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Early Dynamics of Deep Blue XBT Probes

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2253-2263页

作者： Bringas, Francis Goni, Gustavo NOAA Atlantic Oceanog & Meteorol Lab Miami FL 33149 USA

Expendable bathythermographs (XBTs) are probes widely used to monitor global ocean heat content, variability of ocean currents, and meridional heat transports. In the XBT temperature profile, the depth is estimated from the time of descent in the water using a fall-rate equation. There are two main errors in these profiles: temperature and depth errors. The reduction of error in the estimates of the depth allows a corresponding reduction in the errors in the computations in which XBTs are used. Two experiments were carried out to study the effect of the deployment height on the depth estimates of Deep Blue XBT probes. During these experiments, XBTs were deployed from different heights. The motion of the probes after entering the water was analyzed to determine the position and the velocity of the probes as a function of time, which was compared to that obtained using the Hanawa et al. fall-rate equation. Results showed a difference or offset between the experimentally observed depths and those derived from Hanawa et al. This offset was found to be linked to the deployment height. To eliminate the offset in the fall-rate equation for XBTs deployed from different heights, a methodology is proposed here based on the initial velocities of the probes in the water (or deployment height). Results indicate that the depth estimates in the profiles need to be corrected for an offset, which in addition to having a launch height dependence is time dependent during the first 1.5 s of descent of the probe in the water, and constant after that.

关键词： observational techniques and algorithms Data quality control In situ oceanic observations Profilers oceanic

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Interhemispheric Variability of Earth's Radiation

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2015年第12期72卷 4615-4628页

作者： Ruzmaikin, Alexander Aumann, Hartmut H. Jiang, Jonathan H. Jet Prop Lab Pasadena CA 91109 USA

The variability of interhemispheric symmetry of Earth's energy serves as an independent indicator of climate change. The analysis of updated data obtained from satellite measurements at the top of the atmosphere (TOA) shows that in accord with Earth's orbital requirements the annually averaged incident solar radiation is the same in the Northern and Southern Hemispheres, the annual mean of the reflected shortwave radiation is almost north-south symmetric, and the annual mean of the outgoing longwave radiation is larger in the Northern Hemisphere by 1.4 W m(-2). These mean radiations systematically differ from the mean radiations found from the numerical atmospheric models that participated in the Coupled Model Intercomparison Project phase 5 (CMIP5). The hemispheric differences of the TOA radiations vary on the annual and interannual time scales. The multidecadal variability in Earth's north-south temperature difference reveals a similarity of trends in both hemispheres. The Atlantic meridional transport (in contrast to the Pacific meridional transport) is found to be coherent with the interhemispheric ocean heat content (OHC) difference on decadal and multidecadal time scales, indicating a critical role of the Atlantic in the interhemispheric energy balance change.

关键词： Atm Ocean Structure Phenomena Atmosphere-ocean interaction observational techniques and algorithms Climate records Satellite observations Variability Climate variability Interannual variability Oceanic variability

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Interannual Variability of the Mixed Layer Winter Convection and Spice Injection in the Eastern Subtropical North Atlantic

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第2期45卷 504-525页

作者： Kolodziejczyk, Nicolas Reverdin, Gilles Lazar, Alban Univ Paris 06 Sorbonne Univ LOCEAN Lab CNRSIRDMNHN F-75005 Paris France

The Argo dataset is used to study the winter upper-ocean conditions in the northeastern subtropical (NEA) Atlantic during 2006-12. During late winter 2010, the mixed layer depth is abnormally shallow and a negative anomaly of density-compensated salinity, the so-called spiciness, is generated in the permanent pycnocline. This is primarily explained by unusual weak air-sea buoyancy flux during the late winter 2010, in contrast with the five other studied winters. Particularly deep mixed layers and strong spiciness anomalies are observed during late winter 2012. The 2010 winter conditions appear to be related to historically low North Atlantic Oscillation (NAO) and high tropical North Atlantic index (TNA). Interannual variability of the eastern subtropical mixed layer is further investigated using a simple 1D bulk model of mean temperature and salinity linear profiles, based on turbulent kinetic energy conservation in the upper-ocean layer, and forced only with seasonal air-sea buoyancy forcing corresponding to fall-winter 2006-12. It suggests that year-to-year variability of the winter convective mixing driven by atmospheric buoyancy flux is able to generate interannual variability of both late winter mixed layer depth and spiciness in a strongly compensated layer at the base of the mixed layer and in the permanent pycnocline.

