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Simulation of natural earth system variabilityExploring atmospheric, Earth system, and solar processes, and the variability and change of these processes, are critical components to reaching NCAR's strategic goal #1, “Improve understanding of the atmosphere, the Earth system, and the Sun.” The Earth and Sun System Laboratory (ESSL), with partnerships with the universities and other agencies, has the scientific knowledge to attack the problems associated with attaining this goal. Exploration into these areas will focus on three key activities: simulating the natural Earth system variability, researching the magnetic-flux eruptions from the sun, and investigating the coupling between the upper troposphere and lower stratosphere (including gravity waves). For each of these areas, ESSL has numerous activities underway and they are highlighted below. Note the special laboratory highlights on paleoclimate which offers a remarkably fertile ground for testing climate models and the underlying parameterizations and on the recovery and usage of the HIRDLS satellite as well as the discovery of a way to predict the next solar cycle using the memory term linked to the meridional circulation in the Sun. Furthermore, this priority has two highlights at the level of NCAR, namely the research on Space Weather and that on the building of a coronal magnetometer which allows for the first time a direct measurement of the magnetic field in the solar corona. Paleoclimate [Highlight] - CGD Paleoclimate
Paleoclimates offer a unique perspective to understand both the Earth’s climate sensitivity and stability. NCAR climate models have been used to study past natural variability of the Earth system since the 1970’s with the pioneering work of Jill Williams, Eric Barron, John Kutzbach, and Warren Washington. The development of a coupled climate model, the Climate System Model (CSM), in the 1990’s included a lower resolution (but otherwise equal) version of the model, PaleoCSM, which was particularly useful for the long simulations required to study past climates. PaleoCSM was successfully used to study mechanisms responsible for changes in the coupled climate system and to determine associated magnitudes of changes for various climatic variables. Simulations covered a large range of applications, including the last millennium, Holocene ENSO, the Last Glacial Maximum, Eocene, and Cretaceous. These simulations highlighted the importance of considering feedbacks among the atmosphere, ocean, land surface, and sea ice in establishing the magnitudes of past climate change to changes in past forcings. These simulations not only acted as a benchmark for CSM but allowed testing of various hypotheses of mechanisms to explain proxy records of past climate change. A strong test of the Community Climate System Model (CCSM) is to simulate past climate against records from ice cores, tree rings, and other proxy data. Magnitudes and rates of past change also provide an important context for future climate changes. Within ESSL, we are exploring past changes over many different time scales: from the distant geologic past, with radically different continental configurations, when the Earth’s surface temperature and latitudinal gradients were significantly different from present and levels of atmospheric carbon dioxide, methane, and other greenhouse gases reached levels up to ten or more times present levels; the last million years, when the Earth experienced a waxing and waning of ice ages and levels of atmospheric carbon dioxide, methane, and other greenhouse gases during the ice ages were reduced by half or more from present levels; and the last few millennia with colder periods extensively documented in the proxy record associated with solar fluctuations and volcanic eruptions. Each of these time scales gives us an improved understanding of the natural variability of the Earth system and our ability to model feedbacks in the climate system. By comparing climate simulations of Earth’s past to the data from geological and geochemical archives, we can evaluate the accuracy of climate models such as CCSM that are used to look at Earth’s future. At the same time, geologists have started to use CCSM to understand how their specific data can be understood in a more large scale, dynamical context. CCSM has become a valuable partner to field-based geological research. CCSM has been applied to all these different time scales (Nugget graphic). The Permian-Triassic (PT) boundary, approximately 250 Ma, marks the largest extinction recorded in Earth’s history, where across this boundary approximately 95% of marine and terrestrial species were lost. CCSM simulates a warm greenhouse climate for the PT with sea surface temperatures in the western tropical Panthalassic Ocean reaching 33°C as compared to the present-day western Pacific warm pool of 30°C and with poor mixing in the PT ocean consistent with the extinction hypothesis of ocean anoxia. Past glacial cold periods, sometimes referred to as “ice ages”, provide a means of evaluating our understanding and modeling of the response of the climate system to large negative radiative perturbations. The most recent glacial period started ~116 kyr ago, in response to orbital forcing, with the growth of ice sheets and fall of sea level culminating in the Last Glacial Maximum (LGM), around 21 ka. CCSM, when forced with the much reduced greenhouse gas concentrations, a lower sea level, and continental ice sheets of the LGM, simulates the magnitude of observed latitudinal ocean temperature changes, with cooling of tropical sea surface temperatures of about 2°C and much greater cooling and expanded sea ice over the high-latitude oceans. CCSM simulations indicate that changes in solar irradiance and aerosol loading from explosive volcanic eruptions together could have produced periods of relative warmth and cold during the preindustrial portion of the last 1,000 years. Cooler temperatures in the early 1800s A.D., one of the episodes of the Little Ice Age (LIA), can be explained by lower solar irradiance and greater volcanic activity. Looking into the future, an emission scenario of future greenhouse concentrations following “business as usual” (A2) results in global surface temperatures by the end of this century not unlike the period of rapid geologic warming for the Late Paleocene Thermal Maximum (LPTM), about 55 Ma. Instead of 100 years (A2), the warming for the LPTM took on the order of one thousand years. Currently, we are starting to use CCSM to quantify past rates of change and the processes explaining rapid past climate changes, including freshwater input into the high-latitude oceans, rapid meltback of the polar ice caps, and destabilization of methane clathrates. Future plans are to simulate the magnitudes and rates of past climate change on many time scales using the planned NCAR Earth System Model, which will allow us to explore more completely feedbacks with vegetation and ice sheets, atmospheric chemical changes, and the carbon and nitrogen cycles. Chemistry and dynamics of the middle and upper atmosphere
