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Oceanic mixed layer (ML) response to Hurricane Gilbert in the western Gulf of Mexico is investigated in this paper using the Miami Isopycnic Coordinate Ocean Model (MICOM). Three snapshots of oceanic observations indicated that a Loop Current Warm Core Eddy (LCWCE) contributed significantly to the ML heat and mass budgets. To examine the time evolution of different physical processes in the ML, MICOM is initialized with realistic, climatological, and quiescent conditions for the same realistic forcing. The ML evolves differently for the realistic background condition with the LCWCE in the domain; differences between climatological and quiescent conditions remain small. Mixed layer temperature (MLT) and ML depth (MLD) differences of up to 1ЊC and 30 m are directly attributed to horizontal advective processes in the LCWCE regime due to preexisting velocities. Comparison of simulated temperatures using realistic conditions in the model shows improved agreement with profiler observations. Using four entrainment mixing parameterizations, the spatial and temporal ML evolution is investigated in MICOM simulations. Although the rates of simulated cooling and deepening differ for the four schemes, the overall pattern remains qualitatively similar. For the three schemes that use surfaceinduced turbulence to predict entrainment rate, the cooling pattern extends farther away from the track. Based on linear regression analysis, MLTs simulated using the bulk Richardson number closure fit the observed temperatures better than did the other schemes. Averaged surface fluxes ranged from 10% to 30% in the directly forced region, with larger values in the LCWCE regime. Overall, entrainment mixing remains the dominant mechanism in controlling the heat and mass budgets.

The three-dimensional hurricane-induced ocean response is determined from velocity and temperature profiles acquired in the western Gulf of Mexico between 14 and 19 September 1988 during the passage of Hurricane Gilbert. The asymmetric wind structure of Gilbert indicated a wind stress of 4.2 N m Ϫ2 at a radius of maximum winds (R max) of 60 km. Using observed temperature profiles and climatological temperature-salinity relationships, the background and storm-induced geostrophic currents (re: 750 m) were 0.1 m s Ϫ1 and 0.2 m s Ϫ1 , respectively. A Loop Current warm core ring (LCWCR) was also located to the right of the storm track at 4-5 R max , where anticyclonically rotating near-surface and 100-m currents decreased from 0.9 m s Ϫ1 to 0.6 m s Ϫ1 at depth. The relative vorticity in the LCWCR was shifted below the local Coriolis parameter by about 6%. In a storm-based coordinate system, alongtrack residual velocity profiles from 0 to 4 R max were fit to a dynamical model by least squares to isolate the near-inertial content over an e-folding timescale of four inertial periods (IP ഠ 30 h). Observed frequency shifts in the mixed layer currents ranged from 1.03 to 1.05 f in agreement with both the backrotated velocity profiles at 1.04 f relative to the storm profile (where maximum correlation coefficients were 0.8) and the predicted frequency shift from the mixed-layer Burger number. This frequency was increasingly blue shifted in the upper 100 m to 1.1 f, decreasing toward f within the thermocline. Nearinertial currents rotated anticyclonically by 90Њ-180Њ in the upper ocean, providing the velocity shear for layer cooling and deepening observed on the right-hand side of the track. A summation of the first four baroclinic modes described up to 77% of this near-inertial current variability during the first 1.75 IP. However, the variance explained by this modal summation decreased to a minimum of 36% after 2.9 IP following passage due to phase separation between the first baroclinic mode and higher-order modes in the mixed layer. Although the response was complicated by the LCWCR, the evolving three-dimensional current structure can be described by linear, near-inertial wave dynamics.

