Modern-Era Retrospective Analysis For Research And Applications Research Articles

Quantifying the Land–Atmosphere Coupling Behavior in Modern Reanalysis Products over the U.S. Southern Great Plains

Abstract The coupling of the land with the planetary boundary layer (PBL) on diurnal time scales is critical to regulating the strength of the connection between soil moisture and precipitation. To improve understanding of land–atmosphere (L–A) interactions, recent studies have focused on the development of diagnostics to quantify the strength and accuracy of the land–PBL coupling at the process level. In this paper, the authors apply a suite of local land–atmosphere coupling (LoCo) metrics to modern reanalysis (RA) products and observations during a 17-yr period over the U.S. southern Great Plains. Specifically, a range of diagnostics exploring the links between soil moisture, evaporation, PBL height, temperature, humidity, and precipitation is applied to the summertime monthly mean diurnal cycles of the North American Regional Reanalysis (NARR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), and Climate Forecast System Reanalysis (CFSR). Results show that CFSR is the driest and MERRA the wettest of the three RAs in terms of overall surface–PBL coupling. When compared against observations, CFSR has a significant dry bias that impacts all components of the land–PBL system. CFSR and NARR are more similar in terms of PBL dynamics and response to dry and wet extremes, while MERRA is more constrained in terms of evaporation and PBL variability. Each RA has a unique land–PBL coupling that has implications for downstream impacts on the diurnal cycle of PBL evolution, clouds, convection, and precipitation as well as representation of extremes and drought. As a result, caution should be used when treating RAs as truth in terms of their water and energy cycle processes.

A Preliminary Evaluation of Global and East Asian Cloud Radiative Effects in Reanalyses

AbstractCloud radiative effects (CREs) at the top of the atmosphere (TOA) in three reanalysis datasets (the European Center for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), the Japanese 55-yr Reanalysis Project (JRA-55), and the Modern-Era Retrospective Analysis for Research and Applications (MERRA)) are evaluated using recent satellite-based observations. The reanalyses can basically capture the spatial pattern of the annual mean shortwave CRE, but the global mean longwave CRE in ERA-Interim and JRA55 is weaker than observed, leading to overestimations of the net CRE. Moreover, distinct CRE biases of the reanalyses occur in the Intertropical Convergence Zone (ITCZ), coastal Pacific and Atlantic regions, and East Asia. Quantitative examination further indicates that the spatial correlations of CREs and TOA upward radiation fluxes with corresponding observations in ERA-Interim are better than in the other two reanalyses. Although MERRA has certain abilities in producing the magnitudes o...

Validating Atmospheric Reanalysis Data using Tropical Cyclones as Thermometers

Abstract Temperatures in the upper troposphere of the atmosphere, near the tropopause, play a key role in the evolution of tropical cyclones (TC) by controlling their potential intensity (PI), which describes the thermodynamically based maximum TC intensity that the environment will support. Accurately identifying past trends in PI is critical for understanding the causes of observed changes in TC intensity, but calculations of PI trends using different atmospheric reanalysis products can give very different results, largely due to differences in their representation of upper-tropospheric temperatures. Without a means to verify the fidelity of the upper-tropospheric temperatures, PI trends calculated from these products are very uncertain. Here, a method is introduced to validate the upper-tropospheric temperatures in the reanalysis products by using the TCs themselves as thermometers. Using a 30-yr global dataset of TC cloud-top temperatures and three widely utilized atmospheric reanalysis products—Modern-Era Retrospective Analysis for Research and Applications (MERRA), ECMWF interim reanalysis (ERA-Interim), and NCEP–NCAR Global Reanalysis 1—it is shown that storm-local upper-level temperatures in the MERRA and ERA-Interim data vary similarly to the TC cloud-top temperatures on both interannual and decadal time scales, but the NCEP–NCAR data have substantial biases that introduce an increasing trend in storm-local PI not found in the other two products. The lack of global storm-local PI trends is due to a balance between temporal increases in the mean state and the poleward migration of TCs into lower climatological PI, and it has significant implications for the detection and attribution of mean TC intensity trends.