A significant fraction of the solar energy deposited in the upper part of the middle atmosphere is realized as heat as a consequence of exothermic chemical reactions, including reaction between ozone and atomic hydrogen. The heating varies with time in response to variations in composition due to photochemistry and to vertical advection by tides and other processes. ACD scientists are involved in a number of studies to examine the nature of variability in temperature, ozone, and tides. ACD scientists, in collaboration with J. Xu (Chinese Academy of Science), H.-L. Liu and R. Roble (HAO), C. Mertens and M. Mlynczak (NASA) and J. Russell (Hampton U.), investigated the temporal and seasonal variations of the mesopause altitude and temperature using observations from the SABER instrument on the TIMED satellite. The results show that there is a large degree of variability, especially associated with the diurnal cycle in low latitudes. The daily and monthly average mesopause position is fairly steady except for a large downward displacement in summer middle and high latitudes. The study also found a persistent offset between the Northern and Southern Hemispheres during both summer and winter. In an effort to understand ozone variability in the upper mesosphere, ACD scientists used the ROSE model to investigate the processes that account for the so-called secondary ozone maximum near 100 km. The study finds that there are two factors that play a role, of roughly equal importance: 1) this is the altitude of the highest atomic oxygen number density and 2) the extremely cold temperatures favor the formation of ozone. ACD scientists, in collaboration with D. Pancheva and N. Mitchell (Univ. Bath, UK), M. Mlynczak (NASA) and J. Russell (Hampton U.), are investigating tidal variability and its dependence on such factors as planetary waves, background winds, and tide-tide interactions. This study has found a persistent correlation between the semidiurnal tide measured by radar in high northern latitudes and the planetary wave variability in the stratosphere of the southern hemisphere. The planetary waves were observed by the SABER instrument on TIMED. The correlation implies that there is a global scale interection and response between planetary wave and the tide. ACD scientists also used the model and OH airglow data from the SABER instrument on the TIMED satellite to investigate variability in OH airglow emission. They found that much of the diurnal variability is due to the diurnal tide. Tides also play an important role in the annual variability. In collaboration with Jiyao Xu (Chinese Academy of Science), R. Collins (U. of Alaska) and C-Y. She (CSU), ACD scientists looked at the impact of breaking gravity waves on sodium density and mixing ratio. Although sodium is a minor constituent in the mesosphere, it can be detected with very high vertical and temporal resolution by sodium resonance lidar. This makes it valuable for diagnosing how trace species evolve in the presence of waves. The study found that in order to distinguish chemical changes from those due to transport, it is very important to understand the details of density and temperature variations due to propagating and breaking waves. In collaboration with ACD visitors K. Matthes (also at Free University of Berlin) and T. Sekiyama (Meteorological Research Institute of Japan), ACD scientists are using the ROSE model to investigate the response of the atmosphere to the solar flux variations in the presence of a quasi-biennial oscillation (QBO) in tropical winds. Model integrations demonstrate that the phase of the QBO has a significant effect on the atmospheric response to the solar flux changes. Analysis is ongoing. ACD scientists are also involved in long-term measurements of atmospheric constituents. As part of the international Network for the Detection of Atmospheric Composition Change (NDACC) formerly the NDSC, ACD scientists operate an infrared Fourier transform spectrometer (FTS) at Thule, Greenland (76.53°N). The NDACC is a network of high quality ground based observing stations for early measurement of changes in the composition and state of the stratosphere and troposphere and determination of their causes. Operation of the spectrometer at Thule is mostly automatic, with monitoring from Boulder, whenever the weather is suitable and the sun is above the horizon. Observations were made on 95 days of the possible 225 sunlit days of 2005. Missed days usually are due to stormy weather. Those data were analyzed for column amounts and some vertical profiles of gases, including both stratospheric gases important in ozone chemistry and tropospheric gases related to climate change. In conjunction with other observations from the network, composed mostly of research teams from nations other than the US, the ACD Thule measurements are being used in the validation activities of recently launched satellite-borne instruments. Collaborations are ongoing with instruments aboard the ENVISAT (EU) platform, the NASA EOS-Aura satellite (US, UK, Netherlands, Finland) and the Atmospheric Chemistry Experiment (ACE) instrument aboard the Canadian SCISAT-1 satellite. ACD scientists are also providing other measurements that are being used in satellite validation studies. The Solid state, CCD Actinic Flux Spectroradiometers (CAFS) instruments developed in the NCAR/ARIM laboratory were deployed successfully on the NASA WB-57 Costa Rica Aura Validation Experiment (CR-AVE). The CAFS measurements of up and downwelling flux were used in conjunction with radiative transfer calculations to obtain total ozone column abundances above the aircraft. This ozone column calculation performed by Irina Petropavlovskikh of NOAA/ESRL/GMD has been extremely useful for the AURA satellite validation, particularly the OMI and MLS instrumentation. To compare against CAFS data, the MLS profiles are integrated above the altitude of the WB-57 aircraft determined for each co-incidental profile. The agreement between the MLS and CAFS data is within few percent. The summary of comparisons for six of the CR-AVE flights is shown in the figure below. The coincident MLS and CAFS partial ozone columns agree to within +/- 3% for flight altitudes between 16 and 19 km. Additionally during CR-AVE, CAFS data were used for the first time to validate a new OMI profile product based on the algorithm developed for the SBUV V8 profile retrievals. The SBUV type algorithm does not account for the actual altitude of the cloud; however, ozone profile retrieval is sensitive to the cloud altitude. Based on the results provided by the CAFS data, the algorithm for the SBUV-type profile will be re-evaluated and adjusted to account for the altitude of the clouds in the observed scene. FY2007 work will involve continuation of studies evaluating ozone, temperature, and dynamics variability in the mesosphere and lower thermosphere. The NDACC measurements are ongoing and the CAFS measurements will continue to play a role in validation of the Aura instruments. This work was funded by NSF/NCAR and NASA. Hurricanes