关键词： Circulation/ Dynamics Atmosphere-ocean interaction Convective adjustment Entrainment observational techniques and algorithms In situ oceanic observations Variability Interannual variability North Atlantic Oscillation

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Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001-14

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第1期45卷 3-32页

作者： Gladish, Carl V. Holland, David M. Rosing-Asvid, Aqqalu Behrens, Jane W. Boje, Jesper New York Univ Abu Dhabi Abu Dhabi U Arab Emirates NYU New York NY USA Greenland Inst Nat Resources Nuuk Greenland Tech Univ Denmark Charlottenlund Denmark

Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8 degrees C from 2009 to 2013, excluding 2010, when it was 1 degrees C cooler. Despite this variability, summer potential densities in the basin were in the narrow range of 27.20 <= sigma(theta) <= 27.31 kg m(-3), and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011-13 were therefore similar to those in 1998/99, when Jakobshavn Glacier began to retreat, while basin waters in 2010 were as cool as in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability. This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth.

关键词： Geographic location/entity Arctic Glaciers Atm/Ocean Structure/ Phenomena Density currents observational techniques and algorithms In situ oceanic observations Models and modeling Ocean models Variability Oceanic variability

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Distributions of Shallow to Very Deep Precipitation-Convection in Rapidly Intensifying Tropical Cyclones

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JOURNAL OF CLIMATE 2015年第22期28卷 8791-8824页

作者： Tao, Cheng Jiang, Haiyan Florida Int Univ Dept Earth & Environm Miami FL 33199 USA

Shear-relative distributions of four types of precipitation/convection in tropical cyclones (TCs) are statistically analyzed using 14 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data. The dataset of 1139 TRMM PR overpasses of tropical storms through category-2 hurricanes over global TC-prone basins is divided by future 24-h intensity change. It is found that increased and widespread shallow precipitation (defined as where the 20-dBZ radar echo height <6 km) around the storm center is a first sign of rapid intensification (RI) and could be used as a predictor of the onset of RI. The contribution to total volumetric rain and latent heating from shallow and moderate precipitation (20-dBZ echo height between 6 and 10 km) in the inner core is greater in RI storms than in non-RI storms, while the opposite is true for moderately deep (20-dBZ echo height between 10 and 14 km) and very deep precipitation (20-dBZ echo height 14 km). The authors argue that RI is more likely triggered by the increase of shallow-moderate precipitation and the appearance of more moderately to very deep convection in the middle of RI is more likely a response or positive feedback to changes in the vortex. For RI storms, a cyclonic rotation of frequency peaks from shallow (downshear right) to moderate (downshear left) to moderately and very deep precipitation (upshear left) is found and may be an indicator of a rapidly strengthening vortex. A ring of almost 90% occurrence of total precipitation is found for storms in the middle of RI, consistent with the previous finding of the cyan and pink ring on the 37-GHz color product.

关键词： Physical Meteorology and Climatology Hurricanes typhoons observational techniques and algorithms Radars Radar observations Satellite observations

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Satellite Observations of Mesoscale Eddy-Induced Ekman Pumping

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第1期45卷 104-132页

作者： Gaube, Peter Chelton, Dudley B. Samelson, Roger M. Schlax, Michael G. O'Neill, Larry W. Oregon State Univ Coll Earth Ocean & Atmospher Sci Corvallis OR 97331 USA