Development of a Global Fire Weather Database

Abstract. The Canadian Forest Fire Weather Index (FWI) System is the mostly widely used fire danger rating system in the world. We have developed a global database of daily FWI System calculations, beginning in 1980, called the Global Fire WEather Database (GFWED) gridded to a spatial resolution of 0.5° latitude by 2/3° longitude. Input weather data were obtained from the NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA), and two different estimates of daily precipitation from rain gauges over land. FWI System Drought Code calculations from the gridded data sets were compared to calculations from individual weather station data for a representative set of 48 stations in North, Central and South America, Europe, Russia, Southeast Asia and Australia. Agreement between gridded calculations and the station-based calculations tended to be most different at low latitudes for strictly MERRA-based calculations. Strong biases could be seen in either direction: MERRA DC over the Mato Grosso in Brazil reached unrealistically high values exceeding DC = 1500 during the dry season but was too low over Southeast Asia during the dry season. These biases are consistent with those previously identified in MERRA's precipitation, and they reinforce the need to consider alternative sources of precipitation data. GFWED can be used for analyzing historical relationships between fire weather and fire activity at continental and global scales, in identifying large-scale atmosphere–ocean controls on fire weather, and calibration of FWI-based fire prediction models.

Extreme stratospheric springs and their consequences for the onset of polar mesospheric clouds

We use data from the Aeronomy of Ice in the Mesosphere (AIM) explorer and from the NASA Modern Era Retrospective Analysis for Research and Applications (MERRA) stratospheric analysis to explore the variability in the onset of the Northern Hemisphere (NH) Polar Mesospheric Cloud (PMC) season. Consistent with recently published results, we show that the early onset of the NH PMC season in 2013 was accompanied by a warm springtime stratosphere; conversely, we show that the late onset in 2008 coincides with a very cold springtime stratosphere. Similar stratospheric temperature anomalies for 1997 and 2011 also are connected either directly, through observed temperatures, or indirectly, through an early PMC onset, to conditions near the mesopause. These 4 years, 2008, 1997, 2011, and 2013 represent the extremes of stratospheric springtime temperatures seen in the MERRA analysis and correspond to analogous extrema in planetary wave activity. The three years with enhanced planetary wave activity (1997, 2011 and 2013) are shown to coincide with the recently identified stratospheric Frozen In Anticyclone (FrIAC) phenomenon. FrIACs in 1997 and 2013 are associated with early PMC onsets; however, the dramatic FrIAC of 2011 is not. This may be because the 2011 FrIAC occurred too early in the spring. The link between NH PMC onset and stratospheric FrIAC occurrences represents a new mode of coupling between the stratosphere and mesosphere. Since FrIACs appear to be more frequent in recent years, we speculate that as a result, PMCs may occur earlier as well. Finally we compare the zonal mean zonal winds and observed gravity wave activity for the FrIACs of 2011 and 2013. We find no evidence that gravity wave activity was favored in 2013 relative to 2011, thus suggesting that direct forcing by planetary waves was the key mechanism in accelerating the cooling and moistening of the NH mesopause region in May of 2013.

Indian summer monsoon precipitating clouds: role of microphysical process rates

The budget analysis of microphysical process rates based on Modern Era Retrospective-analysis for Research and Applications (MERRA) products are presented in the study. The relative importance of different microphysical process rates, which is crucial for GCMs, is investigated. The autoconversion and accretion processes are found to be vital for Indian Summer Monsoon (ISM). The map-to-map correlations are examined between observed precipitation and MERRA reanalysis. The pattern correlations connote the fidelity of the MERRA datasets used here. Results of other microphysical parameters (e.g. ice water content from CloudSat, high cloud fraction from CALIPSO and MODIS, latent heating from TRMM, cloud ice mixing ratio from MERRA) are presented in this study. The tropospheric temperature from reanalysis product of MERRA and NCEP are also analyzed. Furthermore, the linkages between cloud microphysics production rates and dynamics, which are important for North–South tropospheric temperature gradient for maintaining the ISM circulation, are also discussed. The study demonstrates the microphysical process rates, which are actually responsible for the cloud hydrometeors and precipitation formation on the monsoon intraseasonal oscillations timescale. Cloud to rain water auto-conversion and snow accretion rates are the dominant processes followed by the rain accretion. All these tendency terms replicates the similar spatial patterns as that of precipitation. The quantification of microphysical process rates and precipitation over different regions are shown here. The freezing rate is also imperative for the formation of cloud ice as revealed by the observation. Freezing rates at upper level and snow accretion at middle level may have effect on latent heating release. Further it can modulate the north–south temperature gradient which can influence the large-scale monsoon dynamics. The rain water evaporation is also considered as a key aspect for controlling the low level moisture convergence (source of water vapor) in ISM. This study has highlighted the importance of detailed microphysical production rates for warm and mixed-phase cloud processes, which is a major source of uncertainty in the climate models. Better understanding of these processes will definitely add value to the present generation climate models. Therefore the hypothesis/pathway emerged from the present study may be helpful for the future model development research.

