bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous retrieval of middle atmospheric temperature and trace gas species volume mixing ratios from Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A)
Authors: Miller Steven M. , Snell Hilary E. , Moncet Jean‐Luc
Published: December 2003

We have developed an atmospheric temperature and constituent retrieval code using an efficient derivative of Fast Atmospheric Signature Code 3 coupled with the optimal estimation inversion method. This code provides arbitrary spectral resolution and instrument response function and was thoroughly tested with model generated “data” and then applied to the stratospheric Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) database. The CIRRIS 1A experiment flew aboard space shuttle mission Space Transportation System 39 in April 1991. It included a 1 cm−1 resolution midinfrared interferometer that made numerous scans of the earthlimb. A small subset of these included a survey of the stratosphere during the day at 50°–65°N latitude and during the night at 35°–50°S latitude. The retrieval code provides us with the error analysis tools necessary to determine the relative contributions of the measurements and any a priori information made available to the code. Temperature and constituent profiles are reported along with comparisons to other recent atmospheric measurements. The absence of sufficient information to retrieve certain species is also discussed.
Processes influencing the emission of mercury from soils: A conceptual model
Authors: Zhang H. , Lindberg S. E.
Published: December 2003

In contrast to recent rapid growth in the field data on mercury flux over soils, our knowledge and understanding of the emission processes and controlling mechanisms still remains limited. Many processes could control emission of mercury from soils. The emission processes may involve both Hg(0) and Hg(II) pools, both homogeneous and heterogeneous distributions and reactions, and both dark and light processes. The physical and chemical controlling processes mainly involve (1) distribution of different mercury species among different soil phases, largely associated with adsorption and desorption of Hg(0) and Hg(II) species, and (2) mercury redox reactions in soils, some of which could be induced by sunlight, especially in the UV. The distribution (sorption versus desorption) of Hg(0) in soils could be the rate‐limiting process in the case where Hg(0) is the dominant mercury pool, and the redox reactions could be rate‐limiting in the case where Hg(II) is the major pool. Various hypothetical scenarios of Hg(0) and Hg(II) transformation in soils are discussed here. However, the specific processes that actually occur in soils under natural conditions are far from clear and need to be identified and quantified in future research.
Distributions of brominated organic compounds in the troposphere and lower stratosphere
Authors: Schauffler S. M. , Atlas E. L. , Blake D. R. , Flocke F. , Lueb R. A. , Lee‐Taylor J. M. , Stroud V. , Travnicek W.
Published: December 2003

A comprehensive suite of brominated organic compounds was measured from whole air samples collected during the 1996 NASA Stratospheric Tracers of Atmospheric Transport aircraft campaign and the 1996 NASA Global Tropospheric Experiment Pacific Exploratory Mission‐Tropics aircraft campaign. Measurements of individual species and total organic bromine were utilized to describe latitudinal and vertical distributions in the troposphere and lower stratosphere, fractional contributions to total organic bromine by individual species, fractional dissociation of the long‐lived species relative to CFC‐11, and the Ozone Depletion Potential of the halons and CH3Br. Spatial differences in the various organic brominated compounds were related to their respective sources and chemical lifetimes. The difference between tropospheric mixing ratios in the Northern and Southern Hemispheres for halons was approximately equivalent to their annual tropospheric growth rates, while the interhemispheric ratio of CH3Br was 1.18. The shorter‐lived brominated organic species showed larger tropospheric mixing ratios in the tropics relative to midlatitudes, which may reflect marine biogenic sources. Significant vertical gradients in the troposphere were observed for the short‐lived species with upper troposphere values 40–70% of the lower troposphere values. Much smaller vertical gradients (3–14%) were observed for CH3Br, and no significant vertical gradients were observed for the halons. Above the tropopause, the decrease in organic bromine compounds was found to have some seasonal and latitudinal differences. The combined losses of the individual compounds resulted in a loss of total organic bromine between the tropopause and 20 km of 38–40% in the tropics and 75–85% in midlatitudes. The fractional dissociation of the halons and CH3Br relative to CFC‐11 showed latitudinal differences, with larger values in the tropics.
Increases in mercury emissions from desert soils in response to rainfall and irrigation
Authors: Lindberg S. E. , Zhang H. , Gustin M. , Vette A. , Marsik F. , Owens J. , Casimir A. , Ebinghaus R. , Edwards G. , Fitzgerald C. , Kemp J. , Kock H. H. , London J. , Majewski M. , Poissant L. , Pilote M. , Rasmussen P. , Schaedlich F. , Schneeberger D. , Sommar J. , Turner R. , Wallschläger D. , Xiao Z.
Published: December 2003

