Localized Upper Tropospheric Warming During Tropical Depression and Storm Formation Revealed by the NOAA-15 AMSU (original) (raw)
Related papers
Satellite Analysis of Tropical Cyclones Using the Advanced Microwave Sounding Unit (AMSU)
Bulletin of the American Meteorological Society, 2000
The first Advanced Microwave Sounding Unit (AMSU) was launched aboard the NOAA-15 satellite on 13 May 1998. The AMSU is well suited for the observation of tropical cyclones because its measurements are not significantly affected by the ice clouds that cover tropical storms. In this paper, the following are presented: 1) upper-tropospheric thermal anomalies in tropical cyclones retrieved from AMSU data, 2) the correlation of maximum temperature anomalies with maximum wind speed and central pressure, 3) winds calculated from the temperature anomaly field, 4) comparison of AMSU data with GOES and AVHRR imagery, and 5) tropical cyclone rainfall potential. The AMSU data appear to offer substantial opportunities for improvement in tropical cyclone analysis and forecasting.
Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds
Monthly Weather Review, 2001
The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle-and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables. Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V max). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1-10 T b data (␦ r T b), the squares of these gradients, a channel-15-based scattering index (SI 89), and area-averaged T b. Calculations of T b and ␦ r T b from mesoscale model simulations of Andrew (1992) reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center V max estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V max , the average error standard deviation was 4.7 m s Ϫ1. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m s Ϫ1. Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.
Impact of the Advanced Microwave Sounding Unit Measurements on Hurricane Prediction
Monthly Weather Review, 2002
Due to the lack of meteorological observations over the tropical oceans, almost all the current hurricane models require bogusing of a vortex into the large-scale analysis of the model initial state. In this study, an algorithm to construct hurricane vortices is developed using the Advanced Microwave Sounding Unit (AMSU-A) data. Under rain-free atmospheric conditions, the temperature profile could be retrieved with a root-meansquare error of 1.5ЊC. Under heavy rainfall conditions, measurements from channels 3-5 are removed in retrieving temperatures. An application of this algorithm to Hurricane Bonnie (1998) shows well the warm-core eye and strong thermal gradients across the eyewall. The rotational and divergent winds are obtained by solving the nonlinear balance and omega equations using the large-scale analysis as the lateral boundary conditions. In doing so, the sea level pressure distribution is empirically specified, and the geopotential heights are calculated from the retrieved temperatures using the hydrostatic equation. The so-derived temperature and wind fields associated with Bonnie compare favorably to the dropsonde observations taken in the vicinity of the storm. The initial moisture field is specified based on the AMSU-derived total precipitable water. The effectiveness of using the retrieved hurricane vortex as the model initial conditions is tested using three 48-h simulations of Bonnie with the finest grid size of the 4-km, triply nested version of the fifthgeneration Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5). It is found that the control run captures reasonably well the track and rapid deepening stage of the storm. The simulated radar reflectivity exhibits highly asymmetric structures of the eyewall and cloud bands, similar to the observed. A sensitivity simulation is conducted, in which an axisymmetric vortex is used in the model initial conditions. The simulated features are less favorable compared to the observations. Without the incorporation of the AMSU data, the simulated intensity and cloud structures differ markedly from the observed. The results suggest that this algorithm could provide an objective, observation-based way to incorporate a dynamically consistent vortex with reasonable asymmetries into the initial conditions of hurricane models. This algorithm could also be utilized to estimate three-dimensional hurricane flows after the hurricane warm core and eyewall are developed.
Satellite analysis of tropical cyclones using NOAA-16 AMSU measurements over Indian region
MAUSAM
The first Advanced Microwave Sounding Unit (AMSU) was launched aboard NOAA-15 satellite on 13 May 1998. AMSU measurements are now also available from NOAA-16 and NOAA-17 satellites. The AMSU is well suited for the observation of tropical cyclones because the ice clouds that cover tropical cyclones do not significantly affect its measurements. In this paper the intensity of three tropical cyclones formed over Bay of Bengal and Arabian Sea in the month of October 1999, May and September 2001 were studied using AMSU measurements. The upper tropospheric warm core thermal anomalies over the tropical cyclone areas were computed from temperature profiles using the NOAA-15 and NOAA-16 AMSU-A measurements. It has been observed that the magnitude of the warm core temperature anomaly at about 250 hPa was an indicator of the intensity of tropical cyclones in all three cases. The order of the temperature anomaly was about 6oC in case of super tropical cyclone, 1999 while in other two cases...
We analysed a reaction of the system “ocean-atmosphere” characteristics on the passing of the powerful tropical cyclone Katrina in August 2005 in the Florida Strait in area of the station SMKF1 (Sombrero Key) as well as a behaviour of the system in the period of time preceding to arising and developing the cyclone Humberto in September 2007 in the Mexico Gulf in area of the station 42019. It was shown with the data of station (buoy) meteorological and simultaneous satellite microwave radiometric measurements in these areas that such characteristics as the near-surface air temperature, humidity and pressure, the fluxes of sensible and latent heat and impulse at the ocean-atmosphere boundary as well as the atmosphere integral water vapour content and enthalpy react clearly to the cyclone Katrina passing and to beginning and progress of the cyclone Humberto. The technique of analysis of the atmosphere integral characteristics such as its total water vapour content and enthalpy was developed. It enables us to determine variations of the atmosphere temperature and humidity at various horizons during passing the cyclone Katrina the station SMKF1 and birth of the cyclone Humberto in area of the station 42019. It was shown that in both cases the effect of taking off the heat energy by cyclones from the atmosphere and the ocean surface takes a place. This effect results in strong disturbances of the temperature, humidity and pressure in the near-surface atmosphere and is accompanied by a sharp decrease of the atmosphere enthalpy and considerable increase of the vertical turbulent heat and moisture fluxes at the ocean surface.
