Page info  


Contributors: Johannes Mayer, Michael Mayer, Leopold Haimberger
Info  

 

Easy Heading Macro 

Acronyms
Expand  

 

Introduction
Executive Summary
This dataset provides monthly means of massconsistent atmospheric energy and moisture budget terms derived from 1hourly ERA5 reanalysis data. Mass consistency is achieved by iteratively adjusting the wind field every time step. This dataset allows to evaluate atmospheric energy and moisture budget diagnostics for the period from 1979 onward.
Scope of Documentation
This documentation describes the computation of massconsistent budget terms using 1hourly analysed state quantities from ERA5.
Version History
No previous versions.
Product Description
Product Overview
Data Description
Anchor  


Dataset attribute  Details 
Data type  Gridded 
Projection  Regular grid 
Horizontal coverage  Global 
Horizontal resolution  0.25° x 0.25° 
Vertical coverage  Surface to top of atmosphere 
Vertical resolution  Single level 
Temporal coverage  1979/01  present 
Temporal resolution  Monthly 
File Format  NetCDF 4 
Anchor  


Variable name  Description  Units 
Divergence of vertical integral of total energy flux  This parameter is the horizontal rate of flow of total energy integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. The total energy in this parameter is the sum of sensible heat, latent heat (with latent heat of vaporization varying with temperature), kinetic, and potential energy, which is also referred to as the moist static plus kinetic energy. The total energy flux is the horizontal rate of flow of energy per metre. Its horizontal divergence is positive for a total energy flux that is spreading out, or diverging, and negative for a total energy flux that is concentrating, or converging. The sensible heat is referenced to 0 degree Celsius, whereby sensible heat of water vapour is neglected. Winds used for computation of fluxes of total energy are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass. This parameter is truncated at wave number 180 to reduce numerical noise.  W m^{2} 
Vertical integral of eastward total energy flux  This parameter is the eastward component of the total energy flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. The total energy in this parameter is the sum of sensible heat, latent heat (with latent heat of vaporization varying with temperature), kinetic, and potential energy, which is also referred to as the moist static plus kinetic energy. This parameter is the horizontal rate of flow of energy per metre in eastwest direction. It is positive for a total energy flux in eastward direction, and negative for a total energy flux in westward direction. The sensible heat is referenced to 0 degree Celsius, whereby sensible heat of water vapour is neglected. Winds used for computation of fluxes of total energy are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass.  W m^{1} 
Vertical integral of northward total energy flux  This parameter is the northward component of the total energy flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. The total energy in this parameter is the sum of sensible heat, latent heat (with latent heat of vaporization varying with temperature), kinetic, and potential energy, which is also referred to as the moist static plus kinetic energy. This parameter is the horizontal rate of flow of energy per metre in northsouth direction. It is positive for a total energy flux in northward direction, and negative for a total energy flux in southward direction. The sensible heat is referenced to 0 degree Celsius, whereby sensible heat of water vapour is neglected. Winds used for computation of fluxes of total energy are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass.  W m^{1} 
Tendency of vertical integral of total energy  This parameter is the rate of change of total energy integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. In this parameter, the total energy is the sum of internal energy, latent heat (with latent heat of vaporization varying with temperature), kinetic, and potential energy. The vertical integral of total energy is the total amount of atmospheric energy per unit area. Its tendency, or rate of change, is positive if the total energy increases and negative if the total energy decreases in an atmospheric column. The sensible heat is referenced to 0 degree Celsius, whereby sensible heat of water vapour is neglected.  W m^{2} 