Following the very active 2004 hurricane season in the North Atlantic, there has been much discussion about the likely role of global warming in contributing to increases in intensity of tropical cyclones. This was in part in response to claims by NOAA and elsewhere that it was all due to natural variability. Publications of findings of increases in intensity and duration of tropical storms, and in particular increases in category 4 and 5 storms since 1970, further inflamed the debate. Nature also played a major role by bringing the record breaking 2005 season, with its four category 5 storms, including the devastating Katrina. In the past year, this has been followed up by considerable work within ESSL devoted to understanding the changes in the environment and their effects on tropical cyclones. Several investigators working under different funding (mainly from NSF, but also DOE and NOAA) have been involved. Causes of changes in tropical cyclones have been explored in several studies. The origins of the record breaking 2005 Atlantic hurricane season have been analyzed. Sea surface temperatures (SSTs) in the tropical (10° to 20°N) North Atlantic region critical for hurricanes were at record high levels in spite of all the hurricane activity. However, about half of the SST anomaly was related to global SST changes, and thus global warming. ENSO accounted for another important portion, but North Atlantic SST variations, as given through the Atlantic Multi-decadal Oscillation, contributed in only a minor way. The latter was important for the lull in activity from 1970 to about 1990, however. Climate models have been used to study the possible causes of SST changes in Atlantic and Pacific tropical storm cyclogenesis regions. The observed SST increases in these regions range from 0.32°C to 0.67°C over the 20th Century. The climate models examined suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system. For the period 1906-2005, there is an 84% chance that external forcing explains at least 67% of observed SST increases in the two tropical cyclogenesis regions. Model “20th Century” simulations, with external forcing by combined anthropogenic and natural factors, are generally capable of replicating observed SST increases. In experiments in which forcing factors are varied individually rather than jointly, human-caused changes in greenhouse gases are the main driver of the 20th Century SST increases in both tropical cyclogenesis regions. The observed best track hurricane record has been analyzed for time varying sampling biases that might account for trends in intensity, but the signature of increased duration of weaker storms that might arise from less frequent sampling in the past is not present in the data. In another published study this past year, NCAR scientists outlined issues related to hurricane changes with climate change. This article provides some much needed balance to counter some quite misleading articles and claims that natural variability alone is responsible for the observed changes. Another major topic has been the energy and water cycles of hurricanes and their role in the climate system. A further study has computed how much moisture that ends up as rain in hurricanes comes from local evaporation in the storm versus large-scale convergence. This has been analyzed in a model framework using WRF at high resolution for simulations run for observed storms, in particular Ivan in 2004 and Katrina in 2005 that are realistic. Model sensitivity runs have also been made with SSTs increased and decreased by 1°C. Results demonstrate the overwhelming dominance of moisture convergence into the storms, in spite of the critical role of the surface evaporative source, and have implications for the changing environment on hurricanes as climate changes. In another study, these model results have been related empirically to the maximum sustained wind in the model and the results used with the “best track” global observed data on tropical cyclones to deduce how surface fluxes and precipitation in hurricanes have changed since 1970 (nugget). Hurricanes appear to play a key role in climate and that role is increasing over time as SSTs rise. These sorts of studies are expected to continue especially as models improve and can be run at higher resolution and coupled with ocean models. CLIVAR
ESSL scientists remain involved in leadership of the Climate Variability and Predictability (CLIVAR) initiative of the World Climate Research Programme (WCRP) through membership on various national and international CLIVAR panels, as well as through contributing to CLIVAR goals and objectives as research scientists. The purpose of CLIVAR is to investigate climate variability and predictability on time-scales from months to decades and the response of the climate system to anthropogenic forcing. CLIVAR, as one of the major components of the WCRP, started in 1998 and has a lifetime of 15 years. It focuses on the role of the coupled ocean and atmosphere within the overall climate system, with emphasis on variability, especially within the oceans, on seasonal to centennial time scales. CLIVAR intends to explore predictability and how to improve predictions of climate variability and climate change using existing, reanalyzed, and new global observations, enhanced coupled ocean-atmosphere-land-ice models, and paleoclimate records. A major effort of the U.S. CLIVAR program has been the introduction and fostering of Climate Process Teams (CPTs). A CPT is a team of observationalists, process modelers, and coupled climate modelers formed around specific issues or key uncertainties. They aim to link process-oriented research to modeling for the purpose of addressing key uncertainties in coupled climate models. Within ESSL, major ocean model developments are proceeding under the auspices of the CPTs on both gravity current entrainment and eddy mixed layer interaction. The former has resulted in a parameterization of the ocean exchange through the Strait of Gibraltar that is being adapted to the Denmark