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DOE OSTI2021

Hyperparameter Setting for a Marked Multidimensional Hawkes Process with Dissimilar Decays

We provide further details for using Lim, et al.'s marked multidimensional Hawkes processes with dissimilar decays. We first describe what makes these different from other Hawkes processes, then describe each model hyperparameter and how to initialize it informed by the input data and any prior biases. We derived tighter bounds than Lim, et al. for faster convergence of rejection sampling. The resulting hyperparameters and bounds have been helpful against both synthetic and real-world datasets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1979

Spatial-frequency response of the limb infrared monitor of the stratosphere

Measurements from the Limb Infrared Monitor of the stratosphere (LIMS) are presented and discussed. From the LIMS design model data, the modulation transfer function (MTF) was calculated for the optical system, the detector field mask, the electronics, and the overall system for each channel. The signal output performance of the instrument was predicted from the system MTF data and model input radiance data for each channel. The MTF measurements made on the flight sensor confirmed the analytical results.

Wilson, R. G.↗

NASA NTRS1979

Spatial-frequency response of the Limb Infrared Monitor of the Stratosphere /LIMS/ radiometer

The Limb Infrared Monitor of the Stratosphere (LIMS), an experiment on the Nimbus-7 satellite, is designed to scan the earth's limb vertically and measure spectral emission profiles of trace atmospheric gases believed to be important in processes controlling the stratospheric ozone distribution. Experiment objectives are reviewed and several analyses and measurements are described which were performed to determine the adequacy of the system for satisfying these objectives. Adequate spatial-frequency response for all the spectral channels is required to provide, through inversion of the measured limb-radiance profiles, important information about the temperature, structure, and composition of the atmosphere. From the LIMS design-model data, the MTF was calculated for the optical system, the detector field mask, the electronics, and the overall system, for each channel. The signal output performance of the instrument was predicted from the system MTF data model input radiance data for each channel. MTF measurements made on the flight sensor confirmed the analytical results. The predictions indicate that the instrument can satisfy the basic measurement objectives of the experiment.

Wilson, R. G.↗

NASA NTRS1981

The Limb Infrared Monitor of the Stratosphere /LIMS/ experiment - Temperature and nitrogen dioxide results

The Limb Infrared Monitor of the Stratosphere (LIMS) is a satellite-borne radiometer which scans across the earth's limb, measuring infrared radiation emitted by specific atmospheric gases in a number of broad channels. Instrumentation includes a folded telescope, which focuses the radiation from the limb onto an array of six mercury-cadmium-telluride detectors. A scan mirror within the telescope sweeps the fields of view across the horizon, with each up or down scan lasting 12 seconds. The measurements are inverted to yield distributions of temperature and nitrogen dioxide. The temperature is determined from two channels covering the intervals 595-739 per cm and 645-673 per cm of the 15 micron bands of CO2, with maximum signal to noise ratio of 500-1000. Nitrogen dioxide is determined from measurements in a channel from 1580-1613 per cm, with an S/N of approximately 100. Results show that the LIMS temperature and nitrogen dioxide data are characterized by high precision.

Gille, J. C.↗

NASA NTRS1981

Satellite observations of upper atmosphere O3 and HNO3 from the Limb Infrared Monitor of the Stratosphere /LIMS/ experiment on Nimbus 7

The Limb Infrared Monitor of the Stratosphere (LIMS) experiment, launched on-board the Nimbus satellite, was designed to measure both day and night limb radiance which is used to infer upper atmosphere temperature profiles and chemical compound concentrations important in the study of ozone chemistry. The LIMS instrument is a six channel, limb scanning, thermal radiometer which uses HgCdTe detectors, cooled to approximately 64 K. Measurements include ozone, water vapor, nitrogen dioxide, and nitric acid. The ozone and nitric acid channels are centered at approximately 9.6 microns and 11.3 microns, respectively. Results from the channels are described with an emphasis on data validation. The O3 and HNO3 channels have demonstrated high measurement precision.