Divergence of vertical integral of latent heat flux  This parameter is the horizontal rate of flow of latent heat integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. Latent heat is the amount of energy required to convert liquid water to water vapour. The latent heat flux is the horizontal rate of flow per metre. Its horizontal divergence is positive for a latent heat flux that is spreading out, or diverging, and negative for a latent heat flux that is concentrating, or converging. Winds used for computation of fluxes of latent heat are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass. The latent heat of vaporization is computed as a function of temperature. This parameter is truncated at wave number 180 to reduce numerical noise.  W m^{2} 
Vertical integral of eastward latent heat flux  This parameter is the eastward component of the latent heat flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. Latent heat is the amount of energy required to convert liquid water to water vapour. This parameter is the horizontal rate of flow of latent heat per metre in eastwest direction. It is positive for a latent heat flux in eastward direction, and negative for a latent heat flux in westward direction. Winds used for computation of fluxes of latent heat are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass. The latent heat of vaporization is computed as a function of temperature.  W m^{1} 
Vertical integral of northward latent heat flux  This parameter is the northward component of the latent heat flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. Latent heat is the amount of energy required to convert liquid water to water vapour. This parameter is the horizontal rate of flow of latent heat per metre in northsouth direction. It is positive for a latent heat flux in northward direction, and negative for a latent heat flux in southward direction. Winds used for computation of fluxes of latent heat are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass. The latent heat of vaporization is computed as a function of temperature.  W m^{1} 
Tendency of vertical integral of latent heat  This parameter is the rate of change of latent heat integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. Latent heat is the amount of energy required to convert liquid water to water vapour. The vertical integral of latent heat is the total amount of latent heat per unit area. Its tendency, or rate of change, is positive if the latent heat increases and negative if the latent heat decreases in an atmospheric column. The latent heat of vaporization is computed as a function of temperature.  W m^{2} 
Divergence of vertical integral of water vapour flux  This parameter is the horizontal rate of flow of water vapour integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. The water vapour flux is the horizontal rate of flow per metre. Its divergence is positive for a water vapour flux that is spreading out, or diverging, and negative for a water vapour flux that is concentrating, or converging. Winds used for computation of fluxes of water vapour are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass. This parameter is truncated at wave number 180 to reduce numerical noise.  kg m^{2} s^{1} 
Vertical integral of eastward water vapour flux  This parameter is the eastward component of the water vapour flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. This parameter is the horizontal rate of flow of water vapour per metre in eastwest direction. It is positive for a water vapour flux in eastward direction, and negative for a water vapour flux in westward direction. Winds used for computation of fluxes of water vapour are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass.  kg m^{1} s^{1} 
Vertical integral of northward water vapour flux  This parameter is the northward component of the water vapour flux integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. This parameter is the horizontal rate of flow per metre in northsouth direction. It is positive for a water vapour flux in northward direction, and negative for a water vapour flux in southward direction. Winds used for computation of fluxes of water vapour are massadjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air mass.  kg m^{1} s^{1} 
Tendency of vertical integral of water vapour  This parameter is the rate of change of water vapour integrated over an atmospheric column extending from the surface of the Earth to the top of the atmosphere. The vertical integral of water vapour is the total amount of atmospheric moisture per unit area. Its tendency, or rate of change, is positive if the water vapour increases and negative if the water vapour decreases in an atmospheric column.  kg m^{2} s^{1} 
Anchor  