Strait and Faroe Bank Channel. For the latter, implementation of a near-surface eddy flux parameterization and a new prescription for the surface intensification and abyssal reduction of the tracer diffusivities result in improved model solutions. These improvements include the elimination of strong, near-surface, eddy-induced circulations, and potential temperature distributions that compare more favorably with observations. A second effort of U.S. CLIVAR was the initiation of the Climate Model Evaluation Project (CMEP). The objective of the CMEP project was to increase community-wide diagnostic research into the quality of model simulations, leading to more robust evaluations of model predictions and a better quantification of uncertainty in projections of future climate. ESSL scientists have been very involved in CMEP, for instance analyzing and evaluating the various components of the global water cycle in climate models, and analyzing Antarctic sea ice conditions in climate models. As part of a special issue of the J. Climate arising from the June 2004 CLIVAR science conference, ESSL scientists led a comprehensive review of three interrelated climate phenomena: Tropical Atlantic variability, the North Atlantic Oscillation, and the Atlantic Meridional Overturning Circulation (Figure). These phenomena produce a myriad of impacts on society and the environment on seasonal, interannual, and longer time scales through variability manifest as coherent fluctuations in ocean and land temperature, rainfall, and extreme events. As well as a review of the state of understanding of Atlantic climate variability and achievements to date, considerable discussion was given to future challenges related to building and sustaining observing systems, developing synthesis strategies to support understanding and attribution of observed change, understanding sources of predictability, and developing prediction systems in order to meet the scientific objectives of the CLIVAR Atlantic program. Also featured in the CLIVAR special issue is a write up of a keynote invited presentation on climate observations. It focuses on the need for a climate information system, reprocessing of datasets to create climate data records, reanalysis of observations to create multivariate global gridded fields, and the use of the resulting products, including as initial fields for climate predictions. MOZART: Global chemistry-transport modeling
Model for Ozone and Related chemical Tracers (MOZART) is a three dimensional global chemical transport model designed to study processes that determine the chemical composition of the troposphere. MOZART was used by ACD scientists to constrain sources of CO over South America, to examine the impact of isoprene on tropospheric composition, and to calculate the production of ozone from Alaska wildfires. MOZART-4 was used to constrain sources of CO during 2004 over South America from biomass burning, anthropogenic emissions, biogenic CO emissions and isoprene oxidation. The biomass burning source is estimated as 80 Tg CO yr -1 which accounts for close to 30% of the global biomass burning emissions and reflects the importance of South American biomass burning sources. No robust constraint could be put on biogenic, anthropogenic and isoprene sources, because the contributions from these sources are within the range of uncertainties associated with observations and model results. However, the study reveals the importance of CO produced from isoprene oxidation in CO budgets on both the regional and global scale and thus the need for improved techniques for constraining isoprene emission inventories. ACD scientists also examined how isoprene and differences in its emission inventory affect tropospheric composition. For this purpose they extended the current MOZART chemical scheme to track carbon-containing species produced from isoprene. From the model simulations they estimate the contribution of isoprene to the global CO burden below 100 hPa as 15%. Contributions for HCHO are ~20% and for PAN ~30%. Omitting isoprene in the simulations has a rather small effect on the global annual burden of ozone (~4%), however, regionally the impact on ozone can be significant (e.g. changes in surface ozone levels of up to 20 ppbv occur over the Eastern US in summertime). They are also examining the feasibility of using the model tracers in deriving isoprene emissions estimates from space based HCHO observations. MOZART-4 simulations and CO and ozone observations at the PICO-NARE station in the Azores were used to examine the amount of ozone produced from wildfires in Alaska and Canada in summer 2004. Modeled and observed enhancement ratios on the order of 0.25 ppbv/ppbv were calculated resulting in a global net ozone production from the fires of 12.9±2 Tg O3. On average, the wildfires increased the ozone burden (surface-300 mbar) over Alaska and Canada by 7-9% during summer 2004, and over Europe by 2-3% (Figure 1). In FY2007 MOZART will be used in continued work on closing the global CO budget as well as for analysis of MIRAGE and INTEX-B that will include comparisons with measurements. This work was funded by NSF/NCAR and NASA. WRF-Chem
The Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) is being developed by NOAA scientists, in collaboration with the WRF community including NCAR/ESSL scientists. The model will be used for investigation of regional-scale air quality, for field program analysis, and for cloud-scale interactions between clouds and chemistry. ESSL scientists and staff provide support by integrating and maintaining the chemistry components in the evolving WRF modeling system, as well as contributing new code in the development of WRF-Chem. Models such as WRF-Chem can be used to further the understanding of precipitation and chemical processes, including multiscale atmospheric chemical constituent transport, dispersion and transformations. Atmospheric chemical and aerosol transport, dispersion and transformation
depend on accurate specification of the dynamics and physics across a
wide range of scales, from the microscale to the mesoscale. WRF-Chem is
being utilized to develop a deeper understanding of the dynamics, physics
and chemistry affecting these constituents. To understand the role deep convection has on the composition of the
upper troposphere and in cleansing the atmosphere via removal of pollutants
by wet deposition, simulations are being conducted for both individual
case studies and for regions containing several convective storms. Results
for individual storms have been evaluated with observations and have been
analyzed to estimate the scavenging efficiency and the flux to the upper
troposphere of the important ozone precursors, peroxides and formaldehyde.
