Budget Residuals Research Articles

Water and energy budgets over hydrological basins on short and long timescales

Abstract. Quantifying regional water and energy fluxes much more accurately from observations is essential for assessing the capability of climate and Earth system models and their ability to simulate future change. This study uses satellite observations to produce monthly flux estimates for each component of the terrestrial water and energy budget over selected large river basins from 2002 to 2013. Prior to optimisation, the water budget residuals vary between 1.5 % and 35 % precipitation by basin, and the magnitude of the imbalance between the net radiation and the corresponding turbulent heat fluxes ranges between 1 and 12 W m−2 in the long-term average. In order to further assess these imbalances, a flux-inferred surface storage (Sfi) is used for both water and energy, based on integrating the flux observations. This exposes mismatches in seasonal water storage in addition to important inter-annual variability between GRACE (Gravity Recovery and Climate Experiment) and the storage suggested by the other flux observations. Our optimisation ensures that the flux estimates are consistent with the total water storage changes from GRACE on short (monthly) and longer timescales, while also balancing a coupled long-term energy budget by using a sequential approach. All the flux adjustments made during the optimisation are small and within uncertainty estimates, using a χ2 test, and inter-annual variability from observations is retained. The optimisation also reduces formal uncertainties for individual flux components. When compared with results from the previous literature in basins such as the Mississippi, Congo, and Huang He rivers, our results show better agreement with GRACE variability and trends in each case.

Moist Thermodynamics of Convectively Coupled Waves over the Western Hemisphere

Abstract Convectively coupled waves (CCWs) over the Western Hemisphere are classified based on their governing thermodynamics. It is found that only the tropical depressions (TDs; TD waves) satisfy the criteria necessary to be considered a moisture mode, as in the Rossby-like wave found in an earlier study. In this wave, water vapor fluctuations play a much greater role in the thermodynamics than temperature fluctuations. Only in the eastward-propagating inertio-gravity (EIG) wave does temperature govern the thermodynamics. Temperature and moisture play comparable roles in all the other waves, including the Madden–Julian oscillation over the Western Hemisphere (MJO-W). The moist static energy (MSE) budget of CCWs is investigated by analyzing ERA5 data and data from the 2014/15 observations and modeling of the Green Ocean Amazon (GoAmazon 2014/15) field campaign. Results reveal that vertical advection of MSE acts as a primary driver of the propagation of column MSE in westward inertio-gravity (WIG) wave, Kelvin wave, and MJO-W, while horizontal advection plays a central role in the mixed Rossby gravity (MRG) and TD wave. Results also suggest that cloud radiative heating and the horizontal MSE advection govern the maintenance of most of the CCWs. Major disagreements are found between ERA5 and GoAmazon. In GoAmazon, convection is more tightly coupled to variations in column MSE, and vertical MSE advection plays a more prominent role in the MSE tendency. These results along with substantial budget residuals found in ERA5 data suggest that CCWs over the tropical Western Hemisphere are not represented adequately in the reanalysis. Significance Statement In comparison to other regions of the globe, the weather systems that affect precipitation in the tropical Western Hemisphere have received little attention. In this study, we investigate the structure, propagation, and thermodynamics of convectively coupled waves that impact precipitation in this region. We found that slowly evolving tropical systems are “moisture modes,” i.e., moving regions of high humidity and precipitation that are maintained by interactions between clouds and radiation. The faster waves are systems that exhibit relatively larger fluctuations in temperature. Vertical motions are more important for the movement of rainfall in these waves. Last, we found that reanalysis and observations disagree over the importance of different processes in the waves that occurred over the Amazon region, hinting at potential deficiencies on how the reanalysis represents clouds in this region.

Diagnostic evaluation of river discharge into the Arctic Ocean and its impact on oceanic volume transports