Russell, J. M., III↗

NASA NTRS1983

Characteristics of low-energy plasma in the plasmasphere and plasma trough

Initial results of studies of low-energy plasma using the light ion mass spectrometer (LIMS) on the SCATHA satellite are presented. Results are discussed primarily for plasma flux in the noon to midnight local time sector, examining the behavior of the plasma with geomagnetic activity and local time. Measurements of the ion mass composition in this region for the energy ranges of the LIMS instrument are presented. Results of temperature measurements are given and a possible explanation for the difference between the whistler and OGO 5 plasmapause positions is suggested. The observed pitch angle distributions are presented, limited to a broad characterization of the plasma population. The effects of the spacecraft potential on the low-energy plasma measurements are considered.

Reasoner, D. L.↗

NASA NTRS1984

Kelvin wave packets and flow acceleration - A comparison of modeling and observations

Atmospheric Kelvin waves, as revealed by temperatures obtained from the recent Limb Infrared Monitor of the Stratosphere (LIMS) experiment, commonly occur in packets. A simple two-dimensional gravity-wave model is used to study the upward propagation of these packets through different zonal mean wind profiles derived from the LIMS data. The observed prevalence of high frequency waves in the lower mesosphere and low frequency waves in the lower stratosphere can be exlained by dispersion of energy associated with the range of frequencies comprising a packet. Dominant wave frequencies at upper and lower levels are more distinctly separated if the packet propagates through a layer of westerly winds. Due to dispersion and shear effects, a packet of short temporal length at low levels will have a considerably extended impact on a layer of westerly winds at higher levels. Observed and modeled westerly accelerations resulting from packet absorption occur in the same layer, and are similar in magnitude and duration. These results support the theory that Kelvin waves are responsible for the westerly phase of the semiannual oscillation.

Coy, L.↗

NASA NTRS1985

Transport processes in the stratosphere: Model simulations and comparisons with satellite observations

A three dimensional atmospheric model was used to study transport processes and to simulate the distribution of chemically active species in the stratosphere. The present results are part of a long term simulation of the seasonally varying structure of stratospheric trace constituents. The occurrence of a midwinter stratospheric warming and the associated transport of O3 and HNO3 during the simulation are described. Comparison of the simulated distributions of O3 and HNO3 are made with data from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment. In addition, distributions of Ertel's potential vorticity on isentropic surfaces (IPV) are evaluated as a diagnostic for interpreting transport processes. Comparisons are made with IPV distributions inferred from LIMS temperature data.

Grose, W. L.↗

NASA NTRS1986

Evolution of potential vorticity in the winter stratosphere of January-February 1979

This paper presents observations which are derived from Nimbus 7 LIMS data. Results at 850 K, January-February 1979 are considered, taking into account an overview of the period, January 19-30, January 31-February 11, February 12-23, and a postwarming sequence. Upper stratosphere diagnostics for early February 1979 are discussed, giving attention to the geopotential at 3 mbar, the 1200 K isentropic surface, the isentropic potential vorticity at 1200 K, and isentropic parcel trajectories. The vertical structure of potential vorticity is also examined. This paper helps also to interpret the area diagnostics of Butchart and Remsberg (1985). It is pointed out that the LIMS data allow calculation of the potential vorticity distribution at higher levels of the middle atmosphere.