Fluxes of a suite of species to the upper troposphere will be analyzed
for multiple convective storms to advance our understanding of convective
transport for improvements of convective transport parameterizations in
climate models. Other future applications of WRF-Chem include conducting
preliminary studies for the proposed Deep Convective Clouds and Chemistry
field experiment and utilizing WRF-Chem for studies of interactions between
biogenic aerosols and clouds and the biosphere. This work is supported
by the NSF. Globalization of air quality and intercontinental transport
Ozone acts as both a radiatively important gas and a primary pollutant adversely affecting human health and the environment. ACD scientists have studied temporal and spatial variability of ozone using a combination of the CAM model with chemistry (CAM-Chem) and surface and satellite measurements, as well as a new chemical data assimilation system. Extensive emission controls have been implemented in the U.S. and other countries to reduce surface ozone concentrations, with a significant improvement noted in U.S. emissions. On the other hand significant growth in surface ozone has been reported on the west coast of the U.S. and at Mace Head Ireland with substantial interannual variability. Northern mid-latitude ozone data between 1970 and 1996 also suggests substantial interannual variability with temporal trends varying by region. The combination of variability in ozone precursors and meteorological variability superimposed on climate change makes changes in the ozone record particularly difficult to interpret. ACD scientists have shown substantial ozone variability, up to 5 ppbv, can be explained by meteorological variability in association with the Arctic Oscillation (AO). Further their work shows that much of this variability is explained by variations in stratosphere-troposphere exchange. The CAM-Chem model is being used to investigate the seasonal cycle of tropical tropospheric chemistry (Figure 1). In the left panel, all the ozonesondes between the Equator and 30 o N for the period 1998-2005 are used to represent the mean observed seasonal cycle in ozone. In the middle panel, the model, interpolated to the location of the stations, shows that, while the overall structure is similar, there are striking differences in the mid-troposphere seasonal cycle between the model and the observations. The right panel shows a similar simulation, but in which the lightning source is reduced by a factor of 2. This latter simulation results in a similar pattern, but with perhaps a better timing of the maximum in June. This work was funded by NSF/NCAR and DOE. The onset of near-global and long-term measurements of chemical species from space offers an opportunity to better understand changes in atmospheric composition from regional to global scales through the integration of measurements with global chemical transport models (GCTMs). The goal of several ACD scientists is to build a state-of-science chemical data assimilation system to provide a flexible platform for related studies in chemical weather forecasts, assessing the impact of global air pollution to regional air quality, and estimating anthropogenic emissions. For the past year, ACD and Development Testbed Center scientists have focused on building an ensemble-based system (i.e. using Ensemble Kalman Filter approach). The assimilation system includes the Data Assimilation Research Testbed (DART) software and the Community Atmosphere Model (CAM) which is the atmospheric component of the global climate model Community Climate System Model (CCSM). The initial focus was to use the DART/CAM setup by assimilating meteorological observations and MOPITT CO retrievals. This first step builds on previous inverse modeling and assimilation studies of the CO tracer, with the added complexity of assimilating meteorological variables and making use of ensembles instead of a single representation of the atmosphere. Analyses characterizing uncertainties in modeling CO transport and its impact on emission estimates were conducted to gain more insights on the sensible estimates of CO distribution and CO emissions. The outcome of the analyses provided a more quantitative means to generate initial ensembles of CO state and emissions necessary for the ensemble-based data assimilation. Results using MOPITT CO also show the ability of the current assimilation system to constrain the model state variables. An ensemble of dynamical states to drive the chemical evolution of CO not only produces consistent analyses but more importantly enables better capture of the variability of the CO fields needed for successful assimilation. The work on ozone and DAR/CAM was funded by NSF/NCAR, NSF/ITR, and NSF/Biocomplexity. In addition to the modeling work, ACD scientists participated in The NASA Intercontinental Chemical Transport Experiment phase B (INTEX-B) project, which was designed to understand the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and assess their impact on air quality and climate. The study focused on ozone and its precursors, aerosols and precursors, and long lived greenhouse gases transported from Asia to the U.S. west coast. The project was conducted out of Seattle, Hawaii, and Alaska and involved the NASA DC8 and the NSF/NCAR C-130. This campaign was immediately after MIRAGE and all of the NCAR participants with instruments on both aircraft during MIRAGE also participated in INTEX-B. During both campaigns, ACD scientists used the MOZART-4 chemical transport model to assimilate real-time CO from the MOPITT satellite and then produce global forecasts at approximately 50 km resolution of 3 days. These forecasts were then used for flight planning purposes. In order to achieve this a new MOPITT/MOZART CO data assimilation system was developed. This had the following features: near-real-time MOPITT retrievals, daily and multi-day maps of the MOPITT CO distributions, biomass burning emission estimates based on satellite fire counts, CO tracer forecasts for identifying the sources of CO plumes that were observed in the MOPITT satellite data, and a web presence with mapped CO fields and “curtain” plots for easy data access. Comparison of the forecasts and measured CO on a given day showed good agreement and will be used to refine forecast procedures. ACD scientists also showed the utility of an instrument designed to measure important atmospheric tracer species at very low levels. Methyl tertiary butyl ether (MTBE) is a compound that is added to gasoline to increase the oxygenated content of the fuel. Because of environmental concerns, this compound has been phased out of the gasoline supply in the Western US and Canada. However it is still used as an additive in Asia. Because of its lifetime of approximately 3.5 days, this presents an opportunity for using it as a tracer for pollution from Asia provided that the instrument sensitivity is high enough to detect it in very small quantities. Back trajectories from one of the INTEX-B flights showed that air from Asia was potentially impacting North America. The simultaneous observations of benzene and MTBE confirms that this was indeed the case. This work was funded by NASA and NSF/NCAR. FY2007 work will include continued work on chemical transport and variability, ensemble filter data assimilation, and data reduction, analysis, and interpretation from MIRAGE and INTEX-B. Intense photochemistry in the Antarctic troposphere
