Timothy L. Miller

NASA's Genesis and Rapid Intensification Processes (GRIP) Field Experiment

In August–September 2010, NASA, NOAA, and the National Science Foundation (NSF) conducted separate but closely coordinated hurricane field campaigns, bringing to bear a combined seven aircraft with both new and mature observing technologies. NASAs Genesis and Rapid Intensification Processes (GRIP) experiment, the subject of this article, along with NOAAs Intensity Forecasting Experiment (IFEX) and NSFs Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) experiment, obtained unprecedented observations of the formation and intensification of tropical cyclones. The major goal of GRIP was to better understand the physical processes that control hurricane formation and intensity change, specifically the relative roles of environmental and inner-core processes. A key focus of GRIP was the application of new technologies to address this important scientific goal, including the first ever use of the unmanned Global Hawk aircraft for hurricane science operations. NASA and NOAA conducted coord...

The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes

AbstractLike all reanalysis efforts, the Modern Era Retrospective-Analysis for Research and Applications (MERRA) must contend with an inhomogeneous observing network. Here the effects of the two most obvious observing system epoch changes, the Advanced Microwave Sounding Unit-A (AMSU-A) series in late 1998 and, to a lesser extent, the earlier advent of the Special Sensor Microwave Imager (SSM/I) in late 1987 are examined. These sensor changes affect model moisture and enthalpy increments and thus water and energy fluxes, since the latter result from model physics processes that respond sensitively to state variable forcing. Inclusion of the analysis increments in the MERRA dataset is a unique feature among reanalyses that facilitates understanding the relationships between analysis forcing and flux response.In stepwise fashion in time, the vertically integrated global-mean moisture increments change sign from drying to moistening and heating increments drop nearly 15 W m−2 over the 30 plus years of the as...

The ATLAS Series of Shuttle Missions

The ATLAS space shuttle missions were conducted in March 1992, April 1993, and November 1994. The ATLAS payload and companion instruments made measurements of solar irradiance and middle atmospheric temperatures and trace gas concentrations. The solar irradiance measurements included total and spectrally resolved solar irradiance. The atmospheric measurements included microwave, infrared, and ultraviolet limb sounding, nadir ultraviolet backscatter, and solar occultation techniques. This paper introduces a special section in this issue of Geophysical Research Letters.

Hurricane Wind Speed Measurements in Rainy Conditions Using the Airborne Hurricane Imaging Radiometer (HIRAD)

This paper describes a realistic computer simulation of airborne hurricane surveillance using the recently developed microwave remote sensor, the hurricane imaging radiometer (HIRAD). An end-to-end simulation is described of HIRAD wind speed and rain rate measurements during two hurricanes while flying on a high-altitude aircraft. This simulation addresses the particular challenge which is accurate hurricane wind speed measurements in the presence of intense rain rates. The objective of this research is to develop baseline retrieval algorithms and provide a wind speed measurement accuracy assessment for future hurricane flights including the NASA GRIP hurricane field program that was conducted in summer of 2010. Examples of retrieved hurricane wind speed and rain rate images are presented, and comparisons of the retrieved parameters with two different numerical hurricane models data are made. Special emphasis is provided on the wind speed measurement error, and statistical results are presented over a broad range of wind and rain conditions over the full measurement swath (earth incidence angle).

ATLAS Space Shuttle studies Earth's atmosphere and solar input

A shuttle-based component of NASAs Mission to Planet Earth, the Atmospheric Laboratory for Applications and Science (ATLAS), completed its second mission making detailed measurements of Earths middle atmosphere and solar input in April 1993. ATLAS-1 was successfully conducted in spring 1992. In addition to the standard payload, this mission carried instruments that studied the upper atmosphere, magnetosphere, space plasma physics, and ultraviolet astronomy. The ATLAS-1 mission obtained a large database on the middle and upper atmosphere, and access to much of the data is available through the investigator teams. The mission procured the first space-based measurements of OH in the atmosphere; compared middle atmosphere trace species between 1985 and 1992; and tested critical ionization velocity theory.

The structures and energetics of fully nonlinear symmetric baroclinic waves

Rotating baroclinic flow for Richardson number lower than about 1 is studied by means of a finite difference Navier-Stokes model assuming no variations except in the vertical plane that completely contains the density gradient vector. The horizontally infinite channel to which attention is given further assumes periodic boundary conditions at the vertical computational boundaries and no-slip conducting horizontal boundaries. Two configurations are considered. Symmetric baroclinic waves developed in the flows in a manner consistent with linear theory, and it is noted that the structures and energetics of the fully developed waves were dependent on the Prandtl number Pr. For Pr greater than 1, the conversion from potential energy to wave kinetic energy was direct, via temperature and vertical motion correlation, while for Pr of less than 1, conversion proceeded from potential energy to average kinetic energy by means of an induced meridional flow, and then to wave kinetic energy.

