New high-speed photometry of EH Lib and a binary interpretation of its period change

Six times of maxima of the ultrashort-period cepheid variable EH Librae were measured in 1980 May to June and in 1981 January, with a three-channel photocounting high-speed photoelectric photometer. These, together with all the photoelectric times of maxima over the past 30 years, are used to re-examine the nature of the change of the period. We found that we can fix the times of maxima by the following formula

$\text{T}{}_{\max }\text{= T}{}_0\text{+P}{}_0\text{E+}\text{1}\text{2}\text{βE}{}^2\text{+A}\text{sin}\text{2π}\text{EP}{}_0\text{E}{}_0$

where T₀ = HJD 2433438.6088 and P₀ = 0.0884132445 d represent the initial maximum epoch and the pulsation period, β = ?2.8 × 10^?8/yr; A = 0.0015 d, P₀ = 6251 d = 17.1 yr are the semi-amplitude and the period of the sine curve, and E is the number of periods elapsed since T₀, and (E₀ = 70700).If we interpret this 17.1 year periodicity as a modulation of the phase of maximum by binary motion, then the semi-amplitude of the orbital radial velocity variation is K = 2πasini/E₀ = 0.45 km/s and the mass function is

$\text{f(m)=}\text{m}{}^3{}_2\text{sin}{}^3\text{i}\text{(m}{}_1\text{m}{}_2\text{)}{}^2\text{=}\text{(a}\text{sin}\text{i)}{}^3\text{E}{}^2{}_0\text{=6 x 10}{}^{\mathrm{?5}}\text{M}{}_{\mathrm{\odot }}$

     

Comparison of Quasi-specular radar scatter from the moon with surface parameters obtained from images

Quasi-specular radar data used to determine apparent surface roughness σ_χ of geologic surfaces displays a variable wavelength λ dependence ranging between $\text{σ}{}_{\mathrm{\chi }}\text{～ λ}{}^0\text{and}\text{σ}{}_{\mathrm{\chi }}\text{～ λ}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ for $\text{0.01 ? λ ? 1}\text{m}$. The strongest changes in σ_χ with wavelength are observed in lunar mare, while scatter from lunar highlands is nearly wavelength independent. Commonly used, gently undulating surface models for electromagnetic scatter predict no wavelength dependence. Wavelength dependence occurs whenever a significant fraction of the surface has local radii of curvature comparable to the observing wavelength. This condition can be determined by comparison of the value of the integrated surface curvature spectrum with the radar wavenumber, multiplied by a constant that depends on the geometry. Variations in curvature statistics calculated from photogrammetric reduction of lunar images are consistent with the observed variations in quasi-specular scatter between λ = 13 and 116 cm at the same locations. Variations in the strength of the wavelength dependence are correlated with the sizes of lunar craters that lie near the upper size limit for the local steady-state distribution. This correlation is also consistent with variations in the curvature spectrum calculated from crater size-frequency distributions.     

Small-scale turbulence in the atmosphere of Venus

Previous studies based on radio scintillation measurements of the atmosphere of Venus have identified two regions of small-scale temperature fluctuations located in the vicinity of 45 and 60 km. A global study of the fluctuations near 60 km, which are consistent with wind-shear-generated turbulence, was conducted using the Pioneer Venus measurements. The structure constants of refractive index fluctuations c_n² and temperature fluctuations c_T² increase poleward, peak near 70° latitude, and decrease over the pole; c_n² varies from 2 × 10^?15 to 1.5 × 10^?14m^{$\text{2}\text{3}$} and c_T² from 4 × 10^?3 to 7 × 10^?2°K²m^{$\text{?2}\text{3}$}. These results indicate greater turbulent activity at the higher latitudes. In the region near 45 km the refractive index fluctuations and the corresponding temperature fluctuations are substantially lower. Based on the analysis of one representative occultation measurement, $\text{c}{}_{\mathrm{<mtext>n</mtext>}}{}^2\text{= 2 × 10}{}^{\mathrm{?16}}\text{m}{}^{\mathrm{<mtext>?2</mtext><mtext>3</mtext>}}\text{and}\text{c}{}_{\mathrm{<mtext>T</mtext>}}{}^2\text{= 7.3 × 10}{}^{\mathrm{?4}}\text{°}\text{K}{}^2\text{m}{}^{\mathrm{<mtext>?2</mtext><mtext>3</mtext>}}$ in the 45-km region. The fluctuations in this region also appear to be consistent with wind-shear-generated turbulence. The turbulence level is considerably weaker than that at 60 km; the energy dissipation rate ε is 4.9 × 10^?5m²sec^?3 and the small-scale eddy diffusion coefficient K is 2 × 10³ cm² sec^?1.     

