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P. C. Pandey, E. G. Njoku, and J. W. Waters

Abstract

The Scanning Multichannel Microwave Radiometer (SMMR) on the Seasat and Nimbus-7 satellite measured microwave radiation at 6.6, 10.69, 18.0, 21.0 and 37.0 GHz with both horizontal and vertical polarizations. Numerical simulations have been performed to explore the potential of using the 18.0, 21.0 and 37.0 GHZ SMMR channels with simultaneous infrared measurements of cloud top height for retrieving cloud temperature differential and thickness over the ocean. The results suggest it is possible to infer cloud vertical thickness to ∼0.4 km rms accuracy and cloud temperature differential to ∼3°C rms. These accuracies are approximately half the a prior variances.

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D. L. Wu, E. F. Fishbein, W. G. Read, and J. W. Waters

Abstract

The quasi-2-day wave is known as a strong and transient perturbation in the middle and upper atmosphere that often occurs shortly after solstice. The excitation mechanisms of this transient wave have been discussed for years, but no clear answer has yet been attained. In this paper, propagating characteristics of the 2-day wave are studied based on 8-mon temperature measurements from the Microwave Limb Sounder onboard the Upper Atmosphere Research Satellite. The studies are focused on the wave events that happened in January 1993 and in July–August 1993. The observations suggests that winter planetary waves could be responsible for triggering the summer 2-day wave through long penetration into the summer stratosphere. A connection is evident in the evolution of the wave amplitude between the summer 2-day wave generation and winter wave penetration. The data also suggest that the enhancement of the wave amplitude is a manifestation of both a local unstable wave and a global normal-mode Rossby wave.

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G. L. Manney, R. W. Zurek, L. Froidevaux, J. W. Waters, A. O'Neill, and R. Swinbank

Abstract

Trajectory calculations are used to examine ozone transport in the polar winter stratosphere during periods of the Upper Atmosphere Research Satellite (UARS) observations. The value of these calculations for determining mass transport was demonstrated previously using UARS observations of long-lived tracers. In the middle stratosphere, the overall ozone behavior observed by the Microwave Limb Sounder in the polar vortex is reproduced by this purely dynamical model. Calculations show the evolution of ozone in the lower stratosphere during early winter to be dominated by dynamics in December 1992 in the Arctic. Calculations for June 1992 in the Antarctic show evidence of chemical ozone destruction and indicate that ≈ 50% of the chemical destruction may be masked by dynamical effects, mainly diabatic descent, which bring higher ozone into the lower-stratospheric vortex. Estimating differences between calculated and observed fields suggests that dynamical changes masked ≈20%–35% of chemical ozone loss during late February and early March 1993 in the Arctic. In the Antarctic late winter, in late August and early September 1992, below ≈520 K, the evolution of vortex-averaged ozone is entirely dominated by chemical effects; above this level, however, chemical ozone depiction can be partially or completely masked by dynamical effects. Our calculations for 1992 showed that chemical loss was nearly completely compensated by increases due to diabatic descent at 655 K.

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William J. Randel, Fei Wu, James M. Russell III, Aidan Roche, and Joe W. Waters

Abstract

Measurements of stratospheric methane (CH4) and water vapor (H2O) are used to investigate seasonal and interannual variability in stratospheric transport. Data are from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) spanning 1991–97. Profile measurements are binned according to analyzed potential vorticity fields (equivalent latitude mapping), and seasonal cycles are fit using harmonic regression analysis. Methane data from the UARS Cryogenic Limb Array Etalon Spectrometer and water vapor from the Microwave Limb Sounder are also used to fill in winter polar latitudes (where HALOE measurements are unavailable), yielding complete global seasonal cycles. These data reveal well-known seasonal variations with novel detail, including 1) the presence of enhanced latitudinal gradients (mixing barriers) in the subtropics and across the polar vortices, 2) strong descent inside the polar vortices during winter and spring, and 3) vigorous seasonality in the tropical upper stratosphere, related to seasonal upwelling and the semiannual oscillation. The observed variations are in agreement with aspects of the mean meridional circulation derived from stratospheric meteorological analyses. Interannual variations are also investigated, and a majority of the variance is found to be coherent with the equatorial quasibiennial oscillation (QBO). Strong QBO influence is found in the tropical upper stratosphere: the double-peaked “rabbit ears” structure occurs primarily during QBO westerlies. The QBO also modulates the latitudinal position of the tropical “reservoir” in the middle stratosphere.

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Eric A. Ray, James R. Holton, Evan F. Fishbein, Lucien Froidevaux, and J. W. Waters

Abstract

The first two years of MLS temperature and ozone data are used to examine the tropical upper-stratospheric SAO. Time series analysis revealed that the strongest amplitudes of the SAO occurred near the equator at 2 mb for temperature and 5 mb for ozone, consistent with previous observations. The first cycle of each calendar year was observed to have a much higher amplitude than the second cycle except for the warm phase in late 1991. Interannual variability in the strength of the SAO, such as the much stronger warm phase of late 1991 as compared to late 1992, was significant and could be partly attributed to the QBO in zonal wind.

