Some Physical Aspects of Summer Monsoon Clouds-Comparison of Cloud Model Results with Observations

The physical characteristics of the summer monsoon clouds were investigated. The results of a simple cloud model were compared with the aircraft cloud physical observations collected during the summer monsoon seasons of 1973, 1974, 1976 and 1981 in the Deccan Plateau region.The model predicted profiles of cloud liquid water content (LWC) are in agreement with the observed profiles. There is reasonable agreement between the model predicted cloud vertical thickness and observed rainfall.The observed cloud-drop spectra were found to be narrow and the concentration of drops with diameter > 20um is either low or absent on many occasions. In such clouds the rain-formation cannot take place under natural atmospheric conditions due to the absence of collision-coalescence process. A comparison of the model predicted and observed rainfall suggested that the precipitation efficiency in cumulus clouds of small vertical thickness could be as low as 20 per cent.The clouds forming in the Deccan Plateau region during t     

The Role of In Situ Photochemistry in the Control of Ozone during Spring at the Jungfraujoch (3,580 m asl) – Comparison of Model Results with Measurements

A photochemical box model has been used to model themeasured diurnal ozone cycle in spring at Jungfraujochin the Swiss Alps. The comparison of the modelleddiurnal ozone cycle with the mean measured diurnalozone cycle in spring, over the period 1988–1996,shows a good agreement both with regard to the shapeand amplitude. Ozone concentrations increase duringthe daytime and reach a maximum at about 16:00–17:00(GMT) in both the modelled and the mean observed ozonecycle, indicative of net ozone production during thedaytime at Jungfraujoch in spring. The agreement isbetter when the modelled ozone cycle is compared withthe mean measured diurnal cycle (1988–1996) filteredfor north-westerly winds >5 m/s (representative ofregional background conditions at Jungfraujoch). Inaddition to ozone, the modelled diurnal cycle of[HO₂] + [CH₃O₂] also shows rather goodagreement with the mean diurnal cycle of the peroxyradicals measured during FREETEX '96, a FREETropopsheric Experiment at Jungfraujoch in April/May1996. Furthermore, this mean diurnal cycle of the sumof the peroxy radicals measured during FREETEX '96 isused to calculate, using steady-state expressions, therespective diurnal cycle of the OH radical. Thecomparison of the OH diurnal cycle, calculated fromthe peroxy radical measurements during FREETEX '96,with the modelled one, reveals also good agreement.The net ozone production rate during the day-time is0.27 ppbv h^-1 from the model, and 0.13 ppbvh^-1 from the observations during FREETEX '96. Theobservations and model results both suggest that thediurnal ozone variation in spring at Jungfraujoch isprimarily of photochemical origin. Furthermore, theobserved and modelled positive net ozone productionrates imply that tropospheric in situphotochemistry contributes significantly to theobserved high spring ozone values in the observedbroad spring-summer ozone maximum at Jungfraujoch.     

Comment on: “Corrections to the Mathematical Formulation of a Backwards Lagrangian Particle Dispersion Model” by Gibson and Sailor (2012: Boundary-Layer Meteorology 145, 399–406)

We discuss the results of Gibson and Sailor (Boundary-Layer Meteorol 145:399–406, 2012) who suggest several corrections to the mathematical formulation of the Lagrangian particle dispersion model of Rotach et al. (Q J R Meteorol Soc 122:367–389, 1996). While most of the suggested corrections had already been implemented in the 1990s, one suggested correction raises a valid point, but results in a violation of the well-mixed criterion. Here we improve their idea and test the impact on model results using a well-mixed test and a comparison with wind-tunnel experimental data. The new approach results in similar dispersion patterns as the original approach, while the approach suggested by Gibson and Sailor leads to erroneously reduced concentrations near the ground in convective and especially forced convective conditions.