Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground‐based and, nowadays more and more, also by space‐based measurements. ...Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on 3 December 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground‐based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a CubeSat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modeling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground‐based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modeling demonstrate how even a small 1‐Unit (size: 10 × 10 × 10 cm) CubeSat and its camera, build using cheap commercial off‐the‐shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground‐based observations.
Plain Language Summary
Auroras, or polar lights, have been imaged by ground‐based terrestrial cameras for a long time. However, auroras can also be observed from space with cameras mounted on spacecraft. In the last few years, a number of very small satellites, so‐called nanosatellites with masses less than 10 kg, have been developed and launched into so‐called low Earth orbits at altitudes between 300 and 600 km. These small and light satellites are much cheaper than traditional large and heavy satellites, the masses of which could easily exceed hundreds of kilograms. Therefore, it is anticipated that nanosatellites will provide new possibilities to investigate auroras. In this study, we analyze, to our knowledge, the first image of an aurora taken by a nanosatellite. The satellite is a small, 10 × 10 × 10 cm, Suomi 100 satellite which was launched in December 2018. We show how the obtained auroral image can provide new information about auroras when it is combined with ground‐based observations and numerical modeling. When additional cameras will be included in the design and fabrication of small satellites, we will be able to increase our understanding of auroras and, consequently, the effects of the Sun on the Earth and beyond.
Key Points
The concept of imaging aurora toward the Earth's limb by a CubeSat camera is demonstrated
The dark background available in the Earth‐limb viewing direction facilitates imaging of dim auroras, e.g., for auroral tomography purposes
The analysis shows that auroral imaging at low Earth orbit can provide a new context for ground‐based auroral and ionospheric observations
Short-range forecasts (nowcasts) of rainfall facilitate providing early warning of severe rainfall and flooding, which is particularly important in densely populated urban areas. Nowcasts are ...conventionally obtained by the extrapolation of radar echoes from a constant altitude plan position indicator (CAPPI) or lowest-angle plan position indicator (PPI). Lacking a model for growth or decay, this approach has a limited ability to forecast the summertime convective storms. In a previous attempt to address this shortcoming, called RadVil, the predicted surface rain rate is obtained from mass balance equations of vertically integrated liquid (VIL) retrieved from volumetric reflectivity measurements. Predicting the growth and decay has also been attempted by using an autoregressive (AR) model, which led to the development of spectral prognosis (S-PROG). A novel combination of these two methodologies, called ANVIL, is proposed. In this approach, the growth and decay of VIL are modeled by an autoregressive integrated (ARI) process. It is shown that the predictability of growth and decay is scale-dependent. Thus, the key idea of ANVIL is to decompose the VIL into multiple spatial scales and apply a separate ARI model to each scale. The operational feasibility of ANVIL is evaluated using the Next-Generation Radar (NEXRAD)/WSR-88D radar that covers the Dallas-Fort Worth metropolitan area. The evaluation is done using ten convective events in 2018 and 2019. Using several verification metrics, it is shown that ANVIL has up to 25% improved skill compared to conventional nowcasting techniques. The improvement is consistent for a wide range of spatial scales (1-11 km) and rain rate thresholds (5-20 mmh −1 ).
Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of high frequency (HF) electromagnetic ...waves. We have conducted a transionospheric HF‐propagation research campaign with a nanosatellite on a low‐Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the High frEquency rAdio spectRomEteR (HEARER) onboard 1 Unit (size: 10 × 10 × 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite's radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater's antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O‐ and X‐wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater's electromagnetic wave energy. This paper is, to authors' best knowledge, the first observation of this kind of “self‐absorption” measured from the transionospheric signal path from a powerful radio source on the ground to the satellite‐borne receiver.
Key Points
Active radar‐satellite transionospheric measurements in the high frequency (HF) range with a CubeSat‐size satellite have been performed
A radio spectrometer onboard the Suomi 100 CubeSat detected a clear signal transmitted by the EISCAT HF heater
The properties of ionospheric plasma were found to be affected by the energy of the transmitted heater signal
This study uses snow events from the Biogenic Aerosols–Effects on Clouds and Climate (BAECC) 2014 campaign to investigate the connection between properties of snow and radar observations. The general ...hydrodynamic theory is applied to video-disdrometer measurements to retrieve masses of falling ice particles. Errors associated with the observation geometry and themeasured particle size distribution (PSD) are addressed by devising a simple correction procedure. The value of the correction factor is determined by comparison of the retrieved precipitation accumulation with weighing-gauge measurements. Derived mass–dimensional relations are represented in the power-law form m = amDbm
. It is shown that the retrieved prefactor am and exponent bm react to changes in prevailingmicrophysical processes. From the derived microphysical properties, event-specific relations between the equivalent reflectivity factor Zₑ and snowfall precipitation rate S (Zₑ = azsSbzs
) are determined. For the studied events, the prefactor of the Zₑ–S relation varied between 53 and 782 and the exponent was in the range of 1.19–1.61. The dependence of the factors azs
and bzs
on the m(D) relation and PSD are investigated. The exponent of the Zₑ–S relation mainly depends on the exponent of the m(D) relation, whereas the prefactor azs
depends on both the intercept parameter N₀ of the PSDand the prefactors of the m(D) and v(D) relations. Changes in azs
for a given N₀ are shown to be linked to changes in liquid water path, which can be considered to be a proxy for degree of riming.