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J. W. Waters, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, and D. H. Staelin

Abstract

This article discusses remote sensing of atmospheric temperatures with the NEMS microwave spectrometer on the Nimbus 5 satellite, and the accuracy with which atmospheric temperatures can be determined by NEMS. The sensitivity of the NEMS instrument allows measurement of temperature profiles having vertical resolution of the respective NEMS weighting functions (∼10 km) with an rms accuracy of a few tenths of a degree Kelvin for a 16 s integration time. The accuracy of NEMS in estimating atmospheric temperatures at the discrete levels (∼2 km vertical resolution in the lower troposphere) used in the operational numerical model of the National Meteorological Center (NMC) is ∼2 K rms, as determined by comparing NEMS results with ground truth data obtained from the NMC operational analysis and from coincident radiosondes. These accuracies are consistent with the theoretical accuracies expected for NEMS.

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D. H. Staelin, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, R. W. Wilcox, and J. W. Waters

Abstract

The passive microwave spectrometer on the Nimbus 5 satellite has two channels that measure atmospheric water vapor and liquid water abundances over ocean. Observed water vapor abundances range up to 6 g cm−2 and differ from nearby radiosondes by ∼0.4 g cm−2. Average liquid water abundances over a 300 km observation zone range from −0.01 to 0.2 g cm−2, and have an rms error estimated to be ∼0.01 g cm−2 for most circumstances. These quantitative measurements can be used to construct global maps or to accumulate global statistics.

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D. R. Allen, J. L. Stanford, L. S. Elson, E. F. Fishbein, L. Froidevaux, and J. W. Waters

Abstract

The “4-day wave” is an eastward moving quasi-nondispersive feature with period near 4 days occurring near the winter polar stratopause. This paper presents evidence of the 4-day feature in Microwave Limb Sounder (MLS) temperature, geopotential height, and ozone data from the late southern winters of 1992 and 1993. Space–time spectral analyses reveal a double-peaked temperature structure consisting of one peak near the stratopause and another in the lower mesosphere, with an out-of-phase relationship between the two peaks. This double-peaked structure is reminiscent of recent three-dimensional barotropic/baroclinic instability model predictions and is observed here for the first time. The height variation of the 4-day ozone signal is shown to compare well with a linear advective–photochemical tracer model. Negative regions of quasigeostrophic potential vorticity (PV) gradient and positive Eliassen–Palm flux divergence are shown to occur, consistent with instability dynamics playing a role in wave forcing. Spectral analyses of PV derived from MLS geopotential height fields reveal a 4-day signal peaking near the polar stratopause. The three-dimensional structure of the 4-day wave resembles the potential vorticity “charge” concept, wherein a PV anomaly in the atmosphere (analogous to an electrical charge in a dielectric material) induces a geopotential field, a vertically oriented temperature dipole, and circulation about the vertical axis.

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G.L. Manney, R.W. Zurek, W.A. Lahoz, R.S. Harwood, J.C. Gille, J.B. Kumer, J.L. Mergenthaler, A.E. Roche, A. O'Neill, R. Swinbank, and J.W. Waters

Abstract

The transport of passive tracers observed by the Upper Atmosphere Research Satellite is simulated using computed three-dimensional trajectories of ≈ 100 000 air parcels initialized on a stratosphere grid, with horizontal winds provided by the United Kingdom Meteorological Office data assimilation system, and vertical (cross isentropic) velocities computed using a fast radiation code. The conservative evolution of trace constituent fields is estimated over 20–30-day periods by assigning to each parcel the observed mixing ratio of the long-lived trace gases N20 and CH4 observed by the Cryogenic Limb Army Etalon Spectrometer (CLAES) and H2O observed by the Microwave Limb Sounder (MLS) on the initialization date. Agreement between calculated and observed fields is best inside the polar vortex and is better in the Arctic than in the Antarctic. Although there is not always detailed agreement outside the vortex, the trajectory calculations still reproduce the average large-scale characteristics of passive tracer evolution in midlatitudes. In late winter, synoptic maps from trajectory calculations reproduce all major features of the observations, including large tongues or blobs of material drawn from low latitudes into the region of the anticyclone during February–March 1993. Comparison of lower-stratospheric observations of the CLAES tracers with the calculations suggests that discontinuities seen in CLAES data in the Antarctic late winter lower stratosphere are inconsistent with passive tracer behavior. In the Arctic, and in the Antarctic late winter, MLS H20 observations show behavior that is inconsistent with calculations and with that expected for passive tracers inside the polar vortex in the middle-to-upper stratosphere. Diabatic descent rates in the Arctic lower stratosphere deduced from data are consistent with those from the calculations. In the Antarctic lower stratosphere, the calculations appear to underestimate the diabatic descent. The agreement between large-scale features of calculated and observed tracer fields supports the utility of these calculations in diagnosing trace species transport in the winter polar vortex.

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W. G. Read, J. W. Waters, D. A. Flower, L. Froidevaux, R. F. Jarnot, D. L. Hartmann, R. S. Harwood, and R. B. Rood

Initial results of upper-tropospheric water vapor obtained from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) are presented. MLS is less affected by clouds than infrared or visible techniques, and the UARS orbit provides daily humidity monitoring for approximately two-thirds of the earth. Best results are currently obtained when water vapor abundances are approximately 100–300 ppmv, corresponding to approximately 12-km height in the Tropics and 7 km at high latitudes. The observed latitude variation of water vapor at 215 hPa is in good agreement with the U.K. Universities's Global Atmospheric Modelling Project model. The ability to observe synoptic-scale features associated with tropopause height variations is clearly illustrated by comparison with the National Aeronautics and Space Administration Goddard Space Flight Center assimilation model. Humidity detrainment streams extending from tropical convective regions are also observed.

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