scholarly journals Empirical Localization of Observations for Serial Ensemble Kalman Filter Data Assimilation in an Atmospheric General Circulation Model

2014 ◽  
Vol 142 (5) ◽  
pp. 1835-1851 ◽  
Author(s):  
Lili Lei ◽  
Jeffrey L. Anderson
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
State Variables ◽  
Localization Algorithm ◽  
Localization Function ◽  
Independent Verification ◽  
Community Atmosphere Model ◽  
Verification Period ◽  
Meridional Winds ◽  
Rms Error

Abstract The empirical localization algorithm described here uses the output from an observing system simulation experiment (OSSE) and constructs localization functions that minimize the root-mean-square (RMS) difference between the truth and the posterior ensemble mean for state variables. This algorithm can automatically provide an estimate of the localization function and does not require empirical tuning of the localization scale. It can compute an appropriate localization function for any potential observation type and kind of state variable. The empirical localization algorithm is investigated in the Community Atmosphere Model, version 5 (CAM5). The empirical localization function (ELF) is computed for the horizontal and vertical separately so that the vertical localization is explored explicitly. The horizontal and vertical ELFs are also computed for different geographic regions. The ELFs varying with region have advantages over the single global ELF in the horizontal and vertical, because different localization functions are more effective in different regions. The ELFs computed from an OSSE can be used as the localization in a subsequent OSSE. After three iterations, the ELFs appear to have converged. When used as localization in an OSSE, the converged ELFs produce a significantly smaller RMS error of temperature and zonal and meridional winds than the best Gaspari–Cohn (GC) localization for a dependent verification period using the observations from the original OSSE, and a similar RMS error to the best GC for an independent verification period. The converged ELFs have a significantly smaller RMS error of surface pressure than the best GC for both dependent and independent verification periods.

Climate Response of Linear and Quadratic Functionals Using the Fluctuation–Dissipation Theorem

2008 ◽  
Vol 65 (9) ◽  
pp. 2824-2841 ◽  
Author(s):  
Andrey Gritsun ◽  
Grant Branstator ◽  
Andrew Majda
Keyword(s):  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Heat Fluxes ◽  
Heat Sources ◽  
State Variables ◽  
Fluctuation Dissipation ◽  
Fluctuation Dissipation Theorem ◽  
Low Pass ◽  
Momentum And Heat Fluxes

Abstract A generalization of the fluctuation–dissipation theorem (FDT) that allows generation of linear response operators that estimate the response of functionals of system state variables is tested for a system defined by an atmospheric general circulation model (AGCM). A sketch of the proof of this generalization is provided, followed by comparison of response estimates based on the theory and actual responses of the AGCM for various idealized anomalous equatorial heat sources. Tested response quantities include precipitation, variances of bandpass and low-pass streamfunction, and momentum and heat fluxes. The solutions from the FDT operators are very similar to the AGCM solutions in terms of structure while overestimating response amplitudes by about 20%. As an example of an application of such response operators, the FDT operator that estimates the response of bandpass upper-tropospheric streamfunction variance is used to find the most efficient means of disturbing the Atlantic storm tracks by tropical heating. The results of the study suggest that the generalized FDT is an attractive method for systematically studying response attributes of the climate system that are of interest to climate scientists and society.

scholarly journals Impacts of Frequent Assimilation of Surface Pressure Observations on Atmospheric Analyses

2014 ◽  
Vol 142 (12) ◽  
pp. 4477-4483 ◽  
Author(s):  
Lili Lei ◽  
Jeffrey L. Anderson
Keyword(s):  
Surface Pressure ◽  
Temporal Frequency ◽  
State Variables ◽  
Localization Function ◽  
Community Atmosphere Model ◽  
Entire Depth ◽  
Analysis Error ◽  
Mean Square Difference ◽  
Optimal Localization ◽  
Vertical Localization

