29 research outputs found
Solar spectral irradiance variability from SCIAMACHY on daily to several decades timescales
The sun's radiative output is the primary energy input to the Earth, planets, and the entire heliosphere. It determines the thermal structure of the Earth s atmosphere, and overall it sustains life as we know it. The solar spectral irradiance (SSI) determines the general circulation, ozone photochemistry, and weather-climate system. Both SSI and the total solar irradiance (TSI or 'solar constant') vary in time. The 'solar constant' is obtained by integrating SSI over the entire electromagnetic spectrum. It is now established to vary about 0.2 0.4% during the 27-day solar rotation due to transit of active region across the solar disk and 0.1% over an 11-year solar cycle due to variations of magnetic surface activity of the sun related to the reversal of the solar magnetic field. While SSI variability in the UV is moderately well understood, little is known about variability in the optical and near IR (vis-IR) spectral range. This is because while the variations in UV are large, vis-IR variations are small, which are within the noise level of the instrument. The overall goal of this dissertation, therefore, is to improve our understanding of SSI variability especially at longer wavelengths beyond the UV. Regular monitoring of SSI from space covering the entire UV and vis-IR has become available at a moderately high spectral resolution with SCIAMACHY aboard ENVISAT since 2002. This cumulative dissertation presents in three published manuscripts the most recent progress in understanding SSI variability not only in the UV but also in the vis-IR spectral region using SCIAMACHY data. The first published manuscript ad- dresses the validation of radiometrically calibrated SSI from SCIAMACHY to existing SSI data (from ground and space) and to compare SCIAMACHY SSI variations with various other satellite data from SIM onboard SORCE, SUSIM onboard UARS, and SBUVs. The second published manuscript describes the parametrization of SCIAMACHY SSI time series in terms of solar proxies: Mg II core-to-wing (ctw) ratio for faculae brightening and photometric sunspot index (PSI) for sunspot darkening. This simple irradiance model is referred to as the SCIA proxy model. This model allows us to estimate past solar irradiance variations over several decades well beyond the observation period of the SCIAMACHY satellite. Most satellites observing in the optical spectral range suffer from hard radiation in space, particular in the UV, therefore these satellites optically degrade with time. The parametrization using the solar proxy model also enables the application of a simple degradation correction with the need for detailed re-calibration of solar irradiance measurements, which is not always possible or feasible. So far these two goals focus on short timescales (days to several months). The third published manuscript deals with the application of the model to reconstruct daily SSI variability from 1978 to present, covering several decades. The reconstructed SSI from SCIA proxy on daily to decadal timescales are compared to the solar atmosphere model SRPM and space observations from SIM/SORCE, SUSIM/UARS, the DeLand and Cebula/SSAI UV composite; and other proxy models such as NRLSSI, SIP (formerly Solar2000) and semi-empirical model SATIRE
Calculation of Higher Mass-Dimensional Effective Lagrangians in Quantum Field Theory
A prescription for calculating low-energy one-loop higher-mass dimensional
effective Lagrangians for non-Abelian field theories is constructed in the
spirit of quasilocal background field method. Basis of Lorentz and
gauge-invariant monomials of similar mass-dimensions acting as building blocks
are matrix-multiplied in a specified order (usually dictated by a permutation
of tensorial indices) generating the much needed invariants. The same set of
building blocks is used to generate higher-order corrections for a specific
mass-dimension. Though the gauge group, the spacetime dimensions, the order of
corrections that can be included, and the mass-dimensions that can be formed
are all kept arbitrary in the prescription, we constructed basis invariants
from 3 up to 12 mass-dimensions to accommodate higher-order corrections up to
fourth-order. With these basis, we pursued solving the zeroth-order corrections
leading to invariants from 2 up to 16 mass-dimensions, for first-order from 4
up to 8 mass-dimensions, second and third order corrections from 6 up to 8
mass-dimensions. As a result, we have reproduced the zeroth-order corrections
showing dependence on the covariant derivative of the background matrix
potential. Previous calculation was done up to 12 mass-dimensions but this
dependence was not shown in closed form. For higher-order corrections, the case
for 4 up to 6 mass-dimensions are also reproduced. Finally, we calculated the
case for 8 mass-dimensions which is reduced only by exploiting the antisymmetry
of the fieldstrength tensor and the freedom to throw away total derivatives.Comment: 186 pages, MS Thesi
The influence of spectral solar irradiance data on stratospheric heating rates during the 11 year solar cycle
Heating rate calculations with the FUBRad shortwave (SW) radiation parameterization have been performed to examine the effect of prescribed spectral solar fluxes from the NRLSSI, MPS and IUP data sets on SW heating rates over the 11 year solar cycle 22. The corresponding temperature response is derived from perpetual January General Circulation Model (GCM) simulations with prescribed ozone concentrations. The different solar flux input data sets induce clear differences in SW heating rates at solar minimum, with the established NRLSSI data set showing the smallest solar heating rates. The stronger SW heating in the middle and upper stratosphere in the MPS data warms the summer upper stratosphere by 2 K. Over the solar cycle, SW heating rate differences vary up to 40% between the irradiance data sets, but do not result in a significant change of the solar temperature signal. Lower solar fluxes in the newer SIM data lead to a significantly cooler stratosphere and mesosphere when compared to NRLSSI data for 2007. Changes in SW heating from 2004 to 2007 are however up to six times stronger than for the NRLSSI data.
