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NASA NTRS1998

A Satellite-Derived Upper-Tropospheric Water Vapor Transport Index for Climate Studies

A new approach is presented to quantify upper-level moisture transport from geostationary satellite data. Daily time sequences of Geostationary Operational Environmental Satellite GOES-7 water vapor imagery were used to produce estimates of winds and water vapor mixing ratio in the cloud-free region of the upper troposphere sensed by the 6.7- microns water vapor channel. The winds and mixing ratio values were gridded and then combined to produce a parameter called the water vapor transport index (WVTI), which represents the magnitude of the two-dimensional transport of water vapor in the upper troposphere. Daily grids of WVTI, meridional moisture transport, mixing ratio, pressure, and other associated parameters were averaged to produce monthly fields for June, July, and August (JJA) of 1987 and 1988 over the Americas and surrounding oceanic regions, The WVTI was used to compare upper-tropospheric moisture transport between the summers of 1987 and 1988, contrasting the latter part of the 1986/87 El Nino event and the La Nina period of 1988. A similar product derived from the National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) 40-Year Reanalysis Project was used to help to validate the index. Although the goal of this research was to describe the formulation and utility of the WVTI, considerable insight was obtained into the interannual variability of upper-level water vapor transport. Both datasets showed large upper-level water vapor transport associated with synoptic features over the Americas and with outflow from tropical convective systems. Minimal transport occurred over tropical and subtropical high pressure regions where winds were light. Index values from NCEP-NCAR were 2-3 times larger than that determined from GOES. This difference resulted from large zonal wind differences and an apparent overestimate of upper-tropospheric moisture in the reanalysis model. A comparison of the satellite-derived monthly values between the summers of 1987 and 1988 provided some insight into the impact of the ENSO event on upper-level moisture and its transport during the period. During July 1987, a large portion of the Tropics in the eastern Pacific Ocean and Caribbean Sea was dominated by strong vapor transport in excess of 4.0 g/kg m/s, with relatively small amounts in the other months. JJA 1988 transport values reached similar magnitude and showed similar patterns for all three months. The meridional transport of upper-level water vapor indicated large poleward transport from the Tropics to the higher latitudes. This transport favored the Southern Hemisphere, with large transport occurring south of the ITCZ, which extended across the eastern Pacific and northern South America. Zonally averaged monthly transport values were shown to provide a simple way to quantify the monthly and interannual changes in water vapor transport. Zonally averaged WVTI values peaked in the Southern Hemisphere subtropics during both austral winters. In the Tropics, a single, more- pronounced peak located over the equator and south latitudes occurred in 1988 as opposed to a dual peak in 1987. The second peak around 20'N latitude is consistent with findings of others in which upper-tropospheric winds were noted to be stronger in this region during warm ENSO events. Zonally averaged meridional transport was southward for all summer months and was stronger in 1988. The asymmetric nature of the zonally averaged meridional transport (more southerly water vapor transport) was enhanced during JJA 1988, thus indicating a stronger upper- level branch of the Hadley circulation during this notably strong La Nina period.

Jedlovec, Gray J.↗
NASA NTRS2000

Soil Moisture and Mesoscale Convective Complex Development During the 1993 US Midwest Flood: Results from the MM5-PLACE Atmosphere/Land-Surface Model