Abstract To investigate the impacts of frequently assimilating only surface pressure (PS) observations, the Data Assimilation Research Testbed and the Community Atmosphere Model (DART/CAM) are used for observing system simulation experiments with the ensemble Kalman filter. An empirical localization function (ELF) is used to effectively spread the information from PS in the vertical. The ELF minimizes the root-mean-square difference between the truth and the posterior ensemble mean for state variables. The temporal frequency of the observations is increased from 6 to 3 h, and then 1 h. By observing only PS, the uncertainty throughout the entire depth of the troposphere can be constrained. The analysis error over the entire depth of the troposphere, especially the middle troposphere, is reduced with increased assimilation frequency. The ELF is similar to the vertical localization function used in the Twentieth-Century Reanalysis (20CR); thus, it demonstrates that the current vertical localization in the 20CR is close to the optimal localization function.

scholarly journals The E3SM version 1 single-column model

2020 ◽  
Vol 13 (9) ◽  
pp. 4443-4458
Author(s):  
Peter A. Bogenschutz ◽  
Shuaiqi Tang ◽  
Peter M. Caldwell ◽  
Shaocheng Xie ◽  
Wuyin Lin ◽  
...  
Keyword(s):  
General Circulation ◽  
Model Development ◽  
Circulation Model ◽  
System Model ◽  
Earth System ◽  
Efficient Tool ◽  
Column Model ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Single Column Model

Abstract. The single-column model (SCM) functionality of the Energy Exascale Earth System Model version 1 (E3SMv1) is described in this paper. The E3SM SCM was adopted from the SCM used in the Community Atmosphere Model (CAM) but has evolved significantly since then. We describe changes made to the aerosol specification in the SCM, idealizations, and developments made so that the SCM uses the same dynamical core as the full general circulation model (GCM) component. Based on these changes, we describe and demonstrate the seamless capability to “replay” a GCM column using the SCM. We give an overview of the E3SM case library and briefly describe which cases may serve as useful proxies for replicating and investigate some long-standing biases in the full GCM runs while demonstrating that the E3SM SCM is an efficient tool for both model development and evaluation.

scholarly journals Comparisons of Empirical Localization Techniques for Serial Ensemble Kalman Filters in a Simple Atmospheric General Circulation Model

2014 ◽  
Vol 142 (2) ◽  
pp. 739-754 ◽  
Author(s):  
Lili Lei ◽  
Jeffrey L. Anderson
Keyword(s):  
Root Mean Square ◽  
General Circulation Model ◽  
Kalman Filters ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Mean Square ◽  
Ensemble Kalman Filters ◽  
Localization Function ◽  
Atmospheric General Circulation

Abstract Two techniques for estimating good localization functions for serial ensemble Kalman filters are compared in observing system simulation experiments (OSSEs) conducted with the dynamical core of an atmospheric general circulation model. The first technique, the global group filter (GGF), minimizes the root-mean-square (RMS) difference between the estimated regression coefficients using a hierarchical ensemble filter. The second, the empirical localization function (ELF), minimizes the RMS difference between the true values of the state variables and the posterior ensemble mean. Both techniques provide an estimate of the localization function for an observation’s impact on a state variable with few a priori assumptions about the localization function. The ELF localizations can have values larger than 1.0 at small distances, indicating that this technique addresses localization but also can correct the prior ensemble spread in the same way as a variance inflation when needed. OSSEs using ELF localizations generally have smaller root-mean-square error (RMSE) than the optimal Gaspari and Cohn (GC) localization function obtained by empirically tuning the GC width. The localization functions estimated by the GGF are broader than those from the ELF, and the OSSEs with the GGF localization generally have larger RMSE than the optimal GC localization function. The GGFs are too broad because of spurious correlation biases that occur in the OSSEs. These errors can be reduced by using a stochastic EnKF with perturbed observations instead of a deterministic EAKF.

scholarly journals Using the local ensemble Transform Kalman Filter for upper atmospheric modelling

2019 ◽  
Vol 9 ◽  
pp. A30 ◽  
Author(s):  
Sean Elvidge ◽  
Matthew J. Angling
Keyword(s):  
Kalman Filter ◽  
General Circulation ◽  
Computational Cost ◽  
Circulation Model ◽  
Electron Content ◽  
Total Electron ◽  
Rms Error ◽  
Ensemble Transform Kalman Filter ◽  
Assimilation Model ◽  
Ensemble Transform

