Paul L. Bailey

Evidence for Equatorial Kelvin Modes in Nimbus-7 LIMS

Abstract Eastward propagating disturbances over the equator are diagnosed in two independent Nimbus-7 LIMS (Limb Infrared Monitor of the Stratosphere) data sets. They are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics. The disturbances, which can be seen in wavenumbers 1–3, are in phase and symmetric about the equator, latitudinally evanescent, and have short-moderate vertical phase structure, 10–40 km, which progresses downward. Wavenumber 1 has spectral components which propagate eastward at periods of 6.7–8.6 days (54–69 m s−1) and 3.5–4.0 days (115–135 m s−1). Wavenumber 2 exhibits eastward propagating variance at periods of 6.0–7.5 days (31–39 m s−1) and 3.8–4.3 days (55–62 m s−1). The faster waves appear principally in the upper stratosphere. These features are in reasonable agreement with the structure and dispersion characteristics of simple, quasi-separable Kelvin modes. With the exception of the slower w...

Retrieval of tropospheric carbon monoxide for the MOPITT experiment

A retrieval method for deriving the tropospheric carbon monoxide (CO) profile and column amount under clear sky conditions has been developed for the Measurements of Pollution In The Troposphere (MOPITT) instrument, scheduled for launch in 1998 onboard the EOS-AM1 satellite. This paper presents a description of the method along with analyses of retrieval information content. These analyses characterize the forward measurement sensitivity, the contribution of a priori information, and the retrieval vertical resolution. Ensembles of tropospheric CO profiles were compiled both from aircraft in situ measurements and from chemical model results and were used in retrieval experiments to characterize the method and to study the sensitivity to different parameters. Linear error analyses were carried out in parallel with the ensemble experiments. Results of these experiments and analyses indicate that MOPITT CO column measurements will have better than 10% precision, and CO profile measurement will have approximately three pieces of independent information that will resolve 3-5 tropospheric layers to approximately 10% precision. These analyses are important for understanding MOPITT data, both for application of data in tropospheric chemistry studies and for comparison with in situ measurements.

Implications of the Stratospheric Water Vapor Distribution as Determined from the Nimbus 7 LIMS Experiment

Abstract The LIMS experiment on Nimbus 7 has provided new results on the stratospheric water vapor distribution. The data show 1) a latitudinal gradient with mixing ratios that increase by a factor of 2 from equator to ±60 degrees at 50 mb, 2) most of the time there is a fairly uniform mixing ratio of 5 ppmv at high latitudes, but more variation exists during winter, 3) a well-developed hygropause at low to midlatitudes of the lower stratosphere 4) a source region of water vapor in the upper stratosphere to lower mesosphere that is consistent with methane oxidation chemistry, at least within the uncertainties of the data, 5) an apparent zonal mean H2O distribution that is consistent with the circulation proposed by Brewer in 1949, and 6) a zonal mean distribution in the lower stratosphere that is consistent with the idea of quasi-isentropic transport by eddies in the meridional direction. Limits to the use of the data in the refinement of our understanding of the stratospheric water vapor budget are noted.

Validation of CH4 and N2O measurements by the cryogenic limb array etalon spectrometer instrument on the Upper Atmosphere Research Satellite