Due to a shorter effective integration time for each field‐of‐view (FOV) of the Advanced Microwave Temperature Sounder (ATMS) onboard the Suomi National Polar‐orbiting Partnership (S‐NPP) satellite than that for the Advanced Microwave Sounding Unit‐A (AMSU‐A) onboard previous National Oceanic and Atmospheric Administration (NOAA) polar‐orbiting satellites NOAA‐15 to ‐19, ATMS temperature‐sounding channels have higher observational resolutions and larger noise equivalent differential temperatures (NEDTs) than the corresponding AMSU‐A channels. The high resolution of the ATMS allows hurricane rainband features that are not resolvable by AMSU‐A to be captured. But the larger NEDT of ATMS weakens this capability through the significant impact of observational noise on warm‐core retrievals. In this study, a remapping algorithm is applied to obtain AMSU‐A‐like ATMS FOVs to suppress this noise. A modified warm‐core retrieval algorithm, which consists of two sets of training coefficients for clear‐sky and cloudy conditions, is applied to limb‐corrected ATMS and AMSU‐A measurements using collocated global positioning system radio occultation observations in the previous month of the targeted hurricanes as training datasets. ATMS channels 5, 6, and 7 (AMSU‐A channels 4, 5, and 6) are excluded when training the coefficients for cloudy conditions to avoid cloud/rain contamination. As a result, the abnormal cold core in the low and middle troposphere and the banded warm structures in phase with rainbands are both successfully removed. The warm‐core evolution of Hurricane Matthew (2016) during its entire life span is temporally consistent on intensity as obtained from NOAA‐15, NOAA‐18, and MetOp‐B AMSU‐A observations and S‐NPP ATMS observations.
2024
Purpose. Wind speed accuracy in diverse storm systems is crucial for weather prediction, climate studies and marine applications. This study aims to evaluate the performance of the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation atmospheric reanalysis (ERA5) for wind speeds in extratropical cyclones (ETCs), polar lows (PLs) and tropical cyclones (TCs), as well as to propose a correction function for potential biases. Methods and Results. We compared the ERA5 wind speeds with the data from the Advanced Microwave Scanning Radiometer-2 (AMSR-2) satellite for various storm events. Statistical metrics, including bias, root mean squared error (RMSE) and correlation coefficient (R), were calculated to quantify discrepancies between the two datasets. Based on the observed biases, a simple exponential correction function was proposed to adjust the ERA5 wind speeds. The effectiveness of the correction function was evaluated through visual comparisons and quantitative analyses. The analysis revealed that the ERA5 systematically underestimated wind speeds across large areas within ETCs, PLs and TCs compared to the AMSR-2 observations. The proposed correction function successfully improved the agreement between ERA5 and AMSR-2 wind speeds in ETCs and PLs. However, applying the same function to TCs revealed significant structural discrepancies between the ERA5 and the AMSR-2 wind fields within these systems. Conclusions. This study demonstrates effectiveness of the proposed correction function in enhancing wind speed accuracy for ETCs and PLs, bringing them closer to AMSR-2 observations. However, further research is necessary to develop approaches for addressing wind speed biases in TCs, considering the unique characteristics and limitations of existing reanalysis data. This research contributes to improving our understanding and representation of wind speeds in diverse storm systems, ultimately aiding in more accurate weather forecasting and climate monitoring.
Satellite Microwave Surface Observations in Tropical Cyclones
Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement infrared/ visible satellite images in estimating the strength of tropical cyclones (TCs). Satellite measurements at microwave frequencies are thus key elements of present and future observing systems. Available for more than 20 years, passive microwave measurements are very valuable but still suffer from insufficient resolution and poor wind vector retrievals in the rainy conditions encountered in and around tropical cyclones. Scatterometer and synthetic aperture radar active microwave measurements performed at the C and Ku band on board the European Remote Sensing (ERS), the Meteorological Operational (MetOp), the Quick Scatterometer (QuikSCAT), the Environmental Satellite (Envisat), and RadarSat satellites can also be used to map the surface wind field in storms. Their accuracy is limited in the case of heavy rain and possible saturation of the microwave signals is reported. Altimeter dual-frequency measurements have also been shown to provide along-track information related to surface wind speed, wave height, and vertically integrated rain rate at about 6-km resolution. Although limited for operational use by their dimensional sampling, the dual-frequency capability makes altimeters a unique satellite-borne sensor to perform measurements of key surface parameters in a consistent way. To illustrate this capability two Jason-1 altimeter passes over Hurricanes Isabel and Wilma are examined. The area of maximum TC intensity, as described by the National Hurricane Center and by the altimeter, is compared for these two cases. Altimeter surface wind speed and rainfall-rate observations are further compared with measurements performed by other remote sensors, namely, the Tropical Rainfall Measuring Mission instruments and the airborne Stepped Frequency Microwave Radiometer.