Temperature Soundings Research Articles

Bias characterization of CrIS shortwave temperature sounding channels using fast NLTE model and GFS forecast field

AbstractThe strong nonlocal thermal equilibrium (NLTE) emission in the upper atmosphere impedes the usage of Cross‐track Infrared Sounder (CrIS) temperature channels near 4.3 µm in the operational data assimilation. This study explores the bias characteristics of those temperature channels near 4.3 µm with and without a fast NLTE model implemented in the Community Radiative Transfer Model (CRTM). It is shown that the biases of those temperature channels can reach up to 12 K and are dramatically reduced to below 4 K during daytime by the fast NLTE model with small differences from the nighttime biases. However, the biases after applying the NLTE correction remain large for CrIS upper atmospheric temperature channels during both daytime and nighttime. A further investigation suggests that the remaining biases in those temperature channels mainly originate from the cold biases in the stratospheric temperature profiles of National Center for Environmental Prediction Global Forecast System (GFS) forecasts as input to CRTM. The cold biases reach the maximum of about 8 K near the tropics at about 1 hPa, decreasing toward higher latitudes and lower altitudes.

Retrieval of Atmospheric Thermodynamic State From Synergistic Use of Radio Occultation and Hyperspectral Infrared Radiances Observations

Atmospheric temperature soundings derived from satellite-based advanced infrared (IR) sounder radiance measurements tend to have higher uncertainty in the upper troposphere. In contrast, radio occultation (RO) measurements have high accuracy and high vertical-resolution for atmospheric sounding in the upper troposphere and lower stratosphere (UTLS). It is anticipated that the best estimation of atmospheric thermodynamic state can be obtained by the synergistic use of RO and IR radiance measurements. A physical-based algorithm accounting for the significant geometric difference between the two observing systems has been developed to combine RO refractivity and Atmospheric InfraRed Sounder (AIRS) radiances for atmospheric temperature and humidity vertical profiles. Comparisons between RO/AIRS and AIRS-alone derived profiles showed that the impact of RO observations to be most apparent in the upper troposphere between 100 and 300 hPa, where the root-mean-square difference (RMSD) of estimated temperature is reduced by 24% (0.36 K) to 35% (0.66 K). In addition to having improved temperature profile retrievals in the upper troposphere, the humidity retrievals are also improved; the RMSD below 100 hPa was reduced by 22.4% (0.298 g/kg) when compared with radiosondes observations. Results indicated that the humidity profiles retrieved using this method were overall better than the IR-only retrievals in all of the comparisons, and the temperature profiles improved upon the IR-only retrievals, most notably in the upper troposphere. These improvements are more significant using a three-dimensional (3-D) slant-path collocation procedure.

Morning transition case between the land and the sea breeze regimes

An experimental field campaign took place in September 2013 near the coastline in the southeastern Campos basin in the island of Mallorca to characterize experimentally the transition between the sea and the land breezes and to further study the successful cases with the corresponding high-resolution numerical simulations. Favorable weather conditions were only found for one episode that comprised a well-formed nocturnal land breeze, followed by the morning transition to sea breeze until noon the next day, when incoming clouds switched off the breeze regime.To analyse this transition between land and sea breezes, the official network of stations is used, supplemented by a portable station close to the shore and soundings of temperature (taken by a captive balloon and remotely controlled multicopter). These data are used to check the goodness of the corresponding simulation at a horizontal resolution of 1km. Model and observations see similarly both regimes and the transition, showing some differences in the timing and the details in the surface layer. This transient event is analyzed in terms of phases, going consecutively through land breeze, phase previous to the sea breeze, when land heating starts, but it is still colder than the sea, the preparatory phase when the land becomes warmer than the sea, and the development phase when the breeze front progresses inland.