Abstract. This study analyses river discharge into the Arctic Ocean using state-of-the-art reanalyses such as the fifth-generation European Reanalysis (ERA5) and the reanalysis component from the Global Flood Awareness System (GloFAS). GloFAS, in its operational version 2.1, combines the land surface model (Hydrology Tiled European Centre for Medium-Range Weather Forecasts – ECMWF – Scheme for Surface Exchanges over Land, HTESSEL) from ECMWF’s ERA5 with a hydrological and channel routing model (LISFLOOD). Furthermore, we analyse GloFAS' most recent version 3.1, which is not coupled to HTESSEL but uses the full configuration of LISFLOOD. Seasonal cycles as well as annual runoff trends are analysed for the major Arctic watersheds – Yenisei, Ob, Lena, and Mackenzie – where reanalysis-based runoff can be compared to available observed river discharge records. Furthermore, we calculate river discharge over the whole pan-Arctic region and, by combination with atmospheric inputs, storage changes from the Gravity Recovery and Climate Experiment (GRACE) and oceanic volume transports from ocean reanalyses, we assess closure of the non-steric water volume budget. Finally, we provide best estimates for every budget equation term using a variational adjustment scheme. Runoff from ERA5 and GloFAS v2.1 features pronounced declining trends induced by two temporal inhomogeneities in ERA5's data assimilation system, and seasonal river discharge peaks are underestimated by up to 50 % compared to observations. The new GloFAS v3.1 product exhibits distinct improvements and performs best in terms of seasonality and long-term means; however, in contrast to gauge observations, it also features declining runoff trends. Calculating runoff indirectly through the divergence of moisture flux is the only reanalysis-based estimate that is able to reproduce the river discharge increases measured by gauge observations (pan-Arctic increase of 2 % per decade). In addition, we examine Greenlandic discharge, which contributes about 10 % of the total pan-Arctic discharge and features strong increases mainly due to glacial melting. The variational adjustment yields reliable estimates of the volume budget terms on an annual scale, requiring only moderate adjustments of less than 3 % for each individual term. Approximately 6583±84 km3 of freshwater leaves the Arctic Ocean per year through its boundaries. About two-thirds of this is contributed by runoff from the surrounding land areas to the Arctic Ocean (4379±25 km3 yr−1), and about one-third is supplied by the atmosphere. However, on a seasonal scale budget residuals of some calendar months were too large to be eliminated within the a priori spreads of the individual terms. This suggests that systematical errors are present in the reanalyses and ocean reanalysis data sets, which are not considered in our uncertainty estimation.

Intercomparison of MJO Column Moist Static Energy and Water Vapor Budget among Six Modern Reanalysis Products

AbstractThis study conducts an intercomparison of the column-integrated moist static energy (MSE) and water vapor budget of the Madden–Julian oscillation (MJO) among six modern global reanalysis products (RAs). Inter-RA differences in the mean MSE, MJO MSE anomalies, individual MSE budget terms, and their relative contributions to the propagation and maintenance of MJO MSE anomalies are examined. Also investigated is the relationship between the MJO column water vapor (CWV) budget residuals with the other CWV budget terms as well as with the two parameters that characterize cloud–radiation feedback and moisture–convection coupling. Results show a noticeable inter-RA spread in the mean-state MSE, especially its vertical structure. In all RAs, horizontal MSE advection dominates the propagation of the MJO MSE while column-integrated longwave radiative heating and vertical MSE advection are found to be the key processes for MJO maintenance. The MSE budget terms directly affected by the model parameterization schemes exhibit high uncertainty. The differences in anomalous vertical velocity mainly contribute to the large differences in vertical MSE advection among the RAs. The budget residuals show large inter-RA differences and have nonnegligible contributions to MJO maintenance and propagation in most RAs. RAs that underestimate (overestimate) the strength of cloud–radiation feedback and the convective moisture adjustment time scale tend to have positive (negative) MJO CWV budget residual, indicating the critical role of these processes in the maintenance of MJO CWV anomalies. Our results emphasize that a correct representation of the interactions among moisture, convection, cloud, and radiation is the key for an accurate depiction of the MJO MSE and CWV budget in RAs.

The Nearshore Heat Budget: Effects of Stratification and Surfzone Dynamics

AbstractTemperature variability in the nearshore (from ≈6‐m depth to the shoreline) is influenced by many processes including wave breaking and internal waves. A nearshore heat budget resolving these processes has not been considered. A 7‐month experiment at the Scripps Institution of Oceanography Pier (shoreline to 6‐m depth) measured temperature and surface and cross‐shore heat fluxes to examine a nearshore heat budget with fine cross‐shore spatial (≈20 m) and temporal (5 day to 4 h) resolution. Winds, waves, air and water temperature, and in particular, pier end stratification varied considerably from late Fall to late Spring. The largest heat flux terms were shortwave solar radiation and baroclinic advective heat flux both varying on tidal time scales. The net heat flux is coherent and in phase with the nearshore heat content change at diurnal and semidiurnal frequencies. The binned mean heat budget has squared correlation R2=0.97 and best‐fit slope of 0.76. Including an elevated breaking wave albedo parameterization reduced the residual heat flux and improved the best‐fit slope. Baroclinic and barotropic advective heat fluxes have significant noise, and removing them from the heat budget improves the best‐fit slope when stratification is weak. However, when daily mean stratification is large, baroclinic advective heat flux dominates variability and is required to capture large (≈3 °C h−1) internal wave events. At times, large heat budget residuals highlight neglected heat budget terms, pointing to surfzone alongshore advection of temperature anomalies.