The Curiosity observations of surface pressure, optical thickness (τ), and Mars Year 32 water column values (PWC) were used to force adsorptive column model simulations around the MY34 strong dust ...event. Hourly ground (Tg) and air temperatures and water vapor mixing ratios were used for model validation. The diurnal amplitude of Tg drops from 90 K to 30 K during thick dust (τ up to 7–8.5), then increases back to 90 K in the pace of τ decreasing back to seasonal average values. The model mimics the very large and rapid temperature changes quite well, strong dust downward IR emission being the dominant term in the surface heat budget during thick dust. Sensitivity tests indicate that the thick dust tends to show more solar forward scatter initially, consistent with larger particles. Water vapor mixing ratios are lower than normal before and after the event but a lot higher during it. The required local PWC at Gale is 2–3 μm lower than during the low-dust MY32 before and after the dust event, but about 7–8 μm higher during the peak of it.
•Curiosity observations during the 2018/MY34 global dust storm were used to force and validate a column model.•The model simulated the observed surface and air temperatures quite well.•Thick dust indicates initially more forward scatter, and higher surface albedo afterwards.•Observed water vapor mixing ratios are low before and after the storm but high during it.•The required PWC is 2-3 μm lower than normal before and after the storm, but about 7-8 μm higher during the peak of it.
Abstract
Nowcasts (short-term forecasts) of heavy rainfall causing flash floods are highly valuable in densely populated urban areas. In the Collaborative Adaptive Sensing of the Atmosphere (CASA) ...project, a high-resolution X-band radar network was deployed in the Dallas–Fort Worth (DFW) metroplex. The Dynamic and Adaptive Radar Tracking of Storms (DARTS) method was developed as a part of the CASA nowcasting system. In this method, the advection field is determined in the spectral domain using the discrete Fourier transform. DARTS was recently extended to include a filtering scheme for suppressing small-scale precipitation features that have low predictability. Building on the earlier work, Stochastic DARTS (S-DARTS), a probabilistic extension of DARTS, is developed and tested using the CASA DFW radar network. In this method, the nowcasts are stochastically perturbed in order to simulate uncertainties. Two novel features are introduced in S-DARTS. First, the scale filtering and perturbation based on an autoregressive model are done in the spectral domain in order to achieve high computational efficiency. Second, this methodology is extended to modeling the temporal evolution of the advection field. The performance and forecast skill of S-DARTS are evaluated with different precipitation intensity thresholds and ensemble sizes. It is shown that S-DARTS can produce reliable probabilistic nowcasts in the CASA DFW domain with 250-m spatial resolution up to 45 min for lower precipitation intensities (below 2 mm h
−1
). For higher intensities (above 5 mm h
−1
), adequate skill can be obtained up to 15 min.
•A column model with adsorption was forced by 113 ChemCam passive-mode local PWC retrievals for more than a martian year, and results were compared to REMS-H observations.•The pre-dawn model results ...with regolith adsorption are quite similar to REMS-H at all seasons, whereas without adsorption there is too much nighttime moisture.•The night depletion rate is about 0.25 throughout the year.•Daytime comparisons to ChemCam vmr support a seasonally varying vertical distribution of moisture with a relatively dry lower atmosphere.
Local column precipitable water contents (PWC) for more than a martian year from 113 Curiosity ChemCam passive-mode sky scans were used to force a column model with subsurface adsorption. ChemCam volume mixing ratios (vmr) and T, RH and vmr from REMS-H were compared with model results. The REMS-H observations point to decrease of vmr (i.e. depletion of near-surface water vapor) during every evening and night throughout the year. The model's pre-dawn results are quite similar to the REMS-H observations, if adsorption is allowed. The indicated porosity is about 30% and the night depletion ratio about 0.25. If adsorption is not allowed, RH and vmr become excessive during every night at all seasons, leading to ground frost between Ls 82°–146°; frost has not been observed. As brine formation is unlikely along the Curiosity track, adsorption thus appears to be the depleting process.