CH 4 and N 2 O are useful as dynamical tracers of stratospheric air transport because of their long photochemical lifetimes over a wide range of altitudes. The cryogenic limb array etalon spectrometer (CLAES) instrument on the NASA UARS provided simultaneous global measurements of the altitude profiles of CH 4 and N 2 O mixing ratios in the stratosphere between October 1, 1991, and May 5, 1993. Data between January 9, 1992, and May 5, 1993 (388 days), have been processed using version 7 data processing software, and this paper is concerned with the assessment of the quality of this data set. CLAES is a limb-viewing emission instrument, and approximately 1200 profiles were obtained each 24-hour period for each constituent over a nominal altitude range of 100 to 0.1 mbar (16 to 64 km). Each latitude was sampled 30 times per day between latitudes 34°S and 80°N, or 34°N and 80°S depending on the yaw direction of the UARS, and nearly all local times were sampled in about 36 days. This data set extends the altitude, latitude, and seasonal coverage of previous experiments, particularly in relation to measurements at high winter latitudes. To arrive at estimates of experiment error, we compared CLAES profiles for both gases with a wide variety of correlative data from ground-based, rocket, aircraft, balloon, and space-borne sensors, looked at the repeatability of multiple profiles in the same location, and carried out empirical estimates of experiment error based on knowledge of instrument characteristics. These analyses indicate an average single-profile CH 4 systematic error of about 15% between 46 and 0.46 mbar, with CLAES biased high. The CH 4 random error over this range is 0.08 to 0.05 parts per million, which translates to about 7% in the midstratosphere. For N 2 O the indicated systematic error is less than 15% at all altitudes between 68 and 2 mbar, with CLAES tending to be high below 6.8 mbar and low above. The N 2 O random error is 20 to 5 ppb between 46 and 2 mbar, which also translates to 7% in the low to midstratosphere. Both tracers have useful profile information to as low as 68 mbar, excluding the tropics, and as high as 0.2 mbar (CH 4 ) and 1 mbar (N 2 O). The global fields show generally good spatial correlation and exhibit the major morphological and seasonal features seen in previous global field data. Several morphological features are pointed out for regions and conditions for which there have been essentially no previous data. These include the differential behavior of the tracer isopleths near and inside the Antarctic winter vortex, and local maxima in the tropics in 1992, probably associated with the Mount Pinatubo sulfate aerosol layer. Overall, the results of this validation exercise indicate that the version 7 CH 4 and N 2 O data sets can be used with good confidence for quantitative and qualitative studies of stratospheric and lower-mesospheric atmospheric structure and dynamics.

Quasi-Stationary Zonally Asymmetric Circulations in the Equatorial Lower Mesosphere

Abstract Data from the Limb Infrared Monitor of the Stratosphere (LIMS) are used to identify a new type of planetary scale disturbance in the equatorial lower mesosphere during northern winter 1978/79. The disturbances consist of two or three vertically stacked temperature extrema of alternating sign. They persist for as long as two weeks and do not propagate. Their occurrence is confined to regions of very weak or negative inertial stability, and their meridional to vertical aspect ratio, meridional structure and zonal spectrum are consistent with disturbances predicted by inertial instability theory. However, they are found only when there is strong forcing of the subtropical mesosphere by zonal wavenumber one and two Rossby waves. This fact, together with the absence of zonal propagation, suggests that stationary Rossby waves determine their occurrence and longitudinal structure. These structures can significantly modify the zonal mean flow and should be taken into account in dynamical models of the eq...

Simulation of Stratospheric N2O in the NCAR CCM2: Comparison with CLAES Data and Global Budget Analyses

Abstract Global variability and budgets of stratospheric nitrous oxide (N2O) are studied using output from a stratospheric version of the NCAR Community Climate Model. The model extends over 0–80 km, incorporating an N2O-like tracer with tropospheric source and upper-stratospheric photochemical sink, the latter parameterized using linear damping rates obtained from detailed two-dimensional model calculations. Results from the model over several seasonal cycles are compared with observations of N2O from the Cryogenic Limb Array Etalon Spectrometer instrument on the Upper Atmosphere Research Satellite. The model produces N2O structure and variability that is in reasonable agreement with the observations. Global budgets of stratospheric N2O are furthermore analyzed using model output, based on the transformed Eulerian-mean, zonal-mean framework. These budgets are used to quantify the importance of planetary wave constituent transport in the stratosphere, for both slow seasonal variations and fast planetary w...

Comparison of correlative data with HNO3 version 7 from the CLAES instrument deployed on the NASA Upper Atmosphere Research Satellite