Space–Time Spectral Analysis of the Moist Static Energy Budget Equation

AbstractThe budget of column-integrated moist static energy (MSE) is examined in wavenumber–frequency transforms of longitude–time sections over the tropical belt. Cross-spectra with satellite-derived precipitation (TRMM-3B42) are used to emphasize precipitation-coherent signals in reanalysis [ERA-Interim (ERAI)] estimates of each term in the budget equation. Results reveal different budget balances in convectively coupled equatorial waves (CCEWs) as well as in the Madden–Julian oscillation (MJO) and tropical depression (TD)-type disturbances. The real component (expressing amplification or damping of amplitude) for horizontal advection is modest for most wave types but substantially damps the MJO. Its imaginary component is hugely positive (it acts to advance phase) in TD-type disturbances and is positive for MJO and equatorial Rossby (ERn1) wave disturbances (almost negligible for the other CCEWs). The real component of vertical advection is negatively correlated (damping effect) with precipitation with a magnitude of approximately 10% of total latent heat release for all disturbances except for TD-type disturbance. This effect is overestimated by a factor of 2 or more if advection is computed using the time–zonal mean MSE, suggesting that nonlinear correlations between ascent and humidity would be positive (amplification effect). ERAI-estimated radiative heating has a positive real part, reinforcing precipitation-correlated MSE excursions. The magnitude is up to 14% of latent heating for the MJO and much less for other waves. ERAI-estimated surface flux has a small effect but acts to amplify MJO and ERn1 waves. The imaginary component of budget residuals is large and systematically positive, suggesting that the reanalysis model’s physical MSE sources would not act to propagate the precipitation-associated MSE anomalies properly.

Subsurface Lateral Heat Flux within the Heterogeneous Surface of a Subtropical Wetland and Its Potential Contribution to Energy Imbalance

AbstractIn the eddy covariance technique, lateral heat fluxes in the atmosphere, surfaces, and subsurfaces are often ignored under the assumption of a homogeneous surface. Among lateral heat fluxes, the surface and subsurface fluxes, which might affect the surface energy balance closure over a heterogeneous surface, are less studied. Many wetlands are heterogeneous, with a mix of vegetated areas and shallow open water. This study examined the subsurface lateral heat fluxes between a reed bed and the adjacent water of a subtropical wetland in Hong Kong, China. An array of temperature and water-level sensors was installed in the soil of the reed bed and in the adjacent water. An eddy covariance system was also set up on the reed bed. The subsurface lateral heat fluxes were largest close to the interface of the reed bed and water and decreased as the distance from the interface increased, as expected. However, the subsurface lateral heat fluxes could not account for the energy imbalance because their magnitudes were relatively small and fluctuated in phase with the energy budget residuals during the winter months. The uncertainties of the turbulent fluxes and the lateral heat fluxes were estimated to be 10%–20% and 10%–30%, respectively. This study explored another potential reason behind the energy imbalance of the eddy covariance technique. The results enhance the understanding of water and energy exchanges between a terrestrial biotope and the surrounding water, which might further generate insights into the biochemical processes in wetlands.

Momentum budget diagnosis and the parameterization of subgrid-scale orographic drag in global GRAPES

The initial tendency approach is used to diagnose systematic errors in global GRAPES (Global/Regional Assimilation Prediction System), including overly strong westerlies in the northern midlatitudes, cold/warm bias dipoles in the vicinity of the tropopause, and excessively strong southerlies in downstream regions of the Tibetan Plateau. This approach, involving the use of the assimilation system, focuses on the first few time steps of numerical weather forecasts to identify the deficiencies in diabatic forcing. The results show that there is insufficient diabatic dissipation in the upper troposphere and lower stratosphere of the northern midlatitudes and the lower troposphere of most latitudes, which results from the absence of a parameterization of subgrid orographic drag in global GRAPES. A scheme to parameterize the effects of these drags is therefore tested and the experiments indicate that the newly introduced scheme reduces zonal momentum budget residuals, weakens the northern midlatitude westerlies and southerlies in the downstream regions of the Tibetan Plateau, decreases the cold/warm bias dipoles, and leads to improved objective verification scores.

