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Combining In Situ and Satellite Observations to Retrieve Salinity and Density at the Ocean Surface

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第6期33卷 1211-1223页

作者： Droghei, R. Nardelli, B. Buongiorno Santoleri, R. CNR Ist Sci Atmosfera & Clima Via Fosso Cavaliere 100 I-00133 Rome Italy CNR Ist Ambiente Marino Costiero I-80125 Naples Italy

Monitoring sea surface density (SSD), sea surface salinity (SSS), and sea surface temperature (SST) allows for investigating important aspects of the earth system dynamics, with relevant implications on both local/ regional short-scale processes and global climate. Different approaches combine in situ measurements and satellite data to provide gap-free SSS at regular spatial and temporal resolution, aiming to resolve ocean mesoscale. Depending on the application, however, knowing SSD would be more useful than SSS and/or SST alone. Indeed, even if density can be obtained by combining SSS and SST maps at the same nominal resolution, this procedure can lead to spurious features and larger errors when SSS and SST are obtained from different observations and interpolation techniques, especially at the mesoscale. A multidimensional covariance model is applied to interpolate either in situ salinity or in situ density measurements and to build dynamically coherent surface fields, using satellite SST differences as an additional parameter in the optimal estimate. SSS/SSD level 4 (L4) maps are reconstructed over the North Atlantic area, analyzing one month of data. The L4 data are validated using data from the first Salinity Processes in the Upper Ocean Regional Study (SPURS-1) field campaign. The root-mean-square error (RMSE) ranges between 0.03 and 0.13 for the SSS L4 data, and between 0.09 and 0.32 kg m(-3) for the SSD L4 data, with improvements of up to 20% with respect to standard products. Aholdout validation provides similar values for the SSS RMSE (0.13 divided by 0.17) and the SSD RMSE (0.13 divided by 0.17 kg m(-3)). The limitations and advantages of the two approaches are further discussed and analyzed by looking at spatial wavenumber spectra, showing that the multidimensional optimum interpolation (OI) method significantly increases the L4 effective resolution.

关键词： Geographic location/entity Atlantic Ocean Circulation/ Dynamics Mesoscale processes Physical Meteorology and Climatology Salinity Surface temperature observational techniques and algorithms In situ oceanic observations Remote sensing

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Atmospheric Moisture Transport to the Arctic: Assessment of Reanalyses and Analysis of Transport Components

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JOURNAL OF CLIMATE 2016年第14期29卷 5061-5081页

作者： Dufour, Ambroise Zolina, Olga Gulev, Sergey K. UJF LGGE CNRS Grenoble France PP Shirshov Inst Oceanol Moscow Russia

The atmospheric water cycle of the Arctic is evaluated via seven global reanalyses and in radiosonde observations covering the 1979-2013 period. In the regional moisture budget, evaporation and precipitation are the least consistent terms among different datasets. Despite the assimilation of radiosoundings, the reanalyses present a tendency to overestimate the moisture transport. Aside from this overestimation, the reanalyses exhibit a remarkable agreement with the radiosondes in terms of spatial and temporal patterns. The northern North Atlantic, subpolar North Pacific, and Labrador Sea stand out as the main gateways for moisture to the Arctic in all reanalyses. Because these regions correspond to the end of the storm tracks, the link between moisture transports and extratropical cyclones is further investigated by decomposing the moisture fluxes in the mean flow and transient eddy parts. In all reanalyses, the former term tends to cancel out when averaged over a latitude circle, leaving the latter to provide the bulk of the midlatitude moisture imports ( 89%-94% at 70 degrees N). Although the Arctic warms faster than the rest of the world, the impact of these changes on its water cycle remains ambiguous. In most datasets, evaporation, precipitation, and precipitable water increase in line with what is expected from a warming signal. At the same time, the moisture transports have decreased in all the reanalyses but not in the radiosonde observations, though none of these trends is statistically significant. The fluxes do not scale with the Clausius-Clapeyron relation because the increasing humidity is not correlated with the meridional wind, particularly near the surface.

