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This paper presents an open-access data set of reanalysed radar reflectivities and rainfall rates at sub-kilometre spatial and minute temporal scales. Variability at these scales is a blind spot for both operational rain gauge networks and operational radar networks. In the urban area of Hamburg, precipitation measurements of a single-polarized X-band weather radar operating at high temporal (30s), range (60m), and azimuthal sampling (1°) resolutions are made available for a period of more than 8 years. We describe in detail the reanalysis of the raw radar data, outline the radar performance for the years 2013 to 2021, and discuss open issues and limitations of the data set. Several sources of radar-based errors were adjusted gradually, affecting the radar reflectivity and rainfall measurements, e.g. noise, alignment, non-meteorological echoes, radar calibration, and attenuation. The deployment of additional vertically pointing micro rain radars yields drop size distributions at the radar beam height, which effectively reduces errors concerning the radar calibration and attenuation correction and monitors the radar data quality. A statistical evaluation revealed that X-band radar reflectivities and rainfall rates are in very good agreement with the micro rain radar measurements. Moreover, the analyses of rainfall patterns shown for an event and accumulated rainfall of several months prove the quality of the data set. The provided radar reflectivities facilitate studies on attenuation correction and the derivation of further weather radar products, like an improved rainfall rate. The rainfall rates themselves can be used for studies on the spatial and temporal scales of precipitation and hydrological research, e.g. input data for high-resolution modelling, in an urban area. The radar reflectivities and rainfall rates are available at https://doi.org/10.26050/WDCC/LAWR_UHH_HHG_v2. [ABSTRACT FROM AUTHOR]

Operational rain gauge networks provide reliable local precipitation measurements, but are unable to represent rainfall variability for large domains at small temporal scales. In the urban area of Hamburg, precipitation measurements of a single-polarized X-band weather radar operating at a high temporal (30s), range (60m), and azimuthal sampling (1°) resolution are available for more than eight years. These measurements refine observations of the German nationwide C-band radars within the 20km scan radius. Studies on short time periods (several months) prove the performance of this low-cost local area weather radar. A case study on a tornado in a rain event demonstrates its refined resolution compared to the German nationwide C-band radars. The deployment of additional vertically pointing micro rain radars yields drop size distributions at relevant heights, which reduces errors effectively concerning the radar calibration and required statistical relations (k-Z and Z-R relation), and monitors the radar data quality. This paper describes an open-access data set covering reanalysed radar reflectivities and rainfall estimates measured by an X-band radar at high spatio-temporal resolution in the urban environment of Hamburg between 2013 and 2021. Additionally, this paper outlines the performance of this X-band radar for long time periods, and discuss open issues and limitations of the data set. The provided radar reflectivities facilitate studies on attenuation correction and the derivation of further weather radar products, like an improved rainfall rate. The rainfall rates will be used for studies on the spatial and temporal scale of precipitation and hydrological research, e.g. input data for high-resolution modelling, in an urban area. [ABSTRACT FROM AUTHOR]

This paper presents a novel, simple method to correct reflectivity measurements of weather radars that operate in attenuation-influenced frequency bands using observations from less attenuated radar systems. In recent years radar systems operating in the X-band frequency range have been developed to provide precipitation fields for areas of special interest in high temporal (≤1 min) and spatial (≤250 m) resolution in complement to nationwide radar networks. However, X-band radars are highly influenced by attenuation. C- and S-band radars typically have coarser resolution (250 m-1 km and 5 min) but are less affected by attenuation. Correcting for attenuation effects in simple (non-Doppler) single-polarized X-band radars remains challenging and is often dependent on restriction parameters, for example, those derived from mountain returns. Therefore, these algorithms are applicable only in limited areas. The method proposed here uses measurements from C-band radars and hence can be applied in all regions covered by nationwide C- (or S-) band radar networks. First, a single scan of X-band radar measurements is used exemplary to identify advantages and disadvantages of the novel algorithm compared to a standard single radar algorithm. The performance of the correction algorithms in different types of precipitation is examined in nine case studies. The proposed method provides very promising results for each type of precipitation. Additionally, it is evaluated in a 5-month comparison with Micro Rain Radar (MRR) observations. The bias between uncorrected X-band radar and MRR data is nearly eliminated by the attenuation correction algorithm, and the RMSE is reduced by 20% while the correlation of ~0.9 between both systems remains nearly constant. [ABSTRACT FROM AUTHOR]