Unusual stratospheric ozone anomalies observed in 22 years of measurements from Lauder, New Zealand

Abstract. The Microwave Ozone Profiling Instrument (MOPI1) has provided ozone (O3) profiles for the Network for the Detection of Atmospheric Composition Change (NDACC) at Lauder, New Zealand (45.0° S, 169.7° E), since 1992. We present the entire 22-year data set and compare with satellite O3 observations. We study in detail two particularly interesting variations in O3. The first is a large positive O3 anomaly that occurs in the mid-stratosphere (~ 10–30 hPa) in June 2001, which is caused by an anticyclonic circulation that persists for several weeks over Lauder. This O3 anomaly is associated with the most equatorward June average tracer equivalent latitude (TrEL) over the 36-year period (1979–2014) for which the Modern Era Retrospective-Analysis for Research and Applications (MERRA) reanalysis is available. A second, longer-lived feature, is a positive O3 anomaly in the mid-stratosphere (~ 10 hPa) from mid-2009 until mid-2013. Coincident measurements from the Aura Microwave Limb Sounder (MLS) show that these high O3 mixing ratios are well correlated with high nitrous oxide (N2O) mixing ratios. This correlation suggests that the high O3 over this 4-year period is driven by unusual dynamics. The beginning of the high O3 and high N2O period at Lauder (and throughout this latitude band) occurs nearly simultaneously with a sharp decrease in O3 and N2O at the equator, and the period ends nearly simultaneously with a sharp increase in O3 and N2O at the equator.

A satellite-based hybrid algorithm to determine the Priestley–Taylor parameter for global terrestrial latent heat flux estimation across multiple biomes

Accurate estimation of the terrestrial latent heat flux (LE) for each plant functional type (PFT) at high spatial and temporal scales remains a major challenge. We developed a satellite-based hybrid algorithm to determine the Priestley–Taylor (PT) parameter for estimating global terrestrial LE across multiple biomes. The hybrid algorithm combines a simple empirical equation with physically based ecophysiological constraints to obtain the sum of the weighted ecophysiological constraints (f(e)) from satellite-based normalized difference vegetation index (NDVI) and ground-measured air temperature (Ta), relative humidity (RH), vapor pressure deficit (VPD) and LE for 2000 to 2009 provided by 240 globally distributed FLUXNET eddy covariance (ECOR) tower sites. Cross-validation analysis indicated that the optimization at a PFT level performed well with a RMSE of less than 0.15 and a R2 between 0.61 and 0.88 for estimated monthly f(e). Cross-validation analysis also revealed good performance of the hybrid-based PT method in estimating seasonal variability with a RMSE of the monthly LE varying from 4.3W/m2 (for 6 deciduous needleleaf forest sites) to 18.1W/m2 (for 34 crop sites) and with a R2 of more than 0.67. The algorithm's performance was also good for predicting among-site and inter-annual variability with a R2 of more than 0.78 and 0.70, respectively. We implemented the global terrestrial LE estimation from 2003 to 2005 for a spatial resolution of 0.05°by recalibrating the coefficients of the hybrid algorithm using Modern Era Retrospective Analysis for Research and Applications (MERRA) meteorological data, Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI product and ground-measured LE. This simple but accurate hybrid algorithm provides an alternative method for mapping global terrestrial LE, with a performance generally improved as compared to other satellite algorithms that are not calibrated with tower. The calibrated f(e) differs for different PFTs, and all driving forces of the algorithm can be acquired from satellite and meteorological observations.

