Francisco P. J. Valero

Heating Rates in Tropical Anvils

Abstract The interaction of infrared and solar radiation with tropical cirrus anvils is addressed. Optical properties of the anvils are inferred from satellite observations and from high-altitude aircraft measurements. An infrared multiple-scattering model is used to compute heating rates in tropical anvils. Layer-average heating rates in 2 km thick anvils were found to be on the order of 20 to 30°K day−1. The difference between heating rates at cloud bottom and cloud top ranges from 30 to 200°K day−1, leading to convective instability in the anvil. The calculations are most sensitive to the assumed ice water content, but also are affected by the vertical distribution of ice water content and by the anvil thickness. Solar heating in anvils is shown to be less important than infrared hearing but not negligible The dynamical implications of the computed heating rates are also explored and we conclude that the heating may have important consequences for upward mass transport in the tropics. The potential imp...

Characterization of Thermal Effects in Pyranometers: A Data Correction Algorithm for Improved Measurement of Surface Insolation

Abstract Pyranometers are reliable, economical radiometers commonly used to measure solar irradiances at the surface in a long-term, monitoring mode. This paper presents a discussion of the response of these instruments to varying environmental conditions, including the magnitude and variability of the irradiance being measured. It is found that different conditions, commonly occurring in field experiments, affect the thermal balance and temperature gradients within the instrument in a variety of ways. Such an effect results in variable offset systematic errors whose origin and magnitude are investigated in laboratory and field experiments. It is shown that these offset errors are proportional to the difference between the fourth power of the dome and detector temperatures, following closely the Stefan–Boltzmann radiation law. Results of field experiments are presented for daytime and nighttime operation over a variety of atmospheric conditions ranging from clear to heavy overcast and rain. All measuremen...

A Validation of a Satellite Cloud Retrieval during ASTEX

Abstract An algorithm using NOAA-12 AVHRR (Advanced Very High Resolution Radiometer) solar reflectance measurements for retrieving cloud droplet size and optical thickness has been applied to a boundary layer stratocumulus cloud in the vicinity of the Azores on 12 June 1992 during the Atlantic Stratocumulus Transition Experiment (ASTEX). This day was particularly advantageous for validations because of the absence of cirrus or other higher-level clouds during the satellite overpass and the existence of a large relatively uniform stratus cloud dock. Uncertainty estimates for the retrievals are presented along with a discussion of the algorithm. An in-flight absolute calibration of AVHRR channel 1, necessary for accurate optical thickness retrievals, was done concurrently with the retrievals through comparison with a visible radiometer flown on the National Aeronautics and Space Administrations ER-2 and using the stratus cloud as the common reflectance target. Results are compared with in situ microphysica...

Latitudinal survey of spectral optical depths of the Pinatubo volcanic cloud - Derived particle sizes, columnar mass loadings, and effects on planetary albedo

We have made airborne measurements of spectral optical depths, radiative fluxes, and scattered radiation fields during the NASA Caribbean mission (July 7–14, 1991) to characterize the Pinatubo volcanic cloud. In this paper we report the latitudinal and spectral dependence of the volcanic clouds optical depth. From these measurements we determine moments of the particle size distribution. The change in planetary albedo induced by the volcanic cloud is calculated for the range of measured optical depths with the objective of assessing the impact on the solar radiation budget. Mid-visible optical depths higher than 0.4 were observed, placing the Pinatubo stratospheric cloud among the thickest ever measured. The latitudinal distribution of extinction shows that by July 7, 1991 the volcanic cloud had extended to 30°N. The effective particle radius was determined to be between 0.18 μm and 035 μm with a corresponding columnar mass loading between 35 and 80 mg.m−2.

Cirrus Microphysics and Radiative Transfer: Cloud Field Study on 28 October 1986

Abstract Cloud data acquired during the cirrus intensive field operation of FIRE 86 are analyzed for a 75 × 50-km2 cirrus cloud field that passed over Wausau, Wisconsin, during the morning of 28 October 1986. Remote-sensing measurements from the stratosphere and the ground detect an inhomogeneous cloud structure between 6 and 11 km in altitude. The measurements differentiate between an optically thicker (τ > 3) cirrus deck characterized by sheared precipitation trails and an optically thinner (τ < 2) cirrus cloud field in which individual cells of liquid water are imbedded. Simultaneous measurements of particle-size spectra and broadband radiative fluxes at multiple altitudes in the lower half of the cloud provide the basis for a comparison between measured and calculated fluxes. The calculated fluxes are derived from observations of cloud-particle-size distributions, cloud structure, and atmospheric conditions. Comparison of the modeled fluxes with the measurements shows that the model results underestim...