Version  Release date  Changes from previous version 
1.0  20220531  (first release) 
Input Data
Anchor  


Dataset  Summary  Variables used 
ERA5  Provides global 1hourly analyzed state quantities on 137 atmospheric model levels as well as analyzed surface parameters. Data are represented either on a reduced Gaussian grid N320 or as spectral coefficients with T639 triangular truncation (see ERA5 data documentation).  Temperature, vorticity, divergence, surface geopotential, and logarithm of surface pressure in spherical harmonics. Specific humidity and total column water vapour in grid space. 
Method
Background
All ERA5 input fields are transformed (for details see below) to a full Gaussian grid F480 (quadratic grid with respect to the native spectral resolution T639) to avoid aliasing effects. Vorticity and divergence are used to compute the horizontal wind vector at each atmospheric level. Before individual budget terms are computed, the threedimensional wind field is iteratively adjusted according to the diagnosed imbalance between divergence of vertically integrated dry mass flux and tendency of dry air. This procedure is repeated every time step.
Mass Adjustment
Massconsistent wind fields are obtained by computing the residual of the mass continuity of dry air, which reads as follows
Mathinline 

\begin{equation} Re = \nabla \cdot \dfrac{1}{g} {\displaystyle\int_0^{p_S}} \left[(1  q)\textbf{v}\right] \; dp + \dfrac{1}{g} \dfrac{\partial}{\partial t} {\displaystyle\int_0^{p_S}} (1  q) \; dp, \end{equation} 
where g is the gravitational acceleration, p_{S} is the surface pressure, q is the specific humidity, and v is the horizontal wind vector. The first term on the right side is the divergence of vertically integrated dry mass flux, and second term describes the surface pressure tendency induced by dry air. Inverting the Laplacian of Re and taking the gradient yields a vertically integrated erroneous mass flux, which is converted to a twodimensional spurious wind field. This spurious divergent wind is subtracted from the original wind field at each level (barotropic wind field correction) making it consistent with the analyzed mass tendency of dry air. After a second iteration of this procedure, massadjusted wind fields are used to compute atmospheric energy and moisture budget terms.
Atmospheric Energy Budget
Atmospheric energy fluxes and tendencies are computed according to a simplified version of the energy budget as proposed by Mayer et al. (2017), where vertical and lateral enthalpy fluxes associated with water and snow are consistently neglected, such that
Mathinline 

\begin{equation} F_{TOA}  \underbrace{\nabla\cdot \dfrac{1}{g} {\displaystyle \int_0^{p_S}} [ (1  q) c_p T_c + L_v (T_c) q + \Phi + k] \; \textbf{v}\; dp}_{\text{tediv} = \nabla\cdot (\text{tefle, tefln})^T}  \underbrace{\dfrac{\partial}{\partial t} \dfrac{1}{g} {\displaystyle\int_0^{p_S}} [ (1  q) c_v T_c + L_v (T_c) q + \Phi + k] dp}_{\text{tetend}}  F_S = 0 \end{equation} 
where c_{p} is the specific heat capacity of dry air at constant pressure, T_{c} is the air temperature measured in Celsius, L_{v}(T) is the temperaturedependent latent heat of vaporization, Φ is the potential energy, k is the kinetic energy, and c_{v} is the specific heat capacity of dry air at constant volume. The vertical fluxes F_{TOA} and F_{S} describe the net energy flux at the top of the atmosphere and net surface heat (radiative plus turbulent) flux, which are both not included in this dataset. The second term describes the divergence of the vertical integral of moist static plus kinetic energy flux (i.e., the divergence of north and eastward energy fluxes), and the third term is the tendency of the vertical integral of total energy. Note that the total energy is the sum of internal energy c_{v}T_{c}, latent heat L_{v}q, potential energy Φ, and kinetic energy k, whereas the moist static plus kinetic energy contains the sensible heat c_{p}T_{c} instead of the internal energy. For the sake of simplicity, however, the 'moist static plus kinetic energy' as used in the divergence term is also referred to as the 'total energy' in this dataset, although it contains the sensible heat and not the internal energy. The temperaturedependent latent heat of vaporization is computed according to the IFS documentation, Part IV, and is defined as
Mathinline 

L_v(T_c) = L_v(T_0) + (c_{pv}  c_l)*(T  T_0), 
where L_{v}(T_{0}) = 2.5008x10^{6} J kg^{1} is the latent heat at the triple point temperature T_{0 }(in Kelvin), c_{pv} is the specific heat capacity of water vapour at constant pressure, c_{l} is the specific heat of liquid water, and T is the air temperature measured in Kelvin. To derive energy budget terms with constant latent heat of vaporization (as provided by ERA5), latent heat terms can be subtracted and replaced by corresponding water vapour terms multiplied by L_{v}(T_{0}). The potential energy Φ is computed as described in the IFS documentation, Part III.
Atmospheric Moisture Budget
The atmospheric moisture budget can be written as
Mathinline 