Development of the GEOS-5 atmospheric general circulation model: evolution from MERRA to MERRA2

Abstract. The Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) version of the Goddard Earth Observing System-5 (GEOS-5) atmospheric general circulation model (AGCM) is currently in use in the NASA Global Modeling and Assimilation Office (GMAO) at a wide range of resolutions for a variety of applications. Details of the changes in parameterizations subsequent to the version in the original MERRA reanalysis are presented here. Results of a series of atmosphere-only sensitivity studies are shown to demonstrate changes in simulated climate associated with specific changes in physical parameterizations, and the impact of the newly implemented resolution-aware behavior on simulations at different resolutions is demonstrated. The GEOS-5 AGCM presented here is the model used as part of the GMAO MERRA2 reanalysis, global mesoscale simulations at 10 km resolution through 1.5 km resolution, the real-time numerical weather prediction system, and for atmosphere-only, coupled ocean-atmosphere and coupled atmosphere-chemistry simulations. The seasonal mean climate of the MERRA2 version of the GEOS-5 AGCM represents a substantial improvement over the simulated climate of the MERRA version at all resolutions and for all applications. Fundamental improvements in simulated climate are associated with the increased re-evaporation of frozen precipitation and cloud condensate, resulting in a wetter atmosphere. Improvements in simulated climate are also shown to be attributable to changes in the background gravity wave drag, and to upgrades in the relationship between the ocean surface stress and the ocean roughness. The series of resolution-aware parameters related to the moist physics was shown to result in improvements at higher resolutions and result in AGCM simulations that exhibit seamless behavior across different resolutions and applications.

Annular Mode Variability of the Atmospheric Meridional Energy Transport and Circulation

Abstract Month-to-month variability in the meridional atmospheric energy transport is analyzed in the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis for 1979–2012. The meridional transport of moist static energy (MSE) is composited onto the high and low phases of the northern and southern annular modes (NAM and SAM). While the high phase of the NAM and SAM is known to involve a poleward shift in the midlatitude storm track and jet, it is shown here that the distribution of poleward MSE transport shifts equatorward. This change is explained by examining the variability of the underlying meridional circulation. In particular, changes in the mass transport averaged on dry and moist static energy levels are considered. These circulations have an advantage over the conventional Eulerian circulation for explaining the total energy transport. They are computed using the statistical transformed Eulerian-mean (STEM) formulation, which provides a decomposition of the circulation into Eulerian-mean and eddy-driven components. The equatorward shift in the MSE transport is largely explained by a poleward shift of the Ferrel cell, while changes in the eddy-driven circulation have a comparatively small effect on the energy transport. The changes in the residual circulation and jet are shown to be consistent through momentum balance arguments. Mean-eddy feedback mechanisms that drive and sustain the annular modes are discussed at the end as a possible explanation for why the changes in the eddy-driven circulation are weak compared to the changes in the Eulerian circulation.

On the comparisons of tropical relative humidity in the lower and middle troposphere among COSMIC radio occultations and MERRA and ECMWF data sets

Abstract. The spatial variability of the tropical tropospheric relative humidity (RH) throughout the vertical extent of the troposphere is examined using Global Positioning System Radio Occultation (GPSRO) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission. These high vertical resolution observations capture the detailed structure and moisture budget of the Hadley Cell circulation. We compare the COSMIC observations with the European Center for Medium-range Weather Forecast (ECMWF) Reanalysis Interim (ERA-Interim) and the Modern-Era Retrospective analysis for Research and Applications (MERRA) climatologies. Qualitatively, the spatial pattern of RH in all data sets matches up remarkably well, capturing distinct features of the general circulation. However, RH discrepancies exist between ERA-Interim and COSMIC data sets that are noticeable across the tropical boundary layer. Specifically, ERA-Interim shows a drier Intertropical Convergence Zone (ITCZ) by 15–20% compared to both COSMIC and MERRA data sets, but this difference decreases with altitude. Unlike ECMWF, MERRA shows an excellent agreement with the COSMIC observations except above 400 hPa, where GPSRO observations capture drier air by 5–10%. RH climatologies were also used to evaluate intraseasonal variability. The results indicate that the tropical middle troposphere at ±5–25° is most sensitive to seasonal variations. COSMIC and MERRA data sets capture the same magnitude of the seasonal variability, but ERA-Interim shows a weaker seasonal fluctuation up to 10% in the middle troposphere inside the dry air subsidence regions of the Hadley Cell. Over the ITCZ, RH varies by maximum 9% between winter and summer.