As part of an international Hg flux intercomparison at the Steamboat Springs, Nevada, geothermal area, several dynamic soil flux chambers and micrometeorological gradient systems were operated over desert soils in early September 1997. A series of unanticipated convective rain cells impacted the site with the first rainfall in ∼90 days, and the initial 4‐cm rainfall increased soil moisture from ∼0.01 to 0.06% (vol/vol). Several chambers were operating prior to the events, and two were deployed over wet soils following rainfall. Rainfall resulted in an immediate and steep rise in ambient air Hg concentrations and soil Hg emissions which persisted for 12–24 hours. Fluxes increased most quickly and to a greater degree over the wettest soils, and the rate of increase was related to chamber design and flushing rate. The flux response was also apparent in the micrometeorological data. In general, soil emissions increased by an order of magnitude following the rain, and reached levels ∼6 times above those at the same time the previous day. These fluxes were significantly correlated with temperature, radiation, humidity, wind speed, and soil moisture. After drying for ∼40 hours, selected soil plots were manually irrigated with low‐Hg‐distilled water. Mercury emissions responded similarly across the three treated sites, uniformly increasing from ∼60 ng m−2 h−1 pretreatment to ∼650 ng m−2 h−1 posttreatment, which was a factor of ∼6 higher than adjacent control soils. Possible causes of the increases in flux include soil gas displacement, desorption of Hg° by water molecules, and desorption of Hg(II) and subsequent reduction in solution. The kinetics of the flux response, combined with local soil and climatic conditions, suggest that Hg emissions were responding primarily to soil moisture and solar radiation. These data have interesting implications for the role of changing regional climates on biogeochemical cycling of Hg.
Tropospheric hydroxyl and atomic chlorine concentrations, and mixing timescales determined from hydrocarbon and halocarbon measurements made over the Southern Ocean
Authors: Wingenter Oliver W. , Blake Donald R. , Blake Nicola J. , Sive Barkley C. , Rowland F. Sherwood , Atlas Elliot , Flocke Frank
Published: December 2003

During the First Aerosol Characterization Experiment (ACE 1) field campaign, 1419 whole air samples were collected over the Southern Ocean, of which approximately 700 samples were collected in the marine boundary layer (MBL), 300 samples were taken in the free troposphere (FT), and the remainder were collected in the buffer layer (BuL), the layer between the MBL and FT. Concentrations of tetrachloroethene, ethane, ethyne, and propane decayed over the 24 day duration of the intensive portion of the field campaign, which began November 18, 1995. This decline was consistent with what is known about seasonal increase of HO and the seasonal decrease in biomass burning. Using a simple empirical model, the best fit to the observations was obtained when the average [HO] was 6.1 ± 0.3 × 105 HO cm−3, and an average [Cl] of 720±100 Cl cm−3. The corresponding exchange times were 14±2 days between the MBL and FT, and 49 + 40/−13 days between the MBL in the intensive campaign region and the MBL region to the north (nMBL).
Relative roles of climate and emissions changes on future tropospheric oxidant concentrations
Authors: Johnson C. E. , Collins W. J. , Stevenson D. S. , Derwent R. G.
Published: December 2003

A Lagrangian chemistry‐transport model (STOCHEM) was driven with meteorology derived from a slab ocean general circulation model for conditions appropriate to the present‐day and at double CO2, and with emission scenarios appropriate for present day conditions and for the year 2075. The results show conclusively that the effect of including the predicted changes to future climate is to reduce the simulated tropospheric ozone concentrations. The response of global tropospheric ozone in the period 1990–2075 was an increase of 6.4 ppb when both climate and emissions changes were included, compared to an increase of 10.3 ppb when only emissions changes were considered. This difference is mainly due to water vapor and temperature increases, together with some dynamical effects. There are considerable changes to other tropospheric oxidants, with OH, HO2, and H2O2 all increasing considerably in response to climate changes. In contrast, OH decreases when only the emissions are allowed to change. A replicate run of the control scenario with STOCHEM using a different year of meteorology showed considerable interannual variability in local monthly mean ozone concentrations.
Soot and sulfate aerosol particles in the remote marine troposphere
Authors: Pósfai Mihály , Anderson James R. , Buseck Peter R. , Sievering Herman
Published: December 2003

Sulfate aerosol particles containing soot aggregates were observed in the marine troposphere in both hemispheres under conditions that ranged from extremely clean to heavily polluted. Even in clean air above the remote Southern Ocean during the First Aerosol Characterization Experiment (ACE 1), depending on the sample, between 10 and 45% of sulfate particles contained soot inclusions. We identified aircraft emissions and biomass burning as the most likely major sources of soot. Internally mixed soot and sulfate appear to comprise a globally significant fraction of aerosols in the troposphere. Anthropogenic combustion aerosols can thus potentially change the radiative climate effects of sulfate aerosols and may have an impact on cloud properties even in the remote troposphere.
Climate model simulation of winter warming and summer cooling following the 1991 Mount Pinatubo volcanic eruption
Authors: Kirchner Ingo , Stenchikov Georgiy L. , Graf Hans‐F. , Robock Alan , Antuña Juan Carlos
Published: December 2003