The 1993 US Midwest Flood produced record levels of flooding, in the Mississippi River Basin. This flooding resulted from repeated frontal passages and mesoscale convective complexes (MCCs) during the months of June and July. A better understanding of processes that influenced MCC development during the 1993 Flood may lead to improved forecasts of heavy precipitation and flooding. Here, we consider the impact of soil moisture on MCC development during a two-day period (June 23-24) of the 1993 US Midwest Flood. The purpose of this study is to assess the importance of soil moisture distribution on the timing, intensity, and location of heavy precipitation. In this study, the MM5-PLACE Atmosphere/Land-Surface Model is utilized. The atmospheric component consists of the Penn State/NCAR MM5 mesoscale model, and the land-surface component consists of the Goddard Parameterization for Land Atmosphere-Cloud Exchange (PLACE). Initial soil moisture is provided from two sources: 1) NCEP reanalysis, and 2) Antecedent Precipitation Index (API) using NOAA rain gauge measurements as a proxy for soil moisture. NCEP reanalysis provides coarse resolution initial soil moisture (2.5 degree), while API provides high resolution initial soil moisture (10-200 km depending on NOAA rain gauge spacing). Initial results indicate that the distribution of soil moisture has a significant impact on the timing and location of heavy precipitation during this two-day flood event. Precipitation in simulations with high resolution initial soil moisture agrees more closely with observed precipitation. These results suggest that high resolution soil moisture observations are necessary to accurately predict severe storm development, heavy precipitation, and subsequent flooding.

Baker, R. David↗
NASA NTRS2000

Magnitude, Duration, and Geographic Coherence of Interannual Anomalies of the Great Plains Low-Level Jet

The Great Plains region of the United States is characterized by some of the world's most frequent and regular occurrences of a nocturnal low-level jet (LLJ). While this southerly jet is generally confined to the lowest kilometer of the atmosphere, it may cover a substantial region of the Great Plains and reach wind speed maxima of 20 m/s or more. The temporal and spatial structure of this jet has been well captured by the GEOS-1 15-year reanalysis. The jet is most evident during the warm season, May through August. The year-to-year variability of the seasonally-averaged jet structure is small relative to its diurnal or its intraseasonal variability and is comparable in magnitude to the seasonal variability for the mean climatology. The interannual variance maximum is located to the east of both the jet maximum and the seasonal variance maximum and seems to be related to a biennial oscillation which occurs for the first six years of the reanalysis period. There is a second maximum which is free of this oscillation, which is located at the same latitude but further south in the Gulf of Mexico. Interannual anomalies seem to have a duration of about three weeks and spatial coherences about ten degrees wide. Meridional velocity anomalies for the drought year 1988 and the flood year 1993 are large, but their impacts on the hydrological cycle may be as sensitive to their eastward location as to their magnitudes.

Helfand, H. Mark↗
NASA NTRS2001

Diagnosing Tropical Divergent Circulations From Satellite-Derived Diabatic Forcing and Variational Integral Constraints

Large-scale divergent circulations are part of the atmospheric dynamic response to diabatic heating from condensation, radiative processes, and surface energy fluxes. Vertical motion and the associated divergent wind is thus intimately tied to the hydrologic cycle and the global beat balance. Despite its importance, the divergent circulation is too small in comparison to the rotational flow to measure directly with any accuracy. Vertical motions are recovered diagnostically from reanalyses and, as such, are subject to shortcomings in model physics, numerics, and data availability. While reanalysis estimates of tropical divergent circulations are much improved over those from the Global Weather Experiment, there are still substantial differences between products from operational centers. This is because these circulations are still forced largely by model physics and only secondarily by observations. In order to produce a refined estimate of tropical divergence and its interannual variability we have used a number of remotely-sensed data sets along with variational constraints to improve upon reanalysis estimates. Among these are: precipitation from SSM/I and GPCP, TOVS Path-A vertical cloud distributions; ISCCP radiative cooling rates; TOA radiative fluxes from ERBS, surface radiative fluxes from the SRB project, and surface latent and sensible flux estimates from SSM/I. The TOVS Path-A data constrain the divergent outflow in precipitating regions to have the same vertical structure as observed cloudiness. Using integral constraints for moisture, heat, and mass balance, we retrieve consistent divergent wind flows. We examine the ability of this type analysis to capture regional details of ENSO related perturbations to the divergent wind and associated tropical energy balance. Precipitation from satellite is found to be the major constraint in supplying this horizontal structure. We also consider the ability of this analysis to quantify integrated (land vs. ocean) fluctuations in the global monsoonal flow and energy balance. This depends, of course, on the error characteristics of the data constraints. Some estimate of these properties and their relative importance is provided.