Hysteresis and the transition between axisymmetric flow and wave flow in the baroclinic annulus

Abstract A numerical model is used to determine the transitions between axisymmetric flow and wave flow in the rotating, differentially heated annulus experiments of Fein for both rigid lid and free surface cases. For most of the transitions, the technique of computing a steady axisymmetric flow and then testing its linear stability to wave disturbances results in good agreement with the experiments. Nonlinear calculations with a single azimuthal wave accurately predict the observed hysteresis in the transition for large differential heating rates in the free surface case. Specifically, it is demonstrated that, in the experimentally observed hysteresis region, the Navier-Stokes equations support two stable equilibria for the same values of the external parameters. The hysteresis occurs in conjunction with a jump in wave amplitude as the rotation rate is slowly varied. Analysis of the longitudinal mean states and the linear and nonlinear waves indicates that the jump in amplitude is due to destabilization ...

Laboratory experiments in a baroclinic annulus with heating and cooling on the horizontal boundaries

Abstract Experiments have been performed in a cylindrical annulus with horizontal temperature gradients imposed upon the horizontal boundaries and in which the vertical depth was smaller than the width of the annulus. Qualitative observations were made by the use of small, suspended, reflective flakes in the liquid (water). Four basic regimes of flow were observed: (1) axisymmetric flow, (2) deep cellular convection, (3) boundary layer convective rolls, and (4) baroclinic waves. In some cases there was a mix of baroclinic and convective instabilities present. As a “mean” interior Richardson number was decreased from a value greater than unity to one less than zero, axisymmetric baroclinic instability of the Solberg type was never observed. Rather, the transition was from non-axisymmetric baroclinic waves, to a mix of baroclinic and convective instability, to irregular cellular convection.

Calibration and image reconstruction for The Hurricane Imaging Radiometer (HIRAD)

The Hurricane Imaging Radiometer (HIRAD) is a new airborne passive microwave synthetic aperture radiometer designed to provide wide swath images of ocean surface wind speed under heavy precipitation and, in particular, in tropical cyclones. It operates at 4, 5, 6 and 6.6 GHz and uses interferometric signal processing to synthesize a pushbroom imager in software from a low profile planar antenna with no mechanical scanning. The retrieval algorithm (and the HIRAD instrument itself) is a direct descendant of the nadir-only Stepped Frequency Microwave Radiometer that is used operationally by the NOAA Hurricane Research Division to monitor Tropical Cyclones [1,2]. HIRAD participated in NASAs Genesis and Rapid Intensification Processes (GRIP) mission during Fall 2010 as its first science field campaign. HIRAD produced images of upwelling brightness temperature over a ~70 km swath width with ~3 km spatial resolution. The calibration and image reconstruction algorithms that were used to verify HIRAD functional performance during and immediately after GRIP were only preliminary and used a number of simplifying assumptions and approximations about the instrument design and performance. The development and performance of a more detailed and complete set of algorithms are reported here.

Characteristics of annulus baroclinic flow structure during amplitude vacillation

Abstract An investigation is made of the mechanics of amplitude vacillation in a numerically simulated rotating annulus flow system. Amplitude vacillation is characterized by a periodic change of vertical wave structure in concert with growth and decay of wave amplitude and phase speed. The temperature wave amplitude profile for the dominant component consists of three local maxima: (1) lower boundary layer, (2) upper half layer and (3) lower half layer. The lower layer waves lead the time-dependent structural variation during vacillation. Two types of amplitude vacillation found in the experimental measurements (Buzyna et al., 1989: J. Atmos. Sci. 46, 2716–2729) can be distinguished in the temperature wave by whether the lower layer waves split from and travel behind the upper layer waves by one wave period in each cycle of vacillation. Linear eigenvalue analyses with respect to the instantaneous axisymmetric state at various points in time are performed to elucidate the simple interaction between the dominant wave and the zonal mean state. During the vacillation cycle, the zonal mean state is modified by the wave, which causes a change in growth rate and vertical structure of the linearly most unstable eigenmode. This, in turn, forces the actual changes of the nonlinear solutions.