Jarmo Koistinen

Gauge-Radar network adjustment for the baltic sea experiment

The gauge adjustment technique used to produce 2 × 2 km 3- and 12-hour radar-based accumulated precipitation datasets for the Baltic Sea Experiment is presented. The gauge adjustment technique is based on the gauge-to-radar ratio. A distance-dependent adjustment factor is derived and it is weighted against a spatially analyzed adjustment factor according to the local observation density and estimated spatial decorrelation distance. A preliminary adjustment strategy is applied in order to normalize data from many radars to a common level and to minimize the bias with gauges. The final adjustment field applied to radar accumulations is shown, through validation against independent gauge data, to minimize the bias between radar and gauge sums while raising the explained variance, compared to unadjusted radar sums. Areas not covered by radar are subjected to an optimal interpolation of systematically corrected gauge sums, and this field is merged with the gauge adjusted radar field in order to cover the entire Baltic Sea Experiment region.

Continental-scale radar monitoring of the aerial movements of animals

Billions of organisms travel through the air, influencing population dynamics, community interactions, ecosystem services and our lives in many different ways. Yet monitoring these movements are technically very challenging. During the last few decades, radars have increasingly been used to study the aerial movements of birds, bats and insects, yet research efforts have often been local and uncoordinated between research groups. However, a network of operational weather radars is continuously recording atmospheric conditions all over Europe and these hold enormous potential for coordinated, continental-scale studies of the aerial movements of animals.The European Network for the Radar surveillance of Animal Movement (ENRAM) is a new e-COST research network aiming exactly at exploring this potential. The main objective of ENRAM is to merge expertise to utilize weather radars to monitor the aerial movement of animals across Europe for a broad range of stakeholders at an unprecedented scale and enable researchers to study the causes and consequences of movement. In this paper we describe the aims of ENRAM in more detail and the challenges researchers will address, provide an overview of aero-ecological studies using radar, and present some of the opportunities that a large sensor network can provide for movement ecology research.

Pest insect immigration warning by an atmospheric dispersion model, weather radars and traps

In an experimental set‐up in and around Helsinki, Finland (60°N, 25°E), we have detected pest insect immigration using weather radars and insect traps in the field. This study was part of a project to develop a system to give warning of a possible arrival of long‐range migrant insect pests. Bird‐cherry aphid, Rhopalosiphum padi, and diamondback moth, Plutella xylostella, were found on the ground following migrations in warm airstreams at the end of May 2007. This migration episode was successfully forecast by the meteorologists in the project team. For the summer 2008, we developed a pest insect immigration alarm system based on SILAM, a Finnish Meteorological Institute atmospheric dispersion model. The first important pest insect immigration occurred in late June, bringing bird‐cherry aphids. Our alarm system correctly produced a warning of this immigration. We studied the migration path in the observed events in 2007 and 2008 with the help of the atmospheric dispersion model. Weather radars frequently showed rain echo over the area, but there was also a lot of echoes originating from the migrating insects. Using the polarimetric weather radar in Helsinki, we could differentiate insects from other sources of echoes. Insects were common in layers below 1 km, and were observed up to height of about 2.5 km. Using Doppler weather radars we were able to observe the speed and direction of the migration. The experiment showed that an atmospheric dispersion model is an effective tool for predicting the movement of airborne migrants. The alarm system would work still better, if the sources of the immigrants were known in more detail. In addition, the very simple modelling of airborne migration should be refined. Weather radars, and especially polarimetric systems, are able to detect insect migrations and reveal details of the phenomenon not obtainable by other means.

The Helsinki Testbed: A Mesoscale Measurement, Research, and Service Platform

Abstract The Finnish Meteorological Institute and Vaisala have established a mesoscale weather observational network in southern Finland. The Helsinki Testbed is an open research and quasi-operational program designed to provide new information on observing systems and strategies, mesoscale weather phenomena, urban and regional modeling, and end-user applications in a high-latitude (~60°N) coastal environment. The Helsinki Testbed and related programs feature several components: observing system design and implementation, small-scale data assimilation, nowcasting and short-range numerical weather prediction, public service, and commercial development of applications. Specifically, the observing instrumentation focuses on meteorological observations of meso-gamma-scale phenomena that are often too small to be detected adequately by traditional observing networks. In particular, more than 40 telecommunication masts (40 that are 120 m high and one that is 300 m high) are instrumented at multiple heights. Oth...

Bird migration patterns on weather radars

Abstract Widespread reflectivity and Doppler velocity patterns due to birds are common on weather radar images during preferred seasonal and diurnal periods. The knowledge of the main migration types and the forcing factors of them (wind, visibility, local topography) will make it quite easy for a human analyst to diagnose birds, insects and weather. Automatic diagnosis and elimination of spurious atmospheric winds due to bird migration is important for real time wind monitoring and for the quality of the Doppler winds assimilated into NWP models.