On the latitude dependence of the semidiurnal anisotropy of cosmic rays

The expected diurnal waves with different harmonics in cosmic ray intensity arising from the semidiurnal anisotropy, due to the geometrical inclination of the Earth's axis, are calculated for different cosmic ray stations. The sensitivity of these waves to the exponent n of the latitude dependence function cosⁿ λ for the semidiurnal anisotropy is investigated. The amplitudes of the geometrical tridiurnal waves for high latitude stations show a great sensitivity to n and, therefore, it is concluded that its value can be determined precisely from the tridiurnal wave rather than from the semidiurnal waves observed at different latitudes. Available data from high latitude neutron monitors were used to determine n and it was found as 2±0.4, which is of higher accuracy than the previously determined values. The present results are consistent with either the density gradient or loss cone models of the semidiurnal anisotropy. Furthermore, they show that the geometrical tridiurnal waves have a very small amplitude and can be neglected in any analysis concerning tridiurnal variations in cosmic ray intensity.     

Laboratory measurements of the microwave opacity of sulfur dioxide and other cloud-related gases under simulated conditions for the middle atmosphere of Venus

Recent papers attributing the observed microwave opacity of the middle atmosphere of Venus to gaseous sulfur dioxide (SO₂) and other cloud-related gases have motivated laboratory measurements of their microwave absorbing properties under simulated conditions for this region. In the pressure range from 1 to 5 atmospheres and in the temperature range from 297 to 355°K, the absorption of SO₂ in a carbon dioxide (CO₂) atmosphere, at 2.257 and 8.342 GHz, has been found to be approximately 50% larger than that calculated from Van Vleck-Weisskopf theory. The measured absorption is about $\text{25 × 10}{}^6\text{q?}{}^2\text{p}{}^{1.20}\text{T}{}^{\mathrm{?3.1}}\text{(}\text{dB km}{}^{\mathrm{?1}}\text{)}$, where q is the sulfur dioxide number mixing ratio, ? is frequency in gigahertz, p is pressure in atmospheres, and T is temperature in degrees Kelvin. This represents the best-fit expression to the observed pressure dependence, while theoretical values of frequency and temperature dependence are accepted as being consistent with the measurements. Another cloud-related gas, sulfur trioxide (SO₃), was also tested in a CO₂ atmosphere and found to be relatively transparent. These results reduce the amount of SO₂ in the Venus middle atmosphere required to explain the opacity measured by radio occulatation, but this amount still exceeds the abundance measured in situ by atmospheric probes, suggesting that there must be another important source of opacity. Preliminary measurements of the 13-cm absorptivity of gaseous sulfuric acid (H₂SO₄) show it to be a strong microwave absorber, and thus likely to be responsible for a significant and possibly major part of the observed opacity.     

On the exponential decay of western hemisphere solar particle events

Numerical solutions of the Fokker-Planck equation governing the transport of solar protons are obtained in three dimensions (time t, radial distance r, energy T) with the diffusion coefficient represented by κ = κ₀r^bT^a. The October 4, 1968, solar flare particle event is re-examined, and the rise and decay of the proton flux profiles for > 10, ;30 and > 60 MeV particles can be reasonably well reproduced with an instantaneous injection and a distant (10 AU) free escape boundary. The best fit is achieved with a diffusion coefficient $\text{κ = 1.4 × 10}{}^{20}\text{r}{}^{0.5}\text{T}{}^{0.75}\text{cm}{}^2\text{sec}$ where r is in AU and T in MeV.     

Temperature variation of the plasma sheet during substorms

The temperature and density of the plasma in the Earth's distant plasma sheet at the downstream distances of about 20–25 R_e are examined during a high geomagnetic disturbance period. It is shown that the plasma sheet cools when magnetospheric substorm expansion is indicated by the AE index. During cooling, the plasma sheet temperature, T, and the number density, N, are related by $\text{T ∝ N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ (adiabatic process) in some instances, while by T ∝ N^?1 (isobaric process) in other cases. The total plasma and magnetic pressure decreases when $\text{T ∝ N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ and increases when T ∝ N^?1. Observation also indicates that the dawn-dusk component of plasma flow is frequently large and comparable to the sunward-tailward flow component near the central plasma sheet during substorms.     