关键词： Geographic location/entity Arctic Circulation/ Dynamics Hydrologic cycle Transport observational techniques and algorithms Radiosonde observations Models and modeling Reanalysis data

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Relating Wind and Stress under Tropical Cyclones with Scatterometer

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第6期33卷 1151-1158页

作者： Liu, W. Timothy Tang, Wenqing CALTECH Jet Prop Lab M-S 300-3234800 Oak Grove Dr Pasadena CA 91109 USA

Ocean surface stress, the turbulent transport of momentum, is largely derived from wind through a drag coefficient. In tropical cyclones (TCs), scatterometers have difficulty measuring strong wind and there is large uncertainty in the drag coefficient. This study postulates that the microwave backscatter from ocean surface roughness, which is in equilibrium with local stress, does not distinguish between weather systems. The reduced sensitivity of scatterometer wind retrieval algorithms under the strong wind is an air-sea interaction problem that is caused by a change in the behavior of the drag coefficient rather than a sensor problem. Under this assumption, a stress retrieval algorithm developed over a moderate wind range is applied to retrieve stress under the strong winds of TCs. Over a moderate wind range, the abundant wind measurements and the more established drag coefficient value allow for sufficient stress data to be computed from wind to develop a stress retrieval algorithm for the scatterometer. Using 0.9 million coincident stress and wind pairs, the study shows that the drag coefficient decreases with wind speed at a much steeper rate than previously revealed, for wind speeds over 25 m s(-1). The result implies that the ocean applies less drag to inhibit TC intensification, and that TCs cause less ocean mixing and surface cooling than previous studies indicated.

关键词： Atm/Ocean Structure/ Phenomena Atmosphere-ocean interaction Hurricanes/typhoons Wind Physical Meteorology and Climatology Stress observational techniques and algorithms Satellite observations

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Life Cycle Characteristics of MCSs in Middle East China Tracked by Geostationary Satellite and Precipitation Estimates

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MONTHLY WEATHER REVIEW 2016年第6期144卷 2517-2530页

作者： Ai, Yufei Li, Wanbiao Meng, Zhiyong Li, Jun Peking Univ Lab Climate & Ocean Atmosphere Studies Dept Atmospher & Ocean Sci Sch Phys Beijing 100871 Peoples R China Univ Wisconsin Cooperat Inst Meteorol Satellite Studies Madison WI USA

By combining high temporal and spatial resolution Multifunctional Transport Satellite-1R (MTSAT-1R) infrared (IR) images and precipitation data from the Climate Prediction Center morphing technique (CMORPH), this study tracked mesoscale convective systems (MCSs) from May to August in 2008 and 2009 in the middle of east China with an automatic tracking algorithm based on an areal overlapping methodology. This methodology is adjusted to include those MCSs with a relative weak intensity before formation. The unique advantage of combining high temporal and spatial resolution geostationary satellite brightness temperature images and the precipitation measurements for tracking MCSs is that the cloud-top height along with the coverage and the precipitation intensity can be well identified. Results showed that the MCSs formed most frequently in the southwest Henan Province and at the border of four provincesShandong, Henan, Anhui, and Jiangsuwhich is east of the convergence zone near the terrain's edge. Locations of the highest cloud tops and of the heaviest precipitation rates did not always match. In addition, the MCSs in the study region tended to first reach the maximum precipitation rate, followed soon by the minimum brightness temperature, then the maximum associated precipitation area, and finally the maximum in system area.