Comparisons of polar processing diagnostics from 34 years of the ERA-Interim and MERRA reanalyses

Abstract. We present a comprehensive comparison of polar processing diagnostics derived from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications (MERRA) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim). We use diagnostics that focus on meteorological conditions related to stratospheric chemical ozone loss based on temperatures, polar vortex dynamics, and air parcel trajectories to evaluate the effects these reanalyses might have on polar processing studies. Our results show that the agreement between MERRA and ERA-Interim changes significantly over the 34 years from 1979 to 2013 in both hemispheres and in many cases improves. By comparing our diagnostics during five time periods when an increasing number of higher-quality observations were brought into these reanalyses, we show how changes in the data assimilation systems (DAS) of MERRA and ERA-Interim affected their meteorological data. Many of our stratospheric temperature diagnostics show a convergence toward significantly better agreement, in both hemispheres, after 2001 when Aqua and GOES (Geostationary Operational Environmental Satellite) radiances were introduced into the DAS. Other diagnostics, such as the winter mean volume of air with temperatures below polar stratospheric cloud formation thresholds (VPSC) and some diagnostics of polar vortex size and strength, do not show improved agreement between the two reanalyses in recent years when data inputs into the DAS were more comprehensive. The polar processing diagnostics calculated from MERRA and ERA-Interim agree much better than those calculated from earlier reanalysis data sets. We still, however, see fairly large differences in many of the diagnostics in years prior to 2002, raising the possibility that the choice of one reanalysis over another could significantly influence the results of polar processing studies. After 2002, we see overall good agreement among the diagnostics, which demonstrates that the ERA-Interim and MERRA reanalyses are equally appropriate choices for polar processing studies of recent Arctic and Antarctic winters.

The impact of temperature vertical structure on trajectory modeling of stratospheric water vapor

Abstract. Lagrangian trajectories driven by reanalysis meteorological fields are frequently used to study water vapor (H2O) in the stratosphere, in which the tropical cold-point temperatures regulate the amount of H2O entering the stratosphere. Therefore, the accuracy of temperatures in the tropical tropopause layer (TTL) is of great importance for understanding stratospheric H2O abundances. Currently, most reanalyses, such as the NASA MERRA (Modern Era Retrospective – analysis for Research and Applications), only provide temperatures with ~ 1.2 km vertical resolution in the TTL, which has been argued to miss finer vertical structure in the tropopause and therefore introduce uncertainties in our understanding of stratospheric H2O. In this paper, we quantify this uncertainty by comparing the Lagrangian trajectory prediction of H2O using MERRA temperatures on standard model levels (traj.MER-T) to those using GPS temperatures at finer vertical resolution (traj.GPS-T), and those using adjusted MERRA temperatures with finer vertical structures induced by waves (traj.MER-Twave). It turns out that by using temperatures with finer vertical structure in the tropopause, the trajectory model more realistically simulates the dehydration of air entering the stratosphere. But the effect on H2O abundances is relatively minor: compared with traj.MER-T, traj.GPS-T tends to dry air by ~ 0.1 ppmv, while traj.MER-Twave tends to dry air by 0.2–0.3 ppmv. Despite these differences in absolute values of predicted H2O and vertical dehydration patterns, there is virtually no difference in the interannual variability in different runs. Overall, we find that a tropopause temperature with finer vertical structure has limited impact on predicted stratospheric H2O.

Disagreements in Low-Level Moisture between (Re)Analyses over Summertime West Africa