The influence of a flow field on the stability of the force-free magnetic field

In order to analyse the convective instability of the force-free magnetic field, an exact solution of the MHD equation for the magnetic field (1) together with the flow field (2) of constant speed V₀ making an angle θ with the magnetic field, was chosen as the unperturbed state. The stability of the fields between two parallel conducting walls of seperation d was studied by a linear perturbation method, which led to the eigenvalue problem (12), X being given by (13). It was shown by an approximate variational method that instability will set in by the flow field if V₀ is greater than 1/ $\text{3}$ times Alfven velocity V_A. For , the stability of the force-free field (1) is not influenced by the flow field, which may still be significant in other respects. Perturbations transverse to the magnetic field were found to be the most unstable modes.     

Love numbers of the giant planets

We calculate the Love numbers k_n for n = 2 to 10, and determine the “gravitational noise” from tides. The new values k₂ for Jupiter, Saturn, and Uranus yield new estimates for the planetary dissipation functions: $\text{Q}{}_{\mathrm{<mtext>J</mtext>}}\text{? 2.5 × 10}{}^4$, $\text{Q}{}_{\mathrm{<mtext>S</mtext>}}\text{? 1.4 × 10}{}^4\text{, Q}{}_{\mathrm{<mtext>U</mtext>}}\text{? 5 × 10}{}^3$.     

Linewidth studies on the NI(4S−4P) resonance multiplet

We have measured the linewidths of the NI multiplets $\text{[2p}{}^2\text{3p}{}^4\text{D}{}^0\text{?2p}{}^2\text{3s}{}^4\text{P, λ8691}\text{A}\text{?}\text{; 2p}{}^2\text{3p}{}^4\text{P}{}^0\text{?2p}{}^2\text{3s}{}^4\text{P, λ8212}\text{A}\text{?}\text{; 2p}{}^2\text{3s}{}^4\text{P?2p}{}^3{}^4\text{S}{}^0\text{, λ1200}\text{A}\text{?}\text{]}$ produced in the dissociative excitation of N₂ by energy electrons. The infrared transitions excite the N(⁴P) resonance state by cascade and they account for > 50% of the total N(⁴P) cross section at 100 eV. Both the i.r. and v.u.v. lines are found to be highly Doppler broadened ( ～ 25 times the thermal Doppler line width). These results indicate that dissociative excitation of N₂ produces N (⁴P) atoms with sufficient kinetic energy so that the $\text{λ1200}\text{A}\text{?}$ resonance radiation $\text{[2p}{}^2\text{3s}{}^4\text{P ?2p}{}^3{}^4\text{S}{}^0\text{]}$ emitted by these excited atoms would be optically thin in the Earth's upper atmosphere. We also found that the line strength ratios for the resolved components of the $\text{λ1200}\text{A}\text{?}$ triplet excited by dissociative excitation differ from those predicted by the multiplicities of the states involved and used in current entrapment models; the intensity ratios also vary with the energy of the incident electron. These developments introduce new complications into the analysis of the terrestrial ultraviolet dayglow.     

Substorm energy

It is shown that the area A_k(× 10⁶km²) covered by brightest auroras and the area A_q bounded by the auroral oval have a simple relation given by

$\text{A}{}_{\mathrm{k}}\text{= 0.05(A}{}_{\mathrm{q}}\text{? A}{}_0\text{)}{}^2$

, where A₀ denotes the area of the minimum size oval and the quantity (A_q ? A₀)² is proportional to the energy ε_q which is stored in the magnetotail and is available for substorms. Following the definition of the intensity of solar flares, A_k may be chosen as a measure of the intensity of substorms. It is also found that the joule heat energy produced by the auroral electrojet is also proportional to (A_q ? A₀)². Thus, it may be concluded that the intensity of substorms is proportional to the energy ε_q stored in the magnetotail.     