The Antarctic Tropospheric Chemistry Investigation (ANTCI) study was conducted in Antarctica during November-December 2005. The primary goal of the ANTCI program is to enhance understanding of the processes that control tropospheric levels of HO x , NO x , sulfur, and other trace species over the Antarctic continent. The 2005 study was the third field study of this program. The project included ground based measurements at the South Pole and an airborne component on the NSF Twin Otter based out of McMurdo Station with a short deployment out of the South Pole. ACD scientists were responsible for the design and layout of the experimental package used on the twin otter aircraft, as well as for measurements of OH, H 2 SO 4 , and MSA, along with aircraft state parameters. Highlights of the study include measurements made on the Antarctic plateau, in glacial valleys, and along the coast. These measurements were aimed at evaluating the detailed dynamical and chemical processes that control spring/summertime levels of NO x /NO y and OH/HO x , as well as assessing how representative South Pole and previous ground-based coastal measurements are to the larger polar and near shore Antarctica. Based upon observations of elevated concentrations of NO and OH from previous studies at the South Pole, it has been hypothesized that on the polar plateau, NO is produced from NO 3 - photolysis in the surface layer of snow. As air follows the katabatic flow towards the coast, this NO is converted back into HNO 3 and redeposited back to the snow surface where NO 3 - photolysis can occur again. As the airmass descends from the plateau, it travels down glacial valleys. Thus, one could imagine a large flux of NO off the plateau through the glacial valleys.Preliminary results suggest that while larger concentrations of NO (and OH) were observed on the plateau and at the upper entrances to glacial valleys, these concentrations were not making it down the valleys to the exit at the coast. Further analysis will focus on these results as well as the details of photochemistry and nitrogen cycling in the various regions of Antarctica. Another highlight of the study is the first airborne measurements of the plume emitting from Mt. Erebus, a volcano located near McMurdo Station. Measurements of H 2 SO 4 and SO 2 inside the plume revealed extremely elevated concentrations compared to upwind of the plume. Following the plume downwind of the volcano, these concentrations fell as expected, giving both chemical and dynamic (dilution) information about the plume. The OH measurements will be used to provide information about H 2 SO 4 production rates and lifetimes inside the plume. FY 2007 work will focus on continued data analysis and modeling and will include collaborative efforts with participating university colleagues. This work is funded by NSF/NCAR and NSF Polar Programs. Stratospheric ozone recovery (WACCM group)
ACD scientists were involved in two studies to evaluate stratospheric ozone recovery. The Whole Atmosphere Community Climate Model (WACCM) was used to investigate the recovery of global stratospheric ozone due to the Montreal Protocol and later agreements on curbing the release of chlorofluorocarbons, halons, carbon tetrachloride, methyl chloroform and other halogens for two different scenarios of Greenhouse Gas (GHG =CO 2 , CH 4 , N 2 O) emissions in the 21st century. The black curve in the figure shows the evolution of the globally-averaged ozone column under scenario A1B of WMO (2003) for the expected future change in GHG. The red curve shows the simulation with the well mixed GHG held constant after 2000. Under scenario A1B, the global ozone column recovers to 1980 values by about 2030, 20 years earlier than in the case with no growth of GHG. The faster recovery is due to the fact that the increasing GHG under scenario A1B cool the stratosphere, leading to greater ozone production. These model simulations have supported the WMO 2006 Ozone Assessment. The second study was focused on recovery of the Antarctic ozone hole and was conducted in collaboration with Paul Newman and Randy Kawa (NASA Goddard), Eric Nash (SAIC), and Steve Montzka (NOAA ERL/CSD). For this study, a parametric model of ozone hole area based on estimates late spring stratospheric temperatures and chlorine and bromine levels over Antarctica explained 95% of the variance of the ozone hole area. Future levels of chlorine and bromine were then used to predict ozone hole recovery. The results predict full recovery to 1980 levels around 2068. The ozone hole area will slowly decline between 2001 and 2017, however detection of a statistically significant decrease of area will not occur until about 2024. Nominal greenhouse gas forced temperature change in the Antarctic stratosphere will have a small impact on the ozone hole. FY2007 will focus on further refining future halogen levels in the stratosphere and the impact on ozone recovery. This work was funded by NSF/NCAR and NASA. Long-term climate change in the thermosphere
The long-term change of thermospheric neutral density has been investigated using satellite drag measurements and through sensitivity studies using upper atmosphere general circulation models. This change was first predicted by Roble and Dickinson (1989, GRL, 16, 1144), who hypothesized that as increasing levels of carbon dioxide and other greenhouse gasses from anthropogenic sources warm the lower atmosphere, the upper atmosphere will cool and the thermosphere will contract. This behavior is due to the radiative properties of carbon dioxide, which absorbs in the infrareat low altitude but emits in the infrared at high altitude, thereby cooling the upper atmosphere. During the past five years, several groups have been able to detect the cooling and reduction in density of the thermosphere by analyzing the orbital elements of satellites in elliptical low-Earth orbits. The magnitude of the change has been quantified by these observations, largely confirming the model predictions. These effects are very difficult to measure because