Engineering topics

Park, Jae H.

Publications and source records attributed to Park, Jae H..

12 records

NASA NTRS2001

Properties of Stratospheric Aerosol Estimated from HALOE Data

Extinction coefficients for stratospheric aerosols at 8 HALOE (HALogen Occultation Experiment) wavelengths are determined by comparing transmittances data for two adjacent solar occultation measurements, where one limb path is loaded with aerosols but the other path is free of aerosols. These extinction coefficients are used to infer the aerosol properties such as composition and size distribution parameters. Mie theory has been used to calculate the extinction coefficients, and a nonlinear least square method is applied to determine the aerosol properties. Sixteen cases are selected for the retrieval in southern hemisphere at latitudes from 21 to 48 deg S for the period of 29 Mar - 31 May 1992. Retrieved size width ranges from 1.1 to 1.5 and radius ranges from 0.25 to 0.45 micrometers. These size parameters are within the ranges of in situ measurements at Laramie, Wyoming. Retrieved weight percent of H2SO4 is larger than the equilibrium value by about 5 to approximately 10 weight percent, similar to the results for northern hemisphere at latitudes 20 to 55 deg N for the period from Nov 1991 to Feb. 1992.

Lee, Kwang-Mog↗

NASA NTRS1999

Models and Measurements Intercomparison 2

Models and Measurement Intercomparison II (MM II) summarizes the intercomparison of results from model simulations and observations of stratospheric species. Representatives from twenty-three modeling groups using twenty-nine models participated in these MM II exercises between 1996 and 1999. Twelve of the models were two- dimensional zonal-mean models while seventeen were three-dimensional models. This was an international effort as seven were from outside the United States. Six transport experiments and five chemistry experiments were designed for various models. Models participating in the transport experiments performed simulations of chemically inert tracers providing diagnostics for transport. The chemistry experiments involved simulating the distributions of chemically active trace cases including ozone. The model run conditions for dynamics and chemistry were prescribed in order to minimize the factors that caused differences in the models. The report includes a critical review of the results by the participants and a discussion of the causes of differences between modeled and measured results as well as between results from different models, A sizable effort went into preparation of the database of the observations. This included a new climatology for ozone. The report should help in evaluating the results from various predictive models for assessing humankind perturbations of the stratosphere.

Park, Jae H.↗

NASA NTRS1998

Role of the Quasi-Biennial Oscillation in the Transport of Aerosols from the Tropical Stratospheric Reservoir to Midlatitudes

The temporal evolution of the stratospheric aerosol distribution in the tropical stratospheric reservoir after the eruption of Mount Pinatubo was observed from 1992 to 1995 by the HALOE instrument on the UARS satellite. Since the spatial gradient of aerosol loading is large at the boundaries of the tropical stratospheric reservoir due to the volcanic aerosols, the effect of the meridional circulation on the distribution is seen clearly. The mechanism for dispersal of aerosol in the lower stratosphere from the tropics into midlatitudes strongly depends on the phase of the equatorial zonal wind. The time-latitude cross sections of the normalized distribution of aerosol on isentropic surfaces are used to observe the equatorial variation as well as change in meridional dispersal during the quasi-biennial period. Observed tropical stratospheric winds are used with a simple analytical dynamical model to examine transport processes of tracers from the tropics during several phases of the quasi-biennial oscillation (QBO) from 1992 to 1995. The Lagrangian meridional circulation in the tropics is consistent with the vertical and meridional velocities correlated with the QBO in the zonal wind. We find that vertical motion plays a crucial role in vertical and subsequent meridional transport. The pattern of meridional divergence derived from the vertical velocity is closely related to the observed HALOE aerosol distributions and their temporal development in the equatorial region. The westerly (easterly) shear phase of the QBO is associated with sinking (rising) motions at the equator and subsequent poleward (equatorward) transport in the lower stratosphere.