Total current to cylindrical collectors in collisionless plasma flow

A theory is presented for charged-particle collection by a cylindrical conducting object, such as a spacecraft or an electrostatic probe, which is moving transversely through a collisionless plasma, such as those in the upper atmosphere and space. The calculation is approximate, using symmetric potential profiles which are exact for the infinite-cylinder stationary case. Theoretical current predictions are presented for ratios of collector potential to electron thermal energy eφ_c/kT_e from 0 to ?25, for ion-to-electron temperature ratios T_i/T_c = 1 and 0.5, ratio of collector radius to electron Debye length r_c/λ_D from 0 to 100, and ratio of flow speed to ion thermal speed $\text{S}{}_{\mathrm{i}}\text{= U/(2kT}{}_{\mathrm{i}}\text{/m}{}_{\mathrm{i}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$ from 0 to 10. Comparisons with existing exact calculations by other authors show that none of these fulfil all of the requirements for nontrivial comparison. Appropriate parameter ranges for future exact calculations are thereby suggested. These are as follows: (a) r_c/λ_D should be large enough that the collector not be in or near orbit-limited conditions; (b) the ratio $\text{S}{}_{\mathrm{i}}{}^2\text{/¦χ}{}_{\mathrm{c,\; i}}\text{¦}$ of ion directed energy to potential energy change in the sheath, should be close to unity or if

$\text{S}{}_{\mathrm{i}}{}^2\text{/¦χ}{}_{\mathrm{c,i}}\text{¦? 1,}\text{then}\text{S}{}_{\mathrm{i}}\text{? 1}$

.     

Characteristics of localized resonance coupling oscillations of the slow magnetosonic wave in a non-uniform plasma

We analyze linear resonance oscillations in a non-uniform one-fluid finite-β plasma, which is oversimplified to understand easily fundamental characteristics of the resonance oscillations. A linear resonance oscillation of localized slow magnetosonic mode $\text{[ω}{}^2{}_{\mathrm{s}}\text{=}\text{ω}{}^2{}_{\mathrm{A}}\text{(1 +}\text{V}{}^2{}_{\mathrm{A}}\text{V}{}^2{}_{\mathrm{s}}\text{)}\text{]}$, which has the diamagnetic property in a uniform plasma, is newly found to be excited in the radially non-uniform plasma. The localized slow resonance indicates a radially polarized compressional oscillation (δB_∥ ? δB_H ? δB_D). The sense of the Alfvénic polarizations in the H-D plane near the resonant point is a function of both the propagation in the azimuthal direction and the slope of wave amplitude in the radial direction, whereas the sense of the resonant slow magnetosonic polarizations changes in accordance only with the switch in the azimuthal propagation direction. Further multi-satellite studies are necessary to establish the resonant structures of the slow magnetosonic waves in the magnetosphere.     

Pitch angle dependence of the charge-exchange lifetime of ring current ions

Previous work has parameterized the pitch angle dependence of the charge-exchange lifetime τ of ring current ions in terms of γ, the power of the cosine of the mirror latitude λ_m of the particles, such that $\text{τ(λ}{}_{\mathrm{m}}\text{)}\text{τ(0) ≌}\text{cos}{}^{\mathrm{\gamma }}\text{λ}{}_{\mathrm{m}}$ at given L. Using the atomic hydrogen density model of Johnson and Fish, previous authors have suggested values of γ = 5 or 6. We here evaluate γ as a function of λ_m and L using the more recent Chamberlain density models, and show that γ = 3?4 is more appropriate over most of the pitch angle and L range. Consequently, ion distributions in the ring current decay phase are expected to become rather less anisotropic in pitch angle due to chargeexchange than previously believed. We have also investigated the use of several other simple approximate analytic forms for $\text{τ(λ}{}_{\mathrm{m}}\text{)}\text{τ(0)}$, one of which gives far better agreement with the numerical results than the cos^γ λ_m, variation, and should hence be used in future studies.     

Thinning of the near-earth (10∼15 RE) plasma sheet preceding the substorm expansion phase

The timing of the plasma-sheet thinning relative to the onset of the expansion phase of substorms is examined by the analysis of the OGO 5 electron (79 ± 23 keV) and proton (100～150 keV) data with the aid of simultaneous magnetic field observations. It is found that the timing of the thinning is significantly dependent on the distance. At $\text{x}{}^2\text{+ y}{}^2\text{? 15 R}{}_{\mathrm{E}}$ the thinning often starts before the onset, while at $\text{x}{}^2\text{+ y}{}^2\text{? 15 R}{}_{\mathrm{E}}$ it tends to occur after the onset, where x and y refer to solar magnetospheric coordinates. The thinning that precedes the expansion-phase onset has been found to reduce the thickness to ～1 R_E, and further thinning may occur in a spatially limited region. Hence it is conceivable that the formation of the neutral line characterizing the substorm expansion phase is the consequence of the thinning of the plasma sheet in the near-Earth region.     

