Toward the Assimilation of the Atmospheric Surface Layer Using Numerical Weather Prediction and Radar Clutter Observations

Abstract

Radio wave propagation on low-altitude paths over the ocean above 2 GHz is significantly affected by negative refractivity gradients in the atmospheric surface layer, which form what is often referred to as an evaporation duct (ED). Refractivity from clutter (RFC) is an inversion approach for the estimation of the refractivity profile from radar clutter, and RFC-ED refers to its implementation for the case of evaporation ducts. An approach for fusing RFC-ED output with evaporation duct characterization that is based on ensemble forecasts from a numerical weather prediction (NWP) model is examined here. Three conditions of air–sea temperature difference (ASTD) are examined. Synthetic radar clutter observations are generated using the Advanced Propagation Model. The impacts of ASTD on the evaporation duct refractivity profile, atmospheric parameter inversion, and propagation factor distributions are studied. Relative humidity at a reference height and ASTD are identified as state variables. Probability densities from NWP ensembles, RFC-ED, and joint inversions are compared. It is demonstrated that characterization of the near-surface atmosphere by combining RFC-ED and NWP reduces the estimation uncertainty of ASTD and relative humidity in an evaporation duct, with respect to using either method alone.

Atmospheric Duct Estimation Using Radar Sea Clutter Returns by the Adjoint Method with Regularization Technique

“…Term s is approximated to be a constant determined by the normalized sea RCS s 0 and the radar system parameters C, that is, s 5 s 0 1 C; see Gerstoft et al (2003b). Term z 0 is the effective scattering height, usually approximates 1 m above the ocean surface (Karimian et al 2011). The wavelength is denoted by l, and u is the complex electric field computed from a PE method (Kuttler and Dockery 1991): 8 > > > > > > < > > > > > > :…”

“…It is difficult to get analytical solutions according to current theories, and optimization methods are used to get approximate solutions. In the last decade, many advances have been made in RFC techniques (Rogers et al 2000(Rogers et al , 2005Gerstoft et al 2003aGerstoft et al ,b, 2004Kraut et al 2004;Yardim et al 2006Yardim et al , 2007Yardim et al , 2008Yardim et al , 2009Vasudevan et al 2007;Douvenot et al 2008Douvenot et al , 2010Wang et al 2009;Zhang et al 2011Zhang et al , 2012Karimian et al 2012). Most of these works used the split-step Fourier parabolic equation (PE) method as the forward propagation model to construct the replica clutter returns.…”

“…Park and Fabry (2011) used ray tracing to model the radar coverage at low elevation angles to estimate the vertical gradient of refractivity near the ground. A good review of the above-mentioned works has been provided by Karimian et al (2011).…”

“…Referring to the variational data assimilation studies in numerical weather prediction (NWP) and the work by Karimian et al (2013), the background field may be a better choice to formulate the regularization term. Usually, the background field can be obtained from historical observations and/or from the output of numerical weather prediction models.…”

Direct Electrochemistry and Electrocatalysis of Hemoglobin on Aligned Carbon Nanotubes Based Electrodes Modified with Au Nanoparticles and SiO2 Gel

“…The apparent MichaelisÀMenten constant (K m app ) for the SiO 2 /Hb-AuNPs/ACNTs electrode to H 2 O 2 , which is an important parameter to evaluate the enzyme-substrate kinetics, was then calculated as 0.44 mM by using the LineweaverÀBurk equation, i.e. 1/I ss = 1/I max + K m app /I max C [44], where I ss is the electrocatalytic current, I max the maximum current under saturated substrate conditions, and C the bulk concentration of H 2 O 2 . Finally, the stability of the SiO 2 /Hb-AuNPs/ACNTs electrode was investigated by five successive measurement of its current response to 40 mM H 2 O 2 , resulting in a relative standard deviation of 3.2 %.…”