Patricia M. Pauley

Impact of Satellite-Derived Rapid-Scan Wind Observations on Numerical Model Forecasts of Hurricane Katrina

Abstract The impacts of special Geostationary Operational Environmental Satellite (GOES) rapid-scan (RS) wind observations on numerical model 24–120-h track forecasts of Hurricane Katrina are examined in a series of data assimilation and forecast experiments. The RS wind vectors are derived from geostationary satellites by tracking cloud motions through successive 5-min images. In these experiments, RS wind observations are added over the area 15°–60°N, 60°–110°W, and they supplement the observations used in operational forecasts. The inclusion of RS wind observations reduces errors in numerical forecasts of the Katrina landfall position at 1200 UTC 29 August 2005 by an average of 12% compared to control cases that include “targeted” dropsonde observations in the Katrina environment. The largest average improvements are made to the 84- to 120-h Katrina track forecasts, rather than to the short-range track forecasts. These results suggest that RS wind observations can potentially be used in future cases to...

Direct and Indirect Effects of Latent Heat Release on a Synoptic-Scale Wave System

Abstract The primary goal of this paper is to diagnose, the “direct” and “indirect” effects of latent heat release on a synoptic-scale wave system containing an extratropical cyclone that developed over the eastern United States. To achieve this goal, comparisons are made between MOIST (full model physics) and DRY (latent heating removed) predictions of the wave system during the period 27–29 February 1984 using the National Meteorological Centers Limited-Area Fine Mesh (LFM) model. Both the MOIST and DRY models predict significant cyclone systems, suggesting that the background adiabatic forcing is quite important. However, the DRY model predict a weaker cyclone. The direct and indirect latent heating influences are diagnosed using eddy energy quantities and the extended height tendency equation. Direct effects are restricted to the diabatic generation of available potential energy and height tendencies forced by diabatic heating. Results show that latent heating exerts an important direct influence on ...

Impact of Enhanced Satellite-Derived Atmospheric Motion Vector Observations on Numerical Tropical Cyclone Track Forecasts in the Western North Pacific during TPARC/TCS-08

AbstractEnhanced atmospheric motion vectors (AMVs) produced from the geostationary Multifunctional Transport Satellite (MTSAT) are assimilated into the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS) to evaluate the impact of these observations on tropical cyclone track forecasts during the simultaneous western North Pacific Ocean Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (TPARC) and the Tropical Cyclone Structure—2008 (TCS-08) field experiments. Four-dimensional data assimilation is employed to take advantage of experimental high-resolution (space and time) AMVs produced for the field campaigns by the Cooperative Institute for Meteorological Satellite Studies. Two enhanced AMV datasets are considered: 1) extended periods produced at hourly intervals over a large western North Pacific domain using routinely available MTSAT imagery and 2) limited periods over a smaller storm-centered domain produced using special MTSAT rapid-scan i...

A Comparison of Adiabatic and Diabatic Forcing in an Intense Extratropical Cyclone System

Abstract The primary goal of this study is to compare the principal adiabatic and diabatic mechanisms responsible for the behavior of an extratropical cyclone system. To accomplish this goal, the height tendency is solved from two forms of the height tendency equation. One is the classical quasi-geostrophic (QG) form; the other is a modified form identified as the ‘extended’ height tendency equation. The latter retains the essential components of the QG form but replaces the geostrophic wind where it appears in the equation by the observed wind, adds the effects of diabatic heating (latent heat release), and allows three dimensional varying static stability. In this study, the behavior of an intense cyclone is poorly described by the QG form but is realistically represented by the extended form. Using this latter diagnostic tool, the evolution of a 9–11 January 1975 cyclone event is analyzed with the following major results: 1) a comparison of the terms included in the extended height tendency equation in...

A Comparison of Quasigeostrophic and Nonquasigeostrophic Vertical Motions for a Model-simulated Rapidly Intensifying Marine Extratropical Cyclone

Abstract Large-scale departures from quasigeostrophic vertical motions are diagnosed for a model simulation of the QE II storm (9–11 September 1978). The simulation was performed by the Limited-Area Mesoscale Prediction System (LAMPS), initialized at 1200 UTC 9 September 1978. The model cyclone intensified from a central pressure of 1003 mb to 976 mb in 24 h, considerably short of the 59 mb (24 h)−1 observed deepening but reasonable in comparison to other model simulations of this storm. This diagnosis centers on a hydrostatic generalized omega equation, which scales to the quasigeostiophic omega equation for small Rossby number. Vertical motions were computed both from this generalized omega equation and the quasigeostrophic omega equation in order to examine the importance of nonquasigeostrophic effects. The high correlation of vertical motions from a control experiment (using most of the terms in the generalized omega equation) with the vertical motions predicted by the model establishes the validity o...