Observations and interpretation of spectra and rapid time variations of type-B aurora

Observations of type-B red and normal aurora were made with a high-speed multichannel photometer and a digital grating spectrometer. The ratio $\text{I}\text{(}\text{O}{}_2{}^{\mathrm{+}}\text{1N; 2, 0 + 3, 1)}\text{I}\text{(}\text{N}{}_2{}^{\mathrm{+}}\text{1N; 0, 3)}$ measured in the 5200–5300 Å region with the spectrometer was found to increase by about 16% from normal to type-B aurora. This small change is difficult to reconcile with a height below 90 km for the red border. In the type-B aurora, λ 5577 was weakened by a factor between 1.9 and 3.8 while the ratio $\text{I}\text{(}\text{N}{}_2\text{1P; 5, 2)}\text{I}\text{(}\text{N}{}_2{}^{\mathrm{+}}\text{1N)}$ was enhanced less than 20%. Rapid intensity variations in the type-B lower border were observed in the λ 5577 and other channels of the photometer. A revised time dependent auroral excitation-ion chemistry model is used in an attempt to reproduce the observations. The observed weakening of λ 5577 could be produced at heights equal to or less than 100 km while the short observed time lag of λ 5577 on the N₂⁺ 1N emission is easier to explain at 100 km than at 80 km. It is concluded that some type-B lower borders may occur near 100 km although it is recognized that there is good evidence rare deep crimson lower borders lie at 80 km or below. The mechanism for the excitation of O(¹S) is considered in the light of these results. None of the mechanisms examined is satisfactory on the basis of currently accepted atmospheric models and quenching rate coefficients.     

The locating of hydromagnetic whistler sources and determination of their generating proton spectra

Results are given of the calculations of the group delay time propagating τ(ω, φ₀) of hydromagnetic whistlers, using outer ionospheric models closely resembling actual conditions. The τ(ω, φ₀) dependencies were compared with the experimental data of τ_exp(ω, φ₀) obtained from sonagrams. The sonagrams were recorded in the frequency range $\text{? ? (0.5?2.5) Hz}$ at observation points located at geomagnetic latitudes φ₀ = (53?66)° and in the vicinity of the geomagnetic poles. This investigation has led us to new and important conclusions.The wave packets (W.P.) forming hydromagnetic whistlers (H.W.) are mainly generated in the plasma regions at L = 3.5?4.0. This is not consistent with ideas already expressed in the literature that their generation region is $\text{L ? 3?10}$. The overwhelming majority of the τ_exp values differ considerably from the times at which wave packets would, in theory, propagate along the magnetic field lines corresponding to those of the geomagnetic latitudes φ₀ of the observation points. The second important fact is that the W.P. frequency ω is less than $\text{Ω}{}_{\mathrm{H}}$ everywhere along its propagation trajectory, including the apogee of the magnetic force line ($\text{Ω}{}_{\mathrm{H}}$ is the proton gyrofrequency). Proton flux spectra $\text{E ? (30?120)}$ keV, responsible for H.W. generation, were determined. Comparison of the Explorer-45 and OGO-3 measurements published in the literature, with our data, showed that the proton flux density energy responsible for the H.W. excitation $\text{N}{}_{\mathrm{p}}\text{(}\text{MV}{}_6{}^2\text{2}\text{) ? (5 × 10}{}^{\mathrm{?3}}\text{?10}{}^{\mathrm{?1}}\text{)}\text{H}{}_{\mathrm{a}}{}^2\text{8π}$ where H_a is the magnetic field force in the generation region of these W.P. The electron concentration is $\text{N}{}_{\mathrm{a}}\text{? (10}{}^2\text{?10}{}^3\text{) cm}{}^{\mathrm{?3}}$. The values given in the literature are $\text{N}{}_{\mathrm{a}}\text{? (10}{}^{\mathrm{?10}}\text{?10}{}^3\text{) cm}{}^{\mathrm{?3}}$. The e data considered also leads to the conclusion that the generating mechanism of the W.P. studied probably always co-exists with the mechanism of their amplification.     