Robertson, Franklin R.↗
NASA NTRS2001

Non-seasonal Gravitational Effects of Interannual Meteorological Oscillations in Atmosphere and Ocean

Via mass transport, the interannual meteorological oscillations (ENSO, NAO, etc.) produce slight variations in the global gravitational field, which can be observed by satellite laser ranging (SLR) and anticipated space missions such as GRACE. The meteorological oscillation modes are identified using empirical orthogonal function and principal component decomposition using de-seasoned surface fields produced from the 40-years of NCEP reanalysis. This decompositional analysis requires an accounting for issues associated with area-weighting and non-zero mean. The atmospheric contributions to gravitational variation, mode by mode and in combinations, are then computed via regional integration. To address the corresponding oceanic contributions, we examine the output of the numerical POCM ocean circulation model (1992-1998) in two ways: ocean bottom pressure field and ocean surface topography minus steric effect. The resulting lowest-degree Stokes coefficients for both NCEP reanalysis and POCM are then compared with space geodetic SLR observations, to identify the importance of each meteorological oscillations in gravitational variation signals.

Chao, Benjamin F.↗
NASA NTRS2002

Climatology, Natural Cycles, and Modes of Interannual Variability of the Great Plains Low-Level Jet as Assimilated by the GEOS-1 Data Analysis System

Despite the fact that the low-level jet of the southern Great Plains (the GPLLJ) of the U.S. is primarily a nocturnal phenomenon that virtually vanishes during the daylight hours, it is one of the most persistent and stable features of the low-level continental flow during the warm-season months, May through August. We have first used significant-level data to validate the skill of the GEOS-1 Data Assimilation System (DAS) in realistically detecting this jet and inferring its structure and evolution. We have then carried out a 15-year reanalysis with the GEOS-1 DAS to determine and validate its climatology and mean diurnal cycle and to study its interannual variability. Interannual variability of the GPLLJ is much smaller than mean diurnal and random intraseasonal variability and comparable in magnitude, but not location, to mean seasonal variability. There are three maxima of interannual low-level meridional flow variability of the GPLLJ over the upper Great Plains, southeastern Texas, and the western Gulf of Mexico. Cross-sectional profiles of mean southerly wind through the Texas maximum remain relatively stable and recognizable from year to year with only its eastward flank showing significant variability. This variability, however, exhibits a distinct, biennial oscillation during the first six years of the reanalysis period and only then. Each of the three variability maxima corresponds to a spatially coherent, jet-like pattern of low-level flow interannual variability. There are three prominent modes of interannual. variability. These include the intermittent biennial oscillation (IBO), local to the Texas maximum. Its signal is evident in surface pressure, surface temperature, ground wetness and upper air flow, as well. A larger-scale continental convergence pattern (CCP) of covariance, exhibiting strong anti-correlation between the flow near the Texas and the upper Great Plains variability maxima, is revealed only when the IBO is removed from the interannual time series. A third, subtropical mode of covariance is associated with the Gulf of Mexico variability maximum. Significant interannual anti-correlations of the southeasterly flow over the Arizona/New Mexico region with the CCP and the subtropical mode are enhanced when restricted to the month of July. These anti-correlations may relate to an observed out-of-phase precipitation relationship between the Great Plains and the southwestern U.S.. The typical duration of interannual low-level meridional wind anomalies within a given season increases over the continent with decreasing latitude from two to three weeks over the upper Great Plains to six to seven weeks over eastern Texas.

