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College Park, MD, United States

Zagar N.,University of Ljubljana | Tribbia J.,U.S. National Center for Atmospheric Research | Anderson J.L.,U.S. National Center for Atmospheric Research | Raeder K.,U.S. National Center for Atmospheric Research | Kleist D.T.,National Centers for Environmental Prediction
Quarterly Journal of the Royal Meteorological Society | Year: 2010

This paper applies the normal-mode functions for the three-dimensional diagnosis of systematic analysis increments in the operational systems of ECMWF and NCEP, in the NCEP/NCAR reanalyses and in the ensemble data assimilation system DART/CAM which is developed at NCAR. Non-zero systematic increments are interpreted as the analysis system bias. The main region of tropospheric biases in all systems is the Tropics; most of the large-scale tropical bias resides in the unbalanced (inertio-gravity) motionwiththeeastward-propagatingcomponentbeingdominant insomedatasets. Themagnitudes of troposphericwind-fieldbiases inJuly 2007 were in the range between 1m s1 and 2 ms1, illustrating the importance of diagnosing analysis systems in the Tropics where magnitudes of the large-scale variability are of the same order. The systematic increments integrated over the whole models' atmosphere appear predominantly balanced; this balance is associated with biases in the zonally averaged balanced state and, in case of ECMWF and NCEP, with the biases at the model top levels. Spectra of analysis increments averaged over one month show that, on average, 20% to 45% of total energy in increment fields belongs to the inertio-gravity motions. © 2010 Royal Meteorological Society. Source

Spada M.,Barcelona Supercomputing Center | Jorba O.,Barcelona Supercomputing Center | Perez Garcia-Pando C.,NASA | Perez Garcia-Pando C.,Columbia University | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2013

One of the major sources of uncertainty in model estimates of the global sea-salt aerosol distribution is the emission parameterization. We evaluate a new sea-salt aerosol life cycle module coupled to the online multiscale chemical transport model NMMB/BSC-CTM. We compare 5 yr global simulations using five state-of-the-art sea-salt open-ocean emission schemes with monthly averaged coarse aerosol optical depth (AOD) from selected AERONET sun photometers, surface concentration measurements from the University of Miami's Ocean Aerosol Network, and measurements from two NOAA/PMEL cruises (AEROINDOEX and ACE1). Model results are highly sensitive to the introduction of sea-surface- temperature (SST)-dependent emissions and to the accounting of spume particles production. Emission ranges from 3888 Tg yr-1 to 8114 Tg yr -1, lifetime varies between 7.3 h and 11.3 h, and the average column mass load is between 5.0 Tg and 7.2 Tg. Coarse AOD is reproduced with an overall correlation of around 0.5 and with normalized biases ranging from +8.8% to +38.8%. Surface concentration is simulated with normalized biases ranging from -9.5% to +28% and the overall correlation is around 0.5. Our results indicate that SST-dependent emission schemes improve the overall model performance in reproducing surface concentrations. On the other hand, they lead to an overestimation of the coarse AOD at tropical latitudes, although it may be affected by uncertainties in the comparison due to the use of all-sky model AOD, the treatment of water uptake, deposition and optical properties in the model and/or an inaccurate size distribution at emission. © 2013 Author(s). Source

Gentine P.,Columbia University | Holtslag A.A.K.,Wageningen University | D'Andrea F.,Ecole Normale Superieure de Paris | Ek M.,National Centers for Environmental Prediction
Journal of Hydrometeorology | Year: 2013

The onset of moist convection over land is investigated using a conceptual approach with a slab boundary layer model. The authors determine the essential factors for the onset of boundary layer clouds over land and study their relative importance. They are 1) the ratio of the temperature to the moisture lapse rates of the free troposphere, that is, the inversion Bowen ratio; 2) the mean daily surface temperature; 3) the relative humidity of the free troposphere; and 4) the surface evaporative fraction. Aclear transition is observed between two regimes of moistening of the boundary layer as assessed by the relative humidity at the boundary layer top. In the first so-called wet soil advantage regime, the moistening results from the increase of the mixedlayer specific humidity, which linearly depends on the surface evaporative fraction and inversion Bowen ratio through a dynamic boundary layer factor. In the second so-called dry soil advantage regime, the relative humidity tendency at the boundary layer top is controlled by the thermodynamics and changes in the moist adiabatic induced by the decreased temperature at the boundary layer top and consequent reduction in saturation water vapor pressure. This regime pertains to very deep boundary layers under weakly stratified free troposphere over hot surface conditions. In the context of the conceptual model, a rise in freetropospheric temperature (global warming) increases the occurrence of deep convection and reduces the cloud cover over moist surfaces. This study provides new intuition and predictive capacity on the mechanism controlling the occurrence of moist convection over land. © 2013 American Meteorological Society. Source