Soil Moisture Assimilation Using a Modified Ensemble Transform Kalman Filter Based on Station Observations in the Hai River Basin

Assimilating observations to a land surface model can further improve soil moisture estimation accuracy. However, assimilation results largely rely on forecast error and generally cannot maintain a water budget balance. In this study, shallow soil moisture observations are assimilated into Common Land Model (CoLM) to estimate the soil moisture in different layers. A proposed forecast error inflation and water balance constraint are adopted in the Ensemble Transform Kalman Filter to reduce the analysis error and water budget residuals. The assimilation results indicate that the analysis error is reduced and the water imbalance is mitigated with this approach.

A Framework for Dynamical Seasonal Prediction of Precipitation over the Pacific Islands

Abstract A three-step approach to develop a framework for dynamical seasonal prediction of precipitation over the U.S. Affiliated Pacific Islands (USAPI) is adopted. First, guided by the climatological features of basic variables, a view that climates of the USAPI are connected by large-scale phenomena involving the warm pool, South Pacific convergence zone, tropical monsoons, and subtropical anticyclone is proposed. Second, prediction skill in ensemble hindcasts performed with the Climate Forecast System, version 2 (CFSv2), is evaluated with the hypothesis that ENSO is the leading candidate for large and persisting precipitation departures. Third, moist static energy budget diagnostics are performed to identify physical processes responsible for precipitation anomalies. At leads of 0–6 months, CFSv2 demonstrates useful skill in predicting Niño-3.4 SST and equatorial Pacific precipitation anomalies. During El Niño, positive precipitation anomalies along the central (eastern) equatorial Pacific are anchored by net radiative flux (Frad) and moist advection (evaporation and Frad). The model’s skill in predicting precipitation anomalies over South Pacific (Hawaiian) islands is highest (lowest). Over the west Pacific islands, the skill is low during the rainy season. During El Niño, skill over the USAPI, in particular predicting dryness persistence at long leads is useful. Suppressed precipitation over the Hawaiian and South Pacific (west Pacific) islands are determined by anomalous dry and cold air advection (reduced evaporation and Frad). These processes are local, but are dictated by circulation anomalies forced by ENSO. Model budget estimates are qualitatively consistent with those obtained from reanalysis, boosting confidence for societal benefits. However, observational constraints, as well as budget residuals, pose limitations.

The driving forces behind the Caspian Sea mean water level oscillations

Closed basins such as the Caspian Sea rapidly respond to variations in atmospheric and geological events. This study has been conducted to deduce the role of natural and anthropogenic influences on the Caspian Sea mean water level fluctuations for the period of 1998–2005. It is recognized that climate is the primary mechanism of the Caspian Sea mean water level variations based on the relatively small differences of the Caspian Sea hydrologic budget residuals and the Caspian Sea mean water level fluctuations. This is further supported by the similarity in water-level variations of the Caspian Sea with those of Lake Van and Lake Urmia. On the other hand, the Caspian Sea needed to lose some of its water to attain water balance equilibrium in 2000 and 2001. The year 2000 showed anomalous seismic activity particularly in the southwestern part of the Caspian Sea. Two significant earthquakes with magnitudes of 6.8 and 6.5 Mw occurred on November 25, 2000. The focal mechanisms of these earthquakes and numerous aftershocks indicated normal faulting and, therefore, caused the Caspian Sea lake level to decline in 2000. The contribution of submarine mud volcano eruptions to the Caspian Sea lake level could be insignificant based on the comparison of water budget residuals and the mean water level variations. Neither crustal deformation (based on the GPS measurements) nor the offshore oil and natural gas production activities in the Caspian Sea are responsible for noticeable changes to the level of the Caspian Sea.

A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing

Snow surface and sea-ice energy budgets were measured near 87.5°N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to −7°C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between −50 W m−2 and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m−2, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area.

A possible connection of Caspian Sea level fluctuations with meteorological factors and seismicity

The Caspian Sea has exhibited significant, wide-range fluctuations that have been traditionally attributed to variations in climatic agents. The objective of this research is to estimate the hydrologic budget and sea surface heights of the Caspian Sea from 1998 to 2005 to assess the contribution of meteorological and geological process to the Caspian Sea level variations. The water budget of the Caspian Sea from 1998 to 2005 was calculated using the state-of-the-art remote sensing techniques and ground-truth data. The Sea Surface heights of the Caspian Sea were constructed from the refined Topex/Poseidon altimetry data. The National Centers for Environmental Prediction/Department of Energy Reanalysis 2 meteorological data provided all the variables necessary for the Penman method to estimate evaporation over the Caspian Sea. The data of the Tropical Rainfall Measuring Mission were utilized to estimate precipitation onto the Caspian Sea. A strong agreement between the water budget residuals and Caspian Sea level variations signifies that Caspian Sea level oscillations for this time window are essentially controlled by climate-related factors. On the other hand, the relatively larger gaps between the water balance residuals and Caspian Sea level heights during 2000 and 2001 may indicate an impact of seismicity on Caspian Sea level oscillations as a result of two major earthquakes on November 25, 2000.