Abstract Reanalysis and operational analysis products are routinely used as the best estimates of the atmospheric state for operational and research purposes. However, different models, assimilation techniques, and assimilated datasets lead to differences between products. Here, such differences in the distribution of low-level water vapor over summertime West Africa are analyzed, as reflected in the zonal mean position of the leading edge of the West African monsoon [the intertropical discontinuity (ITD)] using five reanalyses [NCEP–NCAR, NCEP–Department of Energy (DOE), the Modern-Era Retrospective Analysis for Research and Applications (MERRA), the Climate Forecast System Reanalysis (CFSR), and the Interim ECMWF Re-Analysis (ERA-Interim)] and two operational analyses [Global Forecast System (GFS) and ECMWF] during the 11 monsoon seasons (April–September) from 2000 to 2010. Specific humidity differences regularly reach 50% of the mean value over areas spanning hundreds of kilometers and often coincide with northward excursions of the ITD that last several days and bring unusual rainfall to the Sahel and Sahara. The largest disagreements occur during the southward retreat of the ITD and are connected with anomalously high values of aerosol optical depth, consistent with the production of haboob dust storms. The results suggest that known errors in the representation of moist convection and cold pools may contribute to the identified disagreements. A large reduction in disagreement occurs in 2006, when upper-air observations were enhanced during the African Monsoon Multidisciplinary Analysis (AMMA) campaign, pointing to an insufficient observational constraint of the (re)analyses in other years. It is hoped that this work will raise awareness of the limited reliability of (re)analysis products over West Africa during the summer, particularly during northward surges of the ITD, and will instigate further work to improve their quality.

The Impact of Future Offshore Wind Farms on Wind Power Generation in Great Britain

In the coming years the geographical distribution of wind farms in Great Britain is expected to change significantly. Following the development of the “round 3” wind zones (circa 2025), most of the installed capacity will be located in large offshore wind farms. However, the impact of this change in wind-farm distribution on the characteristics of national wind generation is largely unknown. This study uses a 34-year reanalysis dataset (Modern-Era Retrospective Analysis for Research and Applications (MERRA) from National Aeronautics and Space Administration, Global Modeling and Assimilation Office (NASA-GMAO)) to produce a synthetic hourly time series of GB-aggregated wind generation based on: (1) the “current” wind farm distribution; and (2) a “future” wind farm distribution scenario. The derived data are used to estimate a climatology of extreme wind power events in Great Britain for each wind farm distribution. The impact of the changing wind farm distribution on the wind-power statistics is significant. The annual mean capacity factor increased from 32.7% for the current wind farm distribution to 39.7% for the future distribution. In addition, there are fewer periods of prolonged low generation and more periods of prolonged high generation. Finally, the frequency and magnitude of ramping in the nationally aggregated capacity factor remains largely unchanged. However, due to the increased capacity of the future distribution, in terms of power output, the magnitude of the ramping increases by a factor of 5.

Quantifying the reliability of four global datasets for drought monitoring over a semiarid region

Drought is one of the most relevant natural disasters, especially in arid regions such as Iran. One of the requirements to access reliable drought monitoring is long-term and continuous high-resolution precipitation data. Different climatic and global databases are being developed and made available in real time or near real time by different agencies and centers; however, for this purpose, these databases must be evaluated regionally and in different local climates. In this paper, a near real-time global climate model, a data assimilation system, and two gridded gauge-based datasets over Iran are evaluated. The ground truth data include 50 gauges from the period of 1980 to 2010. Drought analysis was carried out by means of the Standard Precipitation Index (SPI) at 2-, 3-, 6-, and 12-month timescales. Although the results show spatial variations, overall the two gauge-based datasets perform better than the models. In addition, the results are more reliable for the western portion of the Zagros Range and the eastern region of the country. The analysis of the onsets of the 6-month moderate drought with at least 3 months’ persistence indicates that all datasets have a better performance over the western portion of the Zagros Range, but display poor performance over the coast of the Caspian Sea. Base on the results of this study, the Modern-Era Retrospective Analysis for Research and Applications (MERRA) dataset is a preferred alternative for drought analysis in the region when gauge-based datasets are not available.

Alternative Source of Climate Data for Mechanistic–Empirical Pavement Performance Prediction

The AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG) and accompanying Pavement ME Design software emphasize the influence of climate on pavement performance. Several hundred weather history files from ground-based operating weather stations (OWSs) are provided with the MEPDG software. An alternate climate data source, the Modern Era Retrospective–Analysis for Research and Application (MERRA) product from the National Aeronautics and Space Administration, is evaluated here. MERRA is a global climate reanalysis procedure that combines computed model fields with ocean-, airborne-, and satellite-based observations. MERRA has the advantage of uniform worldwide spatial coverage at an approximately 0.5° by 0.67° (latitude and longitude) horizontal resolution, continuous hourly time series from 1979 to the present, and a high level of data quality control. Comprehensive statistical comparisons between MERRA climate data and those from various conventional ground-based sources are presented. Comparisons of MEPDG performance predictions with MEPDG OWS and MERRA climate data for 20 locations distributed across the contiguous United States are also summarized. The statistical and performance prediction comparisons support the conclusion that MERRA is an acceptable and advantageous source for climate data that can be used in place of conventional ground-based OWSs.