The Advanced Ensemble electron density (Ne) Assimilation System (AENeAS) is a new data assimilation model of the ionosphere/thermosphere. The background model is provided by the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and the assimilation uses the local ensemble transform Kalman filter (LETKF). An outline derivation of the LETKF is provided and the equations are presented in a form analogous to the classic Kalman filter. An enhancement to the efficient LETKF implementation to reduce computational cost is also described. In a 3 day test in June 2017, AENeAS exhibits a total electron content (TEC) RMS error of 2.1 TECU compared with 5.5 TECU for NeQuick and 6.8 for TIE-GCM (with an NeQuick topside).

scholarly journals Observed and Simulated Upper-Tropospheric Water Vapor Feedback

2008 ◽  
Vol 21 (13) ◽  
pp. 3282-3289 ◽  
Author(s):  
A. Gettelman ◽  
Q. Fu
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Circulation Model ◽  
Specific Humidity ◽  
Upper Troposphere ◽  
Double Peak Structure ◽  
Peak Structure ◽  
Surface Temperatures ◽  
Community Atmosphere Model ◽  
Water Vapor Feedback

Abstract Satellite measurements from the Atmospheric Infrared Sounder (AIRS) in the upper troposphere over 4.5 yr are used to assess the covariation of upper-tropospheric humidity and temperature with surface temperatures, which can be used to constrain the upper-tropospheric moistening due to the water vapor feedback. Results are compared to simulations from a general circulation model, the NCAR Community Atmosphere Model (CAM), to see if the model can reproduce the variations. Results indicate that the upper troposphere maintains nearly constant relative humidity for observed perturbations to ocean surface temperatures over the observed period, with increases in temperature ∼1.5 times the changes at the surface, and corresponding increases in water vapor (specific humidity) of 10%–25% °C−1. Increases in water vapor are largest at pressures below 400 hPa, but they have a double peak structure. Simulations reproduce these changes quantitatively and qualitatively. Agreement is best when the model is sorted for satellite sampling thresholds. This indicates that the model reproduces the moistening associated with the observed upper-tropospheric water vapor feedback. The results are not qualitatively sensitive to model resolution or model physics.

The Formulation and Atmospheric Simulation of the Community Atmosphere Model Version 3 (CAM3)

2006 ◽  
Vol 19 (11) ◽  
pp. 2144-2161 ◽  
Author(s):  
William D. Collins ◽  
Philip J. Rasch ◽  
Byron A. Boville ◽  
James J. Hack ◽  
James R. McCaa ◽  
...  
Keyword(s):  
Finite Volume ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Radiation ◽  
Time Step ◽  
Community Land Model ◽  
Enso Events ◽  
Community Atmosphere Model ◽  
Atmosphere Model

Abstract A new version of the Community Atmosphere Model (CAM) has been developed and released to the climate community. CAM Version 3 (CAM3) is an atmospheric general circulation model that includes the Community Land Model (CLM3), an optional slab ocean model, and a thermodynamic sea ice model. The dynamics and physics in CAM3 have been changed substantially compared to implementations in previous versions. CAM3 includes options for Eulerian spectral, semi-Lagrangian, and finite-volume formulations of the dynamical equations. It supports coupled simulations using either finite-volume or Eulerian dynamics through an explicit set of adjustable parameters governing the model time step, cloud parameterizations, and condensation processes. The model includes major modifications to the parameterizations of moist processes, radiation processes, and aerosols. These changes have improved several aspects of the simulated climate, including more realistic tropical tropopause temperatures, boreal winter land surface temperatures, surface insolation, and clear-sky surface radiation in polar regions. The variation of cloud radiative forcing during ENSO events exhibits much better agreement with satellite observations. Despite these improvements, several systematic biases reduce the fidelity of the simulations. These biases include underestimation of tropical variability, errors in tropical oceanic surface fluxes, underestimation of implied ocean heat transport in the Southern Hemisphere, excessive surface stress in the storm tracks, and offsets in the 500-mb height field and the Aleutian low.