Dunkerton, T. J.↗

NASA NTRS1985

Nitric oxide profile from 7 to 32 km

An analysis is given of some results of the LIMS experiment, launched on the Nimbus 7 satellite on October 24, 1978 for the purpose of sounding the middle atmosphere composition and structure. One of the LIMS channels was centered spectrally in the 6 micron region to measure vertical profiles and the global distribution of NO2 mixing ratio. The data reveal that NO2 is highly variable with altitude, latitude, longitude and time. Steep latitudinal gradients are observed in high latitude winter ('the NO2 cliff') when a wave number one pattern exists in the geopotential height field. The daytime gradient under these conditions is less than that for the night. The summer hemisphere column amount is considerably greater (by a factor of about 2) than in the winter hemisphere. The largest mixing ratios occur at 4 mb at night (about 20 ppbv) and 9 mb in the day (about 7 ppbv) and the latitude region of the peak mixing ratio is skewed toward the Southern Hemisphere. The mixing ratio variability is greater at night (by a factor of about 2 to 3) than in the day and there are significant long-term changes revealed by mixing ratio time series analyses on a pressure vs time grid.

Matthews, W. A.↗

NASA NTRS1986

Transient medium-scale wave activity in the summer stratosphere

Observations of medium-scale transient wave activity in the middle-latitude Southern Hemisphere summer stratosphere are interpreted using isentropic potential vorticity (IPV) distributions inferred from temperature data from the Nimbus-7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument. Despite problems with errors in reference-level synoptic height information, the derived IPV distributions clearly exhibit dynamically coherent signatures of eddy mixing due to medium-scale disturbances in the lower-middle stratosphere during early January 1979. The IPV distributions are shown to be strongly correlated with those of a contemporaneous set of isentropic maps of quasi-conservative tracers such as ozone and nitric acid. The results suggest that IPV maps inferred from satellite temperature data provide a useful diagnostic for studies of large-scale dynamics and/or transport in the extratropical stratosphere. Furthermore, the comparatively high vertical resolution of the LIMS data has enabled the vertical attenuation of Southern Hemisphere wave activity to be diagnosed in greater detail than could be achieved from nadir-viewing satellite information.

Miles, T.↗

NASA NTRS1987

Transport and photochemical modeling. Studies of atmospheric species

A program of research studies related to the photochemistry, radiative transfer, and dynamics of the stratosphere is described. Investigations were conducted in two broad areas: (1) studies of the stratospheric processes and their response to external perturbations, and (2) analysis of satellite measurements in conjunction with theoretical models. Contemporary one dimensional photochemical, radiative-convective model was used to assess the impact of perturbations such as solar flux variability, increases in atmospheric carbon dioxide, chlorofluoromethanes and other greenhouse gases. Data from satellite experiments such as LIMS and SBUV, were used along with theoretical models to develop a climatology of trace species in the stratosphere. The consistency of contemporary ozone photochemistry was examined in the light of LIMS data. Research work also includes analysis of stratospheric nitrogen dioxide distributions from different satellite experiments, investigation of the wintertime latitudinal gradients in NO2, estimation of the stratospheric odd nitrogen level and its variability, and studies related to the changes in ozone in the Antarctic, and mid latitude Southern Hemisphere.

Natarajan, M.↗

NASA NTRS1986

On the radiative balance of the stratosphere

The zonally averaged radiative balance of the stratosphere based on the measured temperature structure and gas concentrations available from the LIMS instrument is examined in detail. These data are extant for seven months (November 1978 to May 1979). The contribution to the net radiative balance due to the individual components of solar heating and longwave cooling is discussed. These components are further broken down by individual gas constituent to understand the role each gas plays in determining the total radiative heating/cooling. The deficiencies of employing a latitudinally and temporally independent Newtonian damping coefficient are also explored. In particular, the Newtonian damping time is shown to vary by a factor of two in both latitude and season. Net zonally averaged stratospheric radiative heating for the seven months of LIMS data are presented. These net heating rates are important in determining the role of advective transport of chemical constituents. An important feature that appears in the derived radiative heating is the existence of a region of net radiative cooling near the equatorial stratopause.