Helfand, H. M.↗
NASA NTRS2003

Sub-problem Optimization With Regression and Neural Network Approximators

Design optimization of large systems can be attempted through a sub-problem strategy. In this strategy, the original problem is divided into a number of smaller problems that are clustered together to obtain a sequence of sub-problems. Solution to the large problem is attempted iteratively through repeated solutions to the modest sub-problems. This strategy is applicable to structures and to multidisciplinary systems. For structures, clustering the substructures generates the sequence of sub-problems. For a multidisciplinary system, individual disciplines, accounting for coupling, can be considered as sub-problems. A sub-problem, if required, can be further broken down to accommodate sub-disciplines. The sub-problem strategy is being implemented into the NASA design optimization test bed, referred to as "CometBoards." Neural network and regression approximators are employed for reanalysis and sensitivity analysis calculations at the sub-problem level. The strategy has been implemented in sequential as well as parallel computational environments. This strategy, which attempts to alleviate algorithmic and reanalysis deficiencies, has the potential to become a powerful design tool. However, several issues have to be addressed before its full potential can be harnessed. This paper illustrates the strategy and addresses some issues.

Guptill, James D.↗
NASA NTRS2002

A National Program for Analysis of the Climate System

Perhaps the single greatest roadblock to fundamental advances in our understanding of climate variability and climate change is the lack of robust and unbiased long-term global observations of the climate system. Such observations are critical for the identification and diagnosis of climate variations, and provide the constraints necessary for developing and validating climate models. The first generation of reanalysis efforts, by using fixed analysis systems, eliminated the artificial climate signals that occurred in analyses generated at the operational numerical weather prediction centers. These datasets are now widely used by the scientific community in a variety of applications including atmosphere-ocean interactions, seasonal prediction, climate monitoring, the hydrological cycle, and a host of regional and other diagnostic studies. These reanalyses, however, had problems that made them sub-optimal or even unusable for some applications. Perhaps the most serious problem for climate applications was that, while the assimilation system remained fixed, changes in the observing systems did produce spurious changes in the perceived climate. The first generation reanalysis products also exposed problems with physical consistency of the products and the accurate representation of physical processes in the climate system. Examples are bias in the estimates of ocean surface fluxes, and inadequate representation of polar hydrology. In this talk, I will describe some initial plans for a national program on reananlysis. The program is envisioned to be part of an on-going activity to maintain, improve, and reprocess our record of climate observations. I will discuss various issues affecting the quality of reanalyses, with a special focus on those relevant to the ocean.

Schubert, Siegfried↗
NASA NTRS2003

Intercomparison of Latent Heat Fluxes Over Global Oceans

Turbulent fluxes of momentum, moisture, and heat at the air-sea interface are essential for climate studies. Version 2 Goddard Satellite-based Surface Turbulent Fluxes (GSSTF2) has been derived from the Special Sensor Microwave/Imager (SSM/I) radiance measurements. This dataset, covering the period July 1987-December 2000 over global oceans, has a spatial resolution of 1 deg x 1 deg lat-long and a temporal resolution of 1 day. Turbulent fluxes are derived from the SSM/I surface winds and surface air humidity, as well as the 2-m air and sea surface temperatures (SST) of the NCEP/NCAR reanalysis, using a bulk aerodynamic algorithm based on the surface layer similarity theory. The GSSTF2 bulk flux model, and retrieved daily wind stress, latent heat flux, wind speed, and surface air humidity validate well with ship observations of ten field experiments over the tropical and midlatitude oceans during 1991-99. The global distributions of 1988-2000 annual- and seasonal-mean turbulent fluxes show reasonable patterns related to the atmospheric general circulation and seasonal variations. Latent heat fluxes and related input parameters over global oceans during 1992-93 have been compared among GSSTF1 (version 1), GSSTF2, HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data), NCEP/NCAR reanalysis, and one based on COADS (Comprehensive Ocean-Atmosphere Data Set). Our analyses suggest that the GSSTF2 latent heat flux, surface air humidity, surface wind, and SST are quite realistic compared to the other four flux datasets examined. However, significant differences are found among these five flux datasets. The GSSTF2, available at http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/hydrology/hd_gsstf2.O.html, is useful for climate studies.

