Estimating 1min rain rate distributions from numerical weather prediction

Internationally recognized prognostic models of rain fade on terrestrial and Earth-space EHF links rely fundamentally on distributions of one-minute rain rates. Currently, in Rec. ITU-R P.837-6, these distributions are generated using the Salonen Poiares-Baptista method where one-minute rain rate distributions are estimated from long-term average annual accumulations provided by Numerical Weather Products (NWP). This paper investigates an alternative to this method based on the distribution of six-hour accumulations available from the same NWPs. Rain rate fields covering the UK, produced by the Nimrod network of radars, are integrated to estimate the accumulations provided by NWP and these are linked to distributions of fine scale rain rates. The proposed method makes better use of the available data. It is verified on 15 NWP regions spanning the UK and the extension to other regions is discussed

Trends in the incidence of rain rates associated with outages on fixed links operating above 10 GHz in the southern United Kingdom

Studies have shown that climate change is leading to an increase in the incidence of heavy rain in the United Kingdom, particularly over winter. The major interest has been on the hydrological impacts of this increase, and so studies have focused on rain accumulations over hours or days and for large catchments. The availability of fixed, microwave links is limited by the incidence of heavy rain with an integration time of a minute or less. This document introduces evidence of an increasing trend in rain rates associated with outages. High-resolution rain data, produced by 30 tipping bucket gauges sited in the south of England, have been analyzed to identify these trends. The data span up to 20 years at each site. Increasing trends in the incidence of rain rates exceeded at annual time percentages between 0.005% and 0.1% are demonstrated. Data suggest that the total annual outage would have doubled or tripled over each decade analyzed for the majority of fixed links operating at rain fade limited frequencies. It is plausible that this trend could continue

Prediction of annual joint rain fade on EHF networks by weighted rain field selection

©2015. American Geophysical Union. All Rights Reserved. We present a computationally efficient method to predict joint rain fade on arbitrary networks of microwave links. Methods based on synthetic rain fields composed of a superposition of rain cells have been shown to produce useful predictions of joint fade, with low computational overhead. Other methods using rain fields derived from radar systems have much higher computational overhead but provide better predictions. The proposed method combines the best features of both methods by using a small number of measured rain fields to produce annual fade predictions. Rain fields are grouped into heavy rain and light rain groups by maximum rain rate. A small selection of rain fields from each group are downscaled and fade predictions generated by pseudointegration of specific attenuation. This paper presents a method to optimize the weights used to combine the heavy rain and light rain fade predictions to yield an estimate of the average annual distribution. The algorithm presented yields estimates of average annual fade distributions with an error small compared to year-to-year variation, using only 0.2% of the annual data set of rain fields

An experimental and theoretical investigation of thick wings at various sweep angles in and out of ground effect

The effects of sweep and aspect ratio on the longitudinal aerodynamics of a wing in and out of ground effect are analyzed. Experimental data were obtained in the Langley 4 by 7 Meter Tunnel for a wing with various sweep angles, aspect ratios, and flap deflections both in and out of ground effect. Theoretical predictions of the out of ground effect lift coefficients and flap effectiveness and the in ground effect lift coefficients are compared with the experimental results. As expected, the lift curve slope and flap effectiveness are reduced when the aspect ratio is reduced or the sweep angle is increased both in and out of ground effect. In ground effect, the lift and flap effectiveness are increased above a wing height to span ratio of 0.15. However, with flap deflections less than or equal to 10 deg and an angle of attack near 0 deg lift is markedly decreased at very low heights above the ground plane. This trend is not predicted by planar theoretical models but is predicted by a surface panel method where thickness effects are included

Effect of sweep and aspect ratio on the longitudinal aerodynamics of a spanloader wing in and out of ground effect

A wind tunnel investigation was conducted in the Langley 4 by 7 meter tunnel to determine the effects of leading edge sweep, aspect ratio, flap deflection, and elevon deflection on the longitudinal aerodynamic characteristics of a span distributed load advanced cargo aircraft (spanloader). Model configurations consisted of leading edge sweeps of 0, 15, 30 and 45 deg and aspect ratios of approximately 2, 4, 6, and 8. Data were obtained for angles of attack of -8 to 18 deg out of ground effect and at angles of attack of -2, 0, and 2 deg in ground effect at Mach number equal 0.14. Flap and elevon deflections ranged from -20 to 20 deg. The data are represented in tabulated form

Evidence of trends in rain event size effecting trends in rain fade

Rain gauge studies have shown that the incidence of rain at rates associated with outage on terrestrial links, has shown an increasing trend in several countries, over the last 30 years. However, no evidence is available from microwave links to show whether outage rates, or the incidence of fade, is similarly increasing. This paper presents evidence of fade trends, derived from a decade of rain radar data. Although a decade is too short a period to observe rain rate trends, evidence is presented that trends in the size of rain events is leading to changes in the relationship between point rain rates and rain fade. Furthermore, these trends are shown to vary significantly across the UK. Temporal trends in both rain rates and their link to rain fade, make it more difficult to adapt ITU-R Recommendation to a changing climate