\underbrace{\nabla \cdot \dfrac{1}{g} {\displaystyle\int_0^{p_S}} (q \textbf{v}) \; dp}_{\text{wvdiv} = \nabla\cdot (\text{wvfle, wvfln})^T} + \underbrace{\dfrac{1}{g} \dfrac{\partial}{\partial t} {\displaystyle\int_0^{p_S}} q \; dp}_{\text{wvtend}} + P + E = 0, 
where precipitation P and evaporation E (not in this dataset) are surface mass fluxes in units kg m^{2} s^{1}. The first term describes the divergence of the vertical integral of atmospheric water vapour flux, the second term describes the tendency of the vertical integral of atmospheric water vapour (i.e., total column vapour). That is, atmospheric fluxes and tendencies of water vapour must balance surface freshwater fluxes P+E. The divergence term of the moisture budget also employs massadjusted wind fields v, albeit it is affected only weakly by spurious divergent winds. Note that tendency terms in this dataset are computed as exact difference from 00 UTC at the first of month to 00 UTC at the first of following month divided by the number of seconds.
Model / Algorithm
The following pseudo code describes the massadjustment procedure and subsequent computation of energy and moisture budget terms. All spectral transformations (i.e., gradient and divergence computations, Laplace inversion) were performed with routines from OpenIFS .
Mathinline 

\begin{align} &\text{for each time step do } \\ &\qquad \Phi_S \;\;\; \leftarrow \text{ Read surface geopotential} \\ &\qquad vort \: \leftarrow \text{ Read vorticity} \\ &\qquad div \;\;\; \leftarrow \text{ Read divergence} \\ &\qquad T \;\;\;\;\;\;\; \leftarrow \text{ Read temperature} \\ &\qquad q \;\;\;\;\;\;\;\: \leftarrow \text{ Read specific humidity} \\ &\qquad p_S \;\;\;\;\: \leftarrow \text{ Read logarithm of surface pressure} \\ &\qquad tcwv \leftarrow \text{ Read total column water vapour} \\ &\qquad \\ &\qquad \text{Transform all input fields to full Gaussian grid F480} \\ &\qquad \\ &\qquad \textbf{v} \leftarrow \text{ Compute horizontal wind field using } vort, div \\ &\qquad wvtend \leftarrow \text{ Compute tendency of the vertical integral of water vapour using } tcwv \\ &\qquad mtend \;\;\leftarrow \text{ Compute tendency of vertically integrated atmospheric mass using } p_S \\ &\qquad \\ &\qquad \text{for each correction step do } \\ &\qquad\qquad mdiv \;\;\;\leftarrow \text{ Compute divergence of vertically integrated atmospheric mass flux using } \textbf{v} \\ &\qquad\qquad wvdiv \;\leftarrow \text{ Compute vertically integrated water vapour divergence using } \textbf{v}, q \\ &\qquad\qquad errdiv \leftarrow mdiv  wvdiv + mtend  wvtend \\ &\qquad\qquad \textbf{v}_{err} \;\;\;\;\;\; \leftarrow \text{ Compute spurious twodimensional wind field using } errdiv \\ &\qquad\qquad \text{ for each atmospheric level } i \text{ in } \textbf{v} \text{ do } \textbf{v}_i \leftarrow \textbf{v}_i  \textbf{v}_{err} \\ &\qquad \text{end do} \\ &\qquad \\ &\qquad T_c \leftarrow T  273.15 \\ &\qquad lhtend \;\;\leftarrow \text{ Compute tendency of the vertical integral of latent heat using } q, T_c \\ &\qquad tetend \;\;\leftarrow \text{ Compute tendency of the vertical integral of total energy using } \textbf{v}, q, T_c, \Phi_S \\ &\qquad lhfle, lhfln \;\;\;\leftarrow \text{ Compute vertical integral of latent heat fluxes using } \textbf{v}, q, T_c \\ &\qquad tefle, tefln \;\;\;\;\leftarrow \text{ Compute vertical integral of total energy fluxes using } \textbf{v}, q, T_c, \Phi_S \\ &\qquad wvfle, wvfln \leftarrow \text{ Compute vertical integral of water vapour fluxes using } \textbf{v}, q \\ &\qquad lhdiv \;\;\leftarrow \text{ Compute divergence of the vertical integral of latent heat fluxes using } lhfle, lhfln \\ &\qquad tediv \;\;\leftarrow \text{ Compute divergence of the vertical integral of total energy fluxes using } tefle, tefln \\ &\qquad wvdiv \leftarrow \text{ Compute divergence of the vertical integral of water vapour fluxes using } wvfle, wvfln \\ &\text{end do} \end{align} 
Validation
The divergence fields in this dataset exhibit zero global mean suggesting optimal computations and good accuracy. Tendency terms are temporally stable and exhibit longterm global zero mean indicating good reliability. Indirectly estimated oceanic F_{S} derived from tediv and tetend in combination with F_{TOA} from CERESEBAF (not in this dataset) agrees with the observationbased ocean heat uptake to within 1 W m^{2 }(see Mayer et al. 2022). All fields are in good qualitative agreement with known patterns of the respective quantities, but satisfaction of physical constraints (e.g., magnitude of oceantoland energy and moisture transport or temporal stability) is much improved compared to earlier evaluations (see Mayer et al. 2021 and 2022 for comprehensive evaluation).
Known issues
 The divergence terms (tediv, lhdiv, wvdiv) with full spectral resolution show artificial pattern of numerical noise over high topography, which are thus spectrally truncated at wave number 180. The divergence fields with full spectral resolution (see example in Fig. 1) can be reconstructed by computing the divergence of corresponding north and eastward fluxes provided in this dataset.
 The oceantoland energy transport as estimated from tediv exhibits an unrealistically strong gradual change in the late 1990s and early 2000s, which likely stems from changes in the observing system that has been assimilated by ERA5 (see Mayer et al. 2021 for discussion).
 Global ocean and land averages of wvdiv exhibit a reasonably strong but statistically insignificant trend over the available period, see Mayer et al. (2021) for further details.
Anchor  