A Review of Sediment Budget Imbalances along Fire Island, New York: Can Nearshore Geologic Framework and Patterns of Shoreline Change Explain the Deficit?

Abstract Sediment budget analyses conducted for annual to decadal timescales report variable magnitudes of littoral transport along the south shore of Long Island, New York. It is well documented that the primary transport component is directed alongshore from east to west, but relatively little information has been reported concerning the directions or magnitudes of cross-shore components. Our review of budget calculations for the Fire Island coastal compartment (between Moriches and Fire Island Inlets) indicates an average deficit of 217,700 m3/y. Updrift shoreline erosion, redistribution of nourishment fills, and reworking of inner-shelf deposits have been proposed as the potential sources of additional sediment needed to rectify budget residuals. Each of these sources is probably relevant over various spatial and temporal scales, but previous studies of sediment texture and provenance, inner-shelf geologic mapping, and beach profile comparison indicate that reworking of inner-shelf deposits is the sou...

The large‐scale energy budget of the Arctic

This paper synthesizes a variety of atmospheric and oceanic data to examine the large‐scale energy budget of the Arctic. Assessment of the atmospheric budget relies primarily on the ERA‐40 reanalysis. The seasonal cycles of vertically integrated atmospheric energy storage and the convergence of energy transport from ERA‐40, as evaluated for the polar cap (defined by the 70°N latitude circle), in general compare well with realizations from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis over the period 1979–2001. However, shortcomings in top of atmosphere radiation, as compared to satellite data, and the net surface flux, contribute to large energy budget residuals in ERA‐40. The seasonal cycle of atmospheric energy storage is strongly modulated by the net surface flux, which is also the primary driver of seasonal changes in heat storage within the Arctic Ocean. Averaged for an Arctic Ocean domain, the July net surface flux from ERA‐40 of −100 W m−2 (i.e., into the ocean), associated with sea ice melt and oceanic sensible heat gain, exceeds the atmospheric energy transport convergence of 91 W m−2. During winter (for which budget residuals are large), oceanic sensible heat loss and sea ice growth yield an upward surface flux of 50–60 W m−2, complemented with an atmospheric energy convergence of 80–90 W m−2 to provide a net radiation loss to space of 175–180 W m−2.

Coupling of Convective Momentum Transport with Convective Heating in Global Climate Simulations

Abstract The effects of convective momentum transport (CMT) on global climate simulations are examined in this study. Comparison between two sets of 20-yr (1979–98) integration using the NCAR Community Climate Model version 3 (CCM3) illustrates that the inclusion of CMT in the convection scheme systematically modifies the climate mean state over the equatorial region. The convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection. This reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the Hadley circulation. The major heating peak during the boreal winter is moved to south of the equator at about 10°S, which is closer to the heat budget residuals of the ECMWF reanalysis data. The responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone.

Impact of time sampling on atmospheric energy budget residuals

Diagnostic time-mean budgets of energy and water are evaluated in many atmospheric process studies. The errors of budget-derived quantities like sub-gridscale fluxes or diabatic heating are governed by the errors of the budgets. Here we consider 3D-budgets on the meso-β scale over Europe. They are compiled from analyses of state quantities available from forecast centres. In the present study we found that the mandatory 6 hours sampling interval between synoptic observations is the main error source for routine time-mean budgets. The errors have been quantified (i) by first sampling forecast data of the German Europamodell every 5 minutes and averaging them over 12 hours (reference budget), and (ii) by sampling the same data only every 6 hours and averaging these also over 12 hours (routine budget). With this method we find that routine budgets in single atmospheric meso-β scale columns show relative random errors of typically 200% and systematic errors of up to 20%, exclusively due to undersampling. Thus routine budgets, if applied to specific days at individual locations, cannot be expected to yield useful results, except perhaps for cases with extremely strong signal. Compositing over several hundreds of columns with similar weather reduces the random budget error down to about 50%; this seems to be the best one can achieve for routine budgets. The systematic error of some budget quantities is caused by a correlation between the time of occurence of certain processes (mainly convection) and the sampling times. While this error cannot be reduced through compositing, we find that it can be crudely estimated by using different time averaging methods. As application for this method we determine sub-gridscale budget quantities over the BALTEX catchment (August-September 1995) for an ensemble of convectively active and an ensemble of rain-active columns. For the ensemble mean profiles we find, in terms of the diagnosed sub-gridscale test quantities diabatic heating and vertical moist enthalpy flux divergence, that their accuracy is sufficient to detect statistically significant differences between both ensembles. The diabatic heating is about the same for both ensembles, while the flux divergence in the convective ensemble is about three times as large as in the rain ensemble.