The cryogenic limb array etalon spectrometer (CLAES) aboard UARS made near-global measurements of HNO3 and 388 days from January 9, 1992, to April 25, 1993, have been processed to data version 7 (V7). Results from UARS instruments, including CLAES, the improved stratospheric and mesospheric sounder, and the microwave limb sounder, provide the first near-global documentation of the evolution of denitrification in the Antarctic 1992 winter and spring vortex. We provide a description of the CLAES HNO3 V7 quality that includes comparisons with correlative measurements to assess overall quality, accuracy, and precision. Correlative profiles of volume mixing ratio (vmr) included those obtained by the space shuttle deployed ATMOS in two missions, March–April 1992 and April 1993, data from a variety of balloon-borne instruments at midlatitude (11 profiles), and in high-latitude northern winter (six profiles), and LIMS data. In general, the CLAES V7 HNO3 maximum values of vmr were of the order of 6–15% less than correlative for CLAES values ≤8 parts per billion by volume (ppbv). However, when CLAES peak vmr values were 10 to 13 ppbv, then CLAES values exceeded correlative by 0–7%. The comparisons were within the combined instrumental error estimates, or observed measurement variability, for the large majority of comparisons. As discussed, the retrieval of future versions will utilize updated spectral parameters and will also correct for a small uncompensated drift in radiometric calibration that occurred in the latter part of the mission. This is expected to improve the comparisons in the ≤8 ppbv range, perhaps at the expense of those in the ≥8 ppbv range. The data obtained January 9 to April 15, 1992, in comparison with data obtained January 9 to April 15, 1993, reveal strikingly evident 1-year period deseasonalized trends on a global basis. These trends agree quantitatively with available correlative data suitable for trend analysis. These include ATMOS in the southern midlatitudes and published long-term time series of HNO3 column obtained at 45°S and 20°N. These trends reveal a large decrease in the southern hemisphere and small increases in the northern hemisphere, such that the global average is toward a decrease. The global average decrease we attribute to the diminishing influence of heterogeneous conversion of N2O5 to HNO3 as the Pinatubo aerosol settles out during this time period, and the HNO3 recovers toward pre-Pinatubo conditions. We establish plausibility that the small increases in the north are due to hemispherically asymmetric QBO-like effects that are strong in the northern hemisphere and weak in the southern hemisphere and are phased to produce an increase in HNO3 over the 1-year time period of just the right magnitude to more than offset decrease due to settling out of the Pinatubo aerosol. Based on this study, our range of confidence in the CLAES HNO3 V7 product is from 70 to 3 mbar, in comparison with correlative data, and the precision on this range is of the order of 0.3–1.0 ppbv. This precision was derived from data repeatability and agrees within a factor of 2 or better with estimates based on instrument characterization and with error estimates embedded within the V7 data.

Temperature and Composition Measurements from the l.r.i.r. and l.i.m.s. Experiments on Nimbus 6 and 7

The limb radiance inversion radiometer (l.r.i.r.) on Nimbus 6 was the first orbiting infrared limb scanner. It had four channels with which to determine temperature, Oz and H aO in the stratosphere and low mesosphere. The limb infrared monitor of the stratosphere (l.i.m.s.) is a similar six-channel instrument launched on Nimbus 7 in October 1978 to measure temperature, O3, H2O , NO2 and HNO3. The instrumentation and inversion techniques are briefly described. In this method, the outwelling radiance in the 15 pm bands of CO2 is inverted to yield temperatures as a function of pressure; the temperature is then used w ith the radiance emitted by a trace gas to determine its concentration. L.r.i.r. temperature and ozone results show high precision and good agreement with rocket measurements from the tropopause into the mesosphere. Preliminary l.i.m.s. results show that temperatures may be retrieved into the troposphere, and the capability to determine constituent concentrations in the part / 109 range from a satellite for the first time. The application of such data for photochemical dynamical and transport problems is discussed.

Accuracy and precision of cryogenic limb array etalon spectrometer (CLAES) temperature retrievals

The Cryogenic Limb Array Etalon Spectrometer (CLAES) measured emission from the 792 cm−1 Q branch of CO2, from which temperature distributions in the stratosphere and low mesosphere were derived. Here we briefly review the measurement technique, concentrating on aspects that affect the temperature determination. Comparison of many pairs of retrievals at the same location (near 32°N or 32°S) measured on sequential orbits (time separation of 96 min) shows a precision ranging from approximately 0.8 K at 68 mbar to about 3.5 K at 0.2 mbar, which agrees with simulations incorporating random noise and short-period spacecraft motions. Comparisons of globally analyzed CLAES data with National Meteorological Center (NMC) and U.K. Meteorological Office (UKMO) analyses show general agreement, with CLAES tending to be cooler by about 2 K, except in the tropics and high-latitude winter conditions. This is supported by comparisons with individual radiosondes and several lidars that indicate that the agreement is within 2 K throughout the profile (except for a narrow layer around 3 mbar). An error analysis also indicates that systematic errors should be roughly 2 K, independent of altitude. The systematic differences at low latitudes appear to be due to tropical waves, which have vertical wavelengths too short to be seen by the TIROS Operational Vertical Sounder (TOVS) instruments. There are no correlative rocketsondes or lidars to help resolve the reasons for the high-latitude differences. Comparisons with other Upper Atmosphere Research Satellite (UARS) data should shed additional light on this question.

Validation studies using multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol

Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISAMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instrumental biases near 30%, and accuracies between 33 and 43%.