A Preliminary Evaluation of Global and East Asian Cloud Radiative Effects in Reanalyses

Cloud radiative effects(CREs) at the top of the atmosphere(TOA) in three reanalysis datasets(the European Center for Medium-Range Weather Forecasts Interim Reanalysis(ERA-Interim), the Japanese 55-yr Reanalysis Project(JRA-55), and the Modern-Era Retrospective Analysis for Research and Applications(MERRA)) are evaluated using recent satellite-based observations. The reanalyses can basically capture the spatial pattern of the annual mean shortwave CRE, but the global mean longwave CRE in ERA-Interim and JRA55 is weaker than observed, leading to overestimations of the net CRE. Moreover, distinct CRE biases of the reanalyses occur in the Intertropical Convergence Zone(ITCZ), coastal Pacific and Atlantic regions, and East Asia. Quantitative examination further indicates that the spatial correlations of CREs and TOA upward radiation fluxes with corresponding observations in ERA-Interim are better than in the other two reanalyses. Although MERRA has certain abilities in producing the magnitudes of global mean CREs, its performance in terms of spatial correlations in winter and summer are worse than for the other two reanalyses. The ability of JRA55 in reflecting CREs lies between the other two datasets. Compared to the global mean results, the spatial correlations of shortwave CRE in East Asia decrease and the biases of regional mean CREs increase in the three reanalyses. This implies that, currently, it is still difficult to reproduce East Asian CREs based on these reanalyses. Relatively, ERA-Interim describes the seasonal variation of East Asian CREs well, albeit weaker than observed. The present study also suggests that in-depth exploration of the ability of reanalysis data to describe aspects relating to cloud properties and radiation is needed using more comprehensive observations.

Associations of Jet Streams with Tornado Outbreaks in the North America

Jet streams, a current of fast winds located about seven miles up near the tropopause, are major weather driving factors in the mid-latitudes. Using the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis data resources for the period 1979 to 1988, we defined the latitudinal distribution of daily wind maxima by month, and analyzed latitudinal distribution of the highest daily wind speed at the selected longitude in the 19th week of the year. We showed the typical diving pattern of jet stream over Central America in spring. We found that latitudinal distribution of daily wind maxima was concurrently oscillated with latitudinal distribution of tornado outbreaks in April, May and June. KZ filter smoothed latitudinal distribution of highest daily wind speed on tornado days showed a substantial increase in number of daily wind maxima over tornado alley region, compared to that on non-tornado-days.

Intraannual variability of tides in the thermosphere from model simulations and in situ satellite observations

AbstractIn this paper, we provide insights into limitations imposed by current satellite‐based strategies to delineate tidal variability in the thermosphere, as well as the ability of a state‐of‐the‐art model to replicate thermospheric tidal determinations. Toward this end, we conducted a year‐long thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) simulation for 2009, which is characterized by low solar and geomagnetic activity. In order to account for tropospheric waves and tides propagating upward into the ∼30–400 km model domain, we used 3‐hourly MERRA (Modern‐Era Retrospective Analysis for Research and Application) reanalysis data. We focus on exospheric tidal temperatures, which are also compared with 72 day mean determinations from combined Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellite observations to assess the model's capability to capture the observed tidal signatures and to quantify the uncertainties associated with the satellite exospheric temperature determination technique. We found strong day‐to‐day tidal variability in TIME‐GCM that is smoothed out when averaged over as few as ten days. TIME‐GCM notably overestimates the 72 day mean eastward propagating tides observed by CHAMP/GRACE, while capturing many of the salient features of other tidal components. However, the CHAMP/GRACE tidal determination technique only provides a gross climatological representation, underestimates the majority of the tidal components in the climatological spectrum, and moreover fails to characterize the extreme variability that drives the dynamics and electrodynamics of the ionosphere‐thermosphere system. A multisatellite mission that samples at least six local times simultaneously is needed to provide this quantification.