Abstract. The evaporation duct is a downward refracting layer that results from the rapid decrease in humidity with respect to altitude occurring in the atmospheric surface layer above bodies of water. The evaporation duct affects radar detection ranges at frequencies of approximately 1 GHz and above. Models based on Monin-Obukhov similarity theory are usually used to calculate evaporation duct refractivity profiles from bulk measurements of air temperature, humidity, wind speed, and the sea surface temperature. Modeling results by Pappert et al. [1992] indicated that the falloff of radar sea echo as a function of range was an increasing function of the evaporation duct height. On the basis of those results, the authors proposed inferring the evaporation duct height by a slope fit to modeled clutter power, a nonlinear least squares inversion procedure. Data for testing the inversion procedure were obtained using the S band Space Range Radar at Wallops Island, Virginia. Evaporation duct heights were inferred from the radar data on the basis of the assumption of a range-independent evaporation duct height and sea clutter radar cross section (o-ø). Validation data consist of buoy and boat in situ bulk measurements. The result of comparing the radar-inferred evaporation duct heights and those calculated from bulk measurements indicates that the radar-inferred duct heights are strongly correlated with those from the in situ measurements, but there is some uncertainty as to whether they are biased or unbiased. That uncertainty arises from the assumed dependence of o -ø on the grazing angle ½. That ½ dependence is currently a matter of debate in the open literature, with the lower and upper ends of modeling results being o.O • ½0 and o -ø • ½4, respectively. We show results for both dependencies and note that the o -ø • ½0 provides the best agreement with our measurements. It should be noted that inferring the evaporation duct height from radar sea echo is a problem that stresses the modeling of low-grazing-angle backscatter. IntroductionEvaporation ducts result from the rapid change in humidity and temperature that occurs within the surface layer of the atmosphere over bodies of water. The resulting vertical profiles of temperature and humidity change the profile of the index of refraction n and the derivative quantities of radio refractivity N and modified refractivity M so as to form a duct that affects electromagnetic (EM) propagation at frequencies of 1 GHz and above. Evaporation duct refractivity profiles are most often calculated using Monin-Obukhov similarity-theory-based models of Jeske [1971, 1973] surements of the sea surface temperature Ts, air temperature Ta, relative humidity RH, and wind speed U at a reference height above the sea surface. These are commonly referred to as "bulk measurements." The Jeske profile under neutral conditions (T a = Ts) is uniquely defined by the evaporation duct height 3, which is the height at which the refractivity profile changes from downward to upward refracting. The J...

Melarsen oxide [p-(4,6-diamino-1,3,5-triazin-2-yl)aminophenylarsonous acid (MEL)], which selectively bridges spatially neighboring bis-cysteinyl residues in (reduced) proteins, was used to trap folding intermediates chemically during 1) time-dependent renaturation of recombinant human macrophage colony-stimulating factor (rhM-CSF); by redox refolding in vitro; 2) reductive unfolding in the presence of the trapping reagent; and 3) denaturing unfolding reactions in urea and guanidinium hydrochloride. Characterization of intermediates from folding and unfolding reactions was performed by electrospray ionization mass spectometry (ESI-MS). In all folding and unfolding reactions a characteristic dimeric intermediate with two attached melarsen oxide (MEL) groups was observed, suggesting that these rhM-CSF beta species were important refolding intermediates. These intermediates presented a characteristic "charge structure" in ESI spectra with a most abundant 26+ charged molecular ion whereas the mature homodimeric rhM-CSF beta showed a most abundant 23+ molecular ion, indicating that the final product was more compact. The major locations of the two MEL groups were identified by mass spectrometric peptide mapping at cysteine residues C157 and C159 from each monomer. Cysteine residues C7 and C90 were minor modification sites. The mass spectrometric results from the in vitro folding reactions of rhM-CSF beta are in agreement with intrinsic tryptophan fluorescence measurements and are consistent with the folding pathway that starts with a fully reduced monomer (R), includes partially folded monomeric intermediates (M) and dimeric intermediates (D), and yields a final product with the native tertiary structure (N): 2R ==> 2M ==> D ==> N. Our results show that selective chemical trapping of bis-thiol groups of proteins with MEL permits study of folding pathways by mass spectrometric structure characterization of intermediates with otherwise transient conformations.

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Recent advances in mesoscale numerical weather prediction (NWP) models have supported four-dimensional (4D) radio-frequency (RF) propagation modeling in challenging heterogeneous refractive marine environments. Numerical weather prediction models typically provide a vertical profi le of refractivity every 1 km to 3 km horizontally in the domain of interest for each hour in a 48-hour forecast. Due to surface roughness and turbulence constraints, these profi les extend from the stratosphere to within 5 m to 10 m of the sea's surface. Because of strong evaporation at the sea's surface, signifi cant impacts on RF system performance can be induced by refractivity gradients in the fi rst 10 m above sea level (ASL). Historically, the lower-layer refractivity profi les have been calculated using Monin-Obukhov-Similarity-(MOS) based turbulence models. This dualmodel approach requires a robust technique for blending on the order of 3 10 profi les per forecast hour without creating non-physical refractivity artifacts. This paper describes a zero-order-closure turbulent-fl ux technique for blending numerical weather prediction and Monin-Obukhov Similarity refractivity profi les, and presents the results of a multi-wavelength data-comparison process.