the secular change so far is only a few percent while the natural solar-cycle driven variation of thermospheric density can be as much as an order of magnitude. An additional intriguing aspect of the change is that models and measurements agree that it is larger at solar minimum than at solar maximum, because under high solar activity conditions there is more cooling by nitric oxide than by carbon dioxide. Understanding the interplay of solar-driven and anthropogenic change in the upper atmosphere is an important goal for NCAR researchers studying the space environment and the nature of the solar influences on the Earth system. In recent work by HAO scientists, the carbon dioxide concentration measured at the Mauna Loa Solar Observatory and the variation in solar ultraviolet radiation were used to calculate the secular change of thermospheric neutral density over the last three decades, using the NCAR global mean upper atmosphere model. The results show that the average density decrease at an altitude of 400 km during the period from 1970 to 2000 is 1.7% per decade. To quantify the impact of solar activity on the computed change in the thermospheric neutral density, the long-term density change for solar minimum and solar maximum conditions were also calculated for the same time period. The average trend was 2.5% per decade for solar minimum conditions, but only 0.7% per decade per decade for solar maximum conditions. These model results are in good agreement with estimates of the density change in the thermosphere derived from satellite drag measurements. HAO researchers plan to continue to monitor and model changing conditions in the Earth's upper atmosphere. The understanding derived from this investigation is important not only for developing a complete picture of global atmospheric change, but for predicting the orbital evolution of objects ranging from hazardous space debris to the International Space Station. Analysis of lower thermospheric dynamics
Observations of winds in the high-latitude lower thermosphere show patterns that strongly reflect the ion-drag forcing associated with electric currents driven by magnetospheric processes. The strength and pattern of the winds and the forcing change rapidly with altitude between 100 and 140 km, and depend on the direction and strength of the interplanetary magnetic field (IMF). The dynamics of this region strongly influence higher thermospheric altitudes, and also affect both the dynamical state of these layers at lower latitudes and the electrical coupling with the magnetosphere. It is not yet known to what extent the magnetospheric influences on thermospheric dynamics may affect lower altitudes of the atmosphere. This study tested the ability of an NCAR community model, the Thermosphere-Ionosphere- Electrodynamics General-Circulation Model (TIE-GCM), to reproduce the observed properties of high-latitude, lower-thermospheric winds, and used the model results in a detailed analysis of the properties of the forcing and the dynamical response of the lower thermosphere. This work supports the ESSL goals of developing realistic simulation models and using these models to address significant questions regarding the impact of the Sun's variable radiative, particulate, and magnetic outputs on the physical state of the Earth's upper atmosphere. The simulations reproduced the complex pattern of average observed winds in the summer-time lower thermosphere reasonably well, when analyzed in a coordinate system oriented with respect to the geomagnetic field and the magnetic longitude of the subsolar point. The analysis of forces on the air confirmed ideas previously suggested on the basis of simpler models, namely, that the diurnally varying winds are in approximate gradient-flow balance, when that balance is modified to include the divergent component of the ion-drag force. The rotational component of the ion-drag force dominates the forcing of the diurnal wind variation. This study quantified the influence of the wind on the ion-drag force and the relative importance of different forces at different altitudes. Future work will examine the variation of the dynamical response to different orientations of the IMF, and will use a general-circulation model that includes both the mesosphere and the thermosphere in order to quantify how the effects penetrate to lower altitudes. WACCM predictability study
Since the pioneering work of Lorenz (1963, J. Atmos. Sci., 20, 130), it has been well established that the atmosphere is chaotic by nature, and thus has finite limit of predictability. An atmospheric model run with slightly different intitial conditions can evolve over time into considerably different physical states. While this behavior has been extensively investigated, previous predictability studies have neglected the influence of the Earth's upper atmospheric layers and focused primarily on the lower atmosphere. An important component of the NCAR mission is to understand how the structure, dynamics, and chemistry of the upper atmosphere are affected by the state of the lower atmosphere, and vice versa. The Whole Atmosphere Community Climate Model (WACCM) has been developed at NCAR for the express purpose of investigating the nature and consequences of the physical couplings between the upper and lower atmosphere. As an investigatory tool, WACCM provides the means to conduct some of the first detailed studies of predictability in the context of the whole atmosphere. NCAR researchers have used WACCM to study the chaotic divergence of initial conditions and the predictability of a model atmosphere that extends from the ground to the thermosphere. From ensemble WACCM simulations, they found that the growth of differences initial conditions becomes apparent first in the upper atmosphere and subsequently progresses downward. The growth rates of the differences change in various atmospheric regions and with the seasons, and correspond closely with the strength of planetary waves. On the other hand, the growth rates are not sensitive to the altitudes at which the small differences in initial conditions are introduced, or to the physical nature of the differences. Furthermore, the growth rates are significantly reduced if the lower atmosphere is regularly reinitialized, with the reduction dependent on the frequency and the altitude range of the reinitialization. Further investigation of the implications of these results for the feedback interactions between the lower and upper atmosphere is planned. TIDI: Overview and recent results