Kiehl, J. T.↗

NASA NTRS1986

Analysis of far-infrared emission Fourier transform spectra

An analysis method that uses the nonlinear least-squares fit technique has been developed for emission spectra obtained with a Fourier transform spectrometer. This method is used for the analysis of submillimeter-region atmospheric emission spectra obtained with a balloon-borne FT spectrometer that was carried out as a correlative measurement for the Limb IR Monitor of the Stratosphere (LIMS) satellite experiment. The retrieved mixing ratios of H2O and O3 in the stratosphere from four spectral intervals have standard deviations of about 10 percent, and the average values agree to within 10 percent of corresponding results from the LIMS satellite experiment which used a broadband emission radiometer in the IR region.

Park, J. H.↗

NASA NTRS1986

Polar stratospheric clouds inferred from satellite data

Anomalously high radiances from the ozone channel of the Limb Infrared Monitor of the Stratosphere (LIMS) sounding instrument have been observed in the Northern Hemisphere winter lower stratosphere. Such events, thought to be due to polar stratospheric clouds (PSCs), are examined further by computing relative humidities using Stratospheric Sounding Unit temperatures and water vapor measurements from the LIMS Map Archive Tape analyses. Regions identified as PSCs are found to correspond closely to regions of high humidity. While instances of saturation were found, the average humidity at the centers of 39 PSCs was calculated to be 58 percent. Possible reasons for this apparent discrepancy are discussed. Applying a similar approach to the Southern Hemisphere, in 1979, virtually no PSCs are found in the vortex after September 10 at 20 km. This result has important implications for a number of proposed explanations for the Antarctic ozone hole.

Austin, J.↗

NASA NTRS1986

Evolution of the zonal mean state in the equatorial middle atmosphere during October 1978-May 1979

The week-to-week evolution of the zonal mean state of the equatorial middle atmosphere is studied using daily mapped temperatures derived with the Limb Infrared Monitor of the Stratosphere (LIMS) instrument on Nimbus 7. The characteristics of the LIMS instrument and rocket data are described. The development of the zonal mean state at low latitudes, and the relation between the evolution of the zonal mean state and extratropical changes are examined. The residual circulation is estimated using a radiative algorithm. Advection by the residual mean circulation, and the role of inertial acceleration in mean meridional circulations are discussed.

Hitchman, Matthew H.↗

NASA NTRS1987

An interim reference model for the middle atmosphere water vapor distribution

Nimbus 7 LIMS data are used to determine monthly and seasonal zonal mean reference stratospheric profiles over selected latitude bands, and other ground and airborne microwave data are combined with the LIMS data to construct an interim reference profile from the tropopause to 80 km for the midlatitude region averaged over the winter and spring periods. The present profiles indicate the presence of a hygropause near 50 mb pressure in the tropics, a relatively constant mixing ratio distribution with a height of 4.7-5 ppmv in the midlatitude and high latitude stratosphere, and a decrease in the midlatitude mesosphere to 1 ppmv at about 80 km.

Russell, J. M., III↗

NASA NTRS1987

Forecast experiments with the NASA/GLA stratospheric/tropospheric data assimilation system

For the first time, a four-dimensional stratospheric/tropospheric data assimilation system with a top analysis level at 0.4 mb has been developed and used to produce physically consistent gridded analyses for the stratosphere as well as the troposphere for a period during the First GARP Global Experiment (FGGE) and Limb Infrared Monitor of the Stratosphere (LIMS) (November 1978-May 1979). The system consists of a two-dimensional optimum interpolation analysis with 18 mandatory pressure levels and a 19-level fourth order stratospheric/tropospheric general circulation model with a horizontal resolution of 4 (latitude) by 5 deg (longitude) and a top at 0.3 mb. The system allows the utilization of stratospheric data including LIMS, Tiros-N retrievals, rocketsondes and vertical temperature profile radiometer soundings in addition to the other FGGE level 2b data. These data are analyzed every six hours. In order to examine the quality of the analyzed data, forecast experiments starting from different analyses are performed for the period of the stratospheric sudden warming of late February 1979. The results indicate that by employing the present four-dimensional assimilation approach, the medium-range forecast skill for this event is improved.

Takano, Kenji↗