Abstract

The vertically integrated global energy budget is evaluated with a direct and an indirect method (both corrected for mass inconsistencies of the forecast model), mainly using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim (ERA-Interim) data. A new estimate for the net poleward total energy transport is given. Comparison to satellite-derived radiation data proves that ERA-Interim is better suited for investigation of interannual variations of the global energy budget than available satellite data since these either cover a relatively short period of time or are too inhomogeneous in time. While much improved compared to the 40-yr ECMWF Re-Analysis (ERA-40), regionally averaged energy budgets of ERA-Interim show that strong anomalies of forecasted vertical fluxes tend to be partly compensated by unrealistically large forecasted energy storage rates. Discrepancies between observed and forecasted monthly mean tendencies can be taken as rough measure for the uncertainties involved in the ERA-Interim energy budget. El Niño–Southern Oscillation (ENSO) is shown to have large impact on regional energy budgets, but strong compensation occurs between the western and eastern Pacific, leading to only small net variations of the total poleward energy transports (similar magnitude as the uncertainty of the computations). However, Hovmöller longitude–time plots of tropical energy exports show relatively strong slowly eastward-moving poleward transport anomalies in connection with ENSO. Verification of these findings using independent estimates still needs to be done.

Abstract

This study uses advanced numerical and diagnostic methods to evaluate the atmospheric energy budget with the fifth major global reanalysis produced by ECMWF (ERA5) in combination with observed and reconstructed top of the atmosphere (TOA) energy fluxes for the period 1985–2018. We assess the meridional as well as ocean–land energy transport and perform internal consistency checks using mass-balanced data. Furthermore, the moisture and mass budgets in ERA5 are examined and compared with previous budget evaluations using ERA-Interim as well as observation-based estimates. Results show that peak annual mean meridional atmospheric energy transports in ERA5 (4.58 ± 0.07 PW in the Northern Hemisphere) are weaker compared to ERA-Interim (4.74 ± 0.09 PW), where the higher spatial and temporal resolution of ERA5 can be excluded as a possible reason. The ocean–land energy transport in ERA5 is reliable at least from 2000 onward (~2.5 PW) such that the imbalance between net TOA fluxes and lateral energy fluxes over land are on the order of ~1 W m⁻². Spinup and spindown effects as revealed from inconsistencies between analyses and forecasts are generally smaller and temporally less variable in ERA5 compared to ERA-Interim. Evaluation of the moisture budget shows that the ocean–land moisture transport and parameterized freshwater fluxes agree well in ERA5, while there are large inconsistencies in ERA-Interim. Overall, the quality of the budgets derived from ERA5 is demonstrably better than estimates from ERA-Interim. Still some particularly sensitive budget quantities (e.g., precipitation, evaporation, and ocean–land energy transport) show apparent inhomogeneities, especially in the late 1990s, which warrant further investigation and need to be considered in studies of interannual variability and trends.

Abstract

This study uses the ECMWF ERA5 reanalysis and observationally constrained top-of-the-atmosphere radiative fluxes to infer net surface energy fluxes covering 1985–2018, which can be further adjusted to match the observed mean land heat uptake. Various diagnostics are applied to provide error estimates of inferred fluxes on different spatial scales. For this purpose, adjusted as well as unadjusted inferred surface fluxes are compared with other commonly used flux products. On a regional scale, the oceanic energy budget of the North Atlantic between the RAPID array at 26.5°N and moorings located farther north (e.g., at the Greenland–Scotland Ridge) is evaluated. On the station scale, a comprehensive comparison of inferred and buoy-based fluxes is presented. Results indicate that global land and ocean averages of unadjusted inferred surface fluxes agree with the observed heat uptake to within 1 W m⁻², while satellite-derived and model-based fluxes show large global mean biases. Furthermore, the oceanic energy budget of the North Atlantic is closed to within 2.7 (−0.2) W m⁻² for the period 2005–09 when unadjusted (adjusted) inferred surface fluxes are employed. Indirect estimates of the 2004–16 mean oceanic heat transport at 26.5°N are 1.09 PW (1.17 PW with adjusted fluxes), which agrees well with observed RAPID transports. On the station scale, inferred fluxes exhibit a mean bias of −20.1 W m⁻² when using buoy-based fluxes as reference, which confirms expectations that biases increase from global to local scales. However, buoy-based fluxes as reference are debatable, and are likely positively biased, suggesting that the station-scale bias of inferred fluxes is more likely on the order of −10 W m⁻².