We simulate climate change for the 2‐year period following the eruption of Mount Pinatubo in the Philippines on June 15, 1991, with the ECHAM4 general circulation model (GCM). The model was forced by realistic aerosol spatial‐time distributions and spectral radiative characteristics calculated using Stratospheric Aerosol and Gas Experiment II extinctions and Upper Atmosphere Research Satellite‐retrieved effective radii. We calculate statistical ensembles of GCM simulations with and without volcanic aerosols for 2 years after the eruption for three different sea surface temperatures (SSTs): climatological SST, El Niño‐type SST of 1991–1993, and La Niña‐type SST of 1984–1986. We performed detailed comparisons of calculated fields with observations. We analyzed the atmospheric response to Pinatubo radiative forcing and the ability of the GCM to reproduce it with different SSTs. The temperature of the tropical lower stratosphere increased by 4 K because of aerosol absorption of terrestrial longwave and solar near‐infrared radiation. The heating is larger than observed, but that is because in this simulation we did not account for quasi‐biennial oscillation (QBO) cooling and the cooling effects of volcanically induced ozone depletion. We estimated that both QBO and ozone depletion decrease the stratospheric temperature by about 2 K. The remaining 2 K stratospheric warming is in good agreement with observations. By comparing the runs with the Pinatubo aerosol forcing with those with no aerosols, we find that the model calculates a general cooling of the global troposphere, but with a clear winter warming pattern of surface air temperature over Northern Hemisphere continents. This pattern is consistent with the observed temperature patterns. The stratospheric heating and tropospheric summer cooling are directly caused by aerosol radiative effects, but the winter warming is indirect, produced by dynamical responses to the enhanced stratospheric latitudinal temperature gradient. The aerosol radiative forcing, stratospheric thermal response, and summer tropospheric cooling do not depend significantly on SST. The stratosphere‐troposphere dynamic interactions and tropospheric climate response in winter are sensitive to SST.
On the use of regularization techniques in the inverse modeling of atmospheric carbon dioxide
Authors: Fan Song‐Miao , Sarmiento Jorge L. , Gloor Manuel , Pacala Stephen W.
Published: December 2003

The global distribution of carbon sources and sinks is estimated from atmospheric CO2 measurements using an inverse method based on the Geophysical Fluid Dynamics Laboratory SKYHI atmospheric general circulation model. Applying the inverse model without any regularization yields unrealistically large CO2 fluxes in the tropical regions. We examine the use of three regularization techniques that are commonly used to stabilize inversions: truncated singular value decomposition, imposition of a priori flux estimates, and use of a quadratic inequality constraint. The regularization techniques can all be made to minimize the unrealistic fluxes in the tropical regions. This brings inversion estimated CO2 fluxes for oceanic regions in the tropics and in the Southern Hemisphere into better agreement with independent estimates of the air‐sea exchange. However, one cannot assume that stabilized inversions give accurate estimates, as regularization merely holds the fluxes to a priori estimates or simply reduces them in magnitude in regions that are not resolvable by observations. By contrast, estimates of flux and uncertainty for the temperate North Atlantic, temperate North Pacific, and boreal and temperate North American regions are far less sensitive to the regularization parameters, consistent with the fact that these regions are better constrained by the present observations.
Numerical simulation of the 1993 midwestern flood: Local and remote sources of water
Authors: Bosilovich Michael G. , Sun Wen‐Yih
Published: December 2003

Local and remote sources of water are estimated by removing the surface source of water vapor in a numerical simulation without significantly influencing the large‐scale dynamical circulation. This is done by reducing the surface moisture flux in the model's hydrologic equations but maintaining latent heat in the surface energy balance and evaporation in the soil water budget. Simulations of the 1993 midwestern flood are used as test cases. Without the local surface source of water vapor, the flood region's atmospheric hydrology budget reduces to an approximate balance between precipitation and moisture flux convergence. Comparison with the control simulation hydrology approximated 12% and 20% of the precipitation with a local source for June and July 1993 respectively. The differences between the two months are reasonable considering that June is dominated by a transient synoptic‐scale wave pattern, but July precipitation is largely related to mesoscale convective complexes. The southern Great Plains source influences the flood region precipitation slightly less than the local anomaly for each month. The differences between June and July are striking. A great deal of variability exists in the modeled interactions between the surface and atmosphere. This indicates that simply using any one month to generalize the interactions or feedback of water does not address the complete problem.
Contrasting evaporative moisture sources during the drought of 1988 and the flood of 1993
Authors: Dirmeyer Paul A. , Brubaker Kaye L.
Published: December 2003

