Arthur D. Richmond

Bio: Arthur D. Richmond is an academic researcher from National Center for Atmospheric Research. The author has contributed to research in topics: Thermosphere & Ionosphere. The author has an hindex of 67, co-authored 262 publications receiving 15605 citations. Previous affiliations of Arthur D. Richmond include University of California, Los Angeles & High Altitude Observatory.

Modeling the ionosphere wind dynamo: a review

Abstract: This paper reviews the current status of research concerned with modeling the ionospheric wind dynamo. Simulation models have been reasonably successful in reproducing the types of magnetic perturbations that are produced by the dynamo. Ionospheric electric fields are less well simulated, particularly at night. The primary areas of research needed to improve our ability to simulate realistically the ionospheric wind dynamo are in the modeling of nighttime conditions, hemispherical asymmetries of thermospheric tides, and mutual dynamic coupling among winds, conductivities, electric fields, and electric currents.

Experiments with a lunar atmospheric tidal model

Abstract: A lunar tidal model similar to that of Forbes [1982] is used to investigate the effects of changes in background zonal winds on the structure of the lunar tide in the upper atmosphere. It is found that changes in the winds have a greater effect than changes in the background temperature profile with latitude. Observed changes in the structure of the lunar tide from year to year at Saskatoon may be explained by introducing stratospheric warnings into the model. The addition of an associated mesospheric cooling gives an even better fit to the observed phase data. It is also seen that northern hemisphere warnings are predicted to give considerable amplitude changes in southern hemisphere lunar tides. It is expected that much of the difficulty in measuring lunar tides in the upper atmosphere is due to changes in the tidal parameters at these levels brought about by variations in the underlying atmosphere.

Forecasting the dynamic and electrodynamic response to the January 2009 sudden stratospheric warming

Abstract: [1] A whole atmosphere model has been used to simulate the changes in the global atmosphere dynamics and electrodynamics during the January 2009 sudden stratospheric warming (SSW) In a companion paper, it has been demonstrated that the neutral atmosphere response to the 2009 warming can be simulated with high fidelity and can be forecast several days ahead The 2009 warming was a major event with the polar stratospheric temperature increasing by 70 K The neutral dynamics from the whole atmosphere model (WAM) was used to drive the response of the electrodynamics The WAM simulation predicted a substantial increase in the amplitude of the 8-hour terdiurnal tide in the lower thermosphere dynamo region in response to the warming, at the expense of the more typical semidiurnal tides The increase in the terdiurnal mode had a significant impact on the diurnal variation of the electrodynamics at low latitude The changes in the winds in the dayside ionospheric E region increased the eastward electric field early in the morning, and drove a westward electric field in the afternoon The initial large increase in upward drifts gradually moved to later local times, and decreased in magnitude The change in the amplitude and phase of the electrodynamic response to the SSW is in good agreement with observations from the Jicamarca radar The agreement with observations serves to validate the whole atmosphere dynamic response Since WAM can forecast the neutral dynamics several days ahead, the simulations indicate that the electrodynamic response can also be predicted

Low-latitude plasma drifts from a simulation of the global atmospheric dynamo

Abstract: The results of a simulation of the global atmospheric dynamo are presented and compared to observations of the ion drift at Jicamarca and the drifts calculated from previous dynamo models. This simulation produces a global plasma distribution which is self-consistent with the global potential distribution. We examine the dynamo-generated potential distribution and the associated E × B drifts induced upon the plasma for two F region winds and a (1,-2) tide in the E region. By using simple diurnal winds and tides and making the plasma and potential distributions self-consistent, the agreement of the calculated E × B with the observed drifts at Jicamarca is improved. The use of an F region wind derived from the DE 2 satellite (Herrero and Mayr, 1986) can further improve the agreement between the calculated E × B drifts and the observed low-latitude plasma drifts. These results lead to the conclusion that the F region dynamo is a very important source of electric fields at low latitudes at all local times. Based on these results, we propose that the postsunset enhancement of the vertical ion drift at Jicamarca is primarily due to a local time gradient in the F region zonal wind in conjunction with the conductivity gradient at the dusk terminator.

Global measures of ionospheric electrodynamic activity inferred from combined incoherent scatter radar and ground magnetometer observations

Abstract: An analysis of several global measures of high-latitude ionospheric electrodynamic activity is undertaken on the basis of results obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure applied to incoherent scatter radar and ground magnetometer observations for January 18–19, 1984. Different global measures of electric potentials, currents, resistances, and energy transfer from the magnetosphere show temporal variations that are generally well correlated. We present parameterizations of these quantities in terms of the AE index and the hemispheric power index of precipitating auroral particles. It is shown how error estimates of the mapped electric fields can be used to correct the estimation of Joule heating. Global measures of potential drop, field-aligned current, and Joule heating as obtained by the AMIE procedure are compared with similar measures presented in previous studies. Agreement is found to within the uncertainties inherent in each study. The mean potential drop through which field-aligned currents flow in closing through the ionosphere is approximately 28% of the total polar cap potential drop under all conditions during these 2 days. We note that order-of-magnitude differences can appear when comparing different global measures of total electric current flow and of effective resistances of the global circuit, so that care must be exercised in choosing characteristic values of these parameters for circuit-analogy studies of ionosphere-magnetosphere electrodynamic coupling.