Chou, Shu-Hsien↗
NASA NTRS2004

More Far-Side Deep Moonquake Nests Discovered

As reported last year, we started to reanalyze the seismic data acquired from 1969 to 1977 with a network of stations established on the Moon during the Apollo mission. The reason for the reanalysis was because recent advances in computer technology make it possible to employ much more sophisticated analysis techniques than was possible previously. The primary objective of the reanalysis was to search for deep moonquakes on the far side of the Moon and, if found, to use them to infer the structure of the Moon's deep interior, including a possible central core. The first step was to identify any new deep moonquakes that escaped our earlier search by applying a combination of waveform cross-correlation and single-link cluster analysis, and then to see if any of them are from previously unknown nests of deep moonquakes. We positively identified 7245 deep moonquakes, more than a five-fold increase from the previous 1360. We also found at least 88 previously unknown deep-moonquake nests. The question was whether any of these newly discovered nets were on the far side of the Moon, and we now report that our analysis of the data indicates that some of them are indeed on the far side.

Nakamura, Y.↗
NASA NTRS2004

A Multi-Wavelength Search for a Counterpart of the Unidentified Gamma-ray source 3EG J2020+4017 (2CG078+2)

In search of the counterpart to the brightest unidentified gamma-ray source 3EG J2020+4017 (2CG078+2) we report on new X-ray and radio observations of the gamma-Cygni field with the Chandra X-ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data. With Chandra it became possible for the first time to measure the position of the putative gamma-ray counterpart RX J2020.2+4026 with sub-arcsec accuracy and to deduce its X-ray spectral characteristics. These observations demonstrate that RX J2020.2+4026 is associated with a K field star and therefore is unlikely to be the counterpart of the bright gamma-ray source 2CG078+2 in the SNR G78.2+2.1 as had been previously suggested. The Chandra observation detected 37 additional X-ray sources which were correlated with catalogs of optical and infrared data. Subsequent GBT radio observations covered the complete 99% EGRET likelihood contour of 3EG J2020+4017 with a sensitivity limit of L(sub 820) approx. 0.1 mJy kpc(exp 2) which is lower than most of the recent deep radio search limits. If there is a pulsar operating in 3EG J2020+4017, this sensitivity limit suggests that the pulsar either does not produce significant amounts of radio emission or that its geometry is such that the radio beam does not intersect with the line of sight. Finally, reanalysis of archival ROSAT data leads to a flux upper limit of f(sub x)(0.1-2.4 keV) < 1.8 x 10(exp -13) erg/s/sq cm for a putative point-like X-ray source located within the 68% confidence contour of 3EG J2020+4017. Adopting the SNR age of 5400 yrs and assuming a spin-down to X-ray energy conversion factor of 10(exp -3) this upper limit constraints the parameters of a putative neutron star as a counterpart for 3EG J2020+4017 to be P > or approx. 160/(d/1.5 kpc) ms, P > or approx. 5 x 10(exp -13)/(d/1.5kpc) s s1 and B > or approx. 9 x 10(exp 12)/(d/1.5 kpc) G.

Becker, Werner↗
NASA NTRS2004

High-Resolution Mesoscale Simulations of the 6-7 May 2000 Missouri Flash Flood: Impact of Model Initialization and Land Surface Treatment