Using hourly observed precipitation data, National Centers for Environmental Prediction reanalyses at 6 hourly intervals, and a quasi‐isentropic back‐trajectory algorithm, we have examined the transport and surface sources of moisture supplying rainfall during the spring and summer over the United States during the drought year of 1988 and the flood year of 1993. These results are compared to calculations using a bulk‐transport approach and monthly mean data. We find that about 41% of precipitation over the Mississippi River basin originated as evaporation from the same basin during April‐July 1988 and 33% during 1993. During the July peak of the 1993 flood the recycling ratio was considerably lower than in other months, while the source of moisture from the western Gulf of Mexico and Caribbean Sea increased enormously. By contrast, at the June climax of the 1988 drought, the recycling ratio reaches a maximum. We also find a small source region in the eastern subtropical Pacific Ocean during both years, which decreases significantly with the onset of the Mexican monsoon around the beginning of July. The back‐trajectory approach represents an improvement over the bulk recycling approach by rejecting the assumption of uniform distributions of rainfall in space and time, instead focusing specifically on the sources and transport of moisture contributing to observed rainfall events.
Surface energy balance and boundary layer development during snowmelt
Authors: Baker J. M. , Davis K. J. , Liknes G. C.
Published: December 2003

Improved prediction of snowmelt requires comprehensive data collection, including surface, subsurface, and atmospheric processes, during the snowmelt period. We report results of field research in which all components of the surface energy balance were measured during two different snowmelt periods, along with boundary layer soundings. The two periods were quite different, the first being overcast and the second occurring under clear skies. However, snowmelt was estimated relatively well from the cumulative residual of the energy balance in both cases. Downward infrared radiation and sensible heat flux were important contributors to the melt during overcast conditions, with net radiation providing about two thirds of the energy for melt and sensible heat providing the remainder. The sunny melt was dominated by direct solar heating of the surface. In both cases, estimation of melt as a residual of the energy balance agreed well with visual and gravimetric observations. The boundary layer soundings revealed the importance of advection, which was generally consistent with synoptic patterns during the period of the study. The data also showed a transition from advection‐dominated to turbulence‐dominated boundary layer budgets as the snowpack disappeared. The potential for convective cloud formation was also examined. Surface heating and entrainment outweighed adiabatic cooling and evaporation, resulting in the boundary layer top relative humidity decreasing as the snow melted and turbulent mixing increased.
Assimilation of photochemically active species and a case analysis of UARS data
Authors: Khattatov Boris V. , Gille John C. , Lyjak Lawrence V. , Brasseur Guy P. , Dvortsov Victor L. , Roche Aidan E. , Waters Joe W.
Published: December 2003

We present a short overview of applications of estimation theory in atmospheric chemistry and discuss some common methods of gridding and mapping of irregular satellite observations of chemical constituents. It is shown that these methods are unable to produce truly synoptic maps of short‐lived photochemically active species due to insufficient temporal and spatial density of satellite observations. The only way to overcome this limitation is to supplement observations with prior independent information given, for instance, by atmospheric numerical models and/or climatologies. Objective approaches to combining such prior information with observations are commonly referred to as data assimilation. Mathematical basis of data assimilation known as optimal estimation equations is presented following Lorenc [1986]. Two particular techniques of data assimilation, the variational method and the extended Kalman filter, are briefly described, and their applications to time‐dependent numerical photochemical models are discussed. We investigate validity of the linear approximation which is utilized in both methods, present time evolution of the linearization and covariance matrices, and discuss some of their properties. On the basis of ideas of Fisher and Lary [1995] we then employ a trajectory model and a photochemical box model for assimilation and mapping of the Upper Atmosphere Research Satellite (UARS) measurements of chemical species. The assimilation is performed using the variational technique and the extended Kalman filter, and results of both methods are presented and discussed.
Numerical simulation studies of rain gage data correction due to wind effect
Authors: Habib Emad , Krajewski Witold F. , Nespor Vladislav , Kruger Anton
Published: December 2003

Investigation of the correction of rain gage measurements due to the wind effect is described. The focus is on the effect of the temporal averaging scale on the estimation of the wind‐induced error correction. Numerically derived correction formulae for a specific class of rain gage types, along with high temporal resolution measurements of rainfall and wind speed, are used to perform the study. The rainfall measurements are corrected on a variety of temporal scales ranging from 1 min to 1 month. The results showed the importance of applying the correction procedure at a short timescale, otherwise a significant overestimation of the wind‐induced bias results. The wind‐induced error is characterized by a nonlinear complex behavior dependent on wind speed, rainfall rate, and the microphysical rain structure quantified by a drop size distribution parameter. The estimated correction factors are found to be sensitive to the change of the drop size distribution. Finally, comparison with certain formulae reported in the literature showed a significant random scatter of the estimated correction if it is expressed only as a function of the wind speed and the drop size distribution characteristics are ignored.
Sensitivity of ground heat flux to vegetation cover fraction and leaf area index
Authors: Yang Z‐L. , Dai Y. , Dickinson R. E. , Shuttleworth W. J.
Published: December 2003