Operational Measurement of Precipitation in Cold Climates

Over the last 50 years, severe weather such as thunderstorms, squall lines, tornadoes, hurricanes, and extreme precipitation events with ensuing flash floods have dominated both scientific and operational radar meteorology (Atlas, 1990, Collier, 2001). This is natural, as one of the main benefits of weather radars is very dense sampling of precipitating systems in time and space, facilitating real-time warning and nowcasting of mesoscale severe weather which may have huge socioecomonic impacts. Also, an implication has been that some commercial radar manufacturers have paid little attention to the sensitivity of weather radar. Maximal sensitivity of a radar system is required for making snowfall measurements. Even greater sensitivity of operational radars is needed for the production of Doppler winds from clear air. The important topic of wind field estimation from Doppler measurements relates to Gekat et al. (2003), Meischner et al. (2003) and Macpherson (2003), all this book. The major proportion of the frequent boundary layer echoes found in summer, even in the north of Europe, originates from insects. For example, classification of 240 000 vertical profiles of reflectivity (VPR) from a one-year-long period in Finland revealed that 40% of all VPRs originated from clear air echoes reaching the ground, 20% from overhanging precipitation, i.e. ice crystal clouds or snowfall layers aloft, and only 40% involved precipitation reaching the ground level (Pohjola and Koistinen, 2002). The reflectivity of both nonprecipitating echo classes was typically between −20 and 5 dBZ. Both Canadian and Nordic radar networks (NORDRAD) mostly operate sensitive C-band systems. The operational Nordic radars are “standard” systems with sensitivities around −110 dBm, beamwidths of around 0.9° and pulse lengths from 0.5–2 µs. In Canada, the sensitivity requirement to detect snowfall and clear air echoes has led to the specification of a multi-pulse length capability (0.8–5 µs) and of a narrow antenna beamwidth (0.65°) (Joe and Lapczak, 2002).

Doppler Velocities at Orthogonal Polarizations in Radar Echoes From Insects and Birds

The differential Doppler velocities (DDVs) measured with weather radar at horizontal and vertical polarizations in echoes from insects and birds are considered. In weather echoes, DDV is usually less than 0.5 ms- 1, whereas in echoes from flying birds and insects, it can reach 5-7 ms- 1. Such large difference can be used as an additional parameter in distinguishing between weather and nonmeteorological echoes. It is shown that large values of DDV pertain to multipeaked Doppler spectra with different spectral differential reflectivity values in the peaks.

The Emergence of Open-Source Software for the Weather Radar Community

AbstractWeather radar analysis has become increasingly sophisticated over the past 50 years, and efforts to keep software up to date have generally lagged behind the needs of the users. We argue that progress has been impeded by the fact that software has not been developed and shared as a community.Recently, the situation has been changing. In this paper, the developers of a number of open-source software (OSS) projects highlight the potential of OSS to advance radar-related research. We argue that the community-based development of OSS holds the potential to reduce duplication of efforts and to create transparency in implemented algorithms while improving the quality and scope of the software. We also conclude that there is sufficiently mature technology to support collaboration across different software projects. This could allow for consolidation toward a set of interoperable software platforms, each designed to accommodate very specific user requirements.

Advection-Based Adjustment of Radar Measurements

AbstractWhen making radar-based precipitation products, a radar measurement is commonly taken to represent the geographical location vertically below the contributing volume of the measurement sample. However, when wind is present during the fall of the hydrometeors, precipitation will be displaced horizontally from the geographical location of the radar measurement. Horizontal advection will introduce discrepancies between the radar-measured and ground level precipitation fields. The significance of the adjustment depends on a variety of factors related to the characteristics of the observed precipitation as well as those of the desired end product. In this paper the authors present an advection adjustment scheme for radar precipitation observations using estimated hydrometeor trajectories obtained from the High-Resolution Limited-Area Model (HIRLAM) MB71 NWP model data. They use the method to correct the operational Finnish radar composite and evaluate the significance of precipitation advection in typi...

The State of Weather Radar Operations, Networks and Products

Do you remember the famous cars of the early 1950s, the 2CV and the Volkswagen “Beetle”? They were simple tin boxes with four wheels, four seats, a motor, a steering wheel, and a speedometer. When opening the bonnet, you could recognise nearly every part, you understood all the functions and could handle most shortcomings yourself. How does a modern upper class car look nowadays in comparison? The front panel is like the cockpit of an aircraft and when opening the bonnet, you just may recognise where to fill the water for cleaning your windows. Similarly, weather radar systems developed from microwave devices transmitting radiation pulses and detecting the location and distance of a target by its reflection — RADAR means “RAdiation Detection And Ranging” — to “high tech” systems delivering a number of products of interest for the user. The “targets” we now have in mind are cloud and precipitation particles.