Three mechanisms for self-induced Ekman pumping in the interiors of mesoscale ocean eddies are investigated. The first arises from the surface stress that occurs because of differences between surface wind and ocean velocities, resulting in Ekman upwelling and downwelling in the cores of anticyclones and cyclones, respectively. The second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient, resulting in dipoles of Ekman upwelling and downwelling. The third mechanism arises from eddy-induced spatial variability of sea surface temperature (SST), which generates a curl of the stress and therefore Ekman pumping in regions of crosswind SST gradients. The spatial structures and relative magnitudes of the three contributions to eddy-induced Ekman pumping are investigated by collocating satellite-based measurements of SST, geostrophic velocity, and surface winds to the interiors of eddies identified from their sea surface height signatures. On average, eddy-induced Ekman pumping velocities approach O(10) cm day(-1). SST-induced Ekman pumping is usually secondary to the two current-induced mechanisms for Ekman pumping. Notable exceptions are the midlatitude extensions of western boundary currents and the Antarctic Circumpolar Current, where SST gradients are strong and all three mechanisms for eddy-induced Ekman pumping are comparable in magnitude. Because the polarity of current-induced curl of the surface stress opposes that of the eddy, the associated Ekman pumping attenuates the eddies. The decay time scale of this attenuation is proportional to the vertical scale of the eddy and inversely proportional to the wind speed. For typical values of these parameters, the decay time scale is about 1.3 yr.

关键词： Circulation/ Dynamics Atmosphere-ocean interaction Eddies Ekman pumping/transport Atm/Ocean Structure/ Phenomena Eddies Ekman pumping observational techniques and algorithms Satellite observations

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Pathways, Volume Transport, and Mixing of Abyssal Water in the Samoan Passage

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第2期45卷 562-588页

作者： Voet, Gunnar Girton, James B. Alford, Matthew H. Carter, Glenn S. Klymak, Jody M. Mickett, John B. Univ Washington Appl Phys Lab Seattle WA 98105 USA Univ Hawaii Honolulu HI 96822 USA Univ Victoria Victoria BC Canada

The flow of dense water through the Samoan Passage accounts for the major part of the bottom water renewal in the North Pacific and is thus an important element of the Pacific meridional overturning circulation. A recent set of highly resolved measurements used CTD/LADCP, a microstructure profiler, and moorings to constrain the complex pathways and variability of the abyssal flow. Volume transport estimates for the dense northward current at several sections across the passage, calculated using direct velocity measurements from LADCPs, range from 3.9x10(6) to 6.0 x 10(6) +/- 1 x 10(6) m(3) s(-1). The deep channel to the east and shallower pathways to the west carried about equal amounts of this volume transport, with the densest water flowing along the main eastern channel. Turbulent dissipation rates estimated from Thorpe scales and direct microstructure agree to within a factor of 2 and provide a region-averaged value of O(10(-8)) Wkg(-1) for layers colder than 0.8 degrees C. Associated diapycnal diffusivities and downward turbulent heat fluxes are about 5 x 10(-3) m(2) s(-1) and O(10) Wm(-2), respectively. However, heat budgets suggest heat fluxes 2-6 times greater. In the vicinity of one of the major sills of the passage, highly resolved Thorpe-inferred diffusivity and heat flux were over 10 times larger than the region-averaged values, suggesting the mismatch is likely due to undersampled mixing hotspots.

关键词： Geographic location/entity Pacific Ocean Circulation/ Dynamics Abyssal circulation Meridional overturning circulation Mixing observational techniques and algorithms In situ oceanic observations

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The Evolution of Lake-Effect Convection during Landfall and Orographic Uplift as Observed by Profiling Radars

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MONTHLY WEATHER REVIEW 2015年第11期143卷 4422-4442页

作者： Minder, Justin R. Letcher, Theodore W. Campbell, Leah S. Veals, Peter G. Steenburgh, W. James SUNY Albany Albany NY 12222 USA Univ Utah Salt Lake City UT USA

