating shallow convective scheme, whereas over the coarse region of the mesh, GF acts as a conventional deep convective scheme. As horizontal resolution increases and subgrid-scale motions become increasingly resolved, the contribution of convective and grid-scale precipitation to the total precipitation decreases and increases, respectively. Probability density distributions of precipitation highlight a smooth transition in the partitioning between convective and grid-scale precipitation, including at gray-zone scales across the transition region between the coarsest and finest regions of the global mesh. Variable-resolution meshes spanning between hydrostatic and nonhydrostatic scales are shown to be ideal tools to evaluate the horizontal scale dependence of parameterized convective and grid-scale moist processes.
Efficient Assimilation of Simulated Observations in a High-Dimensional Geophysical System Using a Localized Particle Filter
Authors: Poterjoy Jonathan , Anderson Jeffrey L.
Published: March 2016

This study presents the first application of a localized particle filter (PF) for data assimilation in a high-dimensional geophysical model. Particle filters form Monte Carlo approximations of model probability densities conditioned on observations, while making no assumptions about the underlying error distribution. Unlike standard PFs, the local PF uses a localization function to reduce the influence of distant observations on state variables, which significantly decreases the number of particles required to maintain the filter’s stability. Because the local PF operates effectively using small numbers of particles, it provides a possible alternative to Gaussian filters, such as ensemble Kalman filters, for large geophysical models. In the current study, the local PF is compared with stochastic and deterministic ensemble Kalman filters using a simplified atmospheric general circulation model. The local PF is found to provide stable filtering results over yearlong data assimilation experiments using only 25 particles. The local PF also outperforms the Gaussian filters when observation networks include measurements that have non-Gaussian errors or relate nonlinearly to the model state, like remotely sensed data used frequently in atmospheric analyses. Results from this study encourage further testing of the local PF on more complex geophysical systems, such as weather prediction models.
Observable Surface Anomalies Preceding Simulated Isolated Convective Initiation
Authors: Madaus Luke E. , Hakim Gregory J.
Published: March 2016

Idealized ensemble simulations of isolated convective initiation (CI) are analyzed to identify storm-scale features in surface weather fields that precede initiation in a variety of background environments and the observations that would be needed to resolve these features. Precipitating storms are identified with an object-based method and composites of surface anomalies are generated for the variables of interest surrounding times and locations of initiation. Correlation length scales and anomaly magnitudes throughout the CI process are examined in detail with the latter comparing favorably to anomaly estimates obtained from previous observational and modeling studies. Negative temperature anomalies due to cloud shadowing are found to be the most prominent storm-scale feature prior to initiation. Significant spatial correlations are shown to extend from the surface throughout the boundary layer and even into the cloud-bearing layer once deep convective clouds become established. The findings are discussed in the context of data assimilation, particularly with respect to current assumptions about surface observation error. It is shown that, to resolve the storm-scale anomalies in these simulations, the minimum necessary temperature and wind observation densities would likely be limited by spatial correlation length scale while moisture and pressure observations are more limited by observation error.
Stakeholder Perceptions of Climate Extremes’ Effects on Management of Protected Grasslands in a Central European Area
Authors: Malatinszky Ákos
Published: March 2016

Since meteorological data have been regularly recorded in Hungary, 2010 has been the rainiest year, whereas 2011 and 2012 have been the driest years. Protected grasslands and their management by low-intensity livestock farming are seriously affected by climatic changes. This paper seeks to shed light on stakeholder perceptions of recent extreme weather events, in order to better understand how to adapt the management of vulnerable habitats to anticipated changes. The status of vulnerable habitats is strongly affected by land use change as well; therefore, this process requires stakeholder involvement. Opinions on what aspects are presumed to be affected most by changes in climate were gathered during semistructured interviews from farmers and conservationists in the Körös-Maros National Park in Hungary. Stakeholders revealed negative impacts resulting from extreme floods, droughts, and changes in rainfall and temperature, and they highlighted challenges relating to conflicting management objectives and perverse incentives arising from policy-level issues (such as regulatory structures and implementation). Subjects noted that years with high precipitation caused adverse conditions for livestock, late mowing due to inaccessible pastures, poor quality of hay, and undergrazing (but still compaction damage). Years with negative precipitation records show decreased quantity and quality of hay, loss of valuable forage, winter shortage of green fodder, land degradation, increased water demand, shifting grazing seasons, decreasing carrying capacity, overgrazing, heat stress, declines in physical activities, expansion of invasive alien species, and conflicts between economic interests and nature conservation objectives. In only a few cases was the awareness of these issues converted into practical adaptation or mitigation activities.
Connecting the Dots: A Communications Model of the North Texas Integrated Warning Team during the 15 May 2013 Tornado Outbreak
Authors: Cavanaugh Dennis , Huffman Melissa , Dunn Jennifer , Fox Mark
Published: March 2016