Two land‐surface models that participated in the recent Project for Intercomparison of Land‐Surface Parameterization Schemes (PILPS, phase 2c) are used to investigate the sensitivity of the ground heat flux to the vegetation cover fraction and leaf area index (LAI). The two models are the Biosphere‐Atmosphere Transfer Scheme (BATS) and the model developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP94). The impacts of including transmission of solar radiation through the canopy in the BATS model are also assessed. The ground heat flux is the energy residual of net radiation minus latent plus sensible heat fluxes at the soil surface (also referred to as the soil heat flux). However, the energy residual above the canopy was used as a surrogate for the ground heat flux by the two models in the PILPS 2c study. The two energy residuals (i.e., above the canopy and at the soil surface) can differ depending on the modeled time step, the order in which the canopy and soil temperatures are computed, and whether canopy heat storage is included or neglected. As expected, reducing the areal coverage of vegetation results in an increased daytime soil heat flux, and increasing LAI leads to decreased soil heat flux and greater above‐canopy latent heat flux. Both models show a strong sensitivity to LAI when LAI is small and little sensitivity when LAI is large. Allowing transmission of solar radiation through the canopy in BATS reduces the sensible heat flux above the canopy and enhances all the flux terms at the soil surface, especially when LAI is low. This model behavior is similar to that from IAP94, which uses a two‐stream radiation scheme. This modification to BATS also results in a soil heat flux that lies within estimated bounds for a wide range of LAI (0.5–5.5).
Seasonal weather prediction as an initial value problem
Authors: Pielke Roger A. , Liston Glen E. , Eastman Joseph L. , Lu Lixin , Coughenour Michael
Published: December 2003

Using a climate version of a regional atmospheric model, we show that the seasonal evolution of weather is dependent on the initial soil moisture and landscape specification. Coupling this model to a land‐surface model, the soil moisture distribution and landscape are shown to cause a significant nonlinear interaction between vegetation growth and precipitation. These results demonstrate that seasonal weather prediction is an initial value problem. Moreover, on seasonal and longer timescales the surface characteristics such as soil moisture, leaf area index, and landcover type must be treated as dynamically evolving dependent variables, instead of prescribed parameters.
A parameterization of snowpack and frozen ground intended for NCEP weather and climate models
Authors: Koren V. , Schaake J. , Mitchell K. , Duan Q.‐Y. , Chen F. , Baker J. M.
Published: December 2003

Extensions to the land surface scheme (LSS) in the National Centers for Environmental Prediction, regional, coupled, land‐atmosphere weather prediction model, known as the mesoscale Eta model, are proposed and tested off‐line in uncoupled mode to account for seasonal freezing and thawing of soils and snow‐accumulation‐ablation processes. An original model assumption that there is no significant heat transfer during redistribution of liquid water was relaxed by including a source/sink term in the heat transfer equation to account for latent heat during phase transitions of soil moisture. The parameterization uses the layer‐integrated form of heat and water diffusion equations adopted by the original Eta‐LSS. Therefore it simulates the total ice content of each selected soil layer. Infiltration reduction under frozen ground conditions was estimated by probabilistic averaging of spatially variable ice content of the soil profile. Off‐line uncoupled tests of the new and original Eta‐LSS were performed using experimental data from Rosemount, Minnesota. Simulated soil temperature and unfrozen water content matched observed data reasonably well. Neglecting frozen ground processes leads to significant underestimation/overestimation of soil temperature during soil freezing/thawing periods and underestimates total soil moisture content after extensive periods of soil freezing.
Global warming in the context of the Little Ice Age
Authors: Free Melissa , Robock Alan
Published: December 2003

Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond. To evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as forcings to an energy‐balance model and compare the results with temperature reconstructions. Our use of a model representing the climate system response to solar and volcanic forcings distinguishes this from previous direct comparisons of forcings with temperature series for the Little Ice Age. Use of the model allows us to assess the effects of the ocean heat capacity on the evolution of the temperature response. Using a middle‐of‐the‐road model sensitivity of 3°C for doubled CO2, solar forcings of less than 0.5% are too small to account for the cooling of the Little Ice Age. Volcanic forcings, in contrast, give climate responses comparable in amplitude to the changes of the Little Ice Age. A combination of solar and volcanic forcings explains much of the Little Ice Age climate change, but these factors alone cannot explain the warming of the twentieth century. The best simulations of the period since 1850 include anthropogenic, solar, and volcanic forcings.
The pH‐dependent dissolution of wind‐transported Saharan dust
Authors: Desboeufs Karine V. , Losno Rémi , Vimeux Françoise , Cholbi Sylvain
Published: December 2003