关键词： Atm Ocean Structure Phenomena Convective clouds Precipitation Physical Meteorology and Climatology Convective storms Mesoscale systems observational techniques and algorithms Cloud tracking cloud motion winds Satellite observations

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Observation-Based Longwave Cloud Radiative Kernels Derived from the A-Train

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JOURNAL OF CLIMATE 2016年第6期29卷 2023-2040页

作者： Yue, Qing Kahn, Brian H. Fetzer, Eric J. Schreier, Mathias Wong, Sun Chen, Xiuhong Huang, Xianglei CALTECH Jet Prop Lab 4800 Oak Grove DrMail Stop 233-302C Pasadena CA 91109 USA Univ Michigan Dept Atmospher Ocean & Space Sci Ann Arbor MI 48109 USA

The authors present a new method to derive both the broadband and spectral longwave observation-based cloud radiative kernels (CRKs) using cloud radiative forcing (CRF) and cloud fraction (CF) for different cloud types using multisensor A-Train observations and MERRA data collocated on the pixel scale. Both observation-based CRKs and model-based CRKs derived from the Fu-Liou radiative transfer model are shown. Good agreement between observation-and model-derived CRKs is found for optically thick clouds. For optically thin clouds, the observation-based CRKs show a larger radiative sensitivity at TOA to cloud-cover change than model-derived CRKs. Four types of possible uncertainties in the observed CRKs are investigated: 1) uncertainties in Moderate Resolution Imaging Spectroradiometer cloud properties, 2) the contributions of clear-sky changes to the CRF, 3) the assumptions regarding clear-sky thresholds in the observations, and 4) the assumption of a single-layer cloud. The observation-based CRKs show the TOA radiative sensitivity of cloud types to unit cloud fraction change as observed by the A-Train. Therefore, a combination of observation-based CRKs with cloud changes observed by these instruments over time will provide an estimate of the short-term cloud feedback by maintaining consistency between CRKs and cloud responses to climate variability.

关键词： Physical Meteorology and Climatology Cloud radiative effects Feedback Radiative forcing observational techniques and algorithms Satellite observations

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Derivation of the Green Vegetation Fraction of the Whole China from 2000 to 2010 from MODIS Data

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EARTH INTERACTIONS 2016年第8期20卷 1-16页

作者： Li, Xiaosong Zhang, Jin Chinese Acad Sci Inst Remote Sensing & Digital Earth Key Lab Digital Earth Sci 1 Beichen West Rd Beijing Peoples R China

The green vegetation fraction Fg, which represents the horizontal density of live vegetation, is an important parameter for the study of global energy, carbon, hydrological, and biogeochemical cycling. A common method of calculating Fg is to create a simple linear mixing model between two NDVI endmembers: bare soil NDVI, NDVI0, and full vegetation NDVI, NDVI infinity. However, many uncertainties exist for the determination of these parameters at large scales. The present study investigates how NDVI infinity and NDVI0 determination can impact Fg calculations for all of China, based on different land-cover datasets, hyperspectral data, and soil type classification maps. The results show the following: 1) The regional ChinaCover dataset, with higher accuracy and more detailed classification, is preferable for calculating Fg in China, compared with the most commonly used MOD12Q1 dataset, although it would not lead to too much difference in NDVI infinity values. 2) The soil NDVI from Hyperion datasets shows that soils have highly variable NDVI values (0.006-0.2), and 79.36% of the area studied has a much larger NDVI value than the commonly used value of 0.05. Therefore, the dynamic NDVI0 values with different soil types are much better for Fg calculation than the invariant NDVI0 value (0.05), which would yield a significant overestimation of Fg, especially for areas with low vegetation coverage. 3) A high-quality Fg dataset for China from 2000 to 2010 was established with NDVI infinity and NDVI0 parameters based on MOD13Q1 250-m NDVI data.