Abstract

A tornado observed on 15 June 1973 in the FACE surface mesonetwork was studied on the mesoscale and cloud scale. Downdrafts from two preexisting cumulonimbi, initially 80 km apart, met along a north-south line in the center of the mesonet 30 min before tornado formation. Fed by the convergence of flow from the outflows of the predecessor cumulonimbi, a line of deep cumuli formed and developed rapidly. A tornado was observed as it dropped from this cumulus line. When the tornado dissipated 10 min later, heavy precipitation was reaching the surface and new outflow began to spread from the now vigorous cumulonimbus that had spawned the tornado. The life cycle of the tornado and a period of 90 rain surrounding its occurrence studied in detail from observed surface winds, radar reflectivity and surface rain gage data. The evolution of the parent cloud and tornado in a tropical thermodynamic environment with local forcing, weak shear and winds, and a potentially unstable sounding contrasts with the conditions that accompany large-scale forcing of the parent clouds in which extratropical tornadoes are found. The 850–200 mb wind shear of <2 m s⁻¹ was the weakest found over many summers of FACE at Miami and was the only unique environmental parameter detectable on the day when the tornado formed. The similarity of the 15 June FACE tornado to Florida waterspout life cycles is noted.

Abstract

A microburst embedded in heavy rain in a humid environment struck very near the Field Observing Site (FOS) of the Florida Area Cumulus Experiment (FACE), producing a diverging pattern of wind damage in sugar cane.

While the dry, virga-type microburst is now beginning to be understood as a result of the SAWS project, the wet, or heavy-rain-embedded, microburst still remains a mystery. The fortuitous occurrence of a wet microburst in a humid environment, with a well-marked wind damage pattern and a well-instrumented site (including upper-air soundings), furnishes a means of gleaning some understanding of the larger-scale processes that are conducive to strong downdrafts in wet environments. In this case several features were present: 1) an elevated dry layer (above 500 mb), 2) overlying a nearly moist adiabatic lower tropospheric layer (below 500 mb), 3) a short-wave trough approaching the area from the north-northeast along the western side of a synoptic-scale trough with 4) increased shear in the lower troposphere, and 5) strong boundary-layer forcing, first by a lake breeze front off Lake Okeechobee, then by convective gust fronts. The site of the microburst itself was in the portion of the storm where a new cell was initiated by a strong gust front in an area where rain was still failing from an older, dissipating cell. The strong boundary-layer forcing may have generated an impulsive updraft surge in a very wet environment with lingering precipitation, which was followed by an impulsive collapse in a water-loaded downdraft. In this case, however, the negative buoyancy due to water loading was an order of magnitude less than that due to evaporation.

Abstract

Remote sensing (RS) and geographic information systems (GIS) techniques are applied to high-resolution satellite imagery to determine characteristics of tornado damage from the 3 May 1999 tornado outbreak. Three remote sensing methods, including principal components analysis, normalized difference vegetation index (NDVI) analysis, and NDVI change analysis, elicit tornado damage paths at different levels of detail on the 23.5-m-resolution images captured by the Linear Imaging Self-Scanning III (LISS-3) sensor on the Indian Remote Sensing (IRS) satellite before and after the outbreak. Remote sensing results were spatially overlaid on F-scale contours compiled by the members of Oklahoma Weather Center. Spatial overlays reveal that results from the principal components analysis correlate well with F3 or greater damage. NDVI analysis shows signatures expanding to F2 damage, and NDVI change analysis is capable of detecting F1 damage in some instances. In general, results of these analyses correspond to more severe damage in rural areas than in urban areas. Comparison with detailed ground surveys shows that the spectral signatures of tornado damage are related to vegetation damage and large debris fields. Variations in spectral signatures with Fujita tornado damage intensity suggest that land cover characteristics may be just as important as tornado damage intensity in creating a track detectable by satellite. It is concluded that RS and GIS techniques on IRS LISS-3 imagery (an example of multispectral satellite imagery) can be useful in assessing tornado damage, particularly for extensive and intense events.

Abstract

Data derived from a large network of electric field mills have been used to determine the average diurnal variation of lightning in a Florida seacoast environment. These data were obtained at the NASA Kennedy Space Center (KSC) and the Cape Canaveral Air Force Station (CCAFS) during the summers of 1976–78 and 1980 and they show a peak in lightning activity between the hours of 2000 and 2100 GMT or about 3 hours after local solar noon. When the statistics of lightning am compared with the statisfies or thunder on the same day, good agreement is round between the start times and the times of peak activity; however, the thunder stop times tend to Rag the lightning by 1 to 2 hours.

The average diurnal variation of cloud-to-ground lightning that was recorded by a network of magnetic diffusion-finders covering the entire South Florida region during the summer of 1978 is in good agreement with the results obtained at KSC and CCAFS and agrees with previous estimates of the time variations in rainfall and the rainfall rate over South Florida. The South Florida lightning data also show substantially less diurnal variation over the Atlantic Ocean and Gulf of Mexico than over the land. The implications of these results for the detection of lightning at local midnight dawn and dusk by a DMSP (Defense Meteorological Satellite Program) satellite are discussed.