Numerical weather prediction models operate on grid spacings of a few kilometers, where deep convection begins to become resolvable. Around this scale, the emergence of coherent structures in the planetary boundary layer, often hypothesized to be caused by cold pools, forces the transition from shallow to deep convection. Yet, the kilometer-scale range is typically not resolved by standard surface operational measurement networks. The measurement campaign Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg (FESSTVaL) aimed at addressing this gap by observing atmospheric variability at the hectometer-to-kilometer scale, with a particular emphasis on cold pools, wind gusts, and coherent patterns in the planetary boundary layer during summer. A unique feature was the distribution of 150 self-developed and low-cost instruments. More specifically, FESSTVaL included dense networks of 80 autonomous cold pool loggers, 19 weather stations, and 83 soil sensor systems, all installed in a rural region of 15-km radius in eastern Germany, as well as self-developed weather stations handed out to citizens. Boundary layer and upper-air observations were provided by eight Doppler lidars and four microwave radiometers distributed at three supersites; water vapor and temperature were also measured by advanced lidar systems and an infrared spectrometer; and rain was observed by a X-band radar. An uncrewed aircraft, multicopters, and a small radiometer network carried out additional measurements during a 4-week period. In this paper, we present FESSTVaL's measurement strategy and show first observational results including unprecedented highly resolved spatiotemporal cold-pool structures, both in the horizontal as well as in the vertical dimension, associated with overpassing convective systems. [ABSTRACT FROM AUTHOR]

The classical rain attenuation correction scheme of Hitschfeld and Bordan (HIBO) and the newer iterative approach by Hildebrand (HL) are reconsidered. Although the motivation for the HL algorithm was an extension into ranges, where HIBO tends to be unstable, it is shown here that the contrary is the case. The finite-range resolution causes an intrinsic instability of HL already at moderate attenuation, where HIBO would still deliver stable results. Therefore, the authors concentrate the further analysis on HIBO, and confirm that the usual implementation of HIBO does not account correctly for finite-range resolution. They suggest a modified scheme that produces exact retrievals in the ideal case of perfect measurements. For vertically pointing Doppler radars a new element is explored in the attenuation correction—namely, calculating rain attenuation κ and rainfall R from Doppler spectra via the raindrop size distributions (RSDs). Although this spectral scheme (SIBO) avoids the uncertainty of Z– R and Z– κ relations, the superiority of this approach is not a priori obvious because of its sensitivity to vertical wind. Therefore, radar rain rates, based on a Z– R relation and on RSDs, respectively, are compared with in situ measurements. The results indicate better agreement for RSD-based retrievals. Because κ is closely correlated with R, the authors assert the advantage of RSD-based retrievals of κ. The application of HIBO and SIBO to real data shows that the uncertainty of standard Z– R relations is the main source of deviation between the two versions. In addition, the comparison of profiles suggests that the parameters of Z– R relations aloft can deviate considerably from near-surface values. Although artifacts cannot be excluded with certainty, there is some evidence that this observation actually reflects microphysical processes. [ABSTRACT FROM AUTHOR]

Data of vertically pointing microrain radars (MRRs), located at various sites around the Baltic Sea, were analyzed for a period of several years. From the Doppler spectra profiles of drop size distributions (DSDs) are obtained. A significant height dependence of the shape of the DSDs—and thus of the Z–R relations—is observed at high rain rates. This implies, for the considered sites, that ground-based Z–R relations lead to underestimation of high rain rates by weather radars. [ABSTRACT FROM AUTHOR]

Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgional-scale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of CHN and CEN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year-1 and precipitation between 624 and 805 mm year-1 for this particular 12 month period. Taking the results of model verification from the present study into account, the best estimate of P–E is about 100 ± 50 mm for this particular 12 month period. But the annual mean of P–E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year-1 for the 12 month period studied here and 32 mm year-1 as an average for 18 years. [ABSTRACT FROM AUTHOR]

Presents a study that calculated the precipitation and evaporation over the Baltic Sea from September 1998 to August 1999 using atmospheric regional models and data-based methods. Description of the investigated period; Analysis of the frequency distributions of hourly values of latent heat fluxes; Determination of the net precipitation of the Baltic Sea and subbasins.