Fredrik Boberg

Solar Wind Variations Related to Fluctuations of the North Atlantic Oscillation

A study on a possible solar wind interaction with the North AtlanticOscillation (NAO) is performed. Results are presented suggesting arelationship between the NAO index and the electric field strength E ofthe solar wind. A possible scenario for the suggested interaction isthat an electromagnetic disturbance is generated by the solar wind inthe global electric circuit of the ionosphere. This disturbance is thendynamically propagating downward through the atmosphere and subsequentlyinfluencing the large-scale pressure system in the North Atlanticregion. A relationship is also evident on longer time-scales when usingthe group sunspot number as a proxy for the solar wind. (Art. No. 1718)

Real time Kp predictions from solar wind data using neural networks

Abstract Multilayer feed-forward neural network models are developed to make three-hour predictions of the planetary magnetospheric Kp index. The input parameters for the networks are the Bz-component of the interplanetary magnetic field, the solar wind density n, and the solar wind velocity V, given as three-hour averages. The networks are trained with the error back-propagation algorithm on data sequences extracted from the 21st solar cycle. The result is a hybrid model consisting of two expert networks providing Kp predictions with an RMS error of 0.96 and a correlation of 0.76 in reference to the measured Kp values. This result can be compared with the linear correlation between V(t) and Kp(t + 3 hours) which is 0.47. The hybrid model is tested on geomagnetic storm events extracted from the 22nd solar cycle. The hybrid model is implemented and real time predictions of the planetary magnetospheric Kp index are available at http://www.astro.lu. se/-fredrikb.

Quantifying Energy and Mass Fluxes Controlling Godthåbsfjord Freshwater Input in a 5-km Simulation (1991–2012)*,+

AbstractFreshwater runoff to fjords with marine-terminating glaciers along the Greenland Ice Sheet margin has an impact on fjord circulation and potentially ice sheet mass balance through increasing heat transport to the glacier front. Here, the authors use the high-resolution (5.5 km) HIRHAM5 regional climate model, allowing high detail in topography and surface types, to estimate freshwater input to Godthabsfjord in southwest Greenland. Model output is compared to hydrometeorological observations and, while simulated daily variability in temperature and downwelling radiation shows high correlation with observations (typically >0.9), there are biases that impact the results. In particular, overestimated albedo leads to underestimation of melt and runoff at low elevations.In the model simulation (1991–2012), the ice sheet experiences increasing energy input from the surface turbulent heat flux (up to elevations of 2000 m) and shortwave radiation (at all elevations). Southerly wind anomalies and declining ...

Dynamical Downscaling with Reinitializations: A Method to Generate Finescale Climate Datasets Suitable for Impact Studies

To retain the sequence of events of a regional climate model (RCM) simulation driven by a reanalysis, a method that has not been widely adopted uses an RCM with frequent reinitializations toward it ...

Solar wind electric field modulation of the NAO: A correlation analysis in the lower atmosphere

Using geopotential height data we find a strong correlation between theelectric field strength E of the solar wind and pressure variations inthe stratosphere and troposphere. The large-scale evolution of E seemsto influence the stratospheric pressure in both hemispheres with theexception of the polar regions. For the tropospheric pressure theinfluence is concentrated to an area in the northern Atlantic. Usingpressure and temperature data at sea level, we conclude that thecorrelation with E resembles the action of the North AtlanticOscillation with an area with negative pressure correlation in theArctic, an area with positive pressure correlation in the subtropics, anarea with negative temperature correlation over Greenland and northeastCanada, and an area with positive temperature correlation over Europe. (Less)

Solar mean magnetic field variability: A wavelet approach to Wilcox Solar Observatory and SOHO/Michelson Doppler Imager observations

Solar mean magnetic field (SMMF) measurements from the Wilcox Solar Observatory and with the SOHO/MDI instrument are described and analyzed. Even though two completely different methods of observation are used, the two data sets obtained show a strong similarity. Using continuous wavelet transforms, SMMF variability is found at a number of temporal scales. Detected SMMF signals with a 1–2 year period are considered to be linked to variations in the internal rotation of the Sun. Intermediate SMMF oscillations with a period of 80–200 days are probably connected to the evolution of large active regions. We also find evidence for 90 min variations with coronal mass ejections as a suggested origin.