The nighttime poleward wind responses to SAPS simulated by TIEGCM: a universal time effect

2020 ◽  
Author(s):  
Kedeng Zhang ◽  
Hui Wang ◽  
Wenbin Wang ◽  
Jing Liu ◽  
Shunrong Zhang ◽  
...  
Keyword(s):  
Coriolis Force ◽  
General Circulation ◽  
Opposite Effect ◽  
Circulation Model ◽  
Meridional Wind ◽  
Universal Time ◽  
Coordinate Systems ◽  
Large Component ◽  
Meridional Winds ◽  
Channel Orientation

<p>The present work investigates the nighttime meridional wind (30º-50º magnetic latitude and 19-22 magnetic local time) in response to subauroral polarization streams (SAPS) that commence at different universal time (UT) by using Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) under geomagnetically disturbed conditions that are closely related to the southward interplanetary magnetic field (IMF) carried by the solar wind. The SAPS effects on the meridional winds show a remarkable UT variation, with larger magnitudes at 00 and 12 UT than at 06 and 18 UT. The strongest poleward wind emerges when SAPS commence at 06 UT, and the weakest poleward wind develops when SAPS occur at 00 UT. A diagnostic analysis of model results shows that the pressure gradient is more prominent for the developing of the poleward wind at 00 and 12 UT. Meanwhile, the effect of the ion drag is important in the modulation of the poleward wind velocity at 06 and 18 UT. This is caused by the misalignment of the geomagnetic and geographic coordinate systems, resulting to a large component of ion drag in geographically northward (southward) direction due to the SAPS channel orientation at 06 and 18 UT (00 and 12 UT). The Coriolis force effect induced by westward winds maximizes (minimizes) when SAPS commence at 12 UT (00 UT). The centrifugal force due to the accelerated westward winds shows similar UT variations as the Coriolis force, but with an opposite effect.</p>

scholarly journals Transient teleconnection event at the onset of a planet-encircling dust storm on Mars

2009 ◽  
Vol 27 (9) ◽  
pp. 3663-3676 ◽  
Author(s):  
O. Martínez-Alvarado ◽  
L. Montabone ◽  
S. R. Lewis ◽  
I. M. Moroz ◽  
P. L. Read
Keyword(s):  
Dust Storm ◽  
General Circulation ◽  
Thermal Emission ◽  
Three Dimensional ◽  
Circulation Model ◽  
Empirical Orthogonal Functions ◽  
State Variables ◽  
Orthogonal Functions ◽  
Teleconnection Patterns ◽  
Pressure Surface

Abstract. We use proper orthogonal decomposition (POD) to study a transient teleconnection event at the onset of the 2001 planet-encircling dust storm on Mars, in terms of empirical orthogonal functions (EOFs). There are several differences between this and previous studies of atmospheric events using EOFs. First, instead of using a single variable such as surface pressure or geopotential height on a given pressure surface, we use a dataset describing the evolution in time of global and fully three-dimensional atmospheric fields such as horizontal velocity and temperature. These fields are produced by assimilating Thermal Emission Spectrometer observations from NASA's Mars Global Surveyor spacecraft into a Mars general circulation model. We use total atmospheric energy (TE) as a physically meaningful quantity which weights the state variables. Second, instead of adopting the EOFs to define teleconnection patterns as planetary-scale correlations that explain a large portion of long time-scale variability, we use EOFs to understand transient processes due to localised heating perturbations that have implications for the atmospheric circulation over distant regions. The localised perturbation is given by anomalous heating due to the enhanced presence of dust around the northern edge of the Hellas Planitia basin on Mars. We show that the localised disturbance is seemingly restricted to a small number (a few tens) of EOFs. These can be classified as low-order, transitional, or high-order EOFs according to the TE amount they explain throughout the event. Despite the global character of the EOFs, they show the capability of accounting for the localised effects of the perturbation via the presence of specific centres of action. We finally discuss possible applications for the study of terrestrial phenomena with similar characteristics.

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