Here's the code I'm using:
hl1 = semilogx(basinput,bas_hpa,'Color',[0 0 0],'linewidth',2);
ax1 = gca;
set(ax1,'XColor',[0 0 0],'YColor',[0 0 0],'Parent',figure1,'YTickLabel',{'200','400','600','800','1000'},...
'YTick',[200 400 600 800 1000],...
'YMinorTick','on',...
'YDir','reverse',...
'XMinorTick','on',...
'Position',[0.13 0.112403846153846 0.710158478605388 0.793461538461539],...
'FontSize',16,...
'FontName','Times');
axis tight;
THEN LATER FOR THE LINE GRAPH:
ax2 = axes('Position',get(ax1,'Position'),...
'XAxisLocation','top',...
'YAxisLocation','right',...
'YTick',[200 400 600 800 1000],...
'YTickLabel',{'11.8','7.18','4.20','1.95',''},...
'YMinorTick','off',...
'XMinorTick','on',...
'YDir','reverse',...
'FontSize',16,...
'FontName','Times',...
'Position',[0.13 0.112403846153846 0.710158478605388 0.793461538461539],...
'Color','none',...
'XColor','k','YColor','k');
hl2 = line(difpercent,dif_hpa,'Parent',ax2,'Color',[0 0 0],...
'linewidth',2,'linestyle',':');