On 15 May 2013, 19 tornadoes occurred across north and central Texas, killing 6, injuring over 50, and causing more than $100 million in property damage. The majority of the impacts to life and property were the direct result of category-3 and category-4 enhanced Fujita scale (EF-3 and EF-4) tornadoes that affected the communities of Cleburne and Granbury, Texas. This study focuses on an examination of the north Texas integrated warning team (IWT) communications through a thorough analysis of interactions between IWT members during this event. Communications from all members of the IWT were collected and organized so that a quantitative analysis of the IWT communications network could be performed. The results of this analysis were used to identify strengths and weaknesses of current IWT communications to improve the consistency of hazardous weather messaging for future high-impact weather events. The results also show how effectively communicating within an IWT leads not only to more consistent messaging but also to broader dissemination of hazardous weather information to the public. The analysis techniques outlined in this study could serve as a model for comprehensive studies of IWTs across the country.
Thin-ideal internalization and body dissatisfaction in Sri Lankan adolescents
Authors: Omori Mika , Yamazaki Yoko , Aizawa Noriko , Zoysa Piyanjali de
Published: March 2016

In this study, a survey of Sri Lankan adolescents explored relationships between thin-ideal internalization and body dissatisfaction—issues that have received greater research attention in East Asia and the West. Girls scored lower in thin-ideal internalization and awareness and higher in self-esteem compared to boys; however, unlike in previous studies, body dissatisfaction did not differ significantly by gender. Hierarchical linear multiple regression analyses revealed that self-esteem moderated the relationship between thin-ideal internalization and body dissatisfaction among girls, but this was not observed for boys. Self-esteem as a protective factor against body dissatisfaction among Sri Lankan female adolescents was confirmed.
The common variant Q192R at the paraoxonase 1 (PON1) gene and its activity are responsible for a portion of the altered antioxidant status in type 2 diabetes
Authors: Zargari Mehryar , Sharafeddin Fahimeh , Mahrooz Abdolkarim , Alizadeh Ahad , Masoumi Parisa
Published: March 2016

In this study, we investigated the effects of paraoxonase 1 (PON1) activities and the variant PON1–Q192R on the ferric reducing ability of plasma (FRAP) and total thiol. In addition, we examined the distribution of genotypes of this variant and the relationship of the genotypes with age in patients with type 2 diabetes (T2D). A total of 115 patients with T2D were enrolled in this study. Paraoxonase activity (PON-para) and arylesterase activity (PON-aryl) were determined using spectrophotometric assays. The distribution of the Q192R genotypes was determined by the double substrate method. The antioxidant status was evaluated by determining FRAP and total thiol. The frequencies of Q and R allozyme were 0.78 and 0.22, respectively. The multivariate analysis identified a significant association between the variables PON1–Q192R (Wilks’ λ = 0.85, P = 0.002) and PON-aryl (Wilks’ λ = 0.896, P = 0.017), with FRAP and total thiol. The significant difference observed for PON1–Q192R and PON-aryl is primarily due to the changes in FRAP levels (η2 = 0.127, P = 0.002 for PON1–Q192R; η2 = 0.083, P = 0.011 for PON-aryl). The interaction PON1–Q192R–PON-aryl increased the effect sizes from 8 to 19% for FRAP. Only in R-carrying genotypes, there were significant correlations between both PON-para/HDL (r = −0.574, P < 0.001) and PON-aryl/HDL (r = −0.577, P < 0.001) with age. Our data suggest that the variant PON1–Q192R and PON1 activity, particularly PON-aryl, influenced the antioxidant status in T2D. The interaction of this variant and PON1 activity increased the effect size on the antioxidant capacity. Moreover, the presence of the R allozyme may potentiate the effects of age on susceptibility to cardiovascular diseases in T2D.
Original Research: A case-control genome-wide association study identifies genetic modifiers of fetal hemoglobin in sickle cell disease
Authors: Liu Li , Pertsemlidis Alexander , Ding Liang-Hao , Story Michael D , Steinberg Martin H , Sebastiani Paola , Hoppe Carolyn , Ballas Samir K , Pace Betty S
Published: March 2016

Sickle cell disease (SCD) is a group of inherited blood disorders that have in common a mutation in the sixth codon of the β-globin ( HBB) gene on chromosome 11. However, people with the same genetic mutation display a wide range of clinical phenotypes. Fetal hemoglobin (HbF) expression is an important genetic modifier of SCD complications leading to milder symptoms and improved long-term survival. Therefore, we performed a genome-wide association study (GWAS) using a case-control experimental design in 244 African Americans with SCD to discover genetic factors associated with HbF expression. The case group consisted of subjects with HbF≥8.6% (133 samples) and control group subjects with HbF≤£3.1% (111 samples). Our GWAS results replicated SNPs previously identified in an erythroid-specific enhancer region located in the second intron of the BCL11A gene associated with HbF expression. In addition, we identified SNPs in the SPARC, GJC1, EFTUD2 and JAZF1 genes as novel candidates associated with HbF levels. To gain insights into mechanisms of globin gene regulation in the HBB locus, linkage disequilibrium (LD) and haplotype analyses were conducted. We observed strong LD in the low HbF group in contrast to a loss of LD and greater number of haplotypes in the high HbF group. A search of known HBB locus regulatory elements identified SNPs 5′ of δ-globin located in an HbF silencing region. In particular, SNP rs4910736 created a binding site for a known transcription repressor GFi1 which is a candidate protein for further investigation. Another HbF-associated SNP, rs2855122 in the cAMP response element upstream of Gγ-globin, was analyzed for functional relevance. Studies performed with siRNA-mediated CREB binding protein (CBP) knockdown in primary erythroid cells demonstrated γ-globin activation and HbF induction, supporting a repressor role for CBP. This study identifies possible molecular determinants of HbF production.