Choi, Wookap↗

NASA NTRS1995

Aerosol effects and corrections in the Halogen Occultation Experiment

The eruptions of Mt. Pinatubo in June 1991 increased stratospheric aerosol loading by a factor of 30, affecting chemistry, radiative transfer, and remote measurements of the stratosphere. The Halogen Occultation Experiment (HALOE) instrument on board Upper Atmosphere Research Satellite (UARS) makes measurements globally for inferring profiles of NO2, H2O, O3, HF, HCl, CH4, NO, and temperature in addition to aerosol extinction at five wavelengths. Understanding and removing the aerosol extinction is essential for obtaining accurate retrievals from the radiometer channels of NO2, H2O and O3 in the lower stratosphere since these measurements are severely affected by contaminant aerosol absorption. If ignored, aerosol absorption in the radiometer measurements is interpreted as additional absorption by the target gas, resulting in anomalously large mixing ratios. To correct the radiometer measurements for aerosol effects, a retrieved aerosol extinction profile is extrapolated to the radiometer wavelengths and then included as continuum attenuation. The sensitivity of the extrapolation to size distribution and composition is small for certain wavelength combinations, reducing the correction uncertainty. The aerosol corrections extend the usable range of profiles retrieved from the radiometer channels to the tropopause with results that agree well with correlative measurements. In situations of heavy aerosol loading, errors due to aerosol in the retrieved mixing ratios are reduced to values of about 15, 25, and 60% in H2O, O3, and NO2, respectively, levels that are much less than the correction magnitude.

Hervig, Mark E.↗

NASA NTRS1994

Summer polar chemistry observations in the stratosphere made by HALOE

Regions of low stratospheric ozone that are anticorrelated with HCl, NO, and NO2 levels have been observed in the Arctic and Antarctic summers of 1992 and 1993 by the Halogen Occultation Experiment on the UARS platform. The low ozone areas are confined to the approximately 8-45 mb (approximately 33-21 km) region and poleward of approximately 60 deg in each hemisphere. While low polar summer ozone has been observed before, this is the first time simultaneous observations of relevant nitrogen and chlorine chemical species have been made. The phenomenon appears to be a recurring geophysical feature, and the satellite data should provide an excellent opportunity to improve our understanding of the chemistry causing these conditions.

Park, Jae H.↗

NASA NTRS1993

The Halogen Occultation Experiment

The Halogen Occultation Experiment (HALOE) uses solar occultation to measure vertical profiles of O3, HCl, HF, CH4, H2O, NO, NO2, aerosol extinction, and temperature versus pressure with an instantaneous vertical field of view of 1.6 km at the earth limb. Latitudinal coverage is from 80 deg S to 80 deg N over the course of 1 year and includes extensive observations of the Antarctic region during spring. The altitude range of the measurements extends from about 15 km to about 60-130 km, depending on channel. Experiment operations have been essentially flawless, and all performance criteria either meet or exceed specifications. Internal data consistency checks, comparisons with correlative measurements, and qualitative comparisons with 1985 atmospheric trace molecule spectroscopy (ATMOS) results are in good agreement. Examples of pressure versus latitude cross sections and a global orthographic projection for the September 21 to October 15, 1992, period show the utility of CH4, HF, and H2O as tracers, the occurrence of dehydration in the Antarctic lower stratosphere, the presence of the water vapor hygropause in the tropics, evidence of Antarctic air in the tropics, the influence of Hadley tropical upwelling, and the first global distribution of HCl, HF, and NO throughout the stratosphere. Nitric oxide measurements extend through the lower thermosphere.

Russell, James M., III↗

NASA NTRS1993

Observations of aerosol by the HALOE experiment onboard UARS - A preliminary validation

The HALOE experiment measures vertical profiles of aerosol extinction at five infrared wavelengths. Four of these observations are obtained using a combination of gas filter and broadband radiometer measurements in bands of HF, HCl, CH4, and NO centered at wavelengths of 2.45, 3.40, 3.45, and 5.26 microns, respectively. The fifth is obtained using broadband radiometer measurements of CO2 transmission at 2.79 microns. Error analysis shows that the random extinction uncertainties are generally less than 10 percent in the aerosol layer, increasing to over 20 percent at the profile tops. HALOE spectral extinction measurements are shown to be consistent with predicted spectral extinction for stratospheric sulfate aerosol. Profile comparisons between HALOE and independent sources result in generally good agreement in the shape and magnitude of peak extinction and the altitude where the peak extinction occurs. In addition, global aerosol distributions obtained from the data are consistent with expected aerosol morphology. Although the validation is preliminary, the HALOE aerosol data appear to be of excellent quality and to accurately represent optical characteristics and distribution of the aerosols.

Hervig, Mark E.↗

NASA NTRS1993

HALOE Antarctic observations in the spring of 1991

HALOE observations of O3, CH4, HF, H2O, NO, NO2, and HCl collected during the October 1991 Antarctic spring period are reported. The data show a constant CH4 mixing ratio of about 0.25 ppmv for the altitude range from 65 km down to about 25 km at the position of minimum wind speed in the vortex: i.e., the vortex center, and depressions in pressure versus longitude contours of NO, NO2, HF, and HCl in this same region. Water vapor, HF, and HCl enhancement are also observed in the vortex center region above about 25 km. Between 10 and 20 km, the expected mixing ratio signatures exist within the vortex, i.e., low ozone and dehydration. The water vapor increased by 50 percent, and the ozone level doubled inside the vortex between October 11 and 24 in the 15-20 km layer. These changes imply a time constant for recovery from ozone hole conditions of 19 and 30 days for O3 and H2O, respectively. The data further show the presence of air inside the vortex between 3 and 30 mb which has mixing ratios characteristic of midlatitudes.