Riemann manifold Langevin and Hamiltonian Monte Carlo methods

Abstract: The paper proposes Metropolis adjusted Langevin and Hamiltonian Monte Carlo sampling methods defined on the Riemann manifold to resolve the shortcomings of existing Monte Carlo algorithms when sampling from target densities that may be high dimensional and exhibit strong correlations. The methods provide fully automated adaptation mechanisms that circumvent the costly pilot runs that are required to tune proposal densities for Metropolis–Hastings or indeed Hamiltonian Monte Carlo and Metropolis adjusted Langevin algorithms. This allows for highly efficient sampling even in very high dimensions where different scalings may be required for the transient and stationary phases of the Markov chain. The methodology proposed exploits the Riemann geometry of the parameter space of statistical models and thus automatically adapts to the local structure when simulating paths across this manifold, providing highly efficient convergence and exploration of the target density. The performance of these Riemann manifold Monte Carlo methods is rigorously assessed by performing inference on logistic regression models, log-Gaussian Cox point processes, stochastic volatility models and Bayesian estimation of dynamic systems described by non-linear differential equations. Substantial improvements in the time-normalized effective sample size are reported when compared with alternative sampling approaches. MATLAB code that is available from http://www.ucl.ac.uk/statistics/research/rmhmc allows replication of all the results reported.

International Reference Ionosphere 2000

Abstract: The International Reference Ionosphere (IRI) is the international standard for the specification of ionospheric densities and temperatures. It was developed and is being improved-updated by a joint working group of the International Union of Radio Science (URSI) and the Committee on Space Research (COSPAR). A new version of IRI is scheduled for release in the year 2000. This paper describes the most important changes compared to the current version of IRI: (1) an improved representation of the electron density in the region from the F peak down to the E peak including a better description of the F1 layer occurrence statistics and a more realistic description of the low-latitude bottomside thickness, (2) inclusion of a model for storm-time conditions, (3) inclusion of an ion drift model, (4) two new options for the electron density in the D region, and (5) an improved model for the topside electron temperatures. The outcome of the most recent IRI Workshops (Kuhlungsborn, 1997, and Nagoya, 1998) will be reviewed, and the status of several ongoing task force activities (e.g., efforts to improve the representation of electron and ion densities in the topside ionosphere and the inclusion of a plasmaspheric extension) will be discussed. A few typical IRI applications will be highlighted in section 6.

DARN/SUPERDARN : A global view of the dynamics of high-latitude convection

Abstract: The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere. Currently, the network consists of the STARE VHF radar system in northern Scandinavia, a northern-hemisphere, longitudinal chain of HF radars that is funded to extend from Saskatoon, Canada to central Finland, and a southern-hemisphere chain that is funded to include Halley Station, SANAE and Syowa Station in Antarctica. When all of the HF radars have been completed they will operate in pairs with common viewing areas so that the Doppler information contained in the backscattered signals may be combined to yield maps of high-latitude plasma convection and the convection electric field. In this paper, the evolution of DARN and particularly the development of its SuperDARN HF radar element is discussed. The DARN/SupperDARN network is particularly suited to studies of large-scale dynamical processes in the magnetosphere-ionosphere system, such as the evolution of the global configuration of the convection electric field under changing IMF conditions and the development and global extent of large-scale MHD waves in the magnetosphere-ionosphere cavity. A description of the HF radars within SuperDARN is given along with an overview of their existing and intended locations, intended start of operations, Principal Investigators, and sponsoring agencies. Finally, the operation of the DARN experiment within ISTP/GGS, the availability of data, and the form and availability of the Key Parameter files is discussed.

The ionospheric disturbance dynamo

Abstract: A numerical simulation study of the thermospheric winds produced by auroral heating during magnetic storms, and of their global dynamo effects, establishes the main features of the ionospheric disturbance dynamo. Driven by auroral heating, a Hadley cell is created with equatorward winds blowing above about 120 km at mid-latitudes. The transport of angular momentum by these winds produces a subrotation of the mid-latitude thermosphere or westward motion with respect to the earth. The westward winds in turn drive equatorward Pedersen currents which accumulate charge toward the equator, resulting in the generation of a poleward electric field, a westward E × B drift, and an eastward current. When realistic local time conductivity variations are simulated, the eastward mid-latitude current is found to close partly via lower latitudes, resulting in an ‘anti-Sq’ type of current vortex. Both electric field and current at low latitudes thus vary in opposition to their normal quiet-day behavior. This total pattern of disturbance winds, electric fields, and currents is superimposed upon the background quiet-day pattern. When the neutral winds are artificially confined on the nightside, the basic pattern of predominantly westward E × B plasma drifts still prevails on the nightside but no longer extends into the dayside. Considerable observational evidence exists, suggesting that the ionospheric disturbance dynamo has an appreciable influence on storm-time ionospheric electric fields at middle and low latitudes.

Riemann manifold Langevin and Hamiltonian Monte Carlo methods

Abstract: The paper proposes Metropolis adjusted Langevin and Hamiltonian Monte Carlo sampling methods defined on the Riemann manifold to resolve the shortcomings of existing Monte Carlo algorithms when sampling from target densities that may be high dimensional and exhibit strong correlations. The methods provide fully automated adaptation mechanisms that circumvent the costly pilot runs that are required to tune proposal densities for Metropolis-Hastings or indeed Hamiltonian Monte Carlo and Metropolis adjusted Langevin algorithms. This allows for highly efficient sampling even in very high dimensions where different scalings may be required for the transient and stationary phases of the Markov chain. The methodology proposed exploits the Riemann geometry of the parameter space of statistical models and thus automatically adapts to the local structure when simulating paths across this manifold, providing highly efficient convergence and exploration of the target density. The performance of these Riemann manifold Monte Carlo methods is rigorously assessed by performing inference on logistic regression models, log-Gaussian Cox point processes, stochastic volatility models and Bayesian estimation of dynamic systems described by non-linear differential equations. Substantial improvements in the time-normalized effective sample size are reported when compared with alternative sampling approaches. MATLAB code that is available from http://www.ucl.ac.uk/statistics/research/rmhmc allows replication of all the results reported.