Figure 1: The divergence of the vertical integral of total energy flux (left) truncated at wave number 180, and (right) with full spectral resolution T639.
Licence, Acknowledgement and Citation
This dataset is provided under the licence to use Copernicus Products.
All users of this dataset must:
 acknowledge according to the licence to use Copernicus Products
 provide clear and visible attribution to the Copernicus programme by citing the web Climate Data Store (CDS) catalogue entry as follows:
Mayer, J., Mayer, M., Haimberger, L.,(2022): Massconsistent atmospheric energy and moisture budget data from 1979 to present derived from ERA5 reanalysis, v1.0, Copernicus Climate Change Service (C3S) Climate Data Store (CDS). (Accessed on 31052022), https://doi.org/10.24381/cds.c2451f6b.
Please refer to How to acknowledge and cite a Climate Data Store (CDS) catalogue entry and the data published as part of it for complete details.
The authors of this dataset are financially supported by the Austrian Science Funds project P33177. The dataset is created as inkind contribution to Copernicus.
Anchor  


Mayer, J., Mayer, M. and Haimberger, L., (2022). Comparison of Surface Energy Fluxes from Global to Local Scale. Accepted in Journal of Climate. https://doi.org/10.1175/JCLID210598.1
Mayer, J., Mayer, M. and Haimberger, L., (2021). Consistency and Homogeneity of Atmospheric Energy, Moisture, and Mass Budgets in ERA5. Journal of Climate 34(10), 39553974. https://doi.org/10.1175/JCLID200676.1
Mayer, M., Haimberger, L., Edwards, J. M., and Hyder, P. (2017). Toward consistent diagnostics of the coupled atmosphere and ocean energy budgets. Journal of Climate, 30(22), 92259246. https://doi.org/10.1175/JCLID170137.1
Info  

 
_{ This document has been produced in the context of the Copernicus Climate Change Service (C3S). } _{ The activities leading to these results have been contracted by the European Centre for MediumRange Weather Forecasts, operator of C3S on behalf of the European Union (Delegation Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. } _{}_{}_{ The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium  Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.} 
Related articles
Content by Label  

