# Presentation: 248689

## Characterizing Tropospheric Dynamics Using MLS Geopotential Height

**Evan Fishbein, Michael Schwartz, **
**Nathaniel Livesey and Richard Cofield**
**Jet Propulsion Laboratory**
**California Institute of Technology**

## Motivation

**Can MLS geopotential height add information to characterize tropospheric dynamics.**
- Weather forecast systems are excellent at representing large scale atmospheric dynamics.
**MLS geopotential height may be especially valuable for characterizing tropical cyclones.**
**Develop over tropical ocean away from in situ measurements.**
**High cloud amounts limit usefulness of microwave and infrared nadir sounders.**
**Perform case study on Hurricane Katrina comparing MLS and NCEP GFS geopotential height.**
**Are differences coherent and physically plausible?**

## Measurement Technique

**MLS measures pressure at tangent point from pressure broadening of thermal O****2**** emissions.**
**Altitude of tangent point from “dead reckoning” of position and attitude of Aura.**
**Complicated error characterization:**
- Component from interpretation of MLS radiances.
- Measurement requires Aura orbit/attitude knowledge and MLS antenna boresight alignment beyond design requirements.
- Error has a time varying orbital and seasonable component from thermal environment of Aura.

## Amount of MLS Geopotential Height Data

**3500 profiles per day.**
**Histogram of repeat time of transects within 400 km of Hurricanes.**
- Repeat measurements 12 hours later 40% of time.
- Longer than 48 hours less than 13%.
**Number of transects over life of storm (260 events).**
- 60% of storms have more than 4 transects.

## Characterizating of Hurricane Dynamics

**Hurricanes form over warm ocean usually in remote areas**
**Low pressure near surface carrying moist air into and upward into eye wall and rain band clouds generating potential vorticity**
**High pressure in upper troposphere as airs detrains from eye wall**
**MLS could improve characterization of upper level high pressure in mature cyclones and surface pressure depression during cyclogenesis (MLS/AMSU)**

## Hurricane Katrina Transects

**6 MLS transects within 400 km **
- 22 Aug 2005 06:41:45 - Dsc
- 23 Aug 2005 18:20:34 - Asc
- 25 Aug 2005 07:11:26 - Dsc
- 26 Aug 2005 18:51:53 - Asc
- 28 Aug 2005 07:42:46 - Dsc
- 29 Aug 2005 19:24:27 – Asc
**26 Aug 2005 18:51 Transect**

**Caveat: MLS pointing drift correction derived from NCEP geopotential height**

## Overview of Environment from NCEP GFS Analysis on 22 Aug 2005

**500 hPa Geopotential Height and Winds**
**Designated tropical depression on 23 Aug   at 2100 UT   **
- Backward extrapolation of storm track
**Three weak lows, one near extrapolate storm track**

## Upper Level Development on 22 Aug 2005

**100 hPa height is monotonically increasing towards  northwest**
**NCEP GFS 100 hPa Geopotential Height and Winds shows no development**
**	**** ****100  hPa****	****	****	****	****500 hPa**

## Comparison of MLS and NCEP 100 hPa Height

**Two data sets are in agreement to within “noise”**

- Need to understand if “noise” is limited by MLS tangent pressure sensitivity or pointing knowledge error.

- Spikes dominates error in surface pressure determination

## Combined MLS and AMSU Surface Pressure

**Apply hypsometric equation to Aqua AMSU temperature layer using  MLS 100 hPa height reference level**

## MLS and NCEP 100 hPa Mature Storm Geopotential Height Comparison

- Coherent structure in MLS Height above storm

## August 25 Surface Pressure Transect

- Cuba

- Katrina

- Gap is missing
- AMSU temperature

## Upper Level Geopotential Height – Mature Cyclone

**100 hPa MLS & NCEP height**
- 28 Aug 2005 07:43
- 1 day before landfall
**Amplitude of high are equivalent, but MLS decays faster toward equator**
**Spike at 5° N  is common near equator and could be dynamics associated with ITCZ**

## Summary

**MLS/AMSU crossed Katrina storm track six times between    22 – 29 August 2005.**
**MLS and NCEP 100 hPa geopotential height track, but differences in structure.**
**Differences between forecast NCEP surface pressure are small and have a spatially correlated component.**
**Largest component of error budget is boresight pointing and satellite orbit uncertainty.**
**MLS/AMSU surface pressures track forecasted pressures, but**
- Core pressures not useful because of low AMSU temperature sensitivity in precipitating scenes.

## Conclusions

**Goal was to determine if MLS geopotential height and MLS/AMSU surface pressure are scientifically useful – YES.**
**Differences between MLS and NCEP height are often coherent, but further validation is required.**
**Further algorithm refinements would:**
- Improve error estimates.
- Improve pressure measurement with more optimal use of unsaturated radiances.
- Improve pointing and drift correction, remove dependence on NCEP gepotential height and include better pointing model.
**Working with FOT,  near real-time geopotential height and surface pressure measurements could be generated for operational weather forecasting.**