Measurement at different temperatures of absolute intensities, line half-widths, and broadening by Ar and N2 for the 3001II←0000 band of CO2

Abstract Absolute intensities, self-broadening coefficients, and foreign-gas broadening by Ar and N 2 were measured at temperatures of 197, 233 and 294 K for the 30 0 1 II ←00 0 0 band of CO 2 at 6348 cm -1 . Also, the intensity parameters and total band intensity were calculated. We obtained for the vibration-rotation interaction factor the value F ( m ) = 1 + (0.26 ± 0.06) × 10 -2 m + (0.92 ±0.32 × 10 -4 m 2 ; for the purely vibrational transition moment, we found ¦ R 00 0 0 30 0 1 II ¦к(0.4351 ± 0.0014)()10 b3 debye; and, for the total band intensity at STP conditions, S band (30 0 1 II ←00 0 0) STP = 1255 ± 9 cm -1 km -1 atm -1 . Self-broadening coefficients at 197 and 294 K were also measured, as well as broadening by Ar and N 2 . Foreign-gas-broadening efficiencies (Ar and N 2 ) were determined. Finally, a comparison is made with measurements by other authors and with theoretically calculated values.

Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) : Experimental and data details

Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) was conducted to study the magnitude and spectral characteristics of the absorption of solar radiation by the clear and cloudy atmosphere. Three aircraft platforms, a Grob Egrett, a NASA ER-2, and a Twin Otter, were used during ARESE in conjunction with the Atmospheric Radiation Measurements (ARM) central and extended facilities in north central Oklahoma. The aircraft were coordinated to simultaneously measure solar irradiances in the total spectral broadband (0.224-3.91 μm), near infrared broadband (0.678-3.3 μm), and in seven narrow band-pass (∼10 nm width) channels centered at 0.500, 0.862, 1.064, 1.249, 1.501, 1.651, and 1.750 μm. Instrumental calibration issues are discussed in some detail, in particular radiometric power, angular, and spectral responses. The data discussed in this paper are available at the ARM ARESE data archive via anonymous FTP to ftp.arm.gov.

Nitric-acid band intensities and band-model parameters from 610 to 1760 cm −1

A set of 59 spectra of pure nitric acid was obtained at temperatures ranging from 236 to 294 K using path lengths from 10 to 50 cm and pressures from 0.05 to 1.1 Torr. No strong temperature dependencies were observed over the range of our measurements. Absorption coefficients and mean line-spacing parameters were determined at each 1-cm−1 interval in the three strong bands at 5.9, 7.5, and 1.3 μm by using a two-parameter random-band model. The resulting intensities for these bands are 1530 ± 100, 1383 ± 70, and 692 ± 35 cm−2 amagat−1, respectively. In addition, the absorption coefficients were determined in the three weak bands at 8.3, 13.2, and 15.5 μm. The band intensities derived are 44 ± 4, 45 ± 4, and 50 ± 5 cm−2 amagat−1, respectively.

Remote sounding of the tropical cirrus cloud temperature and optical depth using 6.5 and 10.5-micron radiometers during STEP

Abstract A dual-channel retrieval technique involving the water vapor band at 6.5 μm and the window region at 10.5 gm has been developed to infer the temperature and emissivity of tropical anvils. This technique has been applied to data obtained from the ER-2 narrow field-of-view radiometers during two flights in the field observation of the Stratosphere-Troposphere Exchange Project (STEP) near Damn, Australia, January-February 1987. The retrieved cloud temperatures are between 190 and 240 K, while the cloud emissivities derived from the retrieval algorithm range from about 0.2 to 1. Moreover, the visible optical depths have been obtained from the cloud emissivity through a theoretical parameterization with values of 0.5-10. A significant portion of tropical cirrus clouds are found to have optical depths greater than about 6. Because of the parameterization, the present technique is unable to precisely determine the optical depth values for optically thick cirrus clouds.

Radiative flux measurements in the troposphere

The results of radiative flux-density measurements in the troposphere, made using an especially designed radiometer mounted on a Cessna 402B aircraft, are reported. The radiometer incorporates several well-known principles that result in highly accurate determinations of radiative fluxes in the atmosphere. Heating rates for gases and for aerosols are calculated, using measurements and radiosonde data. Instrument performance is verified by calculating the solar constant at the top of the atmosphere, using the radiative flux densities measured in the troposphere. Total heating rates of 0.175 and 0.377 K h(-1) are determined for hazy and foggy atmospheres, respectively. Aerosol heating rates of 0.065 and 0.235 K h(-1) are deduced from the total heating rates. Environmental noise measurements during data acquisition are presented. The solar constant value of 1387 +/- 21 W m(-2) derived from the experiments agrees within 4% of the standard value.