Russell, James M., III↗

NASA NTRS1991

Improved Limb Atmospheric Spectrometer (ILAS) for polar stratospheric trace gas measurements

The Improved Limb Atmospheric Spectrometer (ILAS) is a grating spectrometer designed to measure vertical profiles of high latitude stratospheric constituents in a solar occultation mode. ILAS measurement gases are ozone (03), methane (CH4), nitrous oxide (N2O), nitric acid (HNO3), water vapor (H2O), nitrogen dioxide (NO2), and CFC-11 using an IR channel. Temperature, pressure, and aerosol are also measured using a visible channel. The IR channel consists of 44 detector elements which cover the spectral range 6.2 to 11.8 microns, and the visible channel is composed of 1024 pixels that cover 753 to 784 nm. ILAS will be installed on the Advanced Earth Observing Satellite (ADEOS) which will be launched in 1995. Instrument design data are outlined.

Yokota, Tatsuya↗

NASA NTRS1990

Description of SAFIRE for ISES

The SAFIRE (Spectroscopy of the Atmosphere using Far Infrared Emission) is a limb emission experiment using a far-IR Fourier transform spectrometer (FTS) and a mid-IR broadband multispectral radiometer covering the range 80 to 1600/cm. The purpose of this experiment is to obtain vertical distributions of temperature and key constituents of O(y), HO(y), NO(y), ClO(y), and BrO(y) families in the stratosphere, mesosphere, and thermosphere. The spectral channels and gases within each channel are summarized. The instrument includes a 48 element (6 x 8) Ge:GA detector array operating at 4 K in the far-IR and a 105 element (7 x 15) HgCdTe array operating at 80 K in the mid-IR. The SAFIRE uses four different scan modes for vertical coverage and resolution to address various scientific requirements. The SAFIRE data reduction will start with the retrieval of temperature profile as a function of pressure using two CO2 channel data. Constituent distributions then are obtained from other channel data using the retrieved temperature profile. The SAFIRE measurements are limited to the region above the tropopause because of radiance saturation by H2O and clouds. The computational capability necessary to process at the instrument data rate is estimated to be 19 MFLOPS for FTS data and 0.02 MFLOPS for radiometer data. It seems, therefore, that the real-time applications of SAFIRE data using an onboard processing device is not feasible. Although a temperature anomaly may be detected from the two CO2 radiometer channels using an onboard processor for the stratosphere, it is not possible to distinguish between CO2 outflux and temperature anomaly. Temperature anomaly does not, therefore, offer tropospheric information useful for real-time application.

Park, Jae H.↗

NASA NTRS1989

The mixing ratio of the stratospheric hydroxyl radical from far infrared emission measurements

Far infrared emission spectra of the stratosphere, measured with a 0.0033/cm resolution Fourier transform spectrometer using a limb scanning method, are analyzed in order to retrieve the vertical distribution of the hydroxyl radical (OH). The observations cover a time interval between 1300 and 2300 hours, showing a pronounced time decrease of the OH signals. Vertical profiles are obtained for the afternoon and sunset periods. An upper limit is derived from the small signals present in the night measurements. Three different methods of analysis have been applied to the same data set, and the results provided the basis for a critical discussion of the error sources. The results are compared with theoretical predictions and with the results of other experiments.

Carli, Bruno↗

NASA NTRS1988

Simultaneous measurement of minor stratospheric constituents with emission far-infrared spectroscopy

The vertical mixing ratio profiles of H2O, HDO, O3, heavy ozone, HF, HCl, HCN, and OH in the stratosphere are retrieved from high-resolution far-infrared emission spectra. These spectra were obtained with a balloon-borne Fourier transform spectrometer in the spring of 1979 at 32 deg N. The nonlinear least squares fit method is used in the analysis. The results are obtained relative to the O2 mixing ratio, whose emission features can be found in the same spectra. The retrieval of OH together with other species should be particularly significant for the study of upper stratospheric photochemistry, although the errors are relatively large: 28 percent for OH and 16-19 percent for other species.

Carli, Bruno↗