High-resolution mesoscale model simulations of the 6-7 May 2000 Missouri flash flood event were performed to test the impact of model initialization and land surface treatment on timing, intensity, and location of extreme precipitation. In this flash flood event, a mesoscale convective system (MCS) produced over 340 mm of rain in roughly 9 hours in some locations. Two different types of model initialization were employed: 1) NCEP global reanalysis with 2.5-degree grid spacing and 12-hour temporal resolution, and 2) Eta reanalysis with 40- km grid spacing and $hour temporal resolution. In addition, two different land surface treatments were considered. A simple land scheme. (SLAB) keeps soil moisture fixed at initial values throughout the simulation, while a more sophisticated land model (PLACE) allows for r interactive feedback. Simulations with high-resolution Eta model initialization show considerable improvement in the intensity of precipitation due to the presence in the initialization of a residual mesoscale convective vortex (hlCV) from a previous MCS. Simulations with the PLACE land model show improved location of heavy precipitation. Since soil moisture can vary over time in the PLACE model, surface energy fluxes exhibit strong spatial gradients. These surface energy flux gradients help produce a strong low-level jet (LLJ) in the correct location. The LLJ then interacts with the cold outflow boundary of the MCS to produce new convective cells. The simulation with both high-resolution model initialization and time-varying soil moisture test reproduces the intensity and location of observed rainfall.

Baker, R. David↗
NASA NTRS2004

A Multiwavelength Search for a Counterpart of the Brightest Unidentified Gamma-Ray Source 3EG J2020+4017 (2CG 078+2)

In search of the counterpart to the brightest unidentified gamma-ray source, 3EG J2020+4017 (2CG 078+2), we report on new X-ray and radio observations of the gamma Cygni field with the Chandra X-Ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data. With Chandra it became possible for the first time to measure the position of the putative gamma-ray counterpart, RX J2020.2+4026, with subarcsecond accuracy and to deduce its X-ray spectral characteristics. These observations demonstrate that RX J2020.2+4026 is associated with a K field star and therefore is unlikely to be the counterpart of the bright gamma-ray source 2CG 078+2 in the SNR G78.2+2.1 as had been previously suggested. The Chandra observation detected 37 additional X-ray sources, which were correlated with catalogs of optical and infrared data. Subsequent GBT radio observations covered the complete 99% EGRET likelihood contour of 3EG J2020+4017 with a sensitivity limit of L(sub 820) approximately 0.1 mJy kpc(exp 2), which is lower than most of the recent deep radio search limits. If there is a pulsar operating in 3EG J2020+40 17, this sensitivity limit suggests that either the pulsar does not produce significant amounts of radio emission or that its geometry is such that the radio beam does not intersect with the line of sight. Finally, reanalysis of archival ROSAT data leads to a flux upper limit of fx(0.1 - 2.4 keV) less than 1.8 x 10(exp -13) ergs s(exp -1) cm(exp -2) for a putative pointlike X-ray source located within the 68% confidence contour of 3EG J2020+4017. Adopting the supernova remnant age of 5400 yr and assuming a spin-down to X-ray energy conversion factor of 10(exp 14), this upper limit constrains the parameters of a putative neutron star as a counterpart for 3EG J2020+4017 to be P is approximately greater than 160 (d 1.5 kpc)(exp -1) ms, P is approximately greater than 5 x 10(exp -13) ((d 1.5 kpc)(exp -1)) s s(exp -1), and B (perpendicular) is approximately greater than 9 x 10(exp l2) )(d 1.5 kpc)(exp -1)) G.

Becker, Werner↗
NASA NTRS2008

Using Wind and Temperature Fields to Study Dehydration Mechanisms in the Tropical Tropopause Layer