An open flow reactor was developed and used to study the pH dependency of atmospheric aerosol weathering. Under ultraclean conditions, this reactor enables experiments below the saturation of hydroxy salts and over the short time span (2 hours) that is typical for weathering by rain and cloud water. The weathering simulations show a two‐step process of dissolution rates: First, the rate increases quickly during the hydration of the solid particle surface, then after a maximum, it progressively decreases. In general, there is an increase in the dissolution rate of dissolved elements as the pH is lowered. However, between pH 3.80 and 5.30, the dissolution rate for Fe and Cu depends on both H+ and OH− concentrations and exhibits a minimum as a function of pH. This minimum can be related to pHpzc of the mineral containing these elements. The affinity of minerals for H+ was also determined by correlating hydration constants and pH.
Aircraft measurements of the latitudinal, vertical, and seasonal variations of NMHCs, methyl nitrate, methyl halides, and DMS during the First Aerosol Characterization Experiment (ACE 1)
Authors: Blake Nicola J. , Blake Donald R. , Wingenter Oliver W. , Sive Barkley C. , Kang Chang Hee , Thornton Donald C. , Bandy Alan R. , Atlas Elliot , Flocke Frank , Harris Joyce M. , Rowland F. Sherwood
Published: December 2003

Canister sampling for the determination of atmospheric mixing ratios of nonmethane hydrocarbons (NMHCs), selected halocarbons, and methyl nitrate was conducted aboard the National Center for Atmospheric Research (NCAR) C‐130 aircraft over the Pacific and Southern Oceans as part of the First Aerosol Characterization Experiment (ACE 1) during November and December 1995. A latitudinal profile, flown from 76°N to 60°S, revealed latitudinal gradients for most trace gases. NMHC and halocarbon gases with predominantly anthropogenic sources, including ethane, ethyne, and tetrachloroethene, exhibited significantly higher mixing ratios in the northern hemisphere at all altitudes. Methyl chloride exhibited its lowest mixing ratios at the highest northern hemisphere latitudes, and the distributions of methyl nitrate and methyl iodide were consistent with tropical and subtropical oceanic sources. Layers containing continental air characteristic of aged biomass burning emissions were observed above about 3 km over the remote southern Pacific and near New Zealand between approximately 19°S and 43°S. These plumes originated from the west, possibly from fires in southern Africa. The month‐long intensive investigation of the clean marine southern midlatitude troposphere south of Australia revealed decreases in the mixing ratios of ethane, ethyne, propane, and tetrachloroethene, consistent with their seasonal mixing ratio cycle. By contrast, increases in the average marine boundary layer concentrations of methyl iodide, methyl nitrate, and dimethyl sulfide (DMS) were observed as the season progressed to summer conditions. These increases were most appreciable in the region south of 44°S over Southern Ocean waters characterized as subantarctic and polar, indicating a seasonal increase in oceanic productivity for these gases.
Simultaneous measurements of HDO, H2O, and CH4 with MIPAS‐B: Hydrogen budget and indication of dehydration inside the polar vortex
Authors: Stowasser M. , Oelhaf H. , Wetzel G. , Friedl‐Vallon F. , Maucher G. , Seefeldner M. , Trieschmann O. , v. Clarmann T. , Fischer H.
Published: December 2003

For the first time, vertical profiles of HDO inside the Arctic vortex along with CH4 and H2O were retrieved from nighttime infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne instrument (MIPAS‐B) from Kiruna (Sweden, 68°N) on February 11, 1995 and March 24, 1997. The deuterium to hydrogen ratio (D/H) of water vapor shows a strong depletion in comparison to that of standard mean ocean water (SMOW), particularly in the lower stratosphere for the February 1995 flight. This extraordinarily strong depletion indicates an additional isotopic effect due to dehydration by polar stratospheric cloud particles. The maximum dehydration occurs at a lower altitude than that of the denitrification measured on the same flight. A dehydration of up to 0.7(±0.4) ppmv is seen in the compact correlation between CH4 and H2O. For the March 1997 results the exceptionally low D/H ratios and a deviation from the linear H2O‐CH4 correlation could not be found. The H2O results of the February 1995 flight show a peak mixing ratio of 7.1 ppmv at 17.1 hPa and a minimum of 3.6 ppmv at 137.5 hPa. The analysis of the March flight shows a similar profile, but the vertical gradient is less pronounced. The total hydrogen budget of the stratosphere was examined by evaluating the quantity [H] = [H2O] + 2[CH4], revealing values of around 7.25 ppmv on average for both flights. All profiles reflect the subsidence of polar vortex air.
Global variable resolution simulations of Mississippi River basin rains of summer 1993
Authors: Wang Muyin , Paegle Jan , DeSordi Steven P.
Published: December 2003

A variable resolution global model is used to simulate a 13 day period of heavy rainfall during the 1993 Mississippi River basin floods. The model allows interaction between the atmosphere of the inner, fine resolution region that covers most of the United States and the outer global domain. We describe the impact of flow generated by latent heating over the central United States and its interaction with the global atmosphere. For this case, global constraints on the divergent flow impose substantial modifications upon the rainfall evolution within the central region. The most accurate simulations of rainfall occur when both local divergence and local thermal modifications interact with their global counterparts. The moisture budget is strongly influenced by the imposition of both divergence and thermal fields, and the temporal and spatial distribution of horizontal moisture flux and rainfall change substantially with the degree of outer state prespecification.
Inference of snow cover beneath obscuring clouds using optical remote sensing and a distributed snow energy and mass balance model
Authors: Cline Donald W. , Carroll Thomas R.
Published: December 2003

