9 research outputs found
The use of GNSS zenith total delays in operational AROME/Hungary 3D-Var over a central European domain
The delay of satellite signals broadcasted by Global Navigation Satellite
System (GNSS) provides unique atmospheric observations which endorse
numerical weather prediction from global to limited-area models. Due to the
possibility of its frequent and near-real-time estimation, the zenith total
delays (ZTDs) are valuable information for any state-of-the-art data
assimilation system. This article introduces the data assimilation of ZTDs in
a Hungarian numerical weather prediction system, which was carried out by taking
into account observations from central European GNSS analysis and processing
centres. The importance of ZTD observations is described and shown by a
diagnostic tool in the 3-hourly updated 3D-Var assimilation
scheme. Furthermore, observing system experiments are done to evaluate the
impact of GNSS ZTDs on mesoscale limited-area forecasts. The results of the
use of GNSS ZTDs showed a clear added value to improve screen-level
temperature and humidity forecasts when the bias is accurately estimated and
corrected in the data assimilation scheme. The importance of variational, i.e.
adaptive bias correction, is highlighted by verification scores compared to
static bias correction. Moreover, this paper reviews the quality control of
GNSS ground-based stations inside the central European domain, the
calculation of optimal thinning distance and the preparation of the two
above-mentioned bias correction methods. Finally, conclusions are drawn on
different settings of the forecast and analysis experiments with a brief
future outlook.</p
Science with a small two-band UV-photometry mission II: Observations of stars and stellar systems
We outline the impact of a small two-band UV-photometry satellite mission on
the field of stellar physics, magnetospheres of stars, binaries, stellar
clusters, interstellar matter, and exoplanets. On specific examples of
different types of stars and stellar systems, we discuss particular
requirements for such satellite missions in terms of specific mission
parameters such as bandpass, precision, cadence, and mission duration. We show
that such a mission may provide crucial data not only for hot stars that emit
most of their light in UV, but also for cool stars, where UV traces their
activity. This is important, for instance, for exoplanetary studies, because
the level of stellar activity influences habitability. While the main asset of
the two-band UV mission rests in time-domain astronomy, an example of open
clusters proves that such a mission would be important also for the study of
stellar populations. Properties of the interstellar dust are best explored when
combining optical and IR information with observations in UV. It is well known
that dust absorbs UV radiation efficiently. Consequently, we outline how such a
UV mission can be used to detect eclipses of sufficiently hot stars by various
dusty objects and study disks, rings, clouds, disintegrating exoplanets or
exoasteroids. Furthermore, UV radiation can be used to study the cooling of
neutron stars providing information about the extreme states of matter in the
interiors of neutron stars and used for mapping heated spots on their surfaces.Comment: Submitted to Space Science Review
Quick Ultra-VIolet Kilonova surveyor (QUVIK)
We present a near-UV space telescope on a ~70kg micro-satellite with a
moderately fast repointing capability and a near real-time alert communication
system that has been proposed in response to a call for an ambitious Czech
national mission. The mission, which has recently been approved for Phase 0, A,
and B1 study shall measure the brightness evolution of kilonovae, resulting
from mergers of neutron stars in the near-UV band and thus it shall distinguish
between different explosion scenarios. Between the observations of transient
sources, the satellite shall perform observations of other targets of interest,
a large part of which will be chosen in open competition.Comment: SPIE Astronomical Telescopes and Instrumentatio
Science with a small two-band UV-photometry mission I: Mission description and follow-up observations of stellar transients
This is the first in a collection of three papers introducing the science
with an ultra-violet (UV) space telescope on an approximately 100 kg small
satellite with a moderately fast re-pointing capability and a real-time alert
communication system that is being studied for a Czech national space mission.
The mission, called Quick Ultra-Violet Kilonova surveyor - QUVIK, will provide
key follow-up capabilities to increase the discovery potential of gravitational
wave observatories and future wide-field multi-wavelength surveys. The primary
objective of the mission is the measurement of the UV brightness evolution of
kilonovae, resulting from mergers of neutron stars, to distinguish between
different explosion scenarios. The mission, which is designed to be
complementary to the Ultraviolet Transient Astronomy Satellite - ULTRASAT, will
also provide unique follow-up capabilities for other transients both in the
near- and far-UV bands. Between the observations of transients, the satellite
will target other objects described in this collection of papers, which
demonstrates that a small and relatively affordable dedicated UV-space
telescope can be transformative for many fields of astrophysics.Comment: Submitted to Space Science Review