Abstract

Vast amounts of energy are exchanged between the ocean, atmosphere, and space in association with El Niño–Southern Oscillation (ENSO). This study examines energy budgets of all tropical (30°S–30°N) ocean basins and the atmosphere separately using different, largely independent oceanic and atmospheric reanalyses to depict anomalous energy flows associated with ENSO in a consistent framework. It is found that variability of area-averaged ocean heat content (OHC) in the tropical Pacific to a large extent is modulated by energy flow through the ocean surface. While redistribution of OHC within the tropical Pacific is an integral part of ENSO dynamics, variability of ocean heat transport out of the tropical Pacific region is found to be mostly small. Noteworthy contributions arise from the Indonesian Throughflow (ITF), which is anticorrelated with ENSO at a few months lag, and from anomalous oceanic poleward heat export during the La Niña events in 1999 and 2008. Regression analysis reveals that atmospheric energy transport and radiation at the top of the atmosphere (Rad_TOA) almost perfectly balance the OHC changes and ITF variability associated with ENSO. Only a small fraction of El Niño–related heat lost by the Pacific Ocean through anomalous air–sea fluxes is radiated to space immediately, whereas the major part of the energy is transported away by the atmosphere. Ample changes in tropical atmospheric circulation lead to enhanced surface fluxes and, consequently, to an increase of OHC in the tropical Atlantic and Indian Ocean that almost fully compensates for tropical Pacific OHC loss. This signature of energy redistribution is robust across the employed datasets for all three tropical ocean basins and explains the small ENSO signal in global mean Rad_TOA.

Abstract

This study combines state-of-the-art reanalyses such as the fifth-generation European Re-Analysis (ERA5) and the Ocean Reanalysis System 5 (ORAS5) with novel observational products to present an updated estimate of the coupled atmosphere–ocean–sea ice Arctic energy budget, including flux and storage terms covering 2001–17. Observational products provide independent estimates of crucial budget terms, including oceanic heat transport from unique mooring-derived data, radiative fluxes from satellites, and sea ice volume from merged satellite data. Results show that the time averages of independent estimates of radiative, atmospheric, and oceanic energy fluxes into the Arctic Ocean domain are remarkably consistent in the sense that their sum closely matches the observed rate of regional long-term oceanic heat accumulation of ~1 W m⁻². Atmospheric and oceanic heat transports are found to be stronger compared to earlier assessments (~100 and ~16 W m⁻², respectively). Data inconsistencies are larger when considering the mean annual cycle of the coupled energy budget, with RMS values of the monthly budget residual between 7 and 15 W m⁻², depending on the employed datasets. This nevertheless represents an average reduction of ~72% of the residual compared to earlier work and demonstrates the progress made in data quality and diagnostic techniques. Finally, the budget residual is eliminated using a variational approach to provide a best estimate of the mean annual cycle. The largest remaining sources of uncertainty are ocean heat content and latent heat associated with sea ice melt and freeze, which both suffer from the lack of observational constraints. More ocean in situ observations and reliable sea ice thickness observations and their routinely assimilation into reanalyses are needed to further reduce uncertainty.

Abstract

Observations of northward-moving borelike convergence lines over the southern part of the Gulf of Carpentaria region of northern Australia are described. Eleven such disturbances were documented during the 45-day period of the 2002 Gulf Lines Experiment. Of these, six were classified as major and five as minor, depending on their coherence throughout the region. The mean synoptic conditions leading to the two types of events were found to differ. The data for the events provide further insight into the structure and origin of borelike disturbances in the region. Two of the major events, those of 28–29 September and 9 October, are particularly noteworthy. The first of these had a clear double-change structure at all surface stations in the southeastern gulf region with an undular borelike wave preceding and separating from an airmass change in the form of a dryline. It is probably one of the best documented cases of its type. The second, which was documented in unprecedented detail by an instrumented research aircraft, consisted of three separate disturbances: one moving from the southeast, one from the south, and one from the northeast, all of which collided over the gulf. It is believed that the aircraft measurements are the first of their kind anywhere in the world. The aircraft made two long low-level transects through the disturbances and a higher-level transect where they were colliding. Various soundings were also made. The aircraft data showed clearly the undular borelike nature of the southeasterly disturbance. Measured vertical velocities in the waves were as high as 3 m s⁻¹ at a mean altitude of about 230 m. Vertical velocities as high as 5 m s⁻¹ were measured in the region of the collision at an altitude of about 1 km. The longevity of the bores is not explained by the vertical structure of the Scorer parameter, which indicates a leaky waveguide.