关键词： observational techniques and algorithms Data mining Remote sensing Models and modeling Ecological models

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Forecaster Evaluations of High Temporal Satellite Imagery for the GOES-R Era at the NWS Operations Proving Grounds

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WEATHER AND FORECASTING 2016年第4期31卷 1157-1177页

作者： Gravelle, Chad M. Runk, Kim J. Crandall, Katie L. Snyder, Derrick W. NOAA NWS Operat Proving Ground 7220 NW 101st Terr Kansas City MO 64153 USA Univ Wisconsin Cooperat Inst Meteorol Satellite Studies Madison WI USA Univ Wisconsin Cooperat Inst Mesoscale Meteorol Studies Madison WI USA

Between February and April of 2015, the National Weather Service (NWS) Operations Proving Ground (OPG) facilitated an evaluation of the usefulness of 1-min satellite imagery for NWS operations in the Geo-stationary Operational Environmental Satellite-R (GOES-R) series era. The overarching goal of the evaluation was to provide quantitative and qualitative guidance to NWS management, including the regional NWS Scientific Services division chiefs, on how satellite imagery with a refresh rate of 1 min impacts NWS forecaster decision-making. During the simulations, forecasters evaluated 1- and 5-min satellite imagery while completing tasks ranging from aviation forecasting and wildfire decision support services to monitoring where convective initiation would occur and integrating the imagery into the convective warning decision-making process. Feedback was gathered to assess if the satellite imagery had influence on forecaster decision-making, if the satellite imagery provided them with more confidence in making those decisions, if forecasters could assimilate the data into operational practices, and if there were adverse impacts on forecaster workload. Forecasters overwhelmingly were of the opinion that 1-min satellite imagery improved their ability and increased their confidence to make effective forecast and warning decisions. The majority of participants expressed that they were able to internally assimilate the imagery with ease. However, feedback gathered when forecasters were asked how useful and easy the imagery was to use in convective warning operations was mixed. Some forecasters expressed difficulty integrating both satellite imagery and radar data while issuing convective warnings. Others felt that with ample training and experience the imagery would be invaluable in warning operations.

关键词： observational techniques and algorithms Remote sensing Satellite observations Forecasting Forecasting techniques Nowcasting Operational forecasting Applications Communications/decision making

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Determining the Best Method for Estimating the Observed Level of Maximum Detrainment Based on Radar Reflectivity

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MONTHLY WEATHER REVIEW 2016年第8期144卷 2915-2926页

作者： Carletta, Nicholas D. Mullendore, Gretchen L. Starzec, Mariusz Xi, Baike Feng, Zhe Dong, Xiquan Univ North Dakota Dept Atmospher Sci Grand Forks ND 58201 USA NASA Goddard Space Flight Ctr Greenbelt MD USA Sci Syst & Applicat Inc Lanham MD USA Pacific Northwest Natl Lab Richland WA 99352 USA

Convective mass transport is the transport of mass from near the surface up to the upper troposphere and lower stratosphere (UTLS) by a deep convective updraft. This transport can alter the chemical makeup and water vapor balance of the UTLS, which affects cloud formation and the radiative properties of the atmosphere. It is, therefore, important to understand the exact altitudes at which mass is detrained from convection. The purpose of this study was to improve upon previously published methodologies for estimating the level of maximum detrainment (LMD) within convection using data from a single ground-based radar. Four methods were used to identify the LMD and validated against dual-Doppler-derived vertical mass divergence fields for six cases with a variety of storm types. The best method for locating the LMD was determined to be the method that used a reflectivity texture technique to determine convective cores and a multilayer echo identification to determine anvil locations. Although an improvement over previously published methods, the new methodology still produced unreliable results in certain regimes. The methodology worked best when applied to mature updrafts, as the anvil needs time to grow to a detectable size. Thus, radar reflectivity is found to be valuable in estimating the LMD, but storm maturity must also be considered for best results.

关键词： Circulation/ Dynamics Convective clouds Mass fluxes/transport Mesoscale processes Transport observational techniques and algorithms Radars/Radar observations

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Factors Controlling Low-Cloud Evolution over the Eastern Subtropical Oceans: A Lagrangian Perspective Using the A-Train Satellites

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第1期73卷 331-351页

作者： Eastman, Ryan Wood, Robert Univ Washington Dept Atmospher Sci Seattle WA 98195 USA