On the Evaluation of Boundary Errors in the Barnes Objective Analysis Scheme

Abstract The spectral response of the Barnes objective analysis scheme near data boundaries is the focus of this note. First of all, a modification of the results presented by Achtemeier is described. In order for the weighted sum (or integral) defining the Barnes scheme to provide an unbiased estimate of the field at grid points, the sum (or integral) of the normalized weights must equal one. The normalizing factor is therefore written as an integral whose limits of integration are kept identical to those for the weighted integral of observations defining the scheme, even as the integral is truncated near a boundary. This modification serves to phrase the theoretical form of the Barnes scheme in a manner that is more consistent with the commonly used discrete form of the scheme. The amplitude and phase-shifted responses using the proposed normalization at an interpolation point on a boundary differ from Achtemeiers results by a factor of two. The amplitude and phase-shifted responses for a discrete appl...

Response Functions for Arbitrary Weight Functions and Data Distributions. Part II: Response Function Derivation and Verification

Distance-dependent weighted averaging (DDWA) is a process that is fundamental to most of the objective analysis schemes that are used in meteorology. Despite its ubiquity, aspects of its effects are still poorly understood. This is especially true for the most typical situation of observations that are discrete, bounded, and irregularly distributed. To facilitate understanding of the effects of DDWA schemes, a framework that enables the determination of response functions for arbitrary weight functions and data distributions is developed. An essential element of this approach is the equivalent analysis, which is a hypothetical analysis that is produced by using, throughout the analysis domain, the same weight function and data distribution that apply at the point where the response function is desired. This artifice enables the derivation of the response function by way of the convolution theorem. Although this approach requires a bit more effort than an alternative one, the reward is additional insight into the impacts of DDWA analyses. An important insight gained through this approach is the exact nature of the DDWA response function. For DDWA schemes the response function is the complex conjugate of the normalized Fourier transform of the effective weight function. In facilitating this result, this approach affords a better understanding of which elements (weight functions, data distributions, normalization factors, etc.) affect response functions and how they interact to do so. Tests of the response function for continuous, bounded data and discrete, irregularly distributed data verify the validity of the response functions obtained herein. They also reinforce previous findings regarding the dependence of response functions on analysis location and the impacts of data boundaries and irregular data spacing. Interpretation of the response function in terms of amplitude and phase modulations is illustrated using examples. Inclusion of phase shift information is important in the evaluation of DDWA schemes when they are applied to situations that may produce significant phase shifts. These situations include those where data boundaries influence the analysis value and where data are irregularly distributed. By illustrating the attendant movement, or shift, of data, phase shift information also provides an elegant interpretation of extrapolation.

Tropical Cyclone Data Impact Studies: Influence of Model Bias and Synthetic Observations

AbstractThe impacts of assimilating dropwindsonde data and enhanced atmospheric motion vectors (AMVs) on tropical cyclone track forecasts are examined using the Navy global data assimilation and forecasting systems. Enhanced AMVs have the largest impact on eastern Pacific storms, while dropwindsonde data have the largest impact on Atlantic storms. Results in the western Pacific are mixed. Two western Pacific storms, Nuri and Jangmi, are examined in detail. For Nuri, dropwindsonde data and enhanced AMVs are at least as likely to degrade as to improve forecasts. For Jangmi, additional data improve track forecasts in most cases. An erroneous weakening of the forecasted subtropical high appears to contribute to the track errors for Nuri and Jangmi. Assimilation of enhanced AMVs systematically increases the analyzed heights in this region, counteracting this model bias. However, the impact of enhanced AMVs decreases rapidly as the model biases saturate at similar levels for experiments with and without the enh...

The Effect of Resolution on the Depiction of Central Pressure for an Intense Oceanic Extratropical Cyclone

Abstract The effect of resolution on the depiction of central sea level pressure for an intense oceanic extratropical cyclone is examined through a one-dimensional Fourier analysis. Profiles of sea level pressure were manually interpolated along the latitude passing through the storm center from two subjective analyses and the 00-, 24-, and 48-h NMC Nested-Grid Model (NGM) forecasts, all valid at 0000 UTC 5 January 1989. At this time, the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) intensive observing period 4 (IOP 4) cyclone attained its maximum intensity, with a central pressure of 936 mb at 41°N, 58°W in an analysis prepared by Frederick Sanders. After the Fourier coefficients were determined for each pressure profile they were used to recompute a series of pressure profiles truncated at various maximum wavenumbers λmax. The central sea level pressures obtained from these truncated profiles asymptotically approach the central pressure of the original profile as λmax increases....