Current and future climate impacts of aviation emissions are quantified using a combination of atmospheric models, surface and satellite observations, and laboratory experiments. IMPACT OF AVIATION ON CLIMATEFAA's Aviation Climate Change Research Initiative (ACCRI) Phase II by Guy P. brasseur, Mohan GuPta, bruce e. anderson, sathya balasubraManian, steven barrett, david duda, GreGG FleMinG, Piers M. Forster, Jan FuGlestvedt, andrew GettelMan, ranGasayi n. halthore, s. daniel Jacob, Mark Z. Jacobson, areZoo khodayari, kuo-nan liou, Marianne t. lund, richard c. Miake-lye, Patrick Minnis, seth olsen, Joyce e. Penner, ronald Prinn, ulrich schuMann, henry b. selkirk, andrei sokolov, nadine unGer, PhiliP wolFe, hsi-wu wonG, donald w. wuebbles, binGqi yi, PinG yanG, and chenG Zhou D uring the course of flight, aircraft burn fuel and emit gases and particles into the atmosphere, primarily at cruise altitudes within the upper troposphere and the lower stratosphere (UTLS).These emissions include carbon dioxide (CO 2 ), water vapor (H 2 O), hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x or NO + NO 2 ), sulfur oxides (SO x ), and nonvolatile black carbon (BC or AFFILIATIONS: brasseur-Max Planck Institute for Meteorology, Hamburg, Germany, and National Center for Atmospheric Research, Boulder, Colorado; GuPta, halthore, and Jacob-Federal Aviation Administration, Washington, d.c.; anderson and Minnis-nasa Langley Research Center, Hampton, Virginia; balasubraManian and FleMinG-Volpe Center, Department of Transportation, Cambridge, Massachusetts; barrett, Prinn, sokolov, and wolFe-Massachusetts Institute of Technology, Cambridge, Massachusetts; dudassai/nasa Langley Research Center, Hampton, Virginia; ForsterUniversity of Leeds, Leeds, United Kingdom; FuGlestvedt and lundcicero, Norway; GettelMan-National Center for Atmospheric Research, Boulder, Colorado; Jacobson-Stanford University, Palo Alto, California; khodayari*, olsen, and wuebbles-University of Illinois at Urbana-Champaign, Champaign, Illinois; liou-University of California, Los Angeles, Los Angeles, California; Miake-lye and wonG*-Aerodyne Research Inc., Billerica, Massachusetts; Penner and Zhou-University of Michigan, Ann Arbor, Michigan; The impact of these emissions on UTLS has been examined for several decades (Schumann 1994;Brasseur et al. 1998;Penner et al. 1999;Lee et al. 2009 1 Gaseous emissions of SO x and NO x evolve and partially transform into volatile nitrate and sulfate aerosols and those of gaseous HC emissions into semivolatile organic particles, which also contribute to climate change. Particles like sulfates generally have a cooling effect (negative RF) unless they coat soot particles, which exert warming effects. Note that BC particles are normally considered to be the main component of soot particles.Persistent linear contrails produced in the wake of aircraft contribute to net climate warming. Contrailinduced cirrus clouds (AIC) are also expected to affect the solar and terrestrial infrared radiative budget of the atmosphere, but t...

To simulate tropical cyclone (TC) intensification, coupled ocean-atmosphere prediction models must realistically reproduce the magnitude and pattern of storm-forced sea surface temperature (SST) cooling. The potential for the ocean to support intensification depends on the thermal energy available to the storm, which in turn depends on both the temperature and thickness of the upper-ocean warm layer. The ocean heat content (OHC) is used as an index of this potential. Large differences in available thermal energy associated with energetic boundary currents and ocean eddies require their accurate initialization in ocean models. Two generations of the experimental U.S. Navy ocean nowcast-forecast system based on the Hybrid Coordinate Ocean Model (HYCOM) are evaluated for this purpose in the NW Caribbean Sea and Gulf of Mexico prior to Hurricanes Isidore and Lili (2002), Ivan (2004), and Katrina (2005). Evaluations are conducted by comparison to in situ measurements, the navy's three-dimensional Modular Ocean Data Assimilation System (MODAS) temperature and salinity analyses, microwave satellite SST, and fields of OHC and 26°C isotherm depth derived from satellite altimetry. Both nowcast-forecast systems represent the position of important oceanographic features with reasonable accuracy. Initial fields provided by the first-generation product had a large upper-ocean cold bias because the nowcast was initialized from a biased older-model run. SST response in a free-running Isidore simulation is improved by using initial and boundary fields with reduced cold bias generated from a HYCOM nowcast that relaxed model fields to MODAS analyses. A new climatological initialization procedure used for the second-generation nowcast system tended to reduce the cold bias, but the nowcast still could not adequately reproduce anomalously warm conditions present before all storms within the first few months following nowcast initialization. The initial cold biases in both nowcast products tended to decrease with time. A realistic free-running HYCOM simulation of the ocean response to Ivan illustrates the critical importance of correctly initializing both warm-core rings and cold-core eddies to correctly simulate the magnitude and pattern of SST cooling.

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The effect of precipitation on the upper-ocean response during a tropical cyclone passage is investigated using a numerical model in this paper. For realistic wind forcing and empirical rain rates based on satellite climatology, numerical simulations are performed with and without precipitation forcing to delineate the effects of freshwater forcing on the upper-ocean heat and salt budgets. Additionally, the performance of five mixing parameterizations is also examined for the two forcing conditions to understand the sensitivity of simulated ocean response. Overall, results from 15 numerical experiments are analyzed to quantify the precipitation effects on the oceanic mixed layer and the upper ocean. Simulated fields for the same mixing scheme with and without precipitation indicate a decrease in the upper-ocean cooling of about 0.2°–0.5°C. This is mainly due to reduced mixing of colder water from below induced by the increased stability of the added freshwater. The cooler rainwater contributes a maximum of approximately 10% to the total surface heat loss from the ocean. The rate of freshening due to precipitation exceeds the rate of mixing of the more saline water from below, leading to a change in sign of the mixed layer salinity response. As seen in earlier studies, large uncertainty exists in the simulated upper-ocean response due to the choice of mixing parameterization. Although the nature of simulated response remains similar for all the mixing schemes, the magnitude of freshening and cooling varies by as much as 0.5 psu and 1°C between the schemes to the right of the storm track. While changes in the mixed layer and in the top 100 m of heat and salt budgets are strongly influenced by the choice of mixing scheme, integrated budgets in the top 200 m are seen to be affected more by advection and surface fluxes. However, since the estimated surface fluxes depend upon the simulated sea surface temperature, the choice of mixing scheme is crucial for realistic coupled predictive models.