A Lagrangian technique is developed to sample satellite data to quantify and understand factors controlling temporal changes in low-cloud properties (cloud cover, areal-mean liquid water path, and droplet concentration). Over 62 000 low-cloud scenes over the eastern subtropical/tropical oceans are sampled using the A-Train satellites. Horizontal wind fields at 925 hPa from the ERA-Interim are used to compute 24-h, two-dimensional, forward, boundary layer trajectories with trajectory locations starting on the CloudSat/CALIPSO track. Cloud properties from MODIS and AMSR-E are sampled at the trajectory start and end points, allowing for direct measurement of the temporal cloud evolution. The importance of various controls (here, boundary layer depth, lower-tropospheric stability, and precipitation) on cloud evolution is evaluated by comparing cloud evolution for different initial values of these controls. Viewing angle biases are removed and cloud anomalies (diurnal and seasonal cycles removed) are used throughout to quantify cloud evolution relative to the climatological-mean evolution. Cloud property anomalies show temporal changes similar to those expected for a stochastic red noise process, with linear relationships between initial anomalies and their mean 24-h changes. This creates a potential bias when comparing the evolutions of sets of trajectories with different initial anomalies;three methods are introduced and evaluated to account for this. Results provide statistically robust observational support for theoretical/modeling studies by showing that low clouds in deep boundary layers and under weak inversions are prone to break up. Precipitation shows a more complex and less statistically significant relationship with cloud breakup. Cloud cover in shallow precipitating boundary layers is more persistent than in deep precipitating boundary layers. Liquid water path and cloud droplet concentration decrease more rapidly for precipitating clouds and in deep boundar

关键词： Atm Ocean Structure Phenomena Boundary layer Cloud cover Precipitation Stability Stratiform clouds observational techniques and algorithms Satellite observations

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The Measured Relationship between Ice Water Content and Cloud Radar Reflectivity in Tropical Convective Clouds

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第8期55卷 1707-1729页

作者： Protat, A. Delanoe, J. Strapp, J. W. Fontaine, E. Leroy, D. Schwarzenboeck, A. Lilie, L. Davison, C. Dezitter, F. Grandin, A. Weber, M. Australian Bur Meteorol Res & Dev Branch Melbourne Vic Australia Lab Atmosphere Milieux Observat Spatiales LATMOS Guyancourt France Met Analyt Inc Toronto ON Canada Univ Clermont Ferrand Lab Meteorol Phys LaMP Clermont Ferrand France Sci Engn Associates Mansfield Ctr CT USA Natl Res Council Canada Ottawa ON Canada Airbus Inc Toulouse France

In this paper, unprecedented bulk measurements of ice water content (IWC) up to approximately 5 g m(-3) and 95-GHz radar reflectivities Z(95) are used to analyze the statistical relationship between these two quantities and its variability. The unique aspect of this study is that these IWC-Z(95) relationships do not use assumptions on cloud microphysics or backscattering calculations. IWCs greater than 2 g m(-3) are also included for the first time in such an analysis, owing to improved bulk IWC probe technology and a flight program targeting high ice water content. Using a single IW-Z(95) relationship allows for the retrieval of IWC from radar reflectivities with less than 30% bias and 40%-70% rms difference. These errors can be reduced further, down to 10%-20% bias over the whole IWC range, using the temperature variability of this relationship. IWC errors largely increase for Z(95) > 16 dBZ, as a result of the distortion of the IWC-Z(95) relationship by non-Rayleigh scattering effects. A nonlinear relationship is proposed to reduce these errors down to 20% bias and 20%-35% rms differences. This nonlinear relationship also outperforms the temperature-dependent IWC-Z(95) relationship for convective profiles. The joint frequency distribution of IWC and temperature within and around deep tropical convective cores shows that at the -50 degrees +/- 5 degrees C level, the cruise altitude of many commercial jet aircraft, IWCs greater than 1.5 g m(-3) were found exclusively in convective profiles.

关键词： Physical Meteorology and Climatology Cloud microphysics Cloud retrieval Convective storms Convective-scale processes observational techniques and algorithms Cloud retrieval Radars/Radar observations

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