During daytime the ChemCam vmr is in general close to surface values from the Mars Climate Database (MCD) vmr profiles for the Curiosity site when those profiles are scaled to match the ChemCam PWC. Our simulated daytime surface-vmr is in turn close to the ChemCam vmr when moisture is assumed well-mixed to high altitudes, whereas a low moist layer (15 km) leads to overestimates, which are worse during the warm season. Increased TES-like regional PWC also leads to large overestimates of daytime surface-vmr. Hence the crater appears to be drier than the region surrounding Gale and the results support a seasonally varying vertical distribution of moisture with a dry lower atmosphere (by Hadley circulation), as suggested by MCD and other GCM experiments.
Short-term forecasts (nowcasts) of severe rainfall and flooding are of high importance to the society. In the collaborative adaptive sensing of the atmosphere (CASA) project, a high-resolution X-band ...radar network was deployed in the Dallas-Fort Worth (DFW) urban area. The dynamic and adaptive radar tracking of storms (DARTS) is a key component of the precipitation nowcasting system that was developed in the CASA project. In DARTS, the advection field determination is formulated in the spectral domain using the discrete Fourier transform (DFT). Building on the earlier work, an extension of DARTS is proposed. The novelty of the proposed scale filtering (SF-DARTS) method is the formulation of the extrapolation also in the spectral domain. The extrapolation method is combined with autoregressive AR(2) models applied to Fourier frequency bands together with adaptive truncation of DFT coefficients. This effectively filters small spatial scales having low predictability. It is shown that the proposed approach improves forecast skill and gives improved computational efficiency compared to conventional methods. Another important contribution is that DARTS is being evaluated for the first time beyond the urban scale. DARTS and SF-DARTS are evaluated using data from two different sources, namely the urban-scale CASA DFW network (200 km), and the country-wide radar network operated by the Finnish Meteorological Institute (1000 km).
The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station humidity instrument (REMS-H) onboard the Curiosity rover is measuring daily minimum water vapor mixing ratios (min vmr), the ...respective pre-dawn air temperatures (T), and vmr at 2200LT. These are displayed for nearly three martian years (sols 10–2003) and compared with adsorptive column model simulations. The model was initialized with MSL-observed local column water contents, optical depths and surface pressures from sols 230–1291, assuming the same annual cycle outside this period.
The first two and a half MSL years present rather similar annual cycles in the REMS-H data, whereas from about sol 1800 onward the min vmr and T suddenly increase and the 2200LT vmr values get closer to the min vmr, indicating less depletion of water vapor during the nights. Model experiments with typical regolith (ground thermal inertia of 300 SI units and porosity of 30% for adsorption) match the observed min vmr and T relatively well for the first 2.5 years. However, from about sol 1800 onward, when Curiosity started to climb onto Mt. Sharp, simulations with higher thermal inertia of about 400 SI units and very low porosity of ~0.3%, suggesting exposed bedrock, provide a far better fit. Some other periods of bedrock- and dune-dominated ground can be detected from the REMS-H vmr and air-T data along the Curiosity traverse.
•MSL REMS-H daily minimum vmr and T are shown for three martian years and compared with adsorptive column model simulations.•The first 2.5 MSL years display similar annual cycles, whereas from about sol 1800 onward min vmr and T suddenly increase.•Model with typical regolith matches the first 2.5 years of T and vmr relatively well.•Model with exposed bedrock matches T and min vmr relatively well from sol 1800 onward.•Shorter periods of bedrock- and dune-like ground can be detected from both the T- and vmr data along the Curiosity traverse.
The
Mars Regional Atmospheric Modeling System
(
MRAMS
) and a nested simulation of the
Mars Weather Research and Forecasting model
(
MarsWRF
) are used to predict the local meteorological conditions ...at the
Mars 2020 Perseverance
rover landing site inside Jezero crater (Mars). These predictions are complemented with the
COmplutense and MIchigan MArs Radiative Transfer
model (
COMIMART
) and with the local
Single Column Model
(
SCM
) to further refine predictions of radiative forcing and the water cycle respectively. The primary objective is to facilitate interpretation of the meteorological measurements to be obtained by the
Mars Environmental Dynamics Analyzer
(
MEDA
) aboard the rover, but also to provide predictions of the meteorological phenomena and seasonal changes that might impact operations, from both a risk perspective and from the perspective of being better prepared to make certain measurements. A full diurnal cycle at four different seasons (
L
s
0
∘
,
90
∘
,
180
∘
, and
270
∘
) is investigated. Air and ground temperatures, pressure, wind speed and direction, surface radiative fluxes and moisture data are modeled. The good agreement between observations and modeling in prior works Pla-Garcia et al. in Icarus 280:103–113,
2016
; Newman et al. in Icarus 291:203–231,
2017
; Vicente-Retortillo et al. in Sci. Rep. 8(1):1–8,
2018
; Savijärvi et al. in Icarus,
2020
provides confidence in utilizing these models results to predict the meteorological environment at
Mars 2020 Perseverance
rover landing site inside Jezero crater. The data returned by
MEDA
will determine the extent to which this confidence was justified.
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