Recent technology advances in miniature microwave radiometers that can be hosted on very small satellites has made possible a new class of affordable constellation missions that provide very high revisit rates of tropical cyclones and other severe weather. The Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission was selected by NASA as part of the Earth Venture–Instrument (EVI-3) program and is now in development with planned launch readiness in late 2019. The overarching goal for TROPICS is to provide nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones (TCs). TROPICS will provide rapid-refresh microwave measurements (median refresh rate better than 60 minutes for the baseline mission) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. TROPICS will comprise a constellation of at least six CubeSats in three low-Earth orbital planes. Each CubeSat will host a high performance radiometer to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles and low-level moisture. This observing system offers an unprecedented combination of horizontal and temporal resolution in the microwave spectrum to measure environmental and inner-core conditions for TCs on a nearly global scale and is a major leap forward in the temporal resolution of several key parameters needed for assimilation into advanced data assimilation systems capable of utilizing rapid-update radiance or retrieval data. Here, we provide an overview of the mission and an update on current status, with a focus on unique characteristics of the Cubesat system, recent performance simulations on a range of observables to be provided by the constellation, and a summary of science applications.
The instantaneous daytime geographical distribution and radiative effects of high thin clouds (optical thickness < 5) are investigated on the basis of the CloudSat Cloud Profiling Radar (CPR) radiative flux and cloud classification products. The regional features of the fraction and radiative effects of high thin clouds are associated with ITCZ, SPCZ and mid-latitude storm track regions. High thin clouds have positive net cloud-induced radiative effect (CRE) at the top of the atmosphere (TOA) and negative net CRE at the bottom of the atmosphere (BOA). The magnitudes of TOA and BOA CREs depend on cloud optical thickness, cloud fraction and geographical location. The magnitude of the net CRE of high thin clouds increases at both TOA and BOA as cloud optical thickness increases. Net CRE at both TOA and BOA contributes to a positive net CRE in-atmosphere and warms the atmosphere regardless of cloud fraction. The global annual mean of the net CRE multiplied by cloud fraction is 0.49 W/m2 at TOA, -0.54 W/m2 at BOA and 1.03 W/m2 in-atmosphere. The most radiatively effective cloud optical thickness of a high thin cloud is between 1-2 for the TOA and in-atmosphere CREs or 3-4 for the BOA CRE.
Top-of-atmosphere radiances and adjoint sensitivities for ice clouds at 600-2300 cm-1 are studied using a new fast radiative transfer system (forward, tangent linear, and adjoint) developed for the NASA/NOAA/DOD Joint Center for Satellite Data Assimilation. The radiative transfer model is based on a hybrid solution method for computing thermal radiances that fully accounts for multiple scattering and that allows clouds to be placed at any number of arbitrary layers. Called the successive order of interaction model, it has been shown to be faster in most cases and more accurate than the popular delta-Eddington model. Ice particle scattering properties are obtained from rigorous scattering theory for various particle shapes and sizes. Gas optical depths are derived from line-by-line calculations. Results indicate that top-of-atmosphere brightness temperatures are sensitive to ice water path occurring in multiple cloud layers, which suggests major challenges for retrieving cloud properties under conditions other than single-layered clouds.
A new, fast radiative transfer model including scattering
has been developed for the purpose of microwave radiance assimilation
in cloudy and precipitating areas. The model uses a technique called
successive order of interaction (SOI) which is based on a blending of the doubling and the successive order of scattering techniques. An adjoint and tangent linear version of the model are also available. Within this paper we present first applications of the SOI model. We compare brightness temperatures simulated from NCEP's Global Forecasting System (GFS) using a non-scattering version of the SOI model with global satellite data obtained by the Advanced Scanning Microwave Radiometer (AMSR-E) onboard NASA's Aqua spacecraft. Additionally, we show first sensitivity studies using the
adjoint model for cases that include scattering by liquid and frozen
Satellite measurements from the Special Sensor Microwave Water Vapor Sounder are used to study the scattering effects of cirrus clouds at 183 GHz. These measurements are used in conjunction with near-coincident Geostationary Operational Environmental Satellite imager observations of visible optical depth and effective particle size. For a case of extensive cold front cirrus off the eastern US coast, the 183 GHz brightness temperature depression relative to clear skies averaged about 3 K, but sometimes exceeded 6 K. The mean effective radius of the ice particles was 141 +/- 14 micrometers . These results show promise for the estimation of ice water path form combined (Delta) Tb and effective particle size observations.