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Publications (7 of 7) Show all publications
Ridal, M. & Dahlbom, M. (2017). Assimilation of Multinational Radar Reflectivity Data in a Mesoscale Model: A Proof of Concept. Journal of Applied Meteorology and Climatology, 56(6), 1739-1751
Open this publication in new window or tab >>Assimilation of Multinational Radar Reflectivity Data in a Mesoscale Model: A Proof of Concept
2017 (English)In: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 56, no 6, p. 1739-1751Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-4143 (URN)10.1175/JAMC-D-16-0247.1 (DOI)000403093300013 ()
Available from: 2017-08-08 Created: 2017-08-08 Last updated: 2017-08-08Bibliographically approved
Lindskog, M., Ridal, M., Thorsteinsson, S. & Ning, T. (2017). Data assimilation of GNSS zenith total delays from a Nordic processing centre. Atmospheric Chemistry And Physics, 17(22), 13983-13998
Open this publication in new window or tab >>Data assimilation of GNSS zenith total delays from a Nordic processing centre
2017 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 22, p. 13983-13998Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-4450 (URN)10.5194/acp-17-13983-2017 (DOI)000416151800001 ()
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2017-12-12Bibliographically approved
Olsson, J., Simonsson, L. & Ridal, M. (2015). Rainfall nowcasting: predictability of short-term extremes in Sweden. Urban Water Journal, 12(1), 3-13
Open this publication in new window or tab >>Rainfall nowcasting: predictability of short-term extremes in Sweden
2015 (English)In: Urban Water Journal, ISSN 1573-062X, Vol. 12, no 1, p. 3-13Article in journal (Refereed) Published
Abstract [en]

Our current knowledge of the character of rainfall events in Sweden associated with extreme short-term accumulations and their predictability by forecasting, is very limited. In this study, observations from automatic stations and weather radars in Sweden were analysed to identify and characterise extreme short-term events. Often shorter-duration (1-6 h) extreme events were associated with small-scale structures, dominated by single cells, and longer-duration (12-24 h) events with less variable, larger-scale fields. For lead time 3 h, similar to 20% of the events were forecasted at the correct place with an error of <25% by the operational Swedish nowcasting system. If allowing for a 25 km displacement of the forecasted events, the hit rate increased by 10-15 percentage points. Some predictability was found for lead time 8 h but not for 24 h. The results suggest a potential added gain of increasing the temporal resolution of the Swedish flood forecasting system to sub-daily steps.

National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:smhi:diva-2019 (URN)10.1080/1573062X.2015.987428 (DOI)000346568900003 ()
Available from: 2016-03-03 Created: 2016-03-03 Last updated: 2018-01-10Bibliographically approved
Olsson, J., Simonsson, L. & Ridal, M. (2014). Rainfall nowcasting: predictability of short-term extremes in Sweden. Urban Water Journal, 11(7), 605-615
Open this publication in new window or tab >>Rainfall nowcasting: predictability of short-term extremes in Sweden
2014 (English)In: Urban Water Journal, ISSN 1573-062X, Vol. 11, no 7, p. 605-615Article in journal (Refereed) Published
Abstract [en]

Our current knowledge of the character of rainfall events in Sweden associated with extreme short-term accumulations and their predictability by forecasting, is very limited. In this study, observations from automatic stations and weather radars in Sweden were analysed to identify and characterise extreme short-term events. Often shorter-duration (1-6 h) extreme events were associated with small-scale structures, dominated by single cells, and longer-duration (12-24 h) events with less variable, larger-scale fields. For lead time 3 h,,20% of the events were forecasted at the correct place with an error of <25% by the operational Swedish nowcasting system. If allowing for a 25 km displacement of the forecasted events, the hit rate increased by 10-15 percentage points. Some predictability was found for lead time 8 h but not for 24 h. The results suggest a potential added gain of increasing the temporal resolution of the Swedish flood forecasting system to sub-daily steps.

Keywords
precipitation, runoff, flood forecasting
National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:smhi:diva-154 (URN)10.1080/1573062X.2013.847465 (DOI)000338103000008 ()
Available from: 2015-04-08 Created: 2015-03-26 Last updated: 2018-01-11Bibliographically approved
Ridal, M., Lindskog, M., Gustafsson, N. & Haase, G. (2011). Optimized advection of radar reflectivities. Atmospheric research, 100(2-3), 213-225
Open this publication in new window or tab >>Optimized advection of radar reflectivities
2011 (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 100, no 2-3, p. 213-225Article in journal (Refereed) Published
Abstract [en]

A nowcasting system for generation of short-range precipitation forecasts has been developed at the Swedish Meteorological and Hydrological Institute (SMHI). The methodology consists of utilising a time-series of radar reflectivity composites for deriving an advection field, which will give a better representation of the motion of the precipitation pattern compared to a model wind field. The advection field is derived applying a 4-dimensional variational data assimilation technique. The resulting field is then used for a semi-Lagrangian advection of the latest available reflectivity field forward in time. During the forecast, the advected field is gradually replaced by a numerical weather prediction forecast in order to include the onset of convection and advection into the radar coverage area. In an idealised example with simulated observations the functionality of the method is demonstrated. For a case study of a full scale example the resulting precipitation forecast shows large improvements compared to the operational numerical weather prediction model used at SMHI, especially for forecasts up to three hours, where the largest influence from the radar advection occurs. In an objective validation of the structure, amplitude and location of modelled precipitation, where the forecasts are compared to radar observations, these findings are confirmed. The same validation of model runs over a longer time period also clearly indicates that the amplitude, structure and location of the precipitation patterns are significantly improved as compared to a short-range forecast from the operational forecast model used at SMHI. (C) 2010 Elsevier B.V. All rights reserved.