The Thermosphere Ionosphere Mesosphere Energetic and Dynamics (TIMED) mission is a NASA satellite carrying four instruments, intended to study the least explored region of the Earth's upper atmosphere, the thermosphere, ionosphere, and mesosphere. This region is influenced from above by solar radiation and magnetopsheric interactions, and from below by the vertical coupling between the stratosphere and the mesosphere. The TIMED Doppler Interferometer (TIDI) measures neutral winds in the mesosphere and lower thermosphere by limb-scan remote sensing of the Doppler shift in airglow emissions. The neutral wind data contain many strong dynamic features, among which the diurnal and semidiurnal tides are the most prominent. The TIDI instrument has been in operation since shortly after launch of the TIMED satellite in December, 2001, and has been taking data nearly continuously thereafter, with almost no major observing interruptions. The project is jointly run by NCAR/HAO and the University of Michigan. The TIMED mission has recently been extended for an additional four years of operation, through 2010. The objective of the TIMED mission is closely related to NCAR strategic goals and priorities, which include exploring atmospheric, Earth system, and solar processes, variability, and change. The thermosphere, ionosphere, and mesosphere are an important link between the Sun's variability and the Earth's atmosphere. To achieve these objectives, NCAR is developing various coupled models, such as WACCM, which covers a much wider altitude range. TIMED data can help the model development process by providing valuable validation information. Based on combined observations from an earlier NASA mission, the Upper Atmospheric Research Satellite (UARS) High Resolution Doppler Interferometer (HRDI), 1992-2005 and TIDI 2002-2006 measurements, NCAR scientists have been able to examine the long term variations of the diurnal tide. A strong modulation of the diurnal tide by the Quasi-Biennial Oscillation (QBO) has been noted. The TIDI neutral wind observations have also been compared with NCAR Thermosphere-Ionosphere-Mesosphere -Electrodynamics General-Circulation Model (TIME-GCM) run results to study forcing terms in the mesosphere. One of the most important phenomena for mesospheric dynamics is gravity wave forcing from below. An examination of the effects of gravity wave forcing on tidal amplitudes and phases is planned for the future. WACCM model results from runs with an imposed QBO show a significant effect on migrating diurnal tides, and a comparison with TIDI data will be conducted. Geoeffectiveness of CMEs and CIRs in the solar wind
Coronal mass ejections (CMEs) are transient, large-scale eruptions of plasma and magnetic fields from the Sun. They are often referred to as interplanetary coronal mass ejections (ICMEs) after they have propagated away from the Sun into the solar wind and interplanetary medium. Magnetic clouds are a subset of ICMEs which possess a number of specific physical characteristics, including high magnetic field strength, low ion temperature and plasma beta comparable to the ambient solar wind, and a smooth rotation of the magnetic field orientation. Fast ICMEs, which travel supermagnetosonically with respect to the ambient solar wind, often drive interplanetary shocks upstream. Between the shock and the ICME is a region of compressed solar wind plasma and interplanetary magnetic field (IMF) called the "sheath". Inside the sheath region, the magnetic field strength is amplified and the plasmas become denser and hotter due to the compression. It is has been reported that an overwhelming (97%) portion of transient shocks at 1 AU are associated with ICMEs. In addition to ICMEs and interplanetary shocks, high-speed solar wind streams emanating continuously from the Sun's coronal holes form another important type of interplanetary structures. As a consequence of the solar rotation, high-speed streams (HSSs) reappear with a roughly 27-day periodicity, and may last for many solar rotations. When the high-speed wind runs into the slower wind ahead, regions of compression develop between the fast and slow flows. Since these compressive interaction regions also corotate with the Sun, they are called corotating interaction regions (CIRs). Alfvénic fluctuations in the IMF Bz component are commonly observed in HSSs due to stream-stream interactions. CIRs, CMEs, and and interplanetary shocks are common causes of geomagnetic disturbances in the Earth's magnetosphere and ionosphere. The study and characterization of these phenomena contribute to NCAR's efforts to establish the scientific basis for a predictive capability that will enable mitigation of the potentially harmful consequences of such space weather events. In a recent study, NCAR researchers found that on average, the CIR-related events resemble a weak geomagnetic storm, with a minimum Dst value of -40 nT. The average behavior of the shock/ejecta and shock/cloud events displays the characteristics of a two-step main phase storm, showing the first Dst dip in the sheath region and the second Dst dip in the following cloud or ejecta. In addition to a positive excursion in Dst, the solar wind dynamic pressure enhancement associated with interplanetary shocks also induces a prompt increase in ionospheric electric potentials (or PCP), Joule heating (JH), auroral power, the auroral electrojet (AE) index, as well as the solar wind energy input. Among the 53 events studied, there were 8 superstorms with the minimum Dst < -250 nT. Four of these were caused by the sheath region and 4 by magnetic clouds and ejecta combined, making the sheath region as "geoeffective" as the cloud and ejecta in producing superstorms. The next steps in this project will include analysis and characterization of additional events, together with efforts to trace the disturbances responsible for particular events back to their source regions on the Sun. WACCM
The Whole Atmosphere Community Climate Model (WACCM) was used to investigate the impact of solar proton events (SPEs) on the composition of the Arctic stratosphere. The figure below shows WACCM simulation of changes in NOx and ozone in the Arctic stratosphere following the SPEs of late October – early November, 2003 compared with satellite measurements from the MIPAS instrument. Left two panels: changes in observed (top) and modeled NOx (bottom). Right two panels: changes in observed (top) and modeled ozone (bottom). The very large, short-lived ozone decreases above 50 km on Oct. 29 and Nov. 4 are due to HOx enhancements (not shown); the longer-lived depletions extending into the stratosphere are due to the effect of NOx. The MIPAS NOx and ozone observations are from Lopez Puertas et al. (JGR, 2005) FY2007 work will continue evaluation of the impact of solar proton events on the chemical composition of the stratosphere. This work was funded by NSF/NCAR and NASA. |
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