Regional Profiles and Precipitation Retrievals and Analysis Using FY-3C MWHTS

The 89 and 150 GHz channels operated in window are sensitive to precipitation and humidity. The 183 GHz humidity-sensitive channels and 118 GHz temperature-sensitive channels of the Microwave Humidity and Temperature Sounder (MWHTS) on the Chinese Feng Yun 3C MWHTS (FY-3C MWHTS) polar-orbit meteorological satellite responds in part to precipitation. Combining 118 and 183 GHz channels, the paper develops a passive sub-millimeter atmospheric profile and precipitation retrievals algorithm for MWHTS onboard the FY-3C (Feng Yun-3C) satellite. The retrieval algorithm employs a number of back propagation neural network estimators trained and evaluated using the validated global reference physical model NCEP/WRF/ARTS and works for land and seawater with latitude between -40 to 40 degree. NCEP data per 6 hours were downloaded to run the Weather Research and Forecast model WRF, and to derive the typical precipitation data for the whole world. The Atmospheric Radiative Transfer Simulator ARTS is feasible for performing simulations of atmospheric radiative transfer. The results show that the profile retrievals using BP-NN algorithm has the best correlation with those from radiosonde, which is less than 18% and 1 K of root mean square error, respectively. For precipitation rate retrievals, a much better agreement is reached with rain gauge and ECMWF datasets, the RMS is between 0.80 to 30.24 mm/h for sea surface and 0.789 to 33.11 mm/h for land surface according to the classification by precipitation type. Also, the analysis of retrievals located in Tibetan plateau is provided as an example to justify the robustness and performance of retrieving model.

A quality control procedure for Fengyun-3A microwave temperature sounder with emphasis on a new cloud detection algorithm

A cloud detection algorithm for satellite radiance from the microwave temperature sounder (MWTS) on board the first satellite of the Chinese polar-orbiting Fengyun-three series (FY-3A) is proposed based on the measurements at the frequencies of 50.3 and 53.6 GHz. The cloud liquid water path index (LWP index) is calculated using the brightness temperature at these two channels. Analysis of one case carried out in January2010shows the great consistency be-tween this new algorithm result and the available liquid water path product from the Meteorological Operational satellite A (MetOp-A).In general, about 60% of the global MWTS data are considered to be contaminated by cloud by virtue of the new cloud detection algorithm. A quality control (QC) procedure is applied to MWTS measurements with emphasis on the cloud detection. The QC steps are composed of (i) channel 2 over sea ice, land and coastal field of views (FOVs); (ii) channels 2 and 3 over cloudy FOVs; and (iii) outliers with large differences between observations and model simulations. After QC, MWTS measurements of channels 2–4 agree very well with the model simulations using the National Centres for Environmental Prediction (NCEP) forecast data as radiative transfer model input; the scan biases are reduced significantly, especially at the edges of the swath; and the frequency distributions of the differences between observations and model simulations become more Gaussian-like.

A quality control procedure for Fengyun-3A microwave temperature sounder with emphasis on a new cloud detection algorithm

A quality control procedure for Fengyun-3A microwave temperature sounder with emphasis on a new cloud detection algorithm

Lidar Soundings Between 30 and 100 km Altitude During Day and Night for Observation of Temperatures, Gravity Waves and Tides

Ground-based temperature measurements by lidar are an important tool for the understanding of long-term temperature changes as well as the propagation of gravity waves and tides. Though, mesospheric soundings are often limited to nighttime conditions due to the low signal-tonoise ratio during the day. We developed a daylight-capable RMR lidar for temperature soundings in the middle atmosphere. The influences of the narrowband detector on the calculated hydrostatic temperatures as well as their correction are described. The RMR lidar is complemented by a co-located resonance lidar. We present an example for tidal analyses and short-term variability of tidal amplitudes.

Observation‐based evaluation of ensemble reliability

In order to obtain new insight into the reliability of the ensemble prediction system of the European Centre for Medium‐range Weather Forecasts (ECMWF), we compare the ensemble spread‐error relationship obtained from an observation‐based verification to the one obtained from an analysis‐based verification. Observations used in this study are mainly radiosonde temperatures and radiance measurements from the AMSU‐A channel 5 microwave temperature sounder. The observation operators from the 4D‐Var data assimilation scheme are used to map the forecasts into observation space. In ‘observation‐space’, observed radiances are compared with forecast radiances, derived from the ensemble's atmospheric profiles of temperature, gas concentrations, cloud, and surface properties using the ‘RTTOV’ radiative transfer code.The observation‐space assessment yields different results than the analysis‐based assessment in the extratropics for short‐range forecasts (1‐day), and in the Tropics in general. In the extratropics, for 5‐day forecasts the discrepancy between the analysis‐based and observation‐based verification is small and the ensemble variances are quite reliable.The observation‐based diagnostics indicate that the stochastic model error schemes contribute to the well‐tuned ensemble spread in the extratropics, but can degrade the reliability of the ensemble in the Tropics. It is suggested that observation‐based diagnostics should be used more routinely to diagnose the ensemble performance, and help diagnosing the effectiveness of model error schemes and estimating the amplitude of the initial perturbations.