Keywords
Nowcasting, Radar, Advection, Variational data assimilation
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-521 (URN)10.1016/j.atmosres.2010.12.016 (DOI)000290501600007 ()
Available from: 2015-04-17 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved
Ridal, M. (2002). Isotopic ratios of water vapor and methane in the stratosphere: Comparison between ATMOS measurements and a one-dimensional model. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 107(D16), Article ID 4285.
Open this publication in new window or tab >>Isotopic ratios of water vapor and methane in the stratosphere: Comparison between ATMOS measurements and a one-dimensional model
2002 (English)In: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, ISSN 0747-7309, Vol. 107, no D16, article id 4285Article in journal (Refereed) Published
Abstract [en]

[1] A one-dimensional model simulating the transport and chemistry of methane and water vapor including their isotopic ratios in the tropical stratosphere is compared to measurements by the Atmospheric Trace Molecule Spectroscopy experiment (ATMOS) instrument. The model and measurements show good agreement in the isotopic ratio profiles. The deltaD depletion for water vapor is -600parts per thousand to -500parts per thousand at the tropopause with a small increase up to similar to10 hPa. Above this altitude the modeled isotopic ratio shows a strong increase due to methane oxidation. The measured profiles are rather noisy above 10 hPa but give an indication of a stronger increase in the isotopic ratio than modeled. If the isotopic ratio of water vapor is allowed to vary at the tropopause simulating an annual cycle in the input values, a wave pattern that is transported upwards arises on the vertical profile. This is a similar effect as the "tape recorder'' for water vapor. A wave pattern can also be detected in the tropical deltaD profiles from ATMOS. The methane isotopic ratio shows behavior similar to that of water vapor but without the wave pattern. The increase in methane deltaD above 10 hPa is very strong. The measured profiles are again rather noisy above this altitude, but measurements from inside the polar vortex show that the methane isotopic ratio in the upper stratosphere is very high. The deltaD values are in the range of +300parts per thousand to +500parts per thousand at altitudes as low as 40 hPa (similar to25 km) in the polar vortex.

Keywords
HDO, CH3D, tropical stratosphere, isotopic ratio
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-1376 (URN)10.1029/2001JD000708 (DOI)000180325800001 ()
Available from: 2015-08-06 Created: 2015-07-29 Last updated: 2016-05-31Bibliographically approved
Ridal, M., Murtagh, D. P., Merino, F., Pardo, J. R. & Pagani, L. (2002). Microwave temperature and pressure measurements with the Odin satellite: II. Retrieval method. Canadian journal of physics (Print), 80(4), 455-467
Open this publication in new window or tab >>Microwave temperature and pressure measurements with the Odin satellite: II. Retrieval method
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2002 (English)In: Canadian journal of physics (Print), ISSN 0008-4204, E-ISSN 1208-6045, Vol. 80, no 4, p. 455-467Article in journal (Refereed) Published
Abstract [en]

The millimetre receiver on the Swedish satellite Odin, will be used for detection of the 118.750 GHz oxygen line. The temperature and pressure will be determined from the output of a three-channel filter bank measurement. One frequency bin is centred over the emission-line frequency while the other two cover parts of the line wing, where the opacity is less, providing a useful signal at lower altitudes. The bandwidth of each channel is 40 MHz. The signal in the frequency bin covering the line centre is modeled by a high-resolution model including the Zeeman effect, developed by the Observatoire de Paris-Meudon. The other two 40 MHz bins are modeled using the much faster standard Odin forward model, developed at the Department of Meteorology at Stockholm University together with Chalmers University of Technology. The operational retrievals employ an iterative method that uses simulated signals from a reference atmosphere as a lookup table for the pressure. The temperature is then calculated from the equation of hydrostatic equilibrium, and a new lookup table computed. This process is repeated until a convergence criterion is reached. Simulations, including known error sources, show that the temperature can be retrieved with a root mean square (rms) around 3 K, in the altitude range similar to25-90 km using the operational temperature retrieval method (the filter bank method). A sub-millimetre receiver on board Odin will also be used to observe the oxygen line at 487.249 GHz. Both this line and the 118.750 GHz line can be observed in high resolution (150 kHz) for detailed studies of the Zeeman splitting. Retrievals from the high-resolution measurements are expected to give a precision of +/-2 K rms at that resolution. However, this kind of observation will occupy an entire spectrometer and will not be made on a regular basis.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-1389 (URN)10.1139/P02-021 (DOI)000176500700011 ()
Available from: 2015-08-03 Created: 2015-07-29 Last updated: 2017-12-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2716-1571

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