We describe a new method to infer the presence or absence of snow cover when it is obscured to remote sensing by clouds. The inference is based on the spatial distribution of snow water equivalent (SWE) estimated by a physical snow model. The snow model accounts for surface and internal snowpack energy exchanges and mass exchanges including snow accumulation, sublimation, rainfall, and meltwater outflux. We examine two approaches to using the modeled SWE information to infer snow cover: (1) we directly categorize areas with modeled SWE greater than zero as “snow covered” and areas with zero SWE as “no snow”; (2) we classify the modeled SWE field into a binary map of snow covered/no snow, using maximum likelihood logistic estimation (LR). Here the modeled SWE serves as a semicontinuous independent variable, and the binary dependent variable consists of observed snow cover derived from all available ground observations of snow depth and water equivalent, and from samples of snow cover randomly selected from cloud‐free areas of a satellite snow cover product. We demonstrate these methods for a 504,000 km2 region in the north central United States, over a 4 week period during March and April 1997. The snow model was run hourly on a 4 km grid using data normally available in near real time, including numerical weather analysis products, satellite‐derived insolation products, and ground observations of precipitation. We tested two dependent variable data configurations for the LR approach to simulate (1) typical conditions when remotely sensed snow cover observations are available to help develop the logistic model and (2) “worst‐case” conditions where only ground‐based data are available. Averaged over the study period, all three methods, the direct SWE, the worst‐case LR, and the typical LR, yielded comparable results in the range of 78–80% accuracy when compared to satellite‐observed snow cover maps. The results of this study demonstrate that a relatively simple, spatially distributed, physically based snow model is capable of providing useful snow cover information in an operational environment.
Age of air in a “leaky pipe” model of stratospheric transport
Authors: Neu Jessica L. , Plumb R. Alan
Published: December 2003

We discuss the characteristics of analytical solutions for the mean age of air in a simple, one‐dimensional conceptual model of stratospheric transport. This “leaky pipe” model is a version of the “tropical pipe” model which has been modified to include detrainment of surf zone air into the tropics. We examine the dependence of the mean age on advection, diffusive mixing, and quasi‐horizontal mixing between the surf zones and the tropics. In the absence of vertical diffusion across tracer mixing ratio isopleths the age difference between the tropics and midlatitudes does not depend on mixing across the edge of the tropics, but only on advection. The age difference given by this nondiffusive limit is an upper bound on the tropical‐midlatitude age difference. This work provides some insight into the results of recent modeling studies that have used the mean age as a diagnostic of stratospheric transport.
Simulating midsummer climate over southern Africa using a nested regional climate model
Authors: Joubert A. M. , Katzfey J. J. , McGregor J. L. , Nguyen K. C.
Published: December 2003

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) Division of Atmospheric Research limited area model (DARLAM) is used to simulate midsummer (January) climate over southern Africa. Using a one‐way nesting procedure, lateral boundary and initial conditions are supplied by the CSIRO nine‐level Mark 2 general circulation model (GCM), CSIRO9. In general, the DARLAM results are improved in comparison with those from CSIRO9, although certain deficiencies in the GCM climatology over southern Africa are also present in the nested model results. DARLAM captures the spatial pattern of observed rainfall and interannual rainfall variability over the region as a whole more accurately than CSIRO9. Over most parts of the subcontinent, interannual rainfall variability simulated by DARLAM is not significantly different from observations. Over the steep escarpment region of south‐east South Africa, DARLAM simulates more rainfall than CSIRO9 and significantly more rainfall than observed. Over Madagascar, DARLAM simulates more rainfall than CSIRO9, but less than observed, and interannual variability is also significantly less than the observed variability.
Assessment of smoke aerosol impact on surface solar irradiance measured in the Rondônia region of Brazil during Smoke, Clouds, and Radiation ‐ Brazil
Authors: Tarasova T. A. , Nobre C. A. , Holben B. N. , Eck T. F. , Setzer A.
Published: December 2003

The impact of smoke aerosols on the surface solar irradiance in the Rondônia region of Brazil is examined. The climate of this region is subequatorial with two distinct seasons. There is a sharp decline of the precipitation and cloudiness during the dry season which lasts from June to September accompanied by anthropogenic burning of savanna and forest in August and September with the resultant strong emission of smoke into the troposphere. Thus the magnitude of the column aerosol optical depth increases in these months while both precipitable water and cloud amount decrease in accordance with the seasonal cycle of humidity. All these atmospheric constituents influence the magnitude of the solar irradiance at the surface. In order to assess the aerosol and gaseous effects on the surface irradiance as compared with impact of cloudiness, we performed the clear‐sky radiative transfer model calculations by employing a broadband radiation code and both aerosol optical depth and precipitable water retrieved from Sun photometer measurements. Calculation results show that the elevated aerosol optical depth observed in Rondônia during August and September causes a negative trend in the daily mean clear‐sky surface solar irradiance during this period. Since the daily mean solar irradiance measured at the surface under all‐sky conditions demonstrates a similar negative trend, it can be explained by the aerosol influence while the effect of clouds appears in the daily variations of the irradiance. It was also shown that smoke aerosols cause a decrease of the monthly mean values of all‐sky surface irradiance in August and September as compared with July and October. Corresponding decreases in the near surface air temperature due to the smoke aerosols were not found.
A mesoscale cyclone over the Fram Strait and its effects on sea ice
Authors: Brümmer Burghard , Hoeber Heinrich
Published: December 2003