Quenching of O+(2D) by electrons in the thermosphere

A major loss process for the metastable species, O⁺(²D), in the thermosphere is quenching by electrons

$\text{O}{}^{\mathrm{+}}\text{(}{}^2\text{D) + e → O}{}^{\mathrm{+}}\text{(}{}^4\text{S) + e}$

.To date no laboratory measurement exists for the rate coefficient of this reaction. Thermospheric models involving this process have thus depended on a theoretically calculated value for the rate coefficient and its variation with electron temperature. Earlier studies of the O⁺(²D) ion based on the Atmosphere Explorer data gathered near solar minimum, could not quantify this process. However, Atmosphere Explorer measurements made during 1978 exhibit electron densities that are significantly enhanced over those occurring in 1974, due to the large increases that have occurred in the solar extreme ultraviolet flux. Under such conditions, for altitudes ? 280 km, the electron quenching process becomes the major loss mechanism for O⁺(²D), and the chemistry of the N⁺₂ ion, from which the O⁺(²D) density is deduced, simplifies to well determined processes. We are thus able to use the in situ satellite measurements made during 1978 to derive the electron quenching rate coefficient. The results confirm the absolute magnitude of the theoretical calculation of the rate coefficient, given by the analytical expression k(T_e) = 7.8 × 10^?8 (T_e/300)^?0.5cm³s^?1. There is an indication of a stronger temperature dependence, but the agreement is within the error of measurement.     

Branching ratios for the photoionization cross section of atomic oxygen

Branching ratios $\text{σ(}\text{O}{}^0{}^3\text{P}\text{→}\text{O}{}^{\mathrm{+}}{}^2\text{D}{}^0\text{)}\text{σ(}\text{O}{}^0{}^3\text{P}\text{→}\text{O}{}^{\mathrm{+}}{}^4\text{S}{}^0\text{)}$ and $\text{σ(}\text{O}{}^0{}^3\text{P}\text{→}\text{O}{}^{\mathrm{+}}{}^2\text{P}{}^0\text{)}\text{σ (}\text{O}{}^0{}^3\text{P}\text{→}{}^4\text{S}{}^0\text{)}$ are calculated at 584 Å and 304 A employing the close-coupling approximation to compute the photoionization cross section values. The coupled channels include the states dominated by the ground configuration 1s²2s²p³ of O⁺and the next excited configuration ls²2s2p⁴. It is found that the partial c section $\text{σ(}{}^2\text{D}{}^0\text{)}$ decreases more rapidly than $\text{σ(}{}^2\text{P}{}^0\text{)}$, and at the lower wavelength 304 Å, the ratio $\text{σ(}{}^2\text{D}{}^0\text{)}\text{σ(}{}^4\text{S}{}^0\text{)}\text{<}\text{σ(}{}^2\text{P}{}^0\text{)}\text{σ(}{}^4\text{S}{}^0\text{)}$. Present results at 304 Å differ considerably from previous work.     

Laboratory measurements of the microwave opacity and vapor pressure of sulfuric acid vapor under simulated conditions for the middle atmosphere of Venus

Microwave absorption observed in the 35- to 48-km-altitude region of the Venus atmosphere has been attributed to the presence of gaseous sulfuric acid (H₂SO₄) in that region. This has motivated the laboratory measurement of the microwave absorption at 13.4- and 3.6-cm wavelengths from gaseous H₂SO₄ in a CO₂ atmosphere under simulated conditions for that region. As part of the same experiments, upper limits on the saturation vapor pressure of gaseous H₂SO₄ have also been determined. The measurements for microwave absorption have been made in the 1- to 6-atm pressure range, with temperatures in the 500 to 575°K range. Using a theoretically derived temperature dependence, the best-fit expression for absorption from gaseous H₂SO₄ in a CO₂ atmosphere at the 13.4-cm wavelength is $\text{9.0 × 10}{}^9\text{q(P)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{T}{}^{\mathrm{?3}}\text{(}\text{dB km}{}^{\mathrm{?1}}\text{),}\text{where}\text{q}$ is the H₂SO₄ number mixing ratio, P is the pressure in atmospheres, and T is the temperature in degrees Kelvins. The best-fit expression for absorption at the 3.6-cm wavelength is 4.52 × 10¹⁰q(P)^0.85T^?3 (dB km^?1). The inferred H₂SO₄ vapor pressure above liquid H₂SO₄ corresponds to ln p = 8.84 ? 7220/t where p is the H₂SO₄ vapor pressure (in atm) and T is the temperature in degrees Kelvins. These results suggest that abundances of gaseous H₂SO₄ on the order of 15 to 30 ppm could account for the microwave absorption observed by radio occultation experiments at 13.3- and 3.6-cm wavelengths. They also suggest that such abundances would correspond to saturation vapor pressure existing at or above the 46- to 48-km range, which correlates with the observed cloud base. It is suggested that future measurements of absorption in the 1- to 3-cm wavelength range will provide additional tools for monitoring variations in H₂SO₄ abundance via radio occultation and radio astronomical observations.