A pronounced snowfall maximum occurs about 30 km downwind of Lake Ontario over the 600-m-high Tug Hill Plateau (hereafter Tug Hill), a region where lake-effect convection is affected by mesoscale forcing associated with landfall and orographic uplift. Profiling radar data from the Ontario Winter Lake-effect Systems field campaign are used to characterize the inland evolution of lake-effect convection that produces the Tug Hill snowfall maximum. Four K-band profiling Micro Rain Radars (MRRs) were aligned in a transect from the Ontario coast onto Tug Hill. Additional observations were provided by an X-band profiling radar (XPR). Analysis is presented of a major lake-effect storm that produced 6.4-cm liquid precipitation equivalent (LPE) snowfall over Tug Hill. This event exhibited strong inland enhancement, with LPE increasing by a factor of 1.9 over 15-km horizontal distance. MRR profiles reveal that this enhancement was not due to increases in the depth or intensity of lake-effect convection. With increasing inland distance, echoes transitioned from a convective toward a stratiform morphology, becoming less intense, more uniform, more frequent, and less turbulent. An inland increase in echo frequency (possibly orographically forced) contributes somewhat to snowfall enhancement. The XPR observations reproduce the basic vertical structure seen by the MRRs while also revealing a suppression of snowfall below 600 m AGL upwind of Tug Hill, possibly associated with subcloud sublimation or hydrometeor advection. Statistics from 29 events demonstrate that the above-described inland evolution of convection is common for lake-effect storms east of Lake Ontario.

关键词： Circulation Dynamics Convection Lake effects Orographic effects Physical Meteorology and Climatology Mesoscale processes observational techniques and algorithms Profilers atmospheric Radars Radar observations

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On the Estimation of Daily Climatological Temperature Variance

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2297-2304页

作者： James, Richard P. Arguez, Anthony Prescient Weather Ltd State Coll PA 16803 USA NOAA Natl Ctr Environm Informat Asheville NC USA

The climatological daily variance of temperature is sometimes estimated from observed temperatures within a centered window of dates. This method overestimates the true variance of daily temperature when the rate of seasonal temperature change is large, because the seasonal change within the date window introduces additional variance. The contribution of the seasonal change may be removed by performing the variance calculation using daily temperature anomalies, leading to a bias-free estimate of variance. The difference between the variance estimation methods is illustrated using both idealized simulations of temperature variability and observed historical temperature data. The simulation results confirm that removing the climatological temperature cycle eliminates bias in the variance estimates. For several U.S. midlatitude locations, the difference in estimated standard deviation of daily mean temperature is on the order of a few percent near the seasonal peaks in climatological temperature change, but the maximum difference is larger in highly continental climates. These differences are shown to be significant when estimating the probability of temperature extremes under the assumption of a Gaussian distribution.

关键词： Physical Meteorology and Climatology Climate variability Climatology Temperature observational techniques and algorithms algorithms Variability Climate variability

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The Effects of Gridding algorithms on the Statistical Moments and Their Trends of Daily Surface Air Temperature

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JOURNAL OF CLIMATE 2015年第23期28卷 9188-9205页

作者： Cavanaugh, Nicholas R. Shen, Samuel S. P. Univ Calif Berkeley Lawrence Berkeley Natl Lab Div Earth Sci Berkeley CA 94720 USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA San Diego State Univ Dept Math & Stat San Diego CA 92182 USA

This paper explores the effects from averaging weather station data onto a grid on the first four statistical moments of daily minimum and maximum surface air temperature (SAT) anomalies over the entire globe. The Global Historical Climatology Network-Daily (GHCND) and the Met Office Hadley Centre GHCND (HadGHCND) datasets from 1950 to 2010 are examined. The GHCND station data exhibit large spatial patterns for each moment and statistically significant moment trends from 1950 to 2010, indicating that SAT probability density functions are non-Gaussian and have undergone characteristic changes in shape due to decadal variability and/or climate change. Comparisons with station data show that gridded averages always underestimate observed variability, particularly in the extremes, and have altered moment trends that are in some cases opposite in sign over large geographic areas. A statistical closure approach based on the quasi-normal approximation is taken to explore SAT's higher-order moments and point correlation structure. This study focuses specifically on relating variability calculated from station data to that from gridded data through the moment equations for weighted sums of random variables. The higher-order and nonlinear spatial correlations up to the fourth order demonstrate that higher-order moments at grid scale can be determined approximately by functions of station pair correlations that tend to follow the usual Kolmogorov scaling relation. These results can aid in the development of constraints to reduce uncertainties in climate models and have implications for studies of atmospheric variability, extremes, and climate change using gridded observations.

关键词： Physical Meteorology and Climatology Temperature observational techniques and algorithms Surface observations Mathematical and statistical techniques Interpolation schemes Variability Anomalies Climate variability Trends

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