Mary S. Jordan

Objective verifications and false alarm analyses of western North Pacific tropical cyclone event forecasts by the ECMWF 32-day ensemble

An objective tropical cyclone (TC) track analog verification technique has been developed to select all ensemble storm tracks predicted by the ECMWF 32-day ensemble that match the overall Joint Typhoon Warning Center (JTWC) post-season best-tracks. Ensemble storms within specified time and space differences of each JTWC track are first extracted as potential analogs, and four metrics of shortest distance, average distance, distance at formation time, and distance at ending time are calculated. An objective quality measure that assesses the overall track similarity between the potential analogs and each JTWC track is calculated in terms of membership functions for the four track metrics. Weighting factors multiplying these membership functions are adjusted to match with the quality measures for the ECMWF ensemble storm forecasts in a previous subjective evaluation. Objective verifications for the 2009 and 2010 seasons have been summarized in terms of Hits, Misses, False Alarms, and Correct Negatives that no TC would be present in the western North Pacific. The most important result is that the ECMWF ensemble was able to predict nearly all of the TCs in both seasons with only a small number of Misses that generally were short-lived tropical depressions. Good performance in terms of Correct Negatives was achieved during the 2010 season. False alarms are defined to be all ensemble storms that could not be matched any JTWC tracks within the specified thresholds. Evaluations of the characteristics of the false alarms indicate seasonal and geographic biases and that about 50% of the false alarm in the Week 1 forecasts originate from the initial the initial conditions in the model. A minimum of false alarms created in Week 2 forecasts is attributed to the decrease in horizontal resolution in the model that occurs at day 10. A steady and nearly uniform increase in false alarms in the Week 3 and Week 4 forecasts may be attributed to net convective heating in response to persistent environmental forcing in the tropics.

Extended-Range Forecasts of Atlantic Tropical Cyclone Events during 2012 Using the ECMWF 32-Day Ensemble Predictions*

AbstractPrevious studies have demonstrated the capability of the European Centre for Medium-Range Weather Forecasts (ECMWF) 51-member, 32-day ensemble to forecast tropical cyclone (TC) events (formation and tracks) in the western North Pacific on the extended range (5–30 days). In this study, the performance of the ECMWF ensemble in extended-range forecasting of Atlantic TCs during May–December 2012 is evaluated using similar approaches. The conclusion from this evaluation is that Atlantic TC events have lower forecastability using the ECMWF ensemble than in the western North Pacific. Hurricanes Kirk and Leslie and Tropical Storms (TSs) Joyce and Oscar were successfully forecast in weeks 1–4 and, thus, are labeled as highly forecastable. Somewhat forecastable storms that are only forecast in three of the four weeks include Hurricanes Ernesto, Isaac, Nadine, and Sandy plus TS Florence. The limited forecastable storms that were successful in only the first two weeks include Hurricanes Gordon and Rafael plus...

Satellite and ship-based lidar measurements of optical depth during EOPACE

The authors consider methods for obtaining quantitative data of the coastal marine atmospheric boundary layer (MABL). Satellite remote sensing is the only data source that can measure MABL properties in the coastal zone with the needed high spatial resolution. However, many of the uses of satellite data are qualitative. Quantitative satellite remote sensing methods need to be tested to provide littoral data. Ship-based aerosol and lidar backscatter measurements, aircraft-measured aerosol, and rawinsonde data obtained during the Electro-Optical Propagation Assessment in Coastal Environments (EOPACE) Intense Observing Periods (IOPs) provide an opportunity to compare satellite methods with in situ data. The purpose of the EOPACE program is to characterize the aerosol and boundary layer properties in the coastal zone and to determine if air mass parameters in various coastal locations can be derived, to a practical degree, from satellite imagery. The combination of satellite data with several in situ surface and aircraft data sets offers an excellent opportunity to monitor significant optical depth and aerosol changes in the coastal zone. In addition, quantitative comparisons can be made. The objective of this paper is to evaluate satellite-derived aerosol optical depths estimates using aircraft and ship-based aerosol measurements, a ship-based lidar and rawinsonde profiles of the MABL. Results from the April 1996 IOP are presented.

Environmental Factors and Internal Processes Contributing to the Interrupted Rapid Decay of Hurricane Joaquin (2015)

AbstractThe objective in this study is to demonstrate how two unique datasets from the Tropical Cyclone Intensity (TCI-15) field experiment can be used to diagnose the environmental and internal fa...

Air mass parameterization and coastal aerosol modeling

A technique has been developed by which satellite upwelling radiance measurements, MODTRAN, and the NOVAM aerosol model can be used to infer lower tropospheric extinction coefficients as a function of wavelength. This technique utilizes: 1) satellite upwelling radiance measurements for determining the total aerosol optical depth for a specific geographic location and time, 2) MODTRAN to calculate the optical depth associated with tropospheric aerosol scatter, assuming that no aerosols are being entrained into the troposphere from other source,s and 3) NOVAM for modeling the optical depth of the lower troposphere as a function of air mass parameter. By adjusting the air mass NOVAM so that the calculated optical depth matches that required for the lower troposphere, the air mass parameter for the lower troposphere can be inferred from remote satellite radiance measurements. Initial results using the EOPACE, database appear promising for inferring extinction coefficients of the lower troposphere as a function of wavelength from remote satellite radiance measurements. It also shows promise for an initial technique for modeling coastal aerosols.

Remote sensing of the coastal marine atmospheric boundary layer

Coastal region marine atmospheric boundary layer (MABL) properties derived from satellite data are compared with coastal in situ measured conditions. A multispectral approach using visible and IR data is being tested to indirectly estimate important variables such as depth of the MABL. In situ and ground-based remote data were obtained from ship mounted systems and from shoreline stations. In examined cases, remotely sensed information yields reasonable assessments of the height of the top of the boundary layer as well as of conditions immediately above the surface. Remote data describe high resolution horizontal/temporal variations, important in the coastal but not described by point measured in situ data.

Remote measurement of coastal marine atmospheric boundary layer (MABL) features

Coastal region marine atmospheric boundary layer (MABL) properties derived from satellite data are compared with coastal in situ measured conditions. A multispectral approach using visible and IR data is being tested to indirectly estimate important variables such as depth of the MABL. In situ and ground-based remote data were obtained from ship mounted systems and from shoreline stations. In examined cases, remotely sensed information yields reasonable assessments of the height of the top of the boundary layer as well as of conditions immediately above the surface. Remote data describe high resolution horizontal/temporal variations, important in the coastal but not described by point measured in situ data.