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Standard linear and nonlinear downscaling models are compared using identical atmospheric circulation forcing fields. The target variables chosen were observed daily values of average temperature (TAV), precipitation (PRC), and vapor pressure (HPR) at a Central European station. Being without much sophistication, both models show acceptable performance on this time scale only for TAV and HPR; PRC, which behaves in a predominantly nonlinear fashion, handled very poorly. By considerably refining the evaluation it is nevertheless possible to distinguish significant differences between the 2 models and, with the nonlinear model, to describe specific rainfall conditions. We argue that this difference is caused by the limitations of the linear approach, and discuss how this might affect the downscaling of nonlinear quantities in general.

We report on an investigation of the phenol dimer by high-resolution rotational coherence spectroscopy (RCS) using the method of time-resolved fluorescence depletion (TRFD). With this technique we determined with high precision the rotational constants of the ground and electronically excited states. The phenol dimer is an ideal model system to study aromatic-aromatic interaction under the constraints of an intermolecular hydrogen bond, which leads to its unique "V-shaped" structure. The TRFD investigation was complemented by an (1 + 1′) pump-probe ionization (PPI) experiment in order to unequivocally assign ground and excited-state transients. Seven different types of RCS transients have been observed in the RCS spectrum and assigned to H′′-, H′-, J′′-, J′-, C-, K-, and A-type transients. From a detailed analysis by a grid search procedure based on numerical simulations of RCS spectra and a nonlinear least-squares fitting routine, the following values for the rotational constants have been obtained: A′′ ) 1414.4 ( 0.6 MHz, B′′ ) 313.7 ( 0.8 MHz, C′′ ) 287.5 ( 0.7 MHz, A′ ) 1425.7 ( 2.3 MHz, (B′ + C′) ) 590.6 ( 2.7 MHz. Furthermore, information about the alignment of the transition dipole moment in the molecular frame was obtained from the fit procedure. We report a geometry of the O-H‚‚‚O hydrogen bonded phenol dimer as determined by a fit of the intermolecular parameters to the rotational constants. The ground-state results confirm the gross geometry of a former RCS investigation of Felker and co-workers [

A high-resolution rotational coherence spectroscopy (RCS) investigation of para-cyclohexylaniline (pCHA) was performed with a solid-state picosecond laser setup, which allowed for the determination of rotational constants with unprecedented precision for a RCS experiment. The technique of time-resolved fluorescence depletion was used for the RCS measurements. The unique structural features of pCHA enabled the determination of both ground and excited state rotational constants. Three different sets of recurrences were observed in the spectrum and assigned to K″-, K′-, and J″-type transients. From a detailed analysis by a grid search procedure based on the numerical simulation of RCS spectra and a nonlinear least-squares fitting routine the following rotational constants for the ground state were obtained: A″=2406.5±0.6 MHz, (B+C)″=714.9±0.4 MHz. For the electronic excited state two different sets of constants were found to fit the experimental data within the reported uncertainties: set (I) A′=2343.6±1.3 MHz, (B+C)′=714.4±1.7 MHz and set (II) A′=2346.3±1.3 MHz, (B+C)′=719.3±2.1 MHz. From additional information set (II) was found preferable for the description of the excited state. Furthermore, the fluorescence lifetime and the alignment of the transition dipole moment in the molecular frame were obtained from the fit procedure. For a structural characterization of pCHA we performed ab initio calculations of the electronic ground and excited state using HF/6-31G(d) and CIS/6-31G(d) levels of theory, respectively. These results were compared with the experiments and used to investigate the dependence of the rotational constants on characteristic intramolecular coordinates.

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