Key Points:
- Solar minimum and solar cycle differences in SW heating rates and temperature
- Comparison of three spectral solar input data sets for solar cycle 22
- Comparison of the newly compiled SORCE-data with the commonly used NRLSSI-dat
Towards a long-term record of solar total and spectral irradiance
The variation of total solar irradiance (TSI) has been measured since 1978
and that of the spectral irradiance for an even shorter amount of time.
Semi-empirical models are now available that reproduce over 80% of the measured
irradiance variations. An extension of these models into the more distant past
is needed in order to serve as input to climate simulations. Here we review our
most recent efforts to model solar total and spectral irradiance on time scales
from days to centuries and even longer. Solar spectral irradiance has been
reconstructed since 1947. Reconstruction of solar total irradiance goes back to
1610 and suggests a value of about 1-1.5 Wm for the increase in the
cycle-averaged TSI since the end of the Maunder minimum, which is significantly
lower than previously assumed but agrees with other modern models. First steps
have also been made towards reconstructions of solar total and spectral
irradiance on time scales of millennia
Solar irradiance variability: a six-year comparison between SORCE observations and the SATIRE model
Aims: We investigate how well modeled solar irradiances agree with
measurements from the SORCE satellite, both for total solar irradiance and
broken down into spectral regions on timescales of several years. Methods: We
use the SATIRE model and compare modeled total solar irradiance (TSI) with TSI
measurements between 2003 and 2009. Spectral solar irradiance over 200-1630nm
is compared with the SIM instrument on SORCE between 2004 and 2009 during a
period of decline from moderate activity to the recent solar minimum in 10 nm
bands and for three spectral regions of significant interest: the UV integrated
over 200-300nm, the visible over 400-691nm and the IR between 972-1630 nm.
Results: The model captures 97% of observed TSI variation. In the spectral
comparison, rotational variability is well reproduced, especially between 400
and 1200 nm. The magnitude of change in the long-term trends is many times
larger in SIM at almost all wavelengths while trends in SIM oppose SATIRE in
the visible between 500 and 700nm and between 1000 and 1200nm. We discuss the
remaining issues with both SIM data and the identified limits of the model,
particularly with the way facular contributions are dealt with, the limit of
flux identification in MDI magnetograms during solar minimum and the model
atmospheres in the IR employed by SATIRE. It is unlikely that improvements in
these areas will significantly enhance the agreement in the long-term trends.
This disagreement implies that some mechanism other than surface magnetism is
causing SSI variations, in particular between 2004 and 2006, if the SIM data
are correct. Since SATIRE was able to reproduce UV irradiance between 1991 and
2002 from UARS, either the solar mechanism for SSI variation fundamentally
changed around the peak of cycle 23, or there is an inconsistency between UARS
and SORCE UV measurements. We favour the second explanation.Comment: 14 pages, 13 figure
Variationen in der spektralen Strahlungsintensität der Sonne auf Basis der SCIAMACHY-Beobachtungen bei täglichen und jahrzehntelangen Meßzeiträumen.
The sun's radiative output is the primary energy input to the Earth, planets, and the entire heliosphere. It determines the thermal structure of the Earth s atmosphere, and overall it sustains life as we know it. The solar spectral irradiance (SSI) determines the general circulation, ozone photochemistry, and weather-climate system. Both SSI and the total solar irradiance (TSI or 'solar constant') vary in time. The 'solar constant' is obtained by integrating SSI over the entire electromagnetic spectrum. It is now established to vary about 0.2 0.4% during the 27-day solar rotation due to transit of active region across the solar disk and 0.1% over an 11-year solar cycle due to variations of magnetic surface activity of the sun related to the reversal of the solar magnetic field. While SSI variability in the UV is moderately well understood, little is known about variability in the optical and near IR (vis-IR) spectral range. This is because while the variations in UV are large, vis-IR variations are small, which are within the noise level of the instrument. The overall goal of this dissertation, therefore, is to improve our understanding of SSI variability especially at longer wavelengths beyond the UV. Regular monitoring of SSI from space covering the entire UV and vis-IR has become available at a moderately high spectral resolution with SCIAMACHY aboard ENVISAT since 2002. This cumulative dissertation presents in three published manuscripts the most recent progress in understanding SSI variability not only in the UV but also in the vis-IR spectral region using SCIAMACHY data. The first published manuscript ad- dresses the validation of radiometrically calibrated SSI from SCIAMACHY to existing SSI data (from ground and space) and to compare SCIAMACHY SSI variations with various other satellite data from SIM onboard SORCE, SUSIM onboard UARS, and SBUVs. The second published manuscript describes the parametrization of SCIAMACHY SSI time series in terms of solar proxies: Mg II core-to-wing (ctw) ratio for faculae brightening and photometric sunspot index (PSI) for sunspot darkening. This simple irradiance model is referred to as the SCIA proxy model. This model allows us to estimate past solar irradiance variations over several decades well beyond the observation period of the SCIAMACHY satellite. Most satellites observing in the optical spectral range suffer from hard radiation in space, particular in the UV, therefore these satellites optically degrade with time. The parametrization using the solar proxy model also enables the application of a simple degradation correction with the need for detailed re-calibration of solar irradiance measurements, which is not always possible or feasible. So far these two goals focus on short timescales (days to several months). The third published manuscript deals with the application of the model to reconstruct daily SSI variability from 1978 to present, covering several decades. The reconstructed SSI from SCIA proxy on daily to decadal timescales are compared to the solar atmosphere model SRPM and space observations from SIM/SORCE, SUSIM/UARS, the DeLand and Cebula/SSAI UV composite; and other proxy models such as NRLSSI, SIP (formerly Solar2000) and semi-empirical model SATIRE