Vertical structure of humidity and temperature budget residuals over the Mississippi River basin

Analyses have systematic tendencies or budget residuals that are not small. Unlike the budgets in general circulation model simulations, these budget residuals are an important component of analyses’ water and energy budgets. We can either get good budgets or good climates, but not both. To better understand the character of the residuals in the National Centers for Environmental Prediction's (NCEP) global analysis and reanalysis water and energy budgets, the vertical structure of the budget residuals in NCEP's global analyses pertinent to the Mississippi River basin water and energy budgets are described herein. The vertical structure of the residuals is obtained by using NCEP's reanalysis modeling system, which is initialized (started) from NCEP's operational Global Data Assimilation System analyses as well as from the new NCEP reanalyses; forecasts of 1 day duration, 4 times a day, are then made for several years. The budget residuals in the forecasts after the first 6 hours are similar to the original residuals in the analyses and reanalyses. The residuals appear to be related to a summertime “spin‐down” and wintertime “spin‐up” in cumulus convection, an adjustment in boundary layer diffusive transports near the surface and near the top of the boundary layer, and adjustments in large‐scale transports of moisture and temperature. These residuals may thus be providing clues as to what needs to be improved in analysis systems.

Diagnostic and Semiprognostic Studies of Cumulus Effects in the Presence of Mesoscale Circulations

Abstract Heat and moisture budgets of two mesoscale convective systems of a characteristic horizontal scale of approximately 450 km are studied using the Atmospheric Variability Experiment-Severe Environmental Storms and Mesoscale Experiment mesoscale data with a cutoff wavelength of 150 km. The scale dependence of budget residuals is examined by further varying horizontal resolutions of data with low-pass spatial filters. The results show that the horizontal distributions of the vertically integrated heat source 〈Q1〉 and moisture sink 〈Q2〉 are dependent on horizontal resolutions of data. For the mesoscale data, the horizontal distributions of 〈Q1〉 and 〈Q2〉 show pronounced “dipole” patterns that are closely related to the horizontal fluxes of heat and moisture due to mesoscale circulations. For the larger-scale data, the dipole pattern disappears and the horizontal distributions of 〈Q1〉 and 〈Q2〉 show positive values in the area of convection. However, the vertical profiles of the observed heat source and ...

The Diagnosis of Mechanical Dissipation in the Atmosphere from Large-Scale Balance Requirements

The momentum budget for January 1987 is evaluated with global observations analyzed at the European Centre for Medium-Range Weather Forecasts (ECMWF). The dissipation term is diagnosed from the budget as a balance requirement, that is, as that required to balance the sum of the advection, Coriolis, pressure gradient, and local tendency terms. This is then compared with the parameterized subgrid-scale effects in the ECMWF model's momentum equation, with a view of identifying possible errors in those parameterizations. The balance requirement does not support the high parameterized values of orographically induced gravity-wave drag in the lower stratosphere. A deeper analysis also does not suggest a major role for turbulent vertical transports above the boundary layer. On the other hand, our budget does indicate that more effort be spent on a better representation of the potential enstrophy cascade associated with Rossby wave breaking in the upper troposphere. These statements are qualified by the errors in the balance requirement itself. The extent to which this is a problem is discussed. A distinctive feature of these calculations is their internal consistency., that is, all the terms in the budget are evaluated as in the version of the ECMWF model used for assimilating the observations. This offers several advantages, not the least of which is that it makes our budget residuals identical to the systematic initial tendency errors of the operational weather forecasts, thus facilitating their computation and routine monitoring. As such, our calculations explain a large fraction of the systematic short-range forecast errors and, because of their local character, provide clues as to the possible sources of those errors. Experiments with and without gravity-wave drag are described to illustrate its large contribution during this period to the southerly wind error of the operational weather forecasts at 70 mb over western North America.