Resolved complex coastlines and land-sea contrasts in a high-resolution regional climate model: a comparative study using prescribed and modelled SSTs

We configured a coupled model system, comprising a regional climate model (RCM) and a regional ocean model, for the North Sea and Baltic Sea region at 6 nm resolution. A two-way nested fine-grid (1 nm) ocean domain is for the first time included for the Danish coastal waters in coupled RCMs to resolve the water exchange between the two regional seas. Here, we (1) assess the sensitivity of the near-surface atmosphere to prescribed sea surface temperatures (SSTs) from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim (ERAI) reanalysis and those modelled by the coupled system, and (2) examine different ocean responses in coarse and fine grids to atmospheric forcing. The experiments were performed covering the years 1990–2010, both using ERAI lateral boundary conditions. ERAI SSTs generally agree well with satellite SSTs in summer with differences within 1°C, but the ERAI overestimates the ice extent by 72% in winter due to the coarse resolution in the Baltic Sea. The atmosphere in the Baltic land–sea transition was more sensitive to high-resolution modelled SSTs with a significant improvement in winter, but it also provided a cold bias in summer as a combination of errors from both atmospheric and ocean models. Overall, the coupled simulation without observational constraints showed only minor deviations in the air–sea interface in the Baltic coastal region compared to the prescribed simulation, with seasonal mean differences within 2°C in 2 m air temperatures and 1°C in SSTs. An exception was in the Danish water, where the fine-grid ocean model yielded a better agreement with SST measurements and showed a smaller difference between the two simulations than the coarse-grid ocean model did. In turn, the modification on the atmosphere induced by modelled SSTs was negligible. The atmospheric–ocean–ice model in this configuration was found capable of reproducing the observed interannual variability of SST and ice extent in the Baltic Sea as well as the monthly extreme wind speeds and sea levels on a local scale for Denmark during the period 1990–2010. This article provides the first results in an attempt to resolve the Danish coasts with this accuracy in an RCM as a first step towards a fully coupled system for the region of interest.

Coronal mass ejections detected in solar mean magnetic field

One minute resolution solar mean magnetic field sequences during 74 coronal mass ejection events are analyzed using wavelet transforms. A significant fraction of the resulting wavelet power spectra shows a characteristic peak at the time of the coronal mass ejection. With an average period of 13 minutes, the signature in the solar mean field is most likely the result of global waves trigged by the departing CME.

Inflated Uncertainty in Multimodel‐Based Regional Climate Projections

Abstract Multimodel ensembles are widely analyzed to estimate the range of future regional climate change projections. For an ensemble of climate models, the result is often portrayed by showing maps of the geographical distribution of the multimodel mean results and associated uncertainties represented by model spread at the grid point scale. Here we use a set of CMIP5 models to show that presenting statistics this way results in an overestimation of the projected range leading to physically implausible patterns of change on global but also on regional scales. We point out that similar inconsistencies occur in impact analyses relying on multimodel information extracted using statistics at the regional scale, for example, when a subset of CMIP models is selected to represent regional model spread. Consequently, the risk of unwanted impacts may be overestimated at larger scales as climate change impacts will never be realized as the worst (or best) case everywhere.

21st-century climate change around Kangerlussuaq, west Greenland: From the ice sheet to the shores of Davis Strait

ABSTRACT Using regional climate-model runs with a horizontal resolution of 5.5 km for two future scenarios and two time slices (representative concentration pathway [RCP] 4.5 and 8.5; 2031–2050 and 2081–2100) relative to a historical period (1991–2010), we study the climate change for the Qeqqata municipality in general and for Kangerlussuaq in particular. The climate-model runs are validated against observations of temperature and surface mass balance and a reanalysis simulation with the same model setup as the scenario runs, providing high confidence in the results. Clear increases in temperature and precipitation for the end of the 21st century are shown, both on and off the ice sheet, with an off–ice sheet mean annual temperature increase of 2.5–3°C for the RCP4.5 scenario and 4.8–6.0°C for the RCP8.5 scenario, and for precipitation an increase of 20–30% for the RCP4.5 scenario and 30–80% for the RCP8.5 scenario. Climate analogs for Kangerlussuaq for temperature and precipitation are provided, indicating that end-of-the-century Kangerlussuaq mean annual temperature is comparable with temperatures for the south of Greenland today. The extent of glacial retreat is also estimated for the Qeqqata municipality, suggesting that most of the ice caps south of the Kangerlussuaq fjord will be gone before the end of this century. Furthermore, the high-resolution runs are compared with an ensemble of six models run at a 50 km resolution, showing the need for high-resolution model simulations over Greenland.