The tropics are the main region for troposphere-to-stratosphere transport (TST) of air. One of the dominant mechanisms that control tropical TST of water vapor is freeze-drying by the cold tropical tropopause. This mechanism is supported by evidence from satellite observations of the "tape recorder", where seasonal changes in stratospheric water vapor are in phase with seasonal changes in tropopause temperatures in the tropics. Over the last few years, however, the concept of the tropical tropopause has evolved from a single material surface to a layer called the Tropical Tropopause Layer (TTL). A recent hypothesis on dehydration mechanisms suggests that dehydration and entry point into the stratosphere are not always co-located (Holton and Gettelman, 2001). Instead, dehydration can occur during horizontal advection through Lagrangian 'cold pools', or coldest regions along a parcel's trajectory, as air ascends within the TTL while the entry point into the stratosphere occurs at a different geographical location. In this study, we investigate the impact that these Lagrangian cold pools have on TTL moisture. For this purpose, we use in situ measurements of TTL water vapor obtained aboard NASA's WB-57 aircraft over the Eastern Tropical Pacific, and we compare these measurements to minimum saturation water vapor mixing ratios obtained from three-dimensional backward trajectory calculations. Aircraft measurements show frequent unsaturated conditions, which suggest that the entry value of stratospheric water vapor in this region was not set by local saturation conditions. Trajectory calculations, driven by both ECMWF operational analysis and reanalysis winds and temperature fields, are used to explore the impact (e.g., geographical location, timing, dehydration magnitude) of the Lagrangian cold pools intercepted by the parcels sampled by the aircraft. We find noteworthy differences in the location of the Lagrangian cold pools using the two ECMWF data sets, namely influence of the Western Tropical Pacific region when using operational analysis fields versus influence of the Eastern Tropical Pacific and South America regions when using reanalysis fields. These results have a significant impact on our scientific conclusions on dehydration mechanisms affecting the air sampled by the aircraft, given that these regions have different thermodynamic and convective properties.

Pittman, Jasna↗
NASA NTRS2007

The Spatiotemporal Structure of 20th Century Climate Variations in Observations and Reanalyses: Long-term Trend - Part 1

The dominant interannual El Nino-Southern Oscillation phenomenon (ENSO) and the short length of climate observation records make it difficult to study long-term climate variations in the spatiotemporal domain. Based on the fact that the ENS0 signal spreads to remote regions and induces delayed climate variation through atmospheric teleconnections, we develop an ENSO-removal method through which the ENS0 signal can be approximately removed at the grid box level from the spatiotemporal field of a climate parameter. After this signal is removed, long-term climate variations, namely, the global warming trend (GW) and the Pacific pan-decadal variability (PDV), are isolated at middle and low latitudes in the climate parameter fields from observed and reanalyses datasets. Except for known GW characteristics, the warming that occurs in the Pacific basin (approximately 0.4K in the 2oth century) is much weaker than in surrounding regions and the other two ocean basins (approximately 0.8K). The modest warming in the Pacific basin is likely due to its dynamic nature on the interannual and decadal time scales and/or the leakage of upper ocean water through the Indonesian Throughflow. Based on NCEP/NCAR and ERA-40 reanalyses, a comprehensive atmospheric structure associated with GW is given. Significant discrepancies exist between the two datasets, especially in the tightly coupled dynamic and water vapor fields. The dynamic field based on NCEP/NCAR reanalysis, which shows a change in the Walker Circulation, is consistent with the GW change in the surface temperature field. However, intensification in the Hadley Circulation is associated with GW trend in the ERA-40 reanalysis.

Chen, Junye↗
NASA NTRS2009

American Meteorological Society (AMS) - The Modern Era Retrospective-Analysis for Research and Applications (MERRA) Data and Accessibility