The ice export from the Arctic Ocean through the Fram Strait into the Atlantic Ocean is steered by atmospheric processes on the large scale as well as on the local scale. A case study of a mesoscale cyclone over the Fram Strait and its effects on the sea ice drift is presented. The cyclone developed on March 13, 1993, at the ice edge of the Greenland Sea and moved northward over the ice and over the position of the research icebreaker Polarstern and an array of six meteorological ice buoys. The cyclone had a radius of about 150 km and was essentially restricted to the lowest 2 km of the atmosphere. Near the surface the temperature difference between the air in the warm sector and the surrounding cold air was 25 K resulting in a pressure difference of about 15 hPa between center and the surrounding with low‐level wind speeds of up to 20 m/s. The passage of the cyclone caused a full loop of the ice drift otherwise oriented from northeast to southwest. The ratio of ice drift speed to wind speed, increased from 5% before to 9% after the passage. Extreme values of ice deformation and large variations of the ice strain rate tensor occurred during the cyclone passage. It is concluded that passing cyclones can affect the sea‐ice drift through the bottleneck of the Fram Strait and may have integral effects on larger time scales and space scales.
A statistical modeling approach for the simulation of local paleoclimatic proxy records using general circulation model output
Authors: Reichert Bernhard K. , Bengtsson Lennart , Åkesson Ove
Published: December 2003

A statistical modeling approach is proposed for the simulation of local paleoclimatic proxy records using general circulation model (GCM) output. A method for model‐consistent statistical downscaling to local weather conditions is developed which can be used as input for process‐based proxy models in order to investigate to what extent climate variability obtained from proxy data can be represented by a GCM, and whether, for example, the response of glaciers to climatic change can be reproduced. Downscaling is based on a multiple linear forward regression model using daily sets of operational weather station data and large‐scale predictors at various pressure levels obtained from reanalyses of the European Centre for Medium‐Range Weather Forecasts. Composition and relative impact of predictors vary significantly for individual stations within the area of investigation. Owing to a strong dependence on individual synoptic‐scale patterns, daily data give the highest performance which can be further increased by developing seasonal‐specific relationships. The model is applied to a long integration of a GCM coupled to a mixed layer ocean (ECHAM4/MLO) simulating present‐day and preindustrial climate variability. Patterns of variability are realistically simulated compared to observed station data within an area of Norway for the period 1868–1993.
A midterm report on the GEWEX Continental‐Scale International Project (GCIP)
Authors: Lawford R. G.
Published: December 2003

The GEWEX Continental‐Scale International Project (GCIP) is being carried out in the Mississippi River Basin under the auspices of the World Climate Research Program and its Global Energy and Water Cycle Experiment (GEWEX). This paper provides a brief history of GCIP's development and its mission and objectives. The scientific achievements of GCIP are then reviewed against each of these objectives. The paper concludes with a brief discussion of options for the period beyond 2000 after the current phase of the project is completed.
Effect of spatial averaging on temporal statistical and scaling properties of rainfall
Authors: Olsson Jonas , Singh Vijay P. , Jinno Kenji
Published: December 2003

The variation of temporal continuous rainfall properties with spatial scale was investigated by analyses of daily 11.2‐year rainfall time series of point values and spatial averages obtained from a network of 161 rain gauges in southern Sweden. The number of series studied ranged from 16 for point values to 1 for 8000 km2, the latter corresponding to the total network area. The analyses included investigations of general descriptive statistics, power spectra, empirical probability distribution functions, and scaling of statistical moments. Two important characteristics of the rainfall process in the region were indicated. The first was that temporal statistical properties related to extreme values qualitatively changed at a spatial scale of ∼2800 km2, whereas properties of the mean process did not. Although this change may partly be related to changes in the sample size, its presence does raise some important questions concerning the transformation between point values and regional scales in hydroclimatological rainfall modeling. The second important characteristic was a temporal scaling behavior between 1 day and 1 month with properties depending on the spatial averaging area. This finding is in agreement with previous investigations where a spatial variation of temporal scaling properties has been found and suggests the possibility of scaling‐based time series modeling where the regional parameters are adjusted to take local climatological factors affecting the rainfall process into account.