TY  - JOUR
A1  - Bürger, Gerd
A1  - Pfister, A.
A1  - Bronstert, Axel
T1  - Temperature-Driven Rise in Extreme Sub-Hourly Rainfall
JF  - Journal of climate
N2  - Estimates of present and future extreme sub-hourly rainfall are derived from a daily spatial followed by a sub-daily temporal downscaling, the latter of which incorporates a novel, and crucial, temperature sensitivity. Specifically, daily global climate fields are spatially downscaled to local temperature T and precipitation P, which are then disaggregated to a temporal resolution of 10 min using a multiplicative random cascade model. The scheme is calibrated and validated with a group of 21 station records of 10-min resolution in Germany. The cascade model is used in the classical (denoted as MC) and in the new T-sensitive (MC+) version, which respects local Clausius-Clapeyron (CC) effects such as CC scaling. Extreme P is positively biased in both MC versions. Observed T sensitivity is absent in MC but well reproduced by MC+. Long-term positive trends in extreme sub-hourly P are generally more pronounced and more significant in MC+ than in MC. In units of 10-min rainfall, observed centennial trends in annual exceedance counts (EC) of P > 5 mm are +29% and in 3-yr return levels (RL) +27%. For the RCP4.5-simulated future, higher extremes are projected in both versions MC and MC+: per century, EC increases by 30% for MC and by 83% for MC+; the RL rises by 14% for MC and by 33% for MC+. Because the projected daily P trends are negligible, the sub-daily signal is mainly driven by local temperature.
KW  - Extreme events
KW  - Rainfall
KW  - Climate change
KW  - Statistical techniques
KW  - Time series
KW  - Stochastic models
Y1  - 2019
U6  - https://doi.org/10.1175/JCLI-D-19-0136.1
SN  - 0894-8755
SN  - 1520-0442
VL  - 32
IS  - 22
SP  - 7597
EP  - 7609
PB  - American Meteorological Soc.
CY  - Boston
ER  - 
TY  - JOUR
A1  - Bürger, Gerd
T1  - Intraseasonal oscillation indices from complex EOFs
JF  - Journal of climate
N2  - Indices of oscillatory behavior are conveniently obtained by projecting the fields in question into a phase space of a few (mostly just two) dimensions; empirical orthogonal functions (EOFs) or other, more dynamical, modes are typically used for the projection. If sufficiently coherent and in quadrature, the projected variables simply describe a rotating vector in the phase space, which then serves as the basis for predictions. Using the boreal summer intraseasonal oscillation (BSISO) as a test case, an alternative procedure is introduced: it augments the original fields with their Hilbert transform (HT) to form a complex series and projects it onto its (single) dominant EOF. The real and imaginary parts of the corresponding complex pattern and index are compared with those of the original (real) EOF. The new index explains slightly less variance of the physical fields than the original, but it is much more coherent, partly from its use of future information by the HT. Because the latter is in the way of real-time monitoring, the index can only be used in cases with predicted physical fields, for which it promises to be superior. By developing a causal approximation of the HT, a real-time variant of the index is obtained whose coherency is comparable to the noncausal version, but with smaller explained variance of the physical fields. In test cases the new index compares well to other indices of BSISO. The potential for using both indices as an alternative is discussed.
KW  - Madden-Julian oscillation
KW  - Oscillations
KW  - Empirical orthogonal functions
KW  - Filtering techniques
KW  - Statistical techniques
KW  - Forecasting techniques
Y1  - 2021
U6  - https://doi.org/10.1175/JCLI-D-20-0427.1
SN  - 0894-8755
SN  - 1520-0442
VL  - 34
IS  - 1
SP  - 107
EP  - 122
PB  - American Meteorological Soc.
CY  - Boston
ER  -