The AM Short Course on The Modern Era Retrospective-analysis for Research and Applications (MERRA) data and accessibility will be held on January 11, 2009 preceding the 89th Annual Meeting in Phoenix, Arizona. Preliminary programs, registration, hotel, and general information will be posted on the AMS Web site in mid-September 2008. Retrospective-analyses (or reanalyses) have been established as an important tool in weather and climate research over the last decade. As computer power increases, the data assimilation and modeling systems improve and become more advanced, the input data quality increases and so reanalyses become more reliable. In 2008, NASA Global Modeling and Assimilation Office began producing a new reanalysis called the Modem Era Retrospective-analysis for Research and Applications (MERRA). The initial data from the reanalysis has been made available to the community and should be complete through 30 years (1979-present) by Fall of 2009. MERRA has taken advantage of the advancement of computing resources to provide users more data than previously available. The native spatial resolution is nominally 1/2 degrees and the surface two dimensional data are one hourly frequency. In addition to the meteorological analysis data, complete mass, energy and momentum budget data and also stratospheric data are provided. The eventual data holdings will exceed 150Tb. In order to facilitate user accessibility to the data, it will be stored in online hard drives (not tape storage) and available through several portals. Subsetting tools will also be available to allow users to tailor their data requests. The goals of this short course are to provide hands on users of reanalyses instruction on MERRA systems and also interactive experience with the online data and access tools. The course is intended for students and research scientists who will be actively interested in accessing and applying MERRA data in their weather, climate or applications work. The course has three parts. There will be an overview of the MERRA system, the validation of the system and the native data format. Second, Instructors will provide examples of weather and climate data analysis using various software packages (primarily GrADS) as well as the online access tools for subsetting and download, as well as visualization (e.g. Giovanni and Google Earth). This will also include examples on changing the data format to fit user's preferences and also to regrid the data for comparisons to other reanalyses and observational data. Lastly, there will he time set aside for participants to have hands on access to the data and software while interacting with the instructors and other developers. The course convener is Dr. Michael Bosilovich, NASA GSFC Global Modeling and Assimilation Office (GMAO). He will be joined by several GMAO, Goddard Earth Science Data and information Services Center (GES DISC) and Software Integration and Visualization Office (SIVO) staff.

daSilva, Arlindo↗
NASA NTRS2010

Analysis of Air-Sea Interactions in the NASA MERRA Product

Interactions between the ocean and atmosphere influence the global energy and water balance through the exchange of heat, moisture and momentum. These interactions occur over a wide range of space and time scales and need to be properly represented in climate and reanalysis simulations. This study focuses on the representation of the turbulent latent and sensible heat fluxes in the newly developed NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA). It is shown that MERRA achieves realistic estimates of the turbulent fluxes for many space and time scales although some deficiencies are noted. Comparisons are made at high resolution temporal scales with measurements from several research vessels while long term comparisons are made with moored buoys. These results are contrasted with those from several other currently available reanalysis and satellite based products. The representation of feedbacks between the atmosphere and ocean area also examined through the use of simultaneous and lagged correlation analyses with particular focus on precipitation and sea surface temperature relationships. Together, these results demonstrate the consistency of the NASA MERRA product and its applicability for process studies across wide ranging scales of variability.

Roberts, J. Brent↗
NASA NTRS2010

The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes

Because reanalysis data sets offer state variables and fluxes at regular space / time intervals, atmospheric reanalyses have become a mainstay of the climate community for diagnostic purposes and for driving offline ocean and land models. Although one weakness of these data sets is the susceptibility of the flux products to uncertainties because of shortcomings in parameterized model physics, another issue, perhaps less appreciated, is the fact that continual but discreet changes in the evolving observational system, particularly from satellite sensors, may also introduce artifacts in the time series of quantities. In this paper we examine the ability of the NASA MERRA (Modern Era Retrospective Analysis for Research and Applications) and other recent reanalyses to determine variability in the climate system over the satellite record (approximately the last 30 years). In particular we highlight the effect on the reanalysis of discontinuities at the junctures of the onset of passive microwave imaging (Special Sensor Microwave Imager) in late 1987 as well as improved sounding and imaging with the Advanced Microwave Sounding Unit, AMSU-A, in 1998. We first examine MERRA fluxes from the perspective of how physical modes of variability (e.g. ENSO events, Pacific Decadal Variability) are contaminated by artificial step-like trends induced by the onset of new moisture data these two satellite observing systems. Secondly, we show how Redundancy Analysis, a statistical regression methodology, is effective in relating these artifact signals in the moisture and temperature analysis increments to their presence in the physical flux terms (e.g. precipitation, radiation). This procedure is shown to be effective greatly reducing the artificial trends in the flux quantities.

Robertson, Franklin R.↗