BozorgMagham A.E.,University of Maryland University College | Motesharrei S.,National Socio Environmental Synthesis Center | Motesharrei S.,University of Maryland University College | Penny S.G.,University of Maryland University College | And 2 more authors.
PLoS ONE | Year: 2015

Physical systems with time-varying internal couplings are abundant in nature. While the full governing equations of these systems are typically unknown due to insufficient understanding of their internal mechanisms, there is often interest in determining the leading element. Here, the leading element is defined as the sub-system with the largest coupling coefficient averaged over a selected time span. Previously, the Convergent Cross Mapping (CCM) method has been employed to determine causality and dominant component in weakly coupled systems with constant coupling coefficients. In this study, CCM is applied to a pair of coupled Lorenz systems with time-varying coupling coefficients, exhibiting switching between dominant sub-systems in different periods. Four sets of numerical experiments are carried out. The first three cases consist of different coupling coefficient schemes: I) Periodic-constant, II) Normal, and III) Mixed Normal/Non-normal. In case IV, numerical experiment of cases II and III are repeated with imposed temporal uncertainties as well as additive normal noise. Our results show that, through detecting directional interactions, CCM identifies the leading sub-system in all cases except when the average coupling coefficients are approximately equal, i.e., when the dominant sub-system is not well defined. © 2015 BozorgMagham et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Source

Guillod B.P.,ETH Zurich | Orlowsky B.,ETH Zurich | Miralles D.,Ghent University | Miralles D.,University of Bristol | And 11 more authors.
Atmospheric Chemistry and Physics | Year: 2015

The feedback between soil moisture and precipitation has long been a topic of interest due to its potential for improving weather and seasonal forecasts. The generally proposed mechanism assumes a control of soil moisture on precipitation via the partitioning of the surface turbulent heat fluxes, as assessed via the evaporative fraction (EF), i.e., the ratio of latent heat to the sum of latent and sensible heat, in particular under convective conditions. Our study investigates the poorly understood link between EF and precipitation by relating the before-noon EF to the frequency of afternoon precipitation over the contiguous US, through statistical analyses of multiple EF and precipitation data sets. We analyze remote-sensing data products (Global Land Evaporation: the Amsterdam Methodology (GLEAM) for EF, and radar precipitation from the NEXt generation weather RADar system (NEXRAD)), FLUXNET station data, and the North American Regional Reanalysis (NARR). Data sets agree on a region of positive relationship between EF and precipitation occurrence in the southwestern US. However, a region of strong positive relationship over the eastern US in NARR cannot be confirmed with observation-derived estimates (GLEAM, NEXRAD and FLUXNET). The GLEAM-NEXRAD data set combination indicates a region of positive EF-precipitation relationship in the central US. These disagreements emphasize large uncertainties in the EF data. Further analyses highlight that much of these EF-precipitation relationships could be explained by precipitation persistence alone, and it is unclear whether EF has an additional role in triggering afternoon precipitation. This also highlights the difficulties in isolating a land impact on precipitation. Regional analyses point to contrasting mechanisms over different regions. Over the eastern US, our analyses suggest that the EF-precipitation relationship in NARR is either atmospherically controlled (from precipitation persistence and potential evaporation) or driven by vegetation interception rather than soil moisture. Although this aligns well with the high forest cover and the wet regime of that region, the role of interception evaporation is likely overestimated because of low nighttime evaporation in NARR. Over the central and southwestern US, the EF-precipitation relationship is additionally linked to soil moisture variations, owing to the soil-moisture-limited climate regime. © Author(s) 2014. Source

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