Intercalibration and Validation of Observations From ATMS and SAPHIR Microwave Sounders

This paper evaluates the radiometric accuracy of observations from the Advanced Technology Microwave Sounder (ATMS) onboard Suomi National Polar-orbiting Partnership and Sondeur Atmospherique du Profil d' Humidite Intropicale par Radiometrie (SAPHIR) onboard Megha-Tropiques through intercalibration and validation versus in situ radiosonde and Global Positioning System Radio Occultation (GPS-RO) observations. SAPHIR and ATMS water vapor channels operate at slightly different frequencies. We calculated the bias due to radiometric errors as the difference between the observed and simulated differences between the two instruments. This difference, which is often referred to as double difference, ranges between 0.3 and 0.7 K, which shows good consistency between the instruments. We used a radiative transfer model to simulate the satellite brightness temperatures (Tbs) using radiosonde and GPS-RO profiles and then compared simulated and observed Tbs. The difference between radiosonde and ATMS Tbs for the middle and upper tropospheric temperature sounding channels was less than 0.5 K at most stations, but the difference between radiosonde and ATMS/SAPHIR Tbs for water vapor channels was between 0.5 and 2.0 K. The larger bias for the water vapor channels is mainly due to several errors in radiosonde humidity observations. The mean differences between the ATMS observations and the Tbs simulated using GPS-RO profiles were 0.2, 0.3, 0.4, 0.2, and −0.2 K for channels 10–14, respectively; and the uncertainty increases from 0.02 K for channel 10 to 0.07 K for channel 14.

AIRS, IASI, and CrIS Retrieval Records at Climate Scales: An Investigation into the Propagation of Systematic Uncertainty

AbstractUncertainty requirements for climate observations are more stringent than for weather observations because of the scale dependency of natural variation. At present there is no space-based climate observing system, so weather observations have to be aggregated for the study of large-scale change. The management and minimization of uncertainty sources in weather observations are, therefore, a high priority. This work is a first attempt at investigating if a single long-term record can be assembled with temperature retrievals from three hyperspectral satellite sounders in polar orbit: the Atmospheric Infrared Sounder (AIRS) on Aqua in afternoon orbit since 2002, the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp-A in morning orbit since 2006, and the Cross-track Infrared Sounder (CrIS) on board the Suomi National Polar-Orbiting Partnership in afternoon orbit since 2011. These instruments measure not only the vertical atmospheric structure but also atmospheric composition, thus providing coincident observations of many essential climate variables. Two main sources of known systematic differences, namely local sampling time (LST) and instrument type (i.e., interferometer vs grating spectrometer), are characterized. For a 5-yr record it is shown that differences among these temperature soundings are height dependent; a multi-instrument data record could be assembled from measurements of the stratosphere but this is not yet possible for the troposphere, where cloud effects are shown to be dominant and dependent on instrument type. Moreover, LST differences are limited to regional systematic effects in the lower troposphere and boundary layer. This research is a step toward the development of transparent and geophysically consistent methods with which to assemble weather measurements into climate observations.

Assimilation of Chinese Fengyun-3B Microwave Temperature Sounder radiances into the Global GRAPES system with an improved cloud detection threshold

Fengyun-3B (FY-3B) is the second polar-orbiting satellite in the new Fengyun-three series. This paper describes the assimilation of the FY-3B Microwave Temperature Sounder (MWTS) radiances in the Chinese Numerical Weather prediction system — the Global and Regional Assimilation and PrEdiction System (GRAPES). A quality control procedure for the assimilation of the FY-3B MWTS radiance was proposed. Extensive monitoring before assimilation shows that the observations of channel 4 are notably contaminated. Channels 2 and 3 are used in this research. A cloud detection algorithm with an improved cloud-detection threshold is determined and incorporated into the impact experiments. The clear field-of-view (FOV) percentage increased from 42% to 57% with the new threshold. In addition, the newly added FOVs are located in the clear region, as demonstrated by the cloud liquid water path data from NOAA-18. The impact of the MWTS radiances on the prediction of GRAPES was researched. The observation biases of FY-3B MWTS O-B (differences between satellite observations and model simulations) significantly decreased after an empirical bias correction procedure. After assimilation, the residual biases are small. The assimilation of the FY-3B MWTS radiances shows a positive impact in the Northern Hemisphere and a neutral impact in the Southern Hemisphere.

Methodology for determining multilayered temperature inversions

Abstract. Temperature sounding of the atmospheric boundary layer (ABL) and lower troposphere exhibits multilayered temperature inversions specially in high latitudes during extreme winters. These temperature inversion layers are originated based on the combined forcing of local- and large-scale synoptic meteorology. At the local scale, the thermal inversion layer forms near the surface and plays a central role in controlling the surface radiative cooling and air pollution dispersion; however, depending upon the large-scale synoptic meteorological forcing, an upper level thermal inversion can also exist topping the local ABL. In this article a numerical methodology is reported to determine thermal inversion layers present in a given temperature profile and deduce some of their thermodynamic properties. The algorithm extracts from the temperature profile the most important temperature variations defining thermal inversion layers. This is accomplished by a linear interpolation function of variable length that minimizes an error function. The algorithm functionality is demonstrated on actual radiosonde profiles to deduce the multilayered temperature inversion structure with an error fraction set independently.

Cloud and precipitation features of Super Typhoon Neoguri revealed from dual oxygen absorption band sounding instruments on board FengYun‐3C satellite

AbstractA new methodology is developed to detect the cloud structures at different vertical levels using the dual oxygen absorption bands located near 60 GHz and 118 GHz, respectively. Observations from Microwave Temperature Sounder (MWTS) and Microwave Humidity Sounder (MWHS) on board the recently launched Chinese FengYun‐3C satellite are used to prove the concept. It is shown that a paired oxygen MWTS and MWHS sounding channel with the same peak weighting function altitude allows for detecting the vertically integrated cloud water path above that level. A cloud emission and scattering index (CESI) is defined using dual oxygen band measurements to indicate the amounts of cloud liquid and ice water paths. The CESI distributions from three paired channels reveal unique three‐dimensional structures of clouds and precipitation within Super Typhoon Neoguri that occurred in July 2014.

Structural diagnostics of the tropopause inversion layer and its evolution

AbstractThe Tropopause Inversion Layer (TIL) is marked by a peak in static stability directly above the tropopause. The TIL is quantitatively defined with new diagnostics using Global Positioning System Radio Occultation temperature soundings and reanalysis data. A climatology of the TIL is developed from reanalysis data (1980–2011) using diagnostics for the position, depth, and strength of the TIL based on the TIL peak in static stability. TIL diagnostics have defined relationships to the synoptic situation in the Upper Troposphere and Lower Stratosphere. The TIL is present nearly all the time. The TIL becomes hard to define in the subtropics where tropical air overlies midlatitude air, in a region of complex static stability profiles. The mean position of the subtropical TIL gradient is sharp and is co‐located with the subtropical tropopause break. Over the period 1980–2011 the TIL depth below the tropopause has decreased by 5% per decade and increased above the tropical tropopause by a similar percentage. Furthermore, the latitude of the abrupt change in the TIL from tropical to extratropical in the lower stratosphere appears to have shifted poleward in each hemisphere by ∼1° latitude per decade, depending on the diagnostic examined. Reanalysis trends should be treated with caution.

An Assessment of Data from the Advanced Technology Microwave Sounder at the Met Office

An appraisal of the Advanced Technology Microwave Sounder (ATMS) for use in numerical weather prediction (NWP) is presented, including an assessment of the data quality, the impact on Met Office global forecasts in preoperational trials, and a summary of performance over a period of 17 months operational use. After remapping, the noise performance (NEΔT) of the tropospheric temperature sounding channels is evaluated to be approximately 0.1 K, comparing favourably with AMSU-A. However, the noise is not random, differences between observations and simulations based on short-range forecast fields show a spurious striping effect, due to 1/f noise in the receiver. The amplitude of this signal is several tenths of a Kelvin, potentially a concern for NWP applications. In preoperational tests, adding ATMS data to a full Met Office system already exploiting data from four microwave sounders improves southern hemisphere mean sea level pressure forecasts in the 2- to 5-day range by 1-2%. In operational use, where data from five other microwave sounders is assimilated, forecast impact is typically between −0.05 and −0.1 J/kg (3.4% of total mean impact per day over the period 1 April to 31 July 2013). This suggests benefits beyond redundancy, associated with reducing already small analysis errors.

Preliminary investigation of FengYun-3C Microwave Temperature Sounder (MWTS) measurements

The third FengYun satellite (FY-3C) was successfully launched into morning-configured orbit on 23 September 2013. The cross-tracking scanning instrument microwave temperature sounder (MWTS) on board FY-3C provides 13 channels, many more than the four MWTS channels on board FY-3A/B, at frequencies ranging from 50 to 60 GHz, which allow for probing the atmospheric temperature under all conditions except heavy precipitation. This study investigates and assesses the quality of the brightness temperature measurements from MWTS using the rapid radiative transfer model. Overall, MWTS observations (labelled ‘O’) compare favourably with simulations (labelled ‘B’) for troposphere and stratosphere channels except for surface-sensitive channels, the measurements of which provide more detail of thermal structures in the lower troposphere, especially for storm conditions such as tropical cyclones. Moreover, measurements from channels 1 and 4 can be used to derive the cloud liquid water path index (LWPindex) for cloud detection. However, this study also finds that (1) the brightness temperature differences (labelled ‘O-B’) between observations and model simulations exhibit a clear striping pattern for upper level channels; (2) the geolocation result has a systematic bias towards the real geolocation; and (3) the calibrated cold space view is contaminated by light reflected from the moon.

Neural Network Based Retrieval of Atmospheric Temperature Profile Using AMSU-A Observations

The present study describes artificial neural network (ANN) based approach for the retrieval of atmospheric temperature profiles from AMSU-A microwave temperature sounder. The nonlinear relationship between the temperature profiles and satellite brightness temperatures dictates the use of ANN, which is inherently nonlinear in nature. Since latitudinal variation of temperature is dominant one in the Earth’s atmosphere, separate network configurations have been established for different latitudinal belts, namely, tropics, mid-latitudes, and polar regions. Moreover, as surface emissivity in the microwave region of electromagnetic spectrum significantly influences the radiance (or equivalently the brightness temperature) at the satellite altitude, separate algorithms have been developed for land and ocean for training the networks. Temperature profiles from National Center for Environmental Prediction (NCEP) analysis and brightness temperature observations of AMSU-A onboard NOAA-19 for the year 2010 have been used for training of the networks. Further, the algorithm has been tested on the independent dataset comprising several months of 2012 AMSU-A observations. Finally, an error analysis has been performed by comparing retrieved profiles with collocated temperature profiles from NCEP. Errors in the tropical region are found to be less than those in the mid-latitude and polar regions. Also, in each region the errors over ocean are less than the corresponding ones over land.

Radiometer Calibration Using Colocated GPS Radio Occultation Measurements

We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.

Comparison of radio sounding and ground-based remote measurements of temperature profiles in the troposphere

A ground-based experiment on microwave temperature sounding in the troposphere with a RPG-HATPRO instrument, which has been performed at the Faculty of Physics, St. Petersburg State University since June, 2012, is described. On the basis of comparison of the results with radio sounding data, the temperature retrieval errors have been estimated using an algorithm provided by the manufacturer of the instrument. The errors have been compared with corresponding values for similar instruments functioning abroad. The conclusion has been drawn about a need to develop specialized algorithms and data processing procedures which include adaptation and correction of algorithms accounting for peculiarities of a specific instrument and experimental conditions.

S‐NPP ATMS instrument prelaunch and on‐orbit performance evaluation

AbstractThe first of a new generation of microwave sounders was launched aboard the Suomi‐National Polar‐Orbiting Partnership satellite in October 2011. The Advanced Technology Microwave Sounder (ATMS) combines the capabilities and channel sets of three predecessor sounders into a single package to provide information on the atmospheric vertical temperature and moisture profiles that are the most critical observations needed for numerical weather forecast models. Enhancements include size/mass/power approximately one third of the previous total, three new sounding channels, the first space‐based, Nyquist‐sampled cross‐track microwave temperature soundings for improved fusion with infrared soundings, plus improved temperature control and reliability. This paper describes the ATMS characteristics versus its predecessor, the advanced microwave sounding unit (AMSU), and presents the first comprehensive evaluation of key prelaunch and on‐orbit performance parameters. Two‐year on‐orbit performance shows that the ATMS has maintained very stable radiometric sensitivity, in agreement with prelaunch data, meeting requirements for all channels (with margins of ~40% for channels 1–15), and improvements over AMSU‐A when processed for equivalent spatial resolution. The radiometric accuracy, determined by analysis from ground test measurements, and using on‐orbit instrument temperatures, also shows large margins relative to requirements (specified as <1.0 K for channels 1, 2, and 16–22 and <0.75 K for channels 3–15). A thorough evaluation of the performance of ATMS is especially important for this first proto‐flight model unit of what will eventually be a series of ATMS sensors providing